WO2013077052A1

WO2013077052A1 - Wireless base station, wireless terminal, communication system, communication control method and communication control program

Info

Publication number: WO2013077052A1
Application number: PCT/JP2012/071716
Authority: WO
Inventors: 村上憲一; 山本裕嗣; 山本剛史; 田中義三; 岡田洋侍
Original assignee: 住友電気工業株式会社
Priority date: 2011-11-22
Filing date: 2012-08-28
Publication date: 2013-05-30
Also published as: WO2013077051A1

Abstract

A wireless base station (101) is provided with a handover instruction unit (12) for instructing a wireless terminal (202) to perform a handover operation from said wireless base station (101) to another wireless station after receiving a response from the abovementioned other wireless base station to a request for the wireless terminal (202) to perform a handover operation from the wireless base station (101) to the other wireless base station. If a predetermined execution condition pertaining to communication quality between the wireless base station (101) and the wireless terminal (202) is not met after the handover instruction unit (12) receives the abovementioned response, the handover instruction unit (12) stops or suspends the provision of the instruction to the wireless terminal (202).

Description

Radio base station apparatus, radio terminal apparatus, communication system, communication control method, and communication control program

The present invention relates to a radio base station apparatus, a radio terminal apparatus, a communication system, a communication control method, and a communication control program, and more particularly, in a communication system capable of communicating with a plurality of radio base station apparatuses by performing a handover operation. The present invention relates to a radio base station apparatus, a radio terminal apparatus, a communication system, a communication control method, and a communication control program.

Conventionally, in a mobile communication system, a communication service is provided by a radio base station apparatus (hereinafter also referred to as a macro base station) that forms an area in which a cell having a radius of several hundred meters to several tens of kilometers, that is, a radio terminal apparatus can communicate. It was.

In recent years, due to a dramatic increase in the number of subscribers of mobile communication services and an increase in the amount of communication traffic due to data communication, subscribers and communication traffic are distributed by forming smaller radius cells, and a certain level of communication It is desirable to provide speed to users in a stable manner. In addition, in order to deal with dead zones associated with the increase in the number of buildings, it is desired to install radio base station devices on the corporate floor and in ordinary households.

Together with these demands, the processing capability of various devices used in the radio base station apparatus has been dramatically improved, and the miniaturization of the radio base station apparatus has progressed. Collecting.

The radius of the femto cell formed by this small base station (hereinafter also referred to as a femto base station) is as small as about 10 meters, so the femto base station is the macro cell formed by the macro base station. It may be used in places such as indoors and underground malls where it is out of service area and it is difficult to install macro base stations.

Also, since many femto base stations are installed in a specific area, it is difficult to connect the femto base stations directly to the core network. For this reason, it is conceivable that a large number of femto base stations installed in a specific area are once connected to a gateway device such as a HeNB-GW, and the femto base station and the core network are connected via the HeNB-GW.

In addition to the femto base station, a pico base station that forms a pico cell with a radius of 100 to 200 meters, for example, has been developed based on a macro base station.

In a heterogeneous network that is a communication system in which such femto base stations, pico base stations, and macro base stations are mixed, for example, a plurality of femto cells or pico cells are formed in a macro cell. For this reason, handover of a radio terminal device is likely to occur, and the situation of handover is complicated, so that an inappropriate handover operation is performed such as the timing of handover being too early or too late (For example, see 3GPP TR 36.902 V9.3.1 2011.3 (Non-Patent Document 1)).

When an inappropriate handover operation as described in Non-Patent Document 1 is performed, various problems such as communication interruption and increase in communication traffic occur in the communication system. A technique for suppressing such an inappropriate handover operation and constructing a good communication system is desired.

The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a radio base station apparatus capable of stabilizing communication by appropriately controlling a handover operation of the radio terminal apparatus, To provide a wireless terminal device, a communication system, a communication control method, and a communication control program.

(1) A radio base station apparatus according to an aspect of the present invention transmits a radio signal to / from a radio terminal apparatus in a communication system in which the radio terminal apparatus can communicate with a plurality of radio base station apparatuses by performing a handover operation. A radio base station apparatus for transmitting and receiving, for requesting the other radio base station apparatus to perform a handover operation of the radio terminal apparatus from its own radio base station apparatus to another radio base station apparatus An instruction to perform a handover operation from the radio base station apparatus to the other radio base station apparatus to the radio terminal apparatus upon receiving a response from the other radio base station apparatus to the handover request unit and the request The handover instruction unit receives the response, and receives the response from the wireless base station device and the wireless terminal device. When a predetermined execution condition regarding the quality of communication is not satisfied, or suspend abort the application of the instruction to the wireless terminal device.

With such a configuration, the preparation process for the handover operation can be completed prior to the determination of the execution of the handover operation. For example, it is possible to suppress “Too Late HO” in which the timing of handover by the wireless terminal device is too late, for example. it can. Also, unlike the case of adjusting parameters for handover operation, even if “Too Late HO” is suppressed, it is possible to prevent an increase in the probability of occurrence of “Too Early HO” when the timing of handover by the wireless terminal device is too early. . That is, an inappropriate handover operation can be suppressed and a good communication system can be constructed. Therefore, communication can be stabilized by appropriately controlling the handover operation of the wireless terminal device.

(2) Preferably, when the handover instruction unit receives the response and the execution condition is not satisfied, the handover instruction unit stops the handover operation without giving the instruction to the wireless terminal device. To the other radio base station apparatus.

With such a configuration, it is possible to appropriately release various resources secured for the handover operation in other radio base station apparatuses, for example, when the handover operation is stopped.

(3) Preferably, the handover instruction unit receives the response and waits until the execution condition is satisfied when the execution condition is not satisfied, and when the execution condition is satisfied, the wireless terminal Give the above instructions to the device.

With such a configuration, after completion of the handover operation preparation process, when the communication quality between the radio base station apparatus and the radio terminal apparatus satisfies the execution condition, the handover operation instruction is given to the radio terminal apparatus Therefore, the handover operation can be executed at the optimal timing.

(4) More preferably, when the predetermined stop condition is satisfied before the execution condition is satisfied, the handover instruction unit does not give the instruction to the wireless terminal device and performs the handover operation. The other radio base station apparatus is notified of the cancellation.

With such a configuration, it is possible to stop the handover operation at an appropriate timing such as the expiration of the timer or an appropriate condition according to the radio wave environment and prevent an increase in the standby time of the handover operation. Also, with the cancellation of the handover operation, for example, it is possible to appropriately release various resources reserved for the handover operation in other radio base station apparatuses.

(5) Preferably, the handover request unit sends the request to the other radio base station apparatus when a predetermined preparation condition regarding communication quality between the own radio base station apparatus and the radio terminal apparatus is satisfied. Therefore, the communication quality indicated by the preparation condition is better than the communication quality indicated by the execution condition.

With such a configuration, the preparation process for the handover operation can be performed in advance under conditions that are milder than the communication quality that is the basis for determining whether to execute the handover operation.

(6) Preferably, the handover request unit sends the request to the other radio base station apparatus when a predetermined preparation condition regarding communication quality between the own radio base station apparatus and the radio terminal apparatus is satisfied. The communication quality indicated by the preparation condition is equivalent to the communication quality indicated by the execution condition.

With such a configuration, the radio environment of the wireless terminal device improves during the preparation period for the handover operation, and the handover operation that is no longer necessary can be stopped appropriately, thereby suppressing the execution of the unnecessary handover operation. can do.

(7) More preferably, the handover request unit sends the request to the other radio base station apparatus when a predetermined preparation condition regarding communication quality between the own radio base station apparatus and the radio terminal apparatus is satisfied. The cancellation condition is a condition related to communication quality between the own radio base station apparatus and the wireless terminal apparatus, and the communication quality indicated by the preparation condition is equivalent to the communication quality indicated by the execution condition. The communication quality indicated by the cancellation condition is better than the communication quality indicated by the preparation condition.

(8) More preferably, when the handover instructing unit notifies the other radio base station device that the handover operation is stopped, the communication quality between the own radio base station device and the radio terminal device satisfies a condition. Notify the other radio base station apparatus that the mobile station has not been connected.

Thereby, the other radio base station apparatus can distinguish from an event in which the handover operation is stopped due to, for example, an error in parameter setting related to the handover operation. For this reason, it is possible to prevent occurrence of unnecessary processes such as new parameter setting processes in other radio base station apparatuses and appropriately release various resources reserved for the handover operation.

(9) More preferably, the radio base station apparatus further includes a handover condition adjustment unit for adjusting a difference between the communication quality indicated by the execution condition and the communication quality indicated by the preparation condition.

Such a configuration makes it possible to adjust the frequency of inappropriate handover operations such as “Too Late HO” and the frequency of canceling handover operations, thereby realizing more appropriate handover operations.

(10) More preferably, the handover request unit sends the request to the other radio base station apparatus when a predetermined preparation condition regarding communication quality between the own radio base station apparatus and the radio terminal apparatus is satisfied. The radio base station apparatus further adjusts a difference between the communication quality indicated by the execution condition and the communication quality indicated by the preparation condition, and the handover instruction unit cancels the handover operation by another radio base station. A handover condition adjusting unit is provided for adjusting the difference based on the number of times notified to the apparatus.

Such a configuration makes it possible to appropriately adjust the frequency of inappropriate handover operations such as “Too Late HO” and the frequency of cancellation of handover operations from the viewpoint of the frequency of handover operation cancellation.

(11) More preferably, the radio base station apparatus further obtains the number of times that the handover operation from the radio base station apparatus to another radio base station apparatus by the radio terminal apparatus is inappropriate. An information acquisition unit is provided, and the handover condition adjustment unit adjusts the difference based on the number of times acquired by the handover information acquisition unit.

With such a configuration, it is possible to appropriately adjust the frequency of inappropriate handover operations and the frequency of canceling handover operations from the viewpoint of the frequency of inappropriate handover operations such as “Too Late HO”.

(12) A communication control method according to an aspect of the present invention is a communication system capable of communicating with a plurality of radio base station apparatuses by performing a handover operation of the radio terminal apparatus, and transmitting and receiving radio signals to and from the radio terminal apparatus. A communication control method in a radio base station apparatus for performing a request for performing a handover operation of a radio terminal apparatus from itself to another radio base station apparatus to the other radio base station apparatus, Receiving a response from the other radio base station apparatus to the request and determining whether to give an instruction to perform a handover operation from itself to the other radio base station apparatus to the radio terminal apparatus; In the step of determining whether or not to give the instruction, the communication quality between the own radio base station apparatus and the radio terminal apparatus If the constant execution condition is not satisfied, not give the instruction to the wireless terminal device, the effect to stop the handover operation to notify the other radio base station apparatus.

(13) A communication control program according to an aspect of the present invention transmits / receives a radio signal to / from a wireless terminal device in a communication system in which the wireless terminal device can communicate with a plurality of wireless base station devices by performing a handover operation. A communication control program used in a radio base station apparatus for performing a handover operation of a radio terminal apparatus from itself to another radio base station apparatus to the other radio base station apparatus And whether to give an instruction to perform a handover operation from itself to the other radio base station apparatus in response to a response from the other radio base station apparatus to the request. In the step of determining whether to give the above instruction When the predetermined execution condition regarding the communication quality between the own radio base station apparatus and the radio terminal apparatus is not satisfied, the handover operation is stopped without giving the instruction to the radio terminal apparatus. To the other radio base station apparatus.

(14) Preferably, in the radio base station apparatus, the handover request unit makes the request to the plurality of other radio base station apparatuses.

There may be a case where the radio terminal apparatus related to the peripheral base station deteriorates due to the movement of the wireless terminal apparatus after completion of the preparation process for the handover operation to a certain peripheral base station. Even in such a case, since the preparation process for the handover operation with another neighboring base station is completed, the handover operation to the other neighboring base station can be performed in a short time. It is possible to prevent communication between the apparatus and the radio base station apparatus from being interrupted.

In addition, as described above, even when the radio wave condition of the wireless terminal device related to the neighboring base station deteriorates, the preparation process for the handover operation with other neighboring base stations is completed. It is possible to prevent repeated transmission and reception of information for the preparation process and the handover operation cancellation process, and to reduce the load on the communication system.

(15) Preferably, the handover instruction unit receives the response, selects a handover destination radio base station device from the other radio base station devices corresponding to the response, and transmits the response to the radio terminal device. An instruction to perform the handover operation is given to the handover destination radio base station apparatus.

In this way, by selecting a handover destination radio base station apparatus and giving an instruction for a handover operation to the radio terminal apparatus, the amount of information is larger than when a plurality of radio base station apparatuses are presented in the instruction. The instruction content can be simplified.

(16) Preferably, after the response is received, the handover instruction unit obtains a measurement result of received power in the radio terminal device of a radio signal transmitted from the other radio base station device corresponding to the response. Then, based on the measurement result, the handover destination radio base station apparatus is selected.

With this configuration, it is possible to select an appropriate radio base station apparatus as a handover destination according to the radio wave environment in the radio terminal apparatus after completion of preparation for the handover operation.

(17) Preferably, after receiving the response, the handover instruction unit excludes the other radio base station apparatus corresponding to the measurement result that cannot be acquired for a predetermined period from the handover destination candidates.

With such a configuration, for example, a radio base station apparatus that is far away from the radio terminal apparatus to such an extent that the radio terminal apparatus cannot measure received power can be excluded from handover destination candidates. An appropriate radio base station apparatus can be selected.

(18) Preferably, the handover instruction unit receives the response and transmits information indicating the other radio base station device corresponding to the response as a handover destination candidate to the radio terminal device.

In this way, the configuration in which the radio terminal device selects the handover destination radio base station device, the handover destination radio base station device according to the latest radio wave environment as compared with the case where the handover source radio base station device selects Can be selected.

(19) Preferably, the handover instruction unit receives information indicating the handover destination radio base station apparatus selected by the radio terminal apparatus, and the handover destination radio base station apparatus indicated by the received information The predetermined information is transmitted to.

With such a configuration, after the handover source radio base station apparatus grasps the handover destination radio base station apparatus selected by the radio terminal apparatus, information necessary for the handover operation is transferred to the handover destination radio base station apparatus. Therefore, it is possible to transmit and receive information without waste.

(20) Preferably, the handover instruction unit, after the handover operation is completed, of the other radio base station apparatuses other than the handover destination radio base station apparatus among the other radio base station apparatuses corresponding to the response. A request for canceling the handover operation is transmitted to.

Here, for example, after the handover operation to the radio base station apparatus other than the radio base station apparatus selected as the handover destination is canceled before the handover operation is completed, the radio terminal apparatus In the case of moving in the direction approaching, the radio base station apparatus to be canceled may be an optimal handover destination. In this case, it is necessary to perform the handover operation to the radio base station apparatus to be canceled again.

On the other hand, as described above, the radio base station apparatus according to the present invention performs the handover operation to the radio base station apparatus other than the radio base station apparatus selected as the handover destination as the handover operation preparation process of the radio terminal apparatus. Stop after completion. As a result, even when the wireless terminal device moves and the radio wave state changes before the handover operation is completed, and the handover operation to another neighboring base station is performed, the preparation process for the handover operation is performed again. There is no need.

(21) A radio terminal apparatus according to an aspect of the present invention is a radio terminal apparatus capable of communicating with a plurality of radio base station apparatuses by transmitting / receiving radio signals to / from the radio base station apparatus and performing a handover operation. A receiving unit for receiving information indicating a plurality of other radio base station devices as handover destination candidates from a serving base station that is a radio base station device that has established a communication connection with itself; and A selection unit for selecting a handover destination radio base station device from among the plurality of other radio base station devices indicated by the received information, and the handover destination radio base station device selected by the selection unit And a communication control unit for newly establishing a communication connection with the handover destination radio base station apparatus.

(22) A communication system according to an aspect of the present invention is provided for managing a plurality of radio base station apparatuses for transmitting and receiving radio signals to and from a radio terminal apparatus, and one or more radio base station apparatuses. A communication system comprising a plurality of communication control devices, wherein the radio base station device transmits a handover request for performing a handover operation of the radio terminal device from itself to another radio base station device to a corresponding communication control device The corresponding communication control apparatus, when the other radio base station apparatus to be handed over indicated by the handover request is not a management target of the other communication control apparatus, manages the other radio base station apparatus. The other communication control apparatus transmits the received handover request to the other radio base station apparatus, and the other radio base station apparatus transmits the handover request to the other radio base station apparatus. The response to the handover request is received from the corresponding communication control apparatus, and the corresponding communication control apparatus receives the response from the other communication control apparatus and transmits the handover request source. Whether the wireless base station apparatus receives the handover instruction and whether or not a predetermined execution condition relating to communication quality with the wireless terminal apparatus is satisfied. If the execution condition is not satisfied, the provision of an instruction for performing a handover operation to the wireless terminal apparatus is stopped or suspended.

With such a configuration, even when the communication control apparatus that manages the handover source radio base station apparatus is different from the communication control apparatus that manages the handover destination radio base station apparatus, prior to determining whether to execute the handover operation. Since the preparation process for the handover operation can be completed, for example, “Too Late HO” in which the timing of handover by the wireless terminal device is too late can be suppressed. Also, unlike the case of adjusting parameters for handover operation, even if “Too Late HO” is suppressed, it is possible to prevent an increase in the probability of occurrence of “Too Early HO” when the timing of handover by the wireless terminal device is too early. . That is, an inappropriate handover operation can be suppressed and a good communication system can be constructed. Therefore, communication can be stabilized by appropriately controlling the handover operation of the wireless terminal device.

(23) Preferably, in the communication system, the radio base station apparatus sends the handover request to the corresponding communication control apparatus when a predetermined preparation condition regarding communication quality with the radio terminal apparatus is satisfied. The communication quality that is transmitted and indicated by the preparation condition is better than the communication quality indicated by the execution condition.

With such a configuration, the preparation process for the handover operation can be performed in advance under conditions that are milder than the communication quality that is the basis for determining whether to execute the handover operation. In addition, the time required for the handover operation can be greatly shortened by performing transmission / reception of information necessary for switching the communication control device in advance as a preparation process for the handover operation.

(24) Preferably, in the communication system, the corresponding communication control apparatus receives the handover request indicating a plurality of the other radio base station apparatuses as handover destinations from the radio base station apparatus, and Each of the other radio base station devices shown is determined whether it is a management target of itself, and if it is not a management target of itself, the handover to another communication control device that manages the other radio base station device Send a request.

(25) A communication system according to an aspect of the present invention is provided for managing a plurality of radio base station devices for transmitting / receiving radio signals to / from a radio terminal device, and one or more radio base station devices. The communication control device is connected between the one or a plurality of the radio base station devices and the higher level network, transmits communication data received from the radio terminal device via the radio base station device to the higher level network, and A communication system comprising a plurality of gateway devices for transmitting communication data received from a higher-level network to the wireless terminal device via the wireless base station device, wherein the wireless base station device transmits another wireless base station from itself A handover request for performing a handover operation of the wireless terminal device to a station device is transmitted to the communication control device, and the communication control device A gateway device connected between the radio base station device and the upper network, and a gateway device connected between the other radio base station device at the handover destination indicated by the handover request and the upper network Are different from each other, the communication path creation request is transmitted to the gateway apparatus connected between the other radio base station apparatus and the upper network, and the gateway apparatus receives the communication path creation request. Then, a communication path that enables relaying of the communication data addressed to the wireless terminal device transmitted from the upper network and the communication data transmitted from the wireless terminal device to the upper network is created, and in response to the communication path creation request A communication path creation response is transmitted to the communication control device, and the communication control device Upon receiving a route creation response, the handover request is transmitted to the other radio base station device, and when a response to the handover request is received from the other radio base station device, the radio base station that is the transmission source of the handover request A handover instruction is transmitted to the apparatus, the radio base station apparatus receives the handover instruction, determines whether a predetermined execution condition relating to communication quality with the radio terminal apparatus is satisfied, and If the execution condition is not satisfied, the provision of an instruction for performing a handover operation on the wireless terminal apparatus is stopped or suspended.

With such a configuration, the gateway apparatus connected between the handover source radio base station apparatus and the higher level network, and the gateway apparatus connected between the handover destination radio base station apparatus and the higher level network are provided. Even if they are different, the handover operation preparation process can be completed prior to determining whether to execute the handover operation. For example, it is possible to suppress “Too Late HO” when the timing of handover by the wireless terminal device is too late, for example. Can do. Also, unlike the case of adjusting parameters for handover operation, even if “Too Late HO” is suppressed, it is possible to prevent an increase in the probability of occurrence of “Too Early HO” when the timing of handover by the wireless terminal device is too early. . That is, an inappropriate handover operation can be suppressed and a good communication system can be constructed. Therefore, communication can be stabilized by appropriately controlling the handover operation of the wireless terminal device.

(26) Preferably, in the communication system, the radio base station apparatus transmits the handover request to the communication control apparatus when a predetermined preparation condition regarding communication quality with the radio terminal apparatus is satisfied. The communication quality indicated by the preparation condition is better than the communication quality indicated by the execution condition.

With such a configuration, the preparation process for the handover operation can be performed in advance under conditions that are milder than the communication quality that is the basis for determining whether to execute the handover operation. In addition, the time required for the handover operation can be greatly shortened by performing transmission / reception of information necessary for switching the gateway device in advance as a preparation process for the handover operation.

(27) Preferably, in the communication system, the communication control apparatus receives the handover request indicating a plurality of other radio base station apparatuses as handover destinations from the radio base station apparatus, and indicates the handover request indicated by the handover request. For each other radio base station apparatus, a gateway apparatus connected between the radio base station apparatus and the upper network, and a gateway connected between the other radio base station apparatus and the upper network It is determined whether or not the device is different, and the communication path creation request is transmitted to the gateway device determined to be different.

(28) A communication control method according to an aspect of the present invention is for managing a plurality of radio base station apparatuses for transmitting / receiving radio signals to / from a radio terminal apparatus and one or a plurality of the radio base station apparatuses. A communication control method in a communication system comprising a plurality of communication control devices, wherein the radio base station device responds to a handover request for performing a handover operation of the radio terminal device from itself to another radio base station device. The step of transmitting to the communication control device, and the corresponding communication control device, when the other radio base station device of the handover destination indicated by the handover request is not the management target of the other radio base station device A step of transmitting the handover request to another communication control device that manages the communication, and the other communication control device transmits the received handover request to the Transmitting the response to the corresponding communication control apparatus upon receiving a response to the handover request from the other radio base station apparatus, and the corresponding communication control apparatus Receiving the response from the communication control apparatus and transmitting a handover instruction to the radio base station apparatus that is the transmission source of the handover request, and the radio base station apparatus receives the handover instruction and It is determined whether or not a predetermined execution condition regarding communication quality with the terminal device is satisfied, and if the execution condition is not satisfied, an instruction for performing a handover operation to the wireless terminal device is given. Suspending or deferring.

(29) A communication control method according to an aspect of the present invention is for managing a plurality of radio base station devices for transmitting / receiving radio signals to / from a radio terminal device and one or a plurality of the radio base station devices. The communication control device is connected between one or a plurality of the radio base station devices and the upper network, and transmits communication data received from the radio terminal device via the radio base station device to the upper network, A communication control method in a communication system comprising a plurality of gateway devices for transmitting communication data received from the upper network to the wireless terminal device via the wireless base station device, wherein the wireless base station device A handover request for performing a handover operation of the radio terminal device from the mobile station to another radio base station device is transmitted to the communication control device A gateway device connected between the radio base station device and the upper network, the other radio base station device of the handover destination indicated by the handover request, and the upper network; If the gateway device connected between is different from the gateway device connected to the gateway device connected between the other radio base station device and the higher-level network, the communication path creation request, When the gateway device receives the communication path creation request, communication that enables relaying of the communication data addressed to the wireless terminal device transmitted from the upper network and the communication data transmitted from the wireless terminal device to the upper network Create a route and send a communication route creation response to the communication route creation request And when the communication control apparatus receives the communication path creation response, the handover request is transmitted to the other radio base station apparatus, and the other radio base station apparatus responds to the handover request. When receiving the response, a step of transmitting a handover instruction to the radio base station apparatus that is the transmission source of the handover request, and a communication between the radio base station apparatus and the radio terminal apparatus when the radio base station apparatus receives the handover instruction It is determined whether or not a predetermined execution condition related to quality is satisfied. If the execution condition is not satisfied, the provision of an instruction for performing a handover operation to the wireless terminal apparatus is stopped or suspended. Steps.

(30) A communication control program according to an aspect of the present invention manages a plurality of radio base station devices for transmitting / receiving radio signals to / from a radio terminal device and one or a plurality of the radio base station devices. A communication program used in a communication system comprising a plurality of communication control devices, wherein the wireless base station device performs handover operation of the wireless terminal device from itself to another wireless base station device in a computer A step of transmitting a request to the corresponding communication control device; and when the other radio base station device at the handover destination indicated by the handover request is not a management target of the corresponding communication control device, The step of transmitting the handover request to another communication control apparatus that manages the radio base station apparatus, and the other communication control apparatus, Transmitting the received handover request to the other radio base station apparatus, receiving the response to the handover request from the other radio base station apparatus, and transmitting the response to the corresponding communication control apparatus; The communication control apparatus receives the response from the other communication control apparatus and transmits a handover instruction to the radio base station apparatus that is the transmission source of the handover request; and the radio base station apparatus performs the handover An instruction is received and it is determined whether or not a predetermined execution condition relating to communication quality with the wireless terminal apparatus is satisfied, and if the execution condition is not satisfied, handover to the wireless terminal apparatus is performed This is a program for executing a step of canceling or deferring the assignment of an instruction for performing an operation.

(31) A communication control program according to an aspect of the present invention is for managing a plurality of radio base station devices for transmitting / receiving radio signals to / from a radio terminal device and one or a plurality of the radio base station devices. The communication control device is connected between one or a plurality of the radio base station devices and the upper network, and transmits communication data received from the radio terminal device via the radio base station device to the upper network, A communication program used in a communication system comprising a plurality of gateway devices for transmitting communication data received from the upper network to the wireless terminal device via the wireless base station device, the computer storing the wireless base station A handheld device that performs a handover operation of the wireless terminal device from itself to another wireless base station device. Transmitting a communication request to the communication control device; a gateway device connected between the wireless base station device and the higher-level network; and the other handover destination indicated by the handover request. When the gateway device connected between the wireless base station device and the upper network is different, a communication path creation request is connected between the other wireless base station device and the upper network. Transmitting to the gateway device; and when the gateway device receives the communication path creation request, the communication data addressed to the wireless terminal device transmitted from the upper network and the upper network transmitted from the wireless terminal device Create a communication path that can relay communication data to A communication path creation response to the communication control apparatus, and when the communication control apparatus receives the communication path creation response, the handover request is transmitted to the other radio base station apparatus, and the other radio When a response to the handover request is received from the base station device, a step of transmitting a handover instruction to the wireless base station device that is a transmission source of the handover request; and the wireless base station device receives the handover instruction, and It is determined whether or not a predetermined execution condition relating to communication quality with the wireless terminal apparatus is satisfied. If the execution condition is not satisfied, an instruction for performing a handover operation for the wireless terminal apparatus is issued. This is a program for executing the step of canceling or holding the grant.

According to the present invention, it is possible to stabilize the communication by appropriately controlling the handover operation of the wireless terminal device.

It is a figure which shows the structure of the radio | wireless communications system which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the sequence of the hand-over operation | movement in the radio | wireless communications system which concerns on the 1st Embodiment of this invention. FIG. 3 is a diagram illustrating an example of a situation where an inappropriate handover operation (Too Late HO) occurs in the wireless communication system according to the first embodiment of the present invention. It is a figure which shows an example of the sequence of an improper handover operation (Too Late HO) and its detection process in the radio | wireless communications system which concerns on the 1st Embodiment of this invention. FIG. 3 is a diagram illustrating an example of a situation in which an inappropriate handover operation (Too Early HO) occurs in the wireless communication system according to the first embodiment of the present invention. FIG. 3 is a diagram illustrating an example of a situation in which an inappropriate handover operation (Too Early HO) occurs in the wireless communication system according to the first embodiment of the present invention. It is a figure which shows an example of the sequence of the improper handover operation (Too Early HO) and its detection process in the radio | wireless communications system which concerns on the 1st Embodiment of this invention. FIG. 3 is a diagram illustrating an example of a situation in which an inappropriate handover operation (HO to Wong Cell) occurs in the wireless communication system according to the first embodiment of the present invention. It is a figure which shows an example of the sequence of the improper handover operation (HO to Wong Cell) and its detection process in the radio | wireless communications system which concerns on the 1st Embodiment of this invention. It is a figure which shows the simulation result of the reception quality of the radio | wireless terminal apparatus in the radio | wireless communications system which concerns on the 1st Embodiment of this invention. In the radio | wireless communications system which concerns on the 1st Embodiment of this invention, it is a figure which shows event A1 in which a radio | wireless terminal apparatus transmits a notification of a measurement result. FIG. 7 is a diagram illustrating an event A2 in which a wireless terminal device transmits a measurement result notification in the wireless communication system according to the first embodiment of the present invention. FIG. 7 is a diagram illustrating an event A3 in which a wireless terminal device transmits a measurement result notification in the wireless communication system according to the first embodiment of the present invention. It is a figure which shows event A4 which a radio | wireless terminal apparatus transmits a measurement result notification in the radio | wireless communications system which concerns on the 1st Embodiment of this invention. FIG. 7 is a diagram illustrating an event A5 in which a wireless terminal device transmits a measurement result notification in the wireless communication system according to the first embodiment of the present invention. It is a figure which shows the timing control of the hand-over operation by adjustment of hysteresis HS in the radio | wireless communications system which concerns on the 1st Embodiment of this invention. It is a figure which shows the timing control of the hand-over operation by adjustment of TTT in the radio | wireless communications system which concerns on the 1st Embodiment of this invention. FIG. 5 is a diagram illustrating timing control of a handover operation by adjusting an offset OST in the wireless communication system according to the first embodiment of the present invention. It is a figure which shows the structure of the radio base station apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the control part in the radio base station apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the sequence of the hand-over operation | movement in the radio | wireless communications system which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the sequence of the hand-over operation | movement in the radio | wireless communications system which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the sequence of the hand-over operation | movement in the radio | wireless communications system which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the sequence of the hand-over operation | movement in the radio | wireless communications system which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the breakdown of the time which a hand-over operation | movement requires in the radio | wireless communications system which concerns on the 1st Embodiment of this invention. It is a figure which shows the radio | wireless environment parameter in the radio | wireless communications system of simulation object. It is a figure which shows the parameter of the electric power measurement process (Measurement) in the radio | wireless communications system of simulation object. It is a figure which shows the simulation result of a handover failure probability. It is a figure which shows the simulation result of the generation | occurrence | production probability of "Ping Pong HO". FIG. 30 is a diagram showing the sum of the handover failure probability shown in FIG. 28 and the occurrence probability of “Ping Pong HO” shown in FIG. 29. It is a figure which shows the improvement object by the radio base station apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of a structure of the radio | wireless communications system which concerns on the 2nd Embodiment of this invention. In the radio communication system according to the second embodiment of the present invention, the sequence of the handover operation in a situation where the conditions for executing the handover operation are satisfied. In the radio communication system according to the second embodiment of the present invention, the sequence of the handover operation in a situation where the conditions for executing the handover operation are not satisfied. It is a figure which shows an example of a structure of the radio | wireless communications system which concerns on the 2nd Embodiment of this invention. In the radio communication system according to the second embodiment of the present invention, the sequence of the handover operation in a situation where the conditions for executing the handover operation are satisfied. In the radio communication system according to the second embodiment of the present invention, the sequence of the handover operation in a situation where the conditions for executing the handover operation are not satisfied. It is a figure which shows an example of a structure of the radio | wireless communications system which concerns on the 2nd Embodiment of this invention. In the radio communication system according to the second embodiment of the present invention, the sequence of the handover operation in a situation where the conditions for executing the handover operation are satisfied. In the radio communication system according to the second embodiment of the present invention, the sequence of the handover operation in a situation where the conditions for executing the handover operation are not satisfied. It is a figure for demonstrating an example of the condition where two or more radio base station apparatuses which are candidates for a handover destination exist. It is a figure which shows an example of the sequence of the handover operation in the situation shown in FIG. It is a figure for demonstrating the subject in an example of the condition where there exist multiple radio base station apparatuses which are candidates for a handover destination. FIG. 44 is a diagram showing an exemplary sequence of a handover operation in the situation shown in FIG. 43. It is a figure which shows the structure of the radio | wireless communications system which concerns on the 3rd Embodiment of this invention. In the radio communication system according to the third embodiment of the present invention, it is a sequence of a handover operation when a handover source radio base station apparatus selects a handover destination. It is a figure which shows the comparative example of the message structure of a RRC connection reconfiguration | reconstruction instruction | indication. It is a figure which shows an example of the message structure of the RRC connection reconfiguration instruction | indication transmitted from the handover request | requirement part in the radio | wireless communications system which concerns on the 3rd Embodiment of this invention. It is a figure which shows the structure of the radio | wireless terminal apparatus of the radio | wireless communications system which concerns on the 3rd Embodiment of this invention. In the radio communication system according to the third embodiment of the present invention, a sequence of a handover operation when a radio terminal apparatus selects a handover destination. It is a figure which shows an example of a structure of the radio | wireless communications system which concerns on the 4th Embodiment of this invention. It is a sequence of the hand-over operation | movement in the radio | wireless communications system which concerns on the 4th Embodiment of this invention. It is a figure which shows an example of a structure of the radio | wireless communications system which concerns on the 4th Embodiment of this invention. It is a sequence of the hand-over operation | movement in the radio | wireless communications system which concerns on the 4th Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

The radio base station apparatus notifies the radio terminal apparatus of information about the cell and the neighboring cell that it forms, that is, the frequency of the radio signal and the ID (identification) of the neighboring cell. The wireless terminal device detects and measures neighboring cells based on information notified from the wireless base station device. The wireless terminal device starts moving to the neighboring cell based on the measurement result. Here, “movement” of the wireless terminal device means not only handover but also through which cell the wireless terminal device in an idle state starts communication in the future, that is, when a call or data communication is started. This means selecting whether to perform communication.

For example, when the wireless terminal device is communicating with the wireless base station device, the destination of the wireless terminal device is determined by the wireless base station device or the higher-level device in the core network. For example, when the wireless terminal device is not communicating with the wireless base station device, the wireless terminal device determines the destination of the wireless terminal device.

In addition, handover means that a radio base station apparatus that is a communication partner of a radio terminal apparatus during a call or data communication is switched.

The wireless terminal device is located in a cell means that the wireless terminal device selects a wireless base station device forming the cell as a communication destination and can communicate with the wireless base station device. This means that communication is in progress.

The femtocell and access mode are described in 3GPP (Third Generation Partnership Project) SPEC TS 22.220 as follows. That is, a femto base station is a customer premises apparatus that connects a wireless terminal device connected via a wireless interface to a mobile communication carrier network using an IP backhaul.

In addition, in the access mode of the femto cell, the femto base station in the closed access mode provides a service only to related CSG (Closed Subscriber Group) members. The hybrid mode femto base station also provides services to the associated CSG members and CSG non-members. The femto base station in the open access mode operates as a normal base station.

Such a 3GPP definition may also be applied to the wireless communication system according to the embodiment of the present invention.

Also, the following definitions can be applied together with the above definitions or separately.

The macro base station and the pico base station are radio base station devices that are under the control of the operator and that can communicate with the radio base station device that has contracted with the operator. Further, it is considered that the macro base station and the pico base station are basically not turned off.

Also, the femto base station is a radio base station apparatus that is mainly installed in an individual or corporate building and may move or be turned off depending on user circumstances.

In addition, the femto base station operates in an access mode of open / hybrid / closed. When the femto base station operates in the closed access mode, only registered members (terminals) can be connected. When operating in the closed access mode, the service is provided only to registered members. When operating in the hybrid mode, the service is provided to both registered members and unregistered members, that is, non-members. When operating in the open access mode, the same operation as that of the macro base station and the pico base station is performed.

<First Embodiment>
[Configuration and basic operation]
FIG. 1 is a diagram showing a configuration of a wireless communication system according to the first embodiment of the present invention.

Referring to FIG. 1, the radio communication system is a mobile communication system that complies with LTE (Long Term Evolution) standardized by, for example, 3GPP (Third Generation Partnership Project), and includes radio

base station apparatuses

101A and 101B. In FIG. 1, two radio base station apparatuses are representatively shown, but a larger number of radio base station apparatuses may be provided.

Radio

base station apparatuses

101A and 101B are, for example, femto base stations, pico base stations, or macro base stations.

The wireless base station device 101A can communicate with the wireless terminal device 202 by forming a cell CA and transmitting / receiving a wireless signal to / from the wireless terminal device 202 existing in the cell CA. The radio base station apparatus 101B can communicate with the radio terminal apparatus 202 by forming a cell CB and transmitting and receiving radio signals to and from the radio terminal apparatus 202 existing in the cell CB.

Here, the direction from the wireless terminal device to the core network is referred to as an uplink direction, and the direction from the core network to the wireless terminal device is referred to as a downlink direction.

The radio base station apparatus and the radio terminal apparatus in the radio communication system according to the first embodiment of the present invention read and execute a program including each step of the following sequences from a memory (not shown). This program can be installed externally. The installed program is distributed in a state stored in a recording medium, for example.

FIG. 2 is a diagram illustrating an example of a handover operation sequence in the wireless communication system according to the first embodiment of the present invention.

Here, as shown in FIG. 1, it is assumed that the wireless terminal device 202 is located in the cell CA and is in communication with the wireless base station device 101A, and moves to an overlapping area of the cell CA and the cell CB. To do.

Referring to FIG. 2, first, radio base station apparatus 101A sets a frequency to be measured by radio terminal apparatus 202 in communication with itself and another radio base station apparatus that transmits a radio signal of the frequency. (Step S1).

Next, the wireless base station device 101A sends a measurement start request (Measurement Configuration) to the wireless terminal device 202 to cause the wireless terminal device 202 to measure the reception level of the wireless signal transmitted from the set other wireless base station device. Send. This measurement start request includes neighboring cell information, that is, the cell ID of the radio base station apparatus to be measured. Further, the measurement start request includes the transmission frequency of each radio base station device (step S2).

Next, the wireless terminal device 202 receives the measurement start request from the wireless base station device 101A and starts the power measurement process (Measurement), that is, the wireless indicated by the measurement start request at the frequency indicated by the received measurement start request. The received power of the radio signal transmitted from the base station apparatus is measured (step S3).

Next, the wireless terminal device 202 transmits a measurement result notification (Measurement Report) indicating the measurement result of the received power to the wireless base station device 101A. For example, the wireless terminal device 202 periodically measures the received power, when the communication state with the wireless base station device 101A deteriorates, and with other wireless base station devices other than the wireless base station device 101A When the state becomes better, a measurement result notification is transmitted to the radio base station apparatus 101A (step S4).

Next, the radio base station apparatus 101A acquires measurement information indicating the measurement result for each cell ID based on the measurement result notification received from the radio terminal apparatus 202, and stores it in a storage unit (not shown) (step S5).

Next, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A determines whether or not the wireless terminal device 202 should be handed over. For example, the radio base station apparatus 101B is determined as a handover destination with reference to the information (step S6).

Next, the radio base station device 101A transmits a handover request indicating the radio base station device 101B to the higher-level device (step S7).

Next, the host apparatus receives the handover request from the radio base station apparatus 101A and transmits the handover request to the radio base station apparatus 101B (step S8).

Next, the radio base station apparatus 101B receives the handover request from the higher-level apparatus and transmits a handover response to the handover request to the higher-level apparatus (Step S9).

Next, the higher-level device receives a handover response from the radio base station device 101B and transmits a handover instruction to the radio base station device 101A (step S10).

Next, the radio base station apparatus 101A receives a handover instruction from the host apparatus and transmits an RRC (Radio Resource Control) connection reconfiguration instruction (RRC Connection Reconfiguration) to the radio terminal apparatus 202 (step S11).

Next, the wireless base station device 101A transmits a status notification indicating its own communication status and the like to the higher-level device (step S12).

Next, the host device receives the status notification from the radio base station device 101A and transmits the status notification indicating the communication content with the radio terminal device 202 to the radio base station device 101B (step S13).

When the RRC connection is established between the wireless terminal device 202 and the wireless base station device 101B, the wireless terminal device 202 transmits an RRC connection reconfiguration completion notification (RRC Connection Reconfiguration Complete) to the wireless base station device 101B ( Step S14).

Next, the radio base station apparatus 101B receives the RRC connection reconfiguration completion notification from the radio terminal apparatus 202 and transmits a handover completion notification to the higher-level apparatus (step S15).

Next, the host device receives a handover completion notification from the radio base station device 101B and transmits a terminal information release instruction to the radio base station device 101A (step S16).

Next, the wireless base station device 101A receives the terminal information release instruction from the higher-level device, releases the information related to the wireless terminal device 202, and transmits a terminal information release completion notification to the higher-level device (step S17).

[Example of inappropriate handover operation]
Hereinafter, a radio base station apparatus communicating with the radio terminal apparatus 202 or a handover source radio base station apparatus is also referred to as a serving base station, and a handover destination radio base station apparatus is also referred to as a neighboring base station.

FIG. 3 is a diagram illustrating an example of a situation where an inappropriate handover operation (Too Late HO) occurs in the wireless communication system according to the first embodiment of the present invention.

FIG. 4 is a diagram showing an example of an inappropriate handover operation (Too Late HO) and its detection processing sequence in the wireless communication system according to the first embodiment of the present invention.

“Too Late HO” refers to the following cases, for example. That is, before handover starts or during handover processing, a radio link failure (RLF) occurs in the handover source radio base station apparatus, and a radio base station other than the handover source radio base station apparatus. This is a case where connection re-establishment of the wireless terminal device 202 to the device has occurred.

The detection method of “Too Late HO” is as follows, for example. That is, when the radio terminal device 202 reestablishes the radio link to the radio base station device 101B after causing the RLF for the radio base station device 101A, the radio base station device 101B notifies the radio base station device 101A of the RLF. Send. Thereby, the radio base station apparatus 101A detects “Too Late HO”.

Here, as shown in FIG. 3, it is assumed that the wireless terminal device 202 is located in the cell CA and is communicating with the wireless base station device 101A.

Referring to FIG. 3 and FIG. 4, first, radio terminal apparatus 202 measures the received power of a radio signal transmitted from each radio base station apparatus, and wirelessly sends a measurement result notification indicating the measured result of the received power. It transmits to base station apparatus 101A (step S51).

Next, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A determines whether or not the wireless terminal device 202 should be handed over. When it is determined that the radio terminal apparatus 202 should be handed over, the radio base station apparatus 101A refers to the neighboring cell information and determines, for example, the radio base station apparatus 101B as a handover destination (step S52).

Next, the radio base station apparatus 101A transmits a handover request indicating the radio base station apparatus 101B to the radio base station apparatus 101B via the X2 interface that is an inter-base station interface (step S53).

Next, the radio base station apparatus 101B receives the handover request from the radio base station apparatus 101A, and transmits a handover response to the handover request to the radio base station apparatus 101A via the X2 interface (step S54).

Here, while preparing for handover on the network side, that is, while the radio

base station apparatuses

101A and 101B are transmitting and receiving a message for handover as described above, the radio terminal apparatus 202 is out of service area of the cell CA, and Move to within the cell CB (step S55).

Due to the movement of the wireless terminal device 202, the RRC connection reconfiguration instruction (step S56) for instructing the handover transmitted from the wireless base station device 101A does not reach the wireless terminal device 202, and RLF is generated (step S56). S57).

Next, when the radio terminal apparatus 202 detects the occurrence of RLF, the radio terminal apparatus 202 searches for a neighboring radio base station apparatus by measuring the reception power of the radio signal and reconnects to the searched radio base station apparatus 101B. A connection re-establishment request (RRC Connection Reestablishment Request) is transmitted (step S58).

Next, the radio base station apparatus 101B receives the RRC connection re-establishment request from the radio terminal apparatus 202 and transmits an RRC connection re-establishment response to the radio terminal apparatus 202 (step S59). Thereby, an RRC connection is established between the wireless terminal device 202 and the wireless base station device 101B.

Next, the wireless terminal device 202 transmits an RRC connection re-establishment completion notification (RRC Connection Reestablishment Complete) to the wireless base station device 101B (step S60).

This RRC connection re-establishment completion notification includes a parameter “rlf-InfoAvailable”, for example. The wireless terminal device 202 sets this parameter and transmits an RRC connection re-establishment completion notification. Thereby, the radio base station apparatus 101B recognizes that an RLF has occurred in the radio terminal apparatus 202. The radio base station apparatus 101B transmits a terminal information request (UE Information Request) to the radio terminal apparatus 202 in order to acquire detailed information of the RLF (step S61).

Next, the wireless terminal device 202 receives the terminal information request from the wireless base station device 101B, and transmits a terminal information response (UE Information Response) including the RLF report to the wireless base station device 101B (step S62). The RLF report includes the PCI (Physical Cell ID) of the radio base station apparatus in which the RLF has occurred, the PCI and ECGI (E-UTRAN Cell Global Identifier) of the radio base station apparatus in which the RRC connection has been reestablished, and the own radio terminal apparatus 202. C-RNTI (Cell Radio Network Temporary Identifier), etc. Here, the PCI of the RLF occurrence is the ID of the radio base station apparatus 101A, the PCI and ECGI of the RRC connection re-establishment occurrence are the ID of the radio base station apparatus 101B, and the C-RNTI is assigned by the radio base station apparatus 101A ID.

Next, the radio base station apparatus 101B recognizes that RLF has occurred in the radio base station apparatus 101A by referring to the PCI of the RLF report received from the radio terminal apparatus 202. Then, the radio base station apparatus 101B transmits an RLF notification (RLF INDICATION) including the contents of the RLF report to the radio base station apparatus 101A via the X2 interface in order to notify that it is “Too Late HO” ( Step S63).

Next, the radio base station apparatus 101A recognizes that “Too Late HO” has occurred to the cell CB by referring to the PCI, ECGI, and C-RNTI of the RLF notification received from the radio base station apparatus 101B. (Step S64).

Next, the radio base station apparatus 101A executes a handover operation optimization process so as to suppress the occurrence of “Too Late HO” in the cell CB (step S65).

5 and 6 are diagrams illustrating an example of a situation in which an inappropriate handover operation (Too Early HO) has occurred in the wireless communication system according to the first embodiment of the present invention.

5 and 6, cell CB formed by radio base station apparatus 101B includes cell CB1 including the installation area of radio base station apparatus 101B, and radio base station apparatus 101B formed in cell CA. The cell CB2 does not include an installation area.

FIG. 7 is a diagram showing an example of an inappropriate handover operation (Too Early HO) and its detection processing sequence in the wireless communication system according to the first embodiment of the present invention.

“Too Early HO” refers to the following cases, for example. That is, after the wireless terminal device 202 has successfully connected to the handover destination wireless base station device, RLF occurs in a short time, and the wireless terminal device 202 is reconnected to the handover source wireless base station device. This is the case when establishment occurs.

The detection method of “Too Early HO” is as follows, for example. That is, when the handover destination radio base station apparatus 101B receives the RLF report from the handover source radio base station apparatus 101A, the handover to the radio terminal apparatus 202 itself is performed within a predetermined time from the reception timing. When the terminal information release instruction upon completion of the transmission is transmitted to the radio base station apparatus 101A, the radio base station apparatus 101A is notified that “Too Early HO”.

Here, the radio base station apparatus 101B uses a timer to measure the predetermined time. As a result, when the radio base station apparatus 101B receives the RLF report, whether the RLF has occurred due to its own “Too Late HO” or whether the RLF has occurred due to the “Too Early HO” of the radio base station apparatus 101A. Can be determined.

Here, as shown in FIG. 5, a case is assumed in which radio terminal apparatus 202 moves into cell CB2 from a state where it is located in cell CA and is communicating with radio base station apparatus 101A (step S70). .

5 to 7, first, radio terminal apparatus 202 measures the reception power of a radio signal transmitted from a radio base station apparatus, and sends a measurement result notification indicating the measurement result of the measured reception power to radio base station. It transmits to station apparatus 101A (Source eNB, Serving eNB) (step S71).

Next, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A determines whether or not the wireless terminal device 202 should be handed over. When determining that the radio terminal apparatus 202 should be handed over, the radio base station apparatus 101A refers to the neighboring cell information and determines, for example, the radio base station apparatus 101B as a handover destination (step S72).

Next, the radio base station apparatus 101A transmits a handover request indicating the radio base station apparatus 101B to the radio base station apparatus 101B via the X2 interface that is an interface between base stations (step S73).

Next, the radio base station apparatus 101B receives the handover request from the radio base station apparatus 101A, and transmits a handover response to the handover request to the radio base station apparatus 101A via the X2 interface (step S74).

Next, the radio base station apparatus 101A receives a handover response from the radio base station apparatus 101B, and transmits an RRC connection reconfiguration instruction (RRC Connection Reconfiguration) to the radio terminal apparatus 202 (step S75).

Next, when the RRC connection is established between the wireless terminal device 202 and the wireless base station device 101B, the wireless terminal device 202 transmits an RRC connection reconfiguration completion notification (RRC Connection Reconfiguration Complete) to the wireless base station device 101B. (Step S76).

Next, the radio base station apparatus 101B receives the RRC connection reconfiguration completion notification from the radio terminal apparatus 202 and transmits a terminal information release instruction to the radio base station apparatus 101A (step S77).

Also, the radio base station apparatus 101B starts a timer in order to measure the stay time in the cell CB of the radio terminal apparatus 202 (step S78).

Next, the radio base station apparatus 101A receives a terminal information release instruction from the radio base station apparatus 101B, and releases information (UE Context) on the radio terminal apparatus 202 (step S79).

As described above, the handover of the wireless terminal device 202 from the wireless base station device 101A to the wireless base station device 101B is completed (step S80).

Here, before transmitting the measurement result notification (Measurement Report) to the radio base station apparatus 101B, the radio terminal apparatus 202 moves outside the cell CB and within the cell CA (step S81).

Then, since the wireless terminal device 202 cannot communicate with the wireless base station device 101B, RLF occurs (step S83).

Next, when the radio terminal apparatus 202 detects the occurrence of RLF, the radio terminal apparatus 202 searches for a neighboring radio base station apparatus by measuring the reception power of the radio signal and reconnects to the searched radio base station apparatus 101A. A connection re-establishment request (RRC Connection Reestablishment Request) is transmitted (step S84).

Next, since the radio base station apparatus 101A has released and does not hold the information (UE Context) regarding the radio terminal apparatus 202, the radio base station apparatus 101A can accept the RRC connection re-establishment request from the radio terminal apparatus 202. If it is not possible (step S85), an RRC connection re-establishment rejection is transmitted to the wireless terminal device 202 (step S86).

Next, when receiving the RRC connection re-establishment rejection from the radio base station apparatus 101A, the radio terminal apparatus 202 starts a normal connection procedure with the radio base station apparatus 101A (step S87).

That is, first, the wireless terminal device 202 transmits an RRC connection request to the wireless base station device 101A (step S88).

Next, the wireless base station device 101A receives the RRC connection request from the wireless terminal device 202, and transmits RRC connection information (RRC Connection Setup) to the wireless terminal device 202 (step S89).

Next, the wireless terminal device 202 receives the RRC connection information from the wireless base station device 101A, and transmits an RRC connection completion notification (RRC Connection Setup Complete) (step S90).

Next, the wireless base station device 101A receives the RRC connection completion notification from the wireless terminal device 202, and transmits security information (Security Mode Command) to the wireless terminal device 202 (step S91).

Next, the wireless terminal device 202 receives security information from the wireless base station device 101A, and transmits a security completion notification (Security Mode Complete) to the wireless base station device 101A (step S92).

Next, the radio base station apparatus 101A transmits an RRC connection reconfiguration instruction (RRC Connection Reconfiguration) to the radio terminal apparatus 202 (step S93).

Next, when the RRC connection is established between the wireless terminal device 202 and the wireless base station device 101A, the wireless terminal device 202 transmits an RRC connection reconfiguration completion notification (RRC Connection Reconfiguration Complete) to the wireless base station device 101A. (Step S94).

Here, the RRC connection completion notification and the RRC connection reconfiguration completion notification include, for example, a parameter “rlf-InfoAvailable”. The wireless terminal device 202 sets this parameter and transmits an RRC connection completion notification and an RRC connection reconfiguration completion notification. As a result, the radio base station apparatus 101A recognizes that an RLF has occurred in the radio terminal apparatus 202. The wireless base station device 101A transmits a terminal information request (UE Information Request) to the wireless terminal device 202 in order to acquire detailed information of the RLF (step S95).

Next, the wireless terminal device 202 receives the terminal information request from the wireless base station device 101A, and transmits a terminal information response (UE Information Response) including the RLF report to the wireless base station device 101A (step S96). The RLF report includes the PCI of the radio base station apparatus in which the RLF has occurred, the PCI and ECGI of the radio base station apparatus in which the RRC connection re-establishment has occurred, and the C-RNTI of the own radio terminal apparatus 202. Here, the PCI of the RLF occurrence is the ID of the radio base station apparatus 101B, the PCI and ECGI of the RRC connection re-establishment are the ID of the radio base station apparatus 101A, and the C-RNTI is assigned by the radio base station apparatus 101B ID.

Next, the radio base station apparatus 101A recognizes that RLF has occurred in the radio base station apparatus 101B by referring to the PCI of the RLF report received from the radio terminal apparatus 202, and performs “Too Late HO” to the cell CA. "Is generated (step S97).

Next, the radio base station apparatus 101A transmits an RLF notification (RLF INDICATION) including the content of the RLF report to the radio base station apparatus 101B via the X2 interface in order to notify that it is “Too Late HO”. (Step S98).

Next, when the radio base station apparatus 101B receives the RLF notification from the radio base station apparatus 101A, the radio base station apparatus 101B checks the timer that has been started. If the timer is operating, that is, a predetermined time has elapsed since the timer was started. If not, it is determined not to be “Too Late HO” to the cell CA but to “Too Early HO” to the cell CB. When the radio base station apparatus 101B receives the RLF notification from the radio base station apparatus 101A and the timer is not operating, that is, when the predetermined time has elapsed since the timer was started, the cell CA It is determined that it is “Too Late HO”.

When the radio base station apparatus 101B determines that it is “Too Early HO” to the cell CB (step S99), it transmits a handover report to the radio base station apparatus 101A (step S100). This handover report includes, for example, a parameter “Handover Report Type”. The radio base station apparatus 101B notifies the radio base station apparatus 101A of “Too Early HO” by setting this parameter to a predetermined value.

Next, the radio base station apparatus 101A receives the handover report from the radio base station apparatus 101B, recognizes that “Too Early HO” has occurred to the cell CB (step S101), and “Too Early HO”. A handover operation optimization process is executed so as to suppress the occurrence of (step S102).

FIG. 8 is a diagram illustrating an example of a situation where an inappropriate handover operation (HO to Wong Cell) occurs in the wireless communication system according to the first embodiment of the present invention.

Referring to FIG. 8, the wireless communication system further includes a wireless base station device 101 </ b> C as compared with the wireless communication system illustrated in FIG. 1. Radio base station apparatus 101C is, for example, a femto base station, a pico base station, or a macro base station.

The radio base station apparatus 101C can communicate with the radio terminal apparatus 202 by forming a cell CC and transmitting and receiving radio signals to and from the radio terminal apparatus 202 existing in the cell CC.

FIG. 9 is a diagram illustrating an example of an inappropriate handover operation (HO to Wong Cell) and its detection processing sequence in the wireless communication system according to the first embodiment of the present invention.

“HO to Wong Cell” refers to the following cases, for example. That is, after the wireless terminal device 202 has successfully connected to the handover destination wireless base station device, RLF occurs in a short time, and wireless communication is performed with respect to wireless base station devices other than the handover source and handover destination wireless base station devices. This is a case where the connection re-establishment of the terminal device 202 occurs.

For example, the detection method of “HO to Wong Cell” is as follows. That is, when the radio base station apparatus 101B that is the handover destination receives the RLF report from the radio base station apparatus 101C other than the radio base station apparatus 101A that is the handover source, the radio terminal is traced back from the reception timing within a predetermined time. When the terminal information release instruction due to the completion of the handover of the apparatus 202 to itself is transmitted to the radio base station apparatus 101A, the radio base station apparatus 101A is notified that “HO to Wong Cell”.

Here, the radio base station apparatus 101B uses a timer to measure the predetermined time. Thereby, when the radio base station apparatus 101B receives the RLF report, whether the RLF has occurred due to its own “Too Late HO” or whether the RLF has occurred due to the “HO to Wong Cell” of the radio base station apparatus 101A. Can be determined.

Here, as shown in FIG. 8, when the wireless terminal device 202 is located in the cell CA and is communicating with the wireless base station device 101A, the wireless terminal device 202 moves to the overlapping area of the virtual cell CBV and the cell CA ( Assume step S110). The virtual cell CBV is a virtual cell expanded from the cell CB in accordance with the offset OST that is a parameter in order to promote handover from the radio base station apparatus 101A to the radio base station apparatus 101B. In this case, the offset OST is a parameter held by the radio base station apparatus 101A.

Referring to FIG. 8 and FIG. 9, first, radio terminal apparatus 202 measures the received power of a radio signal transmitted from the radio base station apparatus, and sends a measurement result notification indicating the measured result of the received power to radio base station. Transmit to the station apparatus 101A (step S111).

Next, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A determines whether or not the wireless terminal device 202 should be handed over. When it is determined that the radio terminal apparatus 202 should be handed over, the radio base station apparatus 101A refers to the neighboring cell information and determines, for example, the radio base station apparatus 101B as a handover destination (step S112).

Next, the radio base station apparatus 101A transmits a handover request indicating the radio base station apparatus 101B to the radio base station apparatus 101B via the X2 interface that is an interface between base stations (step S113).

Next, the radio base station apparatus 101B receives the handover request from the radio base station apparatus 101A, and transmits a handover response to the handover request to the radio base station apparatus 101A via the X2 interface (step S114).

Next, the radio base station apparatus 101A receives a handover response from the radio base station apparatus 101B, and transmits an RRC connection reconfiguration instruction (RRC Connection Reconfiguration) to the radio terminal apparatus 202 (step S115).

Next, when the RRC connection is established between the wireless terminal device 202 and the wireless base station device 101B, the wireless terminal device 202 transmits an RRC connection reconfiguration completion notification (RRC Connection Reconfiguration Complete) to the wireless base station device 101B. (Step S116).

Next, the radio base station apparatus 101B receives the RRC connection reconfiguration completion notification from the radio terminal apparatus 202, and transmits a terminal information release instruction to the radio base station apparatus 101A (step S117).

Further, the radio base station apparatus 101B starts a timer in order to measure the staying time in the cell CB of the radio terminal apparatus 202 (step S118).

Next, the radio base station apparatus 101A receives a terminal information release instruction from the radio base station apparatus 101B, and releases information (UE Context) on the radio terminal apparatus 202 (step S119).

As described above, the handover of the wireless terminal device 202 from the wireless base station device 101A to the wireless base station device 101B is completed (step S120).

Here, before transmitting the measurement result notification (Measurement Report) to the radio base station apparatus 101B, the radio terminal apparatus 202 moves out of the cell CB and into the virtual cell CBV and the cell CC (step S121).

Then, the radio terminal device 202 has a large interference of radio signals transmitted from the radio base station device 101C (Other eNB), and cannot communicate with the radio base station device 101B, so that RLF occurs (step S123). .

Next, when the radio terminal apparatus 202 detects the occurrence of RLF, the radio terminal apparatus 202 searches for nearby radio base station apparatuses by measuring the reception power of radio signals or the like. In this case, since the reception power of the radio signal from the radio base station apparatus 101C is maximized, the radio terminal apparatus 202 receives an RRC connection re-establishment request (RRC Connection) in order to reconnect to the searched radio base station apparatus 101C. Reestablishment Request) is transmitted to the radio base station apparatus 101C (step S124).

Next, since the wireless base station device 101C does not hold information (UE Context) regarding the wireless terminal device 202, the wireless base station device 101C cannot accept the RRC connection re-establishment request from the wireless terminal device 202 (step S125). ), RRC connection re-establishment rejection is transmitted to the wireless terminal device 202 (step S126).

Next, the radio terminal apparatus 202 receives an RRC connection re-establishment rejection from the radio base station apparatus 101C, and starts a normal connection procedure with the radio base station apparatus 101C (step S127).

That is, first, the wireless terminal device 202 transmits an RRC connection request to the wireless base station device 101C (step S128).

Next, the wireless base station device 101C receives the RRC connection request from the wireless terminal device 202, and transmits RRC connection information (RRC Connection Setup) to the wireless terminal device 202 (step S129).

Next, the wireless terminal device 202 receives RRC connection information from the wireless base station device 101C, and transmits an RRC connection completion notification (RRC Connection Setup Complete) (step S130).

Next, the wireless base station device 101C receives the RRC connection completion notification from the wireless terminal device 202, and transmits security information (Security Mode Command) to the wireless terminal device 202 (step S131).

Next, the wireless terminal device 202 receives security information from the wireless base station device 101C, and transmits a security completion notification (Security Mode Complete) to the wireless base station device 101C (step S132).

Next, the wireless base station device 101C transmits an RRC connection reconfiguration instruction (RRC Connection Reconfiguration) to the wireless terminal device 202 (step S133).

Next, when the RRC connection is established between the wireless terminal device 202 and the wireless base station device 101C, the wireless terminal device 202 transmits an RRC connection reconfiguration completion notification (RRC Connection Reconfiguration Complete) to the wireless base station device 101C. (Step S134).

Here, the RRC connection completion notification and the RRC connection reconfiguration completion notification include, for example, a parameter “rlf-InfoAvailable”. The wireless terminal device 202 sets this parameter and transmits an RRC connection completion notification and an RRC connection reconfiguration completion notification. Thereby, the radio base station apparatus 101C recognizes that an RLF has occurred in the radio terminal apparatus 202. The wireless base station device 101C transmits a terminal information request (UE Information Request) to the wireless terminal device 202 in order to acquire detailed information of the RLF (step S135).

Next, the wireless terminal device 202 receives a terminal information request from the wireless base station device 101C, and transmits a terminal information response (UE Information Response) including an RLF report to the wireless base station device 101C (step S136). The RLF report includes the PCI of the radio base station apparatus in which the RLF has occurred, the PCI and ECGI of the radio base station apparatus in which the RRC connection re-establishment has occurred, and the C-RNTI of the own radio terminal apparatus 202. Here, the PCI of the RLF occurrence is the ID of the radio base station apparatus 101B, the PCI and ECGI of the RRC connection re-establishment are the ID of the radio base station apparatus 101C, and the C-RNTI is assigned by the radio base station apparatus 101B ID.

Next, the wireless base station device 101C recognizes that RLF has occurred in the wireless base station device 101B by referring to the PCI of the RLF report received from the wireless terminal device 202, and performs “Too Late HO” to the cell CC. "Is generated (step S137).

Next, the radio base station apparatus 101C transmits an RLF notification (RLF INDICATION) including the content of the RLF report to the radio base station apparatus 101B via the X2 interface in order to notify that it is “Too Late HO”. (Step S138).

Next, when the radio base station apparatus 101B receives the RLF notification from the radio base station apparatus 101C, the radio base station apparatus 101B checks the timer that has been started. If the timer is operating, that is, a predetermined time has elapsed since the timer was started. If not, it is determined that it is not “Too Late HO” to the cell CC, and further, the RLF notification is received from the radio base station device 101C other than the radio base station device 101A. It is determined that it is not “Too Early HO” but “HO to Wron Cell” to the cell CB. When the radio base station apparatus 101B receives the RLF notification from the radio base station apparatus 101C and the timer is not operating, that is, when the predetermined time has elapsed since the timer was started, the cell CC It is determined that it is “Too Late HO”.

If the radio base station apparatus 101B determines that it is “HO to Wong Cell” to the cell CB (step S139), it transmits a handover report to the radio base station apparatus 101A (step S140). This handover report includes, for example, a parameter “Handover Report Type”. The radio base station apparatus 101B notifies the radio base station apparatus 101A of “HO to Wong Cell” by setting this parameter to a predetermined value.

Next, the radio base station apparatus 101A receives the handover report from the radio base station apparatus 101B, recognizes that “HO to Wong Cell” has occurred to the cell CB (step S141), and performs “HO to Wong”. The optimization process of the handover operation is executed so that the occurrence of “Cell” is suppressed (step S142).

In addition to “Too Late HO”, “Too Early HO”, and “HO to Wong Cell” as described above, there is “Ping Pong HO” as an inappropriate handover operation.

This is a case where two radio base station apparatuses determine a handover to another radio base station apparatus for a certain radio terminal apparatus. When this “Ping Pong HO” occurs, the connection between the wireless terminal device and the wireless base station device will not be cut off, but the processing for the handover operation is repeated for the wireless terminal device, and communication and data communication are performed. Cannot be performed, and the load on the upper network side increases.

[Control parameters for handover operation]
FIG. 10 is a diagram illustrating a reception quality simulation result of the wireless terminal device in the wireless communication system according to the first embodiment of the present invention.

FIG. 10 shows an RSSI (Received Signal Strength Indication) of the wireless terminal device 202 for 100 seconds until the wireless terminal device 202 passes near the pico base station at a speed of 30 km per hour and passes near the macro base station.

10, graphs G1 and G3 indicate RSSIs of radio signals transmitted from the macro base station, and graphs G2 and G4 indicate RSSIs of radio signals transmitted from the pico base station. The graphs G1 and G2 take into account the temporal change in the received power of the radio signal in the radio terminal device 202 caused by shadowing, that is, the relative position change between the radio terminal device 202 and other objects. Simulation results, and graphs G3 and G4 are simulation results that do not consider shadowing.

Referring to FIG. 10, the ideal position for handover of the wireless terminal device 202 from the pico base station to the macro base station is the vicinity of the intersection of the graph, that is, the position where the movement time is about 17 seconds. However, in practice, it is difficult to grasp the future communication environment of the wireless terminal device 202 in the wireless communication system. Therefore, it is possible to optimize the handover operation by adjusting the timing of the handover operation based on various measurement results. It is important to make it easier.

In addition, since the radio signal from each radio base station apparatus is intricate in the travel time of 15 to 20 seconds, for example, “Too Early HO” or “Ping Pong HO” is likely to occur. Also, near the timing when the travel time is 20 seconds, the reception power of the radio signal from the pico base station suddenly decreases, the reception power of the radio signal from the macro base station suddenly increases, and SINR (Signal to Interference) Since “-plus-Noise Ratio” deteriorates rapidly, “Too Late HO” is likely to occur.

Here, if the evaluation function of MRO (Mobility Robustness Optimization) that optimizes handover specified in 3GPP is Y = MRO (X), Y is, for example, the occurrence frequency of “Too Late HO”, “Too Early HO” “Occurrence frequency”, “HO to Wong Cell” occurrence frequency, “Ping Pong HO” unnecessary handover occurrence frequency, etc. Immediately after transmitting the RRC connection information, that is, the radio terminal device 202 connects to the radio base station device This is the frequency of occurrence of handover immediately after being performed.

In addition, for example, X is a parameter for power measurement processing (Measurement), hysteresis HS: 0 dB to +15 dB, TTT (Time to Trigger): 0 ms to 5120 ms, or offset OST (Cell Individual Offset): −24 dB to +24 dB It is. Alternatively, X is a parameter for cell reselection processing.

For example, hysteresis HS and TTT can be set for each event described later, and offset OST can be set for each serving cell formed by the serving base station and each neighboring cell.

Here, it is assumed that, in order to reduce the uplink transmission load of the wireless terminal device 202, the wireless base station device determines handover when receiving a measurement result notification (Measurement Report). That is, the transmission timing of the measurement result notification corresponds to the handover timing.

Hereinafter, the relationship between various events for transmitting the measurement result notification and the parameters of the power measurement process will be described.

FIG. 11 is a diagram showing an event A1 in which the wireless terminal device transmits a measurement result notification in the wireless communication system according to the first embodiment of the present invention. In FIG. 11, the horizontal axis is time, the vertical axis is the reception power or SINR of the radio signal in the wireless terminal device 202, and the SVC is the reception power or SINR of the serving cell, that is, the reception power of the radio signal transmitted by the serving base station or SINR.

Referring to FIG. 11, at event A1, hysteresis HS is set in a positive or negative direction with respect to threshold value Th.

When the received power or SINR of the serving cell becomes larger than (Th + HS), the wireless terminal device 202 transitions to the report on state (timing T1).

Then, when TTT elapses from timing T1 in a state where the condition that the received power or SINR is greater than (Th-HS) is satisfied, the wireless terminal device 202 transmits a measurement result notification (timing T2).

Next, when TTT elapses from timing T2 in a state where the condition is satisfied, the wireless terminal device 202 transmits a measurement result notification (timing T3).

Next, when the condition is not satisfied before TTT elapses from timing T3, the wireless terminal device 202 does not transmit a measurement result notification and transitions to a report off state (timing T4).

Here, the wireless terminal device 202 performs a power measurement process periodically, for example, regardless of the transition between the report-on state and the report-off state, and transmits the latest measurement result as a measurement result notification. Further, for example, radio terminal apparatus 202 performs transition between the report-on state and the report-off state independently for each of received power and SINR. That is, the wireless terminal device 202 transmits a measurement result notification if a condition is satisfied for one of the received power and SINR.

FIG. 12 is a diagram illustrating an event A2 in which the wireless terminal device transmits a measurement result notification in the wireless communication system according to the first embodiment of the present invention. The way of viewing the figure is the same as in FIG.

Referring to FIG. 12, at event A2, hysteresis HS is set in a positive or negative direction with respect to threshold value Th.

When the received power or SINR of the serving cell becomes smaller than (Th-HS), the wireless terminal device 202 transitions to the report on state (timing T11).

The wireless terminal device 202 transmits a measurement result notification when TTT elapses from timing T11 in a state where the condition that the received power or SINR is smaller than (Th + HS) is satisfied (timing T12).

Next, when TTT has elapsed from timing T12 in a state where the condition is satisfied, the wireless terminal device 202 transmits a measurement result notification (timing T13).

Next, when the condition is not satisfied before TTT elapses from timing T13, the wireless terminal device 202 does not transmit a measurement result notification and transitions to a report off state (timing T14).

FIG. 13 is a diagram showing an event A3 in which the wireless terminal device transmits a measurement result notification in the wireless communication system according to the first embodiment of the present invention. In FIG. 13, the horizontal axis is time, the vertical axis is the reception power or SINR of the radio signal in the wireless terminal device 202, SVC is the reception power or SINR of the serving cell, and NBC is the reception power or SINR of the neighboring cell, that is, This is the reception power or SINR of a radio signal transmitted by a neighboring base station.

Referring to FIG. 13, at event A3, offset OST1 is set in the positive direction with respect to the reception power or SINR of the serving cell, and hysteresis HS is set in the positive and negative directions. Also, the offset OST2 is set in the positive direction with respect to the reception power or SINR of the neighboring cells.

The wireless terminal device 202 transitions to the report-on state when {(reception power or SINR of neighboring cells) + OST2} becomes larger than {(reception power or SINR of the serving cell) + OST1 + HS} (timing T21).

Then, the wireless terminal device 202 performs the processing from the timing T21 to the TTT in a state where {(neighboring cell received power or SINR) + OST2} is larger than {(serving cell received power or SINR) + OST1-HS}. When the time has elapsed, a measurement result notification is transmitted (timing T22).

Next, when TTT has elapsed from timing T22 in a state where the condition is satisfied, the wireless terminal device 202 transmits a measurement result notification (timing T23).

Next, when the condition is not satisfied before TTT elapses from timing T23, the wireless terminal device 202 does not transmit a measurement result notification and transitions to a report off state (timing T24).

FIG. 14 is a diagram showing an event A4 in which the wireless terminal device transmits a measurement result notification in the wireless communication system according to the first embodiment of the present invention. The way of viewing the figure is the same as in FIG.

Referring to FIG. 14, at event A4, the offset OST is set in the positive direction with respect to the reception power or SINR of the neighboring cells, and the hysteresis HS is set in the positive and negative directions with respect to the threshold Th.

Wireless terminal apparatus 202 transitions to a report-on state when {(reception power or SINR of neighboring cells) + OST} is greater than (Th + HS) (timing T31).

Then, wireless terminal apparatus 202 transmits a measurement result notification when TTT elapses from timing T31 while the condition that {(reception power or SINR of the neighboring cell) + OST} is larger than (Th−HS) is satisfied. (Timing T32).

Next, when TTT has elapsed from timing T32 in a state where the condition is satisfied, the wireless terminal device 202 transmits a measurement result notification (timing T33).

Next, when the condition is not satisfied before TTT elapses from timing T33, the wireless terminal device 202 does not transmit a measurement result notification and transitions to a report off state (timing T34).

FIG. 15 is a diagram showing an event A5 in which the wireless terminal device transmits a measurement result notification in the wireless communication system according to the first embodiment of the present invention. The way of viewing the figure is the same as in FIG.

Referring to FIG. 15, at event A5, the offset OST is set in the positive direction with respect to the reception power or SINR of the neighboring cell, and the hysteresis HS1 is set in the positive and negative direction with respect to the threshold Th1. Hysteresis HS2 is set in the positive and negative directions with respect to Th2.

When the received power or SINR of the serving cell becomes smaller than (Th1-HS1) and {(reception power or SINR of neighboring cells) + OST} becomes larger than (Th2 + HS2), the wireless terminal device 202 transitions to the report on state. (Timing T41).

Radio terminal 202 satisfies the condition that the reception power or SINR of the serving cell is smaller than (Th1 + HS1) and {(reception power or SINR of the neighboring cell) + OST} is larger than (Th2-HS2). When TTT elapses from timing T41 in a state where it is in a state, a measurement result notification is transmitted (timing T42).

Next, when the condition is not satisfied before TTT elapses from timing T42, the wireless terminal device 202 does not transmit a measurement result notification and transitions to a report off state (timing T43).

As described above, the timing of the handover operation of the wireless terminal device 202 can be controlled by adjusting the parameters described in the events A1 to A5, that is, the hysteresis HS, TTT, and the offset OST.

FIG. 16 is a diagram showing handover operation timing control by adjusting the hysteresis HS in the wireless communication system according to the first embodiment of the present invention. FIG. 16 shows the case of event A3.

Referring to FIG. 16, when hysteresis HS is set to zero, a transition is made to the report on state at timing T51, a measurement result notification is transmitted at timing T53, and a transition to the report off state is made at timing T55.

On the other hand, when the hysteresis HS is set larger than zero, the state transits to the report-on state at timing T52 after timing T51, the measurement result notification is transmitted at timing T54 after timing T53, and timing T55. At a later timing T56, the state transits to the report off state.

That is, when the hysteresis HS is increased, the transmission timing of the measurement result notification, that is, the timing of the handover operation can be delayed.

FIG. 17 is a diagram showing timing control of the handover operation by adjusting the TTT in the wireless communication system according to the first embodiment of the present invention. FIG. 17 shows the case of event A3.

Referring to FIG. 17, when TTT is set to be small, a measurement result notification is transmitted at timing T62.

On the other hand, when TTT is set large, a measurement result notification is transmitted at timing T63 after timing T61.

That is, when the TTT is increased, the transmission timing of the measurement result notification, that is, the timing of the handover operation can be delayed.

FIG. 18 is a diagram showing handover operation timing control by adjusting the offset OST in the wireless communication system according to the first embodiment of the present invention. FIG. 18 shows the case of event A3.

Referring to FIG. 18, when the offset OST is set to zero, a transition is made to the report on state at timing T71, a measurement result notification is transmitted at timing T73, and a transition to the report off state is made at timing T76.

On the other hand, when the offset OST is set to be smaller than zero, a transition is made to the report-on state at timing T72 after timing T71, a measurement result notification is transmitted at timing T74 after timing T73, and timing T76. Transition to the report-off state at an earlier timing T75.

That is, if the offset OST is reduced, the transmission timing of the measurement result notification, that is, the timing of the handover operation can be delayed. Further, the transition from the report off state to the report on state is delayed, and the transition from the report on state to the report off state is accelerated.

As described above, the timing of the handover operation is delayed by increasing the hysteresis HS, increasing the TTT, or decreasing the offset OST. That is, since the time for which the wireless terminal device 202 is connected to the serving base station becomes longer, the occurrence frequency of “Too Early HO”, “HO to Wong Cell” and “Ping Pong HO” is reduced, and “Too Late HO” The frequency of occurrence will increase.

Here, the difference in the effect of adjusting the hysteresis HS, TTT and offset OST will be considered.

The handover timing can be adjusted by adjusting any of the parameters, but these effects differ depending on the topography including interference, the moving speed of the wireless terminal device, and the like.

Adjusting the hysteresis HS and the offset OST corresponds to adjusting the position where the handover is performed by virtually increasing or decreasing the cell. For example, by increasing the hysteresis HS of the serving cell, the received power of the radio signal is increased and the handover to another cell is difficult to be performed. Also, by setting the offset OST of the neighboring cell to a negative value, the received power of the radio signal from the neighboring cell appears to be small, and handover to another cell is difficult to be performed.

Further, the hysteresis HS and the offset OST are parameters that are not easily influenced by the moving speed of the wireless terminal device.

Here, in the measurement start request (Measurement Configuration) and the RRC connection reconfiguration instruction (RRC Connection Reconfiguration) transmitted from the radio base station apparatus to the radio terminal apparatus 202, for example, an offset OST is set for each neighboring cell, and the event At least one of A1 to A5 is set, and hysteresis HS and TTT corresponding to the set event are set.

[Radio base station equipment]
FIG. 19 is a diagram illustrating a configuration of the radio base station apparatus according to the first embodiment of the present invention.

Referring to FIG. 19, the radio base station apparatus 101 includes an antenna 91, a circulator 92, a radio reception unit 93, a radio transmission unit 94, a signal processing unit 95, and a control unit 98. The signal processing unit 95 includes a reception signal processing unit 96 and a transmission signal processing unit 97. The signal processing unit 95 and the control unit 98 are realized by a CPU (Central Processing Unit) or a DSP (Digital Signal Processor).

The circulator 92 outputs the radio signal from the radio terminal device 202 received by the antenna 91 to the radio reception unit 93 and outputs the radio signal received from the radio transmission unit 94 to the antenna 91.

The radio reception unit 93 converts the frequency of the radio signal received from the circulator 92 into a baseband signal or IF (Intermediate Frequency) signal, converts the frequency-converted signal into a digital signal, and outputs the digital signal to the reception signal processing unit 96.

The reception signal processing unit 96 performs signal processing such as despreading in the CDMA (Code Division Multiple Access) system on the digital signal received from the wireless reception unit 93, and performs part or all of the digital signal after this signal processing. The data is converted into a predetermined frame format and transmitted to the core network side.

The transmission signal processing unit 97 uses IFFT (Inverse Fast Fourier Transform) in the OFDM (Orthogonal Frequency Division Multiplex) method for communication data obtained by converting communication data received from the core network side into a predetermined frame format or communication data generated by itself. The digital signal after the signal processing is output to the wireless transmission unit 94.

The wireless transmission unit 94 converts the digital signal received from the transmission signal processing unit 97 into an analog signal, converts the frequency of the converted analog signal into a wireless signal, and outputs the converted signal to the circulator 92.

The control unit 98 exchanges various types of information with each unit and the core network in the radio base station apparatus 101.

In FIGS. 3 to 9, an inappropriate handover operation and its detection processing have been described. When an inappropriate handover operation is detected, the radio base station apparatus optimizes the handover operation by adjusting parameters such as hysteresis HS, offset OST, and TTT as described above.

However, for example, “Too Late HO” and “Too Early HO” are contradictory events, and there is a trade-off relationship with respect to parameter adjustment, so it may be difficult to adjust in a balanced manner. Instead of such parameter adjustment or in addition to parameter adjustment, a technique for suppressing an inappropriate handover operation is desired.

FIG. 2 illustrates an example of a sequence of a handover operation in the wireless communication system according to the first embodiment of the present invention. In this sequence, after the wireless terminal device 202 transmits a measurement result notification from which the wireless base station device 101A determines that the handover operation should be performed, a preparation process on the core network side, that is, the wireless base station device 101A Consider a preparation period T101 until various information is exchanged between the host apparatus and the radio base station apparatus 101B, and then the radio base station apparatus 101A performs a process of transmitting an RRC connection reconfiguration instruction to the radio terminal apparatus 202. In the sequence shown in FIG. 2, when the radio wave environment of the wireless terminal device 202 deteriorates during the preparation period T101, “Too Late HO” may occur. In particular, in the preparation process on the core network side, information is often transmitted and received via a general communication line. Therefore, it takes a long time to complete the preparation process, and the preparation period T101 is significantly increased. there is a possibility.

Therefore, in the wireless communication system according to the first embodiment of the present invention, “Too Late HO” is effectively suppressed by the following configuration.

FIG. 20 is a diagram illustrating a configuration of a control unit in the radio base station apparatus according to the first embodiment of the present invention.

Referring to FIG. 20, the control unit 98 includes a handover request unit 11, a handover instruction unit 12, a handover condition adjustment unit 13, a handover information acquisition unit 14, and a terminal measurement result acquisition unit 15.

The terminal measurement result acquisition unit 15 acquires the measurement result notification from the wireless terminal device 202, obtains the communication quality between the wireless base station device 101 and the wireless terminal device 202 from the acquired measurement result notification, and determines the communication quality. The handover request unit 11 and the handover instruction unit 12 are notified.

The handover request unit 11 makes a request for performing a handover operation of the radio terminal device 202 from its own radio base station device 101 to another radio base station device to other radio base station devices, that is, makes a handover request to other radio base station devices. Transmit to the radio base station apparatus. For example, the handover request unit 11 makes the request to another radio base station apparatus when a predetermined handover preparation condition regarding the communication quality between the radio base station apparatus 101 and the radio terminal apparatus 202 is satisfied.

In response to the response from the other radio base station apparatus to the request, the handover instruction unit 12 instructs the radio terminal apparatus 202 to perform a handover operation from its own radio base station apparatus 101 to another radio base station apparatus. That is, an RRC connection reconfiguration instruction is transmitted to the wireless terminal device 202. Here, the handover instructing unit 12 receives the above response, and when the handover execution condition regarding the communication quality between the own radio base station apparatus 101 and the radio terminal apparatus 202 is not satisfied, Cancel or suspend giving instructions. For example, when a predetermined handover execution condition is not satisfied, the handover instructing unit 12 does not give the above instruction to the wireless terminal device 202 and notifies other wireless base station devices to stop the handover operation. To do.

Note that the components surrounded by a broken line in FIG. 20, that is, the handover condition adjusting unit 13, the handover information acquiring unit 14, and the terminal measurement result acquiring unit 15 are not essential components in the present invention. Even if the radio base station apparatus 101 does not include these components, it is possible to achieve the object of the present invention to stabilize communication by appropriately controlling the handover operation of the radio terminal apparatus. .

FIG. 21 is a diagram showing an exemplary sequence of a handover operation in the wireless communication system according to the first embodiment of the present invention.

Referring to FIG. 21, first, radio base station apparatus 101A sets a frequency to be measured by radio terminal apparatus 202 in communication with itself and another radio base station apparatus that transmits a radio signal of the frequency. (Step S161).

Next, the wireless base station device 101A transmits to the wireless terminal device 202 a measurement start request for causing the wireless terminal device 202 to measure the reception level of the wireless signal transmitted from the other wireless base station device that has been set. This measurement start request includes neighboring cell information, that is, the cell ID of the radio base station apparatus to be measured. Further, the measurement start request includes the transmission frequency of each radio base station device (step S162).

Next, the radio terminal apparatus 202 receives the measurement start request from the radio base station apparatus 101A and starts power measurement processing, that is, the radio base station apparatus indicated by the measurement start request at the frequency indicated by the received measurement start request. The received power of the radio signal transmitted from is measured (step S163).

Next, the wireless terminal device 202 transmits a measurement result notification indicating the measurement result of the received power to the wireless base station device 101A. For example, the wireless terminal device 202 periodically measures the received power, when the communication state with the wireless base station device 101A deteriorates, and with other wireless base station devices other than the wireless base station device 101A When the state becomes better, a measurement result notification is transmitted to the radio base station apparatus 101A (step S164).

Next, the radio base station apparatus 101A acquires measurement information indicating the measurement result for each cell ID based on the measurement result notification received from the radio terminal apparatus 202, and stores it in a storage unit (not shown) (step S165).

Next, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A acquires the communication quality between itself and the wireless terminal device 202. Then, when the acquired communication quality satisfies a predetermined handover preparation condition, the radio base station apparatus 101A determines that a handover preparation process should be performed, and refers to neighboring cell information, for example, the radio base station apparatus 101B is determined as the handover destination (step S166).

Next, the radio base station device 101A transmits a handover request indicating the radio base station device 101B to the higher-level device (step S167).

Next, the host device receives the handover request from the radio base station device 101A and transmits the handover request to the radio base station device 101B (step S168).

Next, the radio base station apparatus 101B receives the handover request from the higher-level apparatus and transmits a handover response to the handover request to the higher-level apparatus (Step S169).

Next, the host device receives the handover response from the radio base station device 101B and transmits a handover instruction to the radio base station device 101A (step S170).

While the above preparation process is being performed, the wireless terminal device 202 transmits a new measurement result notification to the wireless base station device 101A (step S171).

Then, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A newly acquires the communication quality between itself and the wireless terminal device 202. In this way, the radio base station apparatus 101A updates the communication quality every time it receives a measurement result notification (step S172).

Next, when the radio base station apparatus 101A receives the handover instruction from the host apparatus and the newly acquired communication quality satisfies a predetermined handover execution condition, the radio base station apparatus 101A should execute the handover operation of the radio terminal apparatus 202 (Step S173).

Next, the radio base station apparatus 101A transmits an RRC connection reconfiguration instruction to the radio terminal apparatus 202 (step S174).

Next, the wireless base station device 101A transmits a status notification indicating its own communication status to the higher-level device (step S175).

Next, the host device receives the status notification from the radio base station device 101A and transmits the status notification indicating the communication content with the radio terminal device 202 to the radio base station device 101B (step S176).

Further, when the RRC connection is established between the wireless terminal device 202 and the wireless base station device 101B, the wireless terminal device 202 transmits an RRC connection reconfiguration completion notification to the wireless base station device 101B (step S177).

Next, the radio base station apparatus 101B receives the RRC connection reconfiguration completion notification from the radio terminal apparatus 202 and transmits a handover completion notification to the higher-level apparatus (step S178).

Next, the host device receives a handover completion notification from the radio base station device 101B and transmits a terminal information release instruction to the radio base station device 101A (step S179).

Next, the wireless base station device 101A receives the terminal information release instruction from the higher-level device, releases information related to the wireless terminal device 202, and transmits a terminal information release completion notification to the higher-level device (step S180).

FIG. 22 is a diagram showing an exemplary sequence of a handover operation in the wireless communication system according to the first embodiment of the present invention. FIG. 22 shows an example of a sequence for canceling the handover operation. The case assumed in FIG. 22 is the same as FIG.

Referring to FIG. 22, the operations in steps S191 to S202 are the same as the operations in steps S161 to S172 shown in FIG. 21, and thus detailed description thereof will not be repeated here.

Next, the radio base station apparatus 101A receives the handover instruction from the host apparatus, and executes the handover operation of the radio terminal apparatus 202 when the finally acquired communication quality does not satisfy the predetermined handover execution condition. It is determined that the handover operation for which the preparation process has been performed should be stopped (step S203).

Next, the wireless base station device 101A transmits a handover cancellation notification to the higher-level device (step S204).

Here, in the radio base station apparatus 101A, when the handover instructing unit 12 notifies the radio base station apparatus 101B that the handover operation is stopped, the communication quality between the radio base station apparatus 101A and the radio terminal apparatus 202 is set as a condition. Notify the upper apparatus and the radio base station apparatus 101B that it is not satisfied.

Specifically, the radio base station apparatus 101A sets a flag indicating that the handover operation is canceled due to the communication quality with the radio terminal apparatus 202 in the handover cancellation notification, and transmits the flag to the host apparatus and the radio base station apparatus 101B. To do.

Thereby, the host apparatus and the radio base station apparatus 101B can distinguish from an event in which the handover operation is stopped due to, for example, an error in parameter setting regarding the handover operation. For this reason, it is possible to prevent unnecessary processing such as new parameter setting processing from occurring in the higher-level device and the radio base station device 101B, and to appropriately release various resources reserved for the handover operation.

The host apparatus receives the handover cancellation notification from the radio base station apparatus 101A, and performs handover cancellation processing such as erasure of stored information for the handover operation corresponding to the handover cancellation notification, if necessary, and the radio base station apparatus The handover stop notification is transmitted to 101B (step S205).

Next, the radio base station apparatus 101B receives the handover cancellation notification, and performs handover cancellation processing such as erasure of stored information for the handover operation corresponding to the handover cancellation notification (step S206).

As a specific example of the communication quality between the radio base station apparatus and the radio terminal apparatus in the sequences shown in FIG. 21 and FIG. 22, for example, the radio base station apparatus 101 uses the conditional expression of event A3 to Set the preparation conditions. That is, the radio base station apparatus 101 determines execution of the handover operation when the following expression is satisfied.
(Receiving power of serving cell + offset OST1 of serving cell + hysteresis HS) <(received power of neighboring cell + offset OST2 of neighboring cell)

Also, the radio base station apparatus 101 determines the start of preparation for handover operation when the following expression is satisfied. However, the control value P is a value of zero or more.
(Receiving power of serving cell + offset OST1 of serving cell + hysteresis HS) <(received power of neighboring cell + offset OST2 + of neighboring cell + control value P)

In this equation, by increasing the control value P, the preparation start timing for the handover operation is advanced. Thereby, the execution timing of the handover operation can be advanced, and “Too Late HO” can be suppressed.

However, if the control value P is increased too much, the handover operation is not executed and the case where the preparation process for the handover operation is wasted increases. In such a case, by reducing the control value P, the preparation start timing of the handover operation approaches the execution timing of the handover operation, and the possibility that unnecessary preparation processing is performed can be reduced.

Also, when the control value P is set to a positive value, the communication quality indicated by the handover preparation condition is better than the communication quality indicated by the handover execution condition. That is, the handover preparation condition is a condition where it is less necessary to perform a handover operation from the radio base station apparatus 101 to another radio base station apparatus by the radio terminal apparatus 202 as compared with the handover execution condition. In this case, in the radio base station apparatus 101A, the latest communication quality grasped at the time of receiving the handover instruction from the higher-level apparatus is deteriorated by the amount corresponding to the control value P or more compared with the time when the preparation process for the handover operation is started. In this case, it is determined that a handover operation should be executed. That is, when the control value P is set to a positive value, the preparatory process for the handover operation can be performed in advance under conditions that are milder than the communication quality that is the criterion for determining whether to execute the handover operation. It becomes possible to quickly execute a handover operation in response to an environmental change.

Further, when the control value P is set to zero, the communication quality indicated by the handover preparation condition is equivalent to the communication quality indicated by the handover execution condition. In this case, the radio base station apparatus 101A performs the handover operation when the latest communication quality grasped at the time of receiving the handover instruction from the host apparatus is better than when the preparation process for the handover operation is started. It is determined that should be stopped. That is, when the control value P is set to zero, the handover operation that is no longer necessary due to the improvement of the radio wave environment of the wireless terminal device 202 can be appropriately stopped.

In the radio base station apparatus 101, the handover condition adjusting unit 13 can adjust the difference between the communication quality indicated by the handover execution condition and the communication quality indicated by the handover preparation condition.

For example, the handover information acquisition unit 14 acquires the number of times that the handover instruction unit 12 has notified the cancellation of the handover operation to another radio base station apparatus. Then, the handover condition adjusting unit 13 adjusts the communication quality difference based on the number of times acquired by the handover information acquiring unit 14.

Alternatively, the handover information acquisition unit 14 acquires the number of times that the handover operation from the wireless base station device 101 to another wireless base station device by the wireless terminal device 202 is inappropriate. Then, the handover condition adjusting unit 13 adjusts the communication quality difference based on the number of times acquired by the handover information acquiring unit 14.

Specifically, the handover condition adjusting unit 13 adjusts the control value P according to the following equation. However, W1 and W2 are weighting coefficients, and are a positive value and a negative value, respectively.
P = W1 × “Too Late HO” number of times + W2 × number of times of useless preparation processing (number of times of handover operation cancellation)

It should be noted that the number of times described above is not limited to the number of times for one other wireless base station device in a certain wireless base station device, but may be the total number of times for a plurality of other wireless base station devices.

Further, the radio base station apparatus 101 may use, for example, the value of the CQI report as the communication quality.

The CQI report does not directly notify the current radio wave condition in each cell, but is a value expressed in 16 levels from 0 to 15 by the following formula using SINR. When CQI = 0, the reception quality of the wireless terminal device 202 is the worst, and when CQI = 15, the reception quality of the wireless terminal device 202 is the best.
CQI = min (max (round ((SINR [dB] +8) /1.892), 0), 15)

Further, the radio base station apparatus 101 may be configured to wait until the communication quality satisfies the handover execution condition after receiving a response from another radio base station apparatus to the handover request. That is, in radio base station apparatus 101, handover instruction unit 12 receives a response from another radio base station apparatus and waits until the handover execution condition is satisfied when the handover execution condition is not satisfied. Then, when the handover execution condition is satisfied, the handover instruction unit 12 gives a handover operation instruction to the wireless terminal device 202. On the other hand, if a predetermined handover suspension condition related to communication quality is satisfied before the handover execution condition is satisfied, the handover instruction unit 12 does not give a handover operation instruction to the wireless terminal device 202 and performs the handover operation. Notify other radio base station apparatus to cancel.

That is, the radio base station apparatus 101 monitors communication quality between itself and the radio terminal apparatus 202 based on a measurement result notification that arrives periodically, for example, from the radio terminal apparatus 202 after completion of the handover operation preparation process. When the communication quality satisfies the handover execution condition, the wireless terminal device 202 is instructed to perform a handover operation.

As a result, the earlier the start timing of the preparation process for the handover operation, the higher the possibility that the handover operation can be executed at the optimum timing.

FIG. 23 is a diagram illustrating an example of a handover operation sequence in the wireless communication system according to the first embodiment of the present invention. The case assumed in FIG. 23 is the same as that in FIG.

Referring to FIG. 23, the operations in steps S211 to S220 are the same as the operations in steps S161 to S170 shown in FIG. 21, and thus detailed description thereof will not be repeated here.

While the handover operation preparation process is being performed, the wireless terminal device 202 transmits a new measurement result notification to the wireless base station device 101A (step S221).

Then, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A newly acquires the communication quality between itself and the wireless terminal device 202. In this way, the radio base station apparatus 101A updates the communication quality every time it receives a measurement result notification (step S222).

Next, the radio base station apparatus 101A receives a handover instruction from the host apparatus and waits until the communication quality satisfies a predetermined handover execution condition or handover cancellation condition (step S223).

Next, if the updated communication quality satisfies the handover execution condition, the radio base station apparatus 101A determines that the handover operation of the radio terminal apparatus 202 should be executed (step S224).

Next, the radio base station apparatus 101A transmits an RRC connection reconfiguration instruction to the radio terminal apparatus 202 (step S225).

Since operations in steps S226 to S231 are the same as those in steps S175 to S180 shown in FIG. 21, detailed description thereof will not be repeated here.

FIG. 24 is a diagram illustrating an example of a handover operation sequence in the wireless communication system according to the first embodiment of the present invention. FIG. 24 shows an example of a sequence for canceling the handover operation. The case assumed in FIG. 24 is the same as that in FIG.

Referring to FIG. 24, the operations in steps S241 to S253 are the same as the operations in steps S211 to S223 shown in FIG. 23, and therefore detailed description will not be repeated here.

Next, when the updated communication quality satisfies the handover cancel condition, the radio base station apparatus 101A should not execute the handover operation of the radio terminal apparatus 202, and cancel the handover operation for which the preparation process has been performed. It is determined that it should be (step S254).

Next, the radio base station device 101A transmits a handover cancellation notification to the higher-level device (step S255).

Here, similarly to the sequence shown in FIG. 22, the radio base station apparatus 101A sets a flag indicating that the handover operation is canceled due to the communication quality with the radio terminal apparatus 202 in the handover cancellation notification, and sends it to the host apparatus. Send.

Next, the higher-level apparatus receives the handover cancellation notification from the radio base station apparatus 101A, and performs handover cancellation processing such as erasure of retained information for the handover operation corresponding to the handover cancellation notification, if necessary. The handover cancellation notification is transmitted to the base station apparatus 101B (step S256).

Next, the radio base station apparatus 101B receives the handover cancellation notification, and performs handover cancellation processing such as erasure of retained information for the handover operation corresponding to the handover cancellation notification (step S257).

As a specific example of the communication quality between the radio base station apparatus and the radio terminal apparatus in the sequences shown in FIG. 23 and FIG. 24, for example, the radio base station apparatus 101 sets a handover cancellation condition using the conditional expression of event A3. To do. That is, in addition to the conditional expressions for determining whether to perform handover operation and determining whether to start preparation described with reference to the sequences illustrated in FIGS. 22 and 23, the radio base station apparatus 101 determines to cancel handover operation when the following expression is satisfied. . However, the control value Q is a positive value.
(Receiving power of serving cell + offset OST1 of serving cell + hysteresis HS + control value Q) <(received power of neighboring cell + offset OST2 of neighboring cell)

In this equation, when the control value Q is set to a positive value, the communication quality indicated by the handover cancellation condition is better than the communication quality indicated by the handover preparation condition. In this case, the radio base station apparatus 101A determines that the handover operation should be stopped when the communication quality is improved by an amount corresponding to the control value Q or more compared to when the preparation process for the handover operation is started. That is, when the control value Q is set to a positive value, the handover operation can be appropriately stopped with respect to the improvement of the radio wave environment of the wireless terminal device 202.

Further, when the control value Q is set to zero, the handover preparation condition and the handover cancellation condition become equal, and the handover preparation process and the cancellation process are repeated. However, by setting the control value Q to a positive value, The occurrence of such an event can be prevented.

Note that the handover cancel condition is not limited to a condition related to communication quality, and may be an elapsed time, for example.

Specifically, in FIG. 24, the radio base station apparatus 101A starts a timer before and after transmitting a handover request indicating the radio base station apparatus 101B to the higher-level apparatus (step S247). To do. Then, when the timer started before the handover execution condition expires, the radio base station apparatus 101A should not execute the handover operation of the radio terminal apparatus 202, and cancels the handover operation for which the preparation process has been performed. It is determined that it should be, and a handover stop notification is transmitted to the host device (step S254).

FIG. 25 is a diagram illustrating an example of a breakdown of time required for the handover operation in the wireless communication system according to the first embodiment of the present invention.

Referring to FIG. 25, the time required for the handover operation is, for example, a time T111 corresponding to an interval of power measurement processing in radio terminal apparatus 202, a time T112 corresponding to TTT, a preparation processing time T113 for handover operation, and a handover This is the sum of the operation execution time, that is, the time T114 from when the RRC connection reconfiguration instruction is transmitted to when the handover completion notification is transmitted.

Note that, as described above, TTT is a period for the wireless terminal device 202 to transmit measurement result notifications at regular intervals after transition to the report-on state. For this reason, time T111 and time T112 may overlap. FIG. 25 shows a case where the handover operation is performed based on the measurement result notification first transmitted by the wireless terminal device 202 after the transition to the report-on state, in order to simplify the description.

The time T111 is, for example, 200 ms, and 5 ms when using the CQI report. The time T112 is, for example, 0 ms to 2000 ms. The time T113 is, for example, 50 ms to 150 ms. The time T114 is 40 ms, for example.

The time T111 and the time T112 can be shortened by adjusting parameters such as the hysteresis HS, the offset OST, and the TTT.

Then, in the radio base station apparatus according to the first embodiment of the present invention, time T113 is ideally reduced to 0 ms by the configuration for performing the handover operation preparation process and the handover operation execution determination process as described above. Is possible.

That is, when the frequency of occurrence of “Too Late HO” is high and parameter adjustment for advancing the timing of the handover operation is more difficult than this, for example, the control value P described above is increased. Thereby, the timing of the preparation process for the handover operation can be advanced and an appropriate handover operation can be realized.

By the way, when an inappropriate handover operation as described in Non-Patent Document 1 is performed, various problems such as communication disconnection and increase in communication traffic occur in the communication system.

On the other hand, in the radio base station apparatus according to the first embodiment of the present invention, the handover request unit 11 performs handover of the radio terminal apparatus 202 from its own radio base station apparatus 101 to another radio base station apparatus. A request for operation is made to another radio base station apparatus. In response to a response from the other radio base station apparatus to the request, the handover instruction unit 12 instructs the radio terminal apparatus 202 to perform a handover operation from the radio base station apparatus 101 to another radio base station apparatus. give. When the handover instruction unit 12 receives the above response and the predetermined handover execution condition regarding the communication quality between the wireless base station device 101 and the wireless terminal device 202 is not satisfied, Cancel or hold the above instructions.

With such a configuration, the preparation process for the handover operation can be completed prior to determining whether to execute the handover operation, so that “Too Late HO” can be suppressed. In addition, unlike the case of adjusting the parameters of the handover operation, even if “Too Late HO” is suppressed, it is possible to prevent the occurrence probability of “Too Early HO” from increasing. That is, an inappropriate handover operation can be suppressed and a good communication system can be constructed.

Therefore, in the radio base station apparatus according to the first embodiment of the present invention, communication can be stabilized by appropriately controlling the handover operation of the radio terminal apparatus.

Moreover, in the radio base station apparatus according to the first embodiment of the present invention, the handover instruction unit 12 receives the response and performs a predetermined communication quality between the radio base station apparatus 101 and the radio terminal apparatus 202. When the handover execution condition is not satisfied, the wireless terminal device 202 is not instructed to perform the handover operation, and notifies the other wireless base station device that the handover operation is to be stopped.

Moreover, in the radio base station apparatus according to the first embodiment of the present invention, the handover instruction unit 12 receives the above response from another radio base station apparatus and receives its own radio base station apparatus 101 and radio terminal apparatus 202. If a predetermined handover execution condition regarding the communication quality is not satisfied, the system waits until the handover execution condition is satisfied. Then, the handover instruction unit 12 gives a handover instruction to the wireless terminal device 202 when the handover execution condition is satisfied.

With such a configuration, after the preparation process for the handover operation is completed, when the communication quality between the radio base station apparatus 101 and the radio terminal apparatus 202 satisfies the handover execution condition, the handover operation is performed on the radio terminal apparatus 202. Since an instruction can be given, a handover operation can be executed at an optimal timing.

Also, in the radio base station apparatus according to the first embodiment of the present invention, the handover instruction unit 12 waits until the handover execution condition is satisfied, and before the handover execution condition is satisfied, the handover stop condition regarding the communication quality is set. When the condition is satisfied, a handover instruction is not given to the radio terminal apparatus 202, and the other radio base station apparatus is notified that the handover operation is to be stopped.

Moreover, in the radio base station apparatus according to the first embodiment of the present invention, the handover request unit 11 satisfies a predetermined handover preparation condition relating to communication quality between its own radio base station apparatus 101 and radio terminal apparatus 202. In this case, a handover request is made to another radio base station apparatus. The communication quality indicated by the handover preparation condition is better than the communication quality indicated by the handover execution condition.

Also, in the radio base station apparatus according to the first embodiment of the present invention, the communication quality indicated by the handover preparation condition is equivalent to the communication quality indicated by the handover execution condition.

Also, in the radio base station apparatus according to the first embodiment of the present invention, the communication quality indicated by the handover preparation condition is equal to or better than the communication quality indicated by the handover execution condition, and the handover is canceled. The communication quality indicated by the condition is better than the communication quality indicated by the handover preparation condition.

Moreover, in the radio base station apparatus according to the first embodiment of the present invention, when the handover instruction unit 12 notifies other radio base station apparatuses of the cancellation of the handover operation, the handover instruction unit 12 and the radio base station apparatus 101 The other radio base station apparatus is notified that the communication quality between the terminal apparatuses 202 does not satisfy the condition.

Moreover, in the radio base station apparatus according to the first embodiment of the present invention, the handover condition adjustment unit 13 adjusts the difference between the communication quality indicated by the handover execution condition and the communication quality indicated by the handover preparation condition.

Further, in the radio base station apparatus according to the first embodiment of the present invention, the handover condition adjustment unit 13 is based on the number of times that the handover instruction unit 12 notifies the other radio base station apparatus of the cancellation of the handover operation. Adjust the communication quality difference.

Further, in the radio base station apparatus according to the first embodiment of the present invention, the handover information acquisition unit 14 performs the handover operation from the radio base station apparatus 101 to another radio base station apparatus by the radio terminal apparatus 202. Get the number of times it was inappropriate. Then, the handover condition adjusting unit 13 adjusts the communication quality difference based on the number of times acquired by the handover information acquiring unit 14.

In the radio base station apparatus according to the first embodiment of the present invention, as the communication quality between radio base station apparatus 101 and radio terminal apparatus 202, the relationship between the reception power of the serving cell and the reception power of neighboring cells, or the CQI Although the configuration uses report values, the present invention is not limited to this. It is not limited to the received power of the wireless terminal device 202, and any configuration that uses some index indicating communication quality between the wireless base station device and the wireless terminal device, such as an error rate of a pilot signal, may be used. Moreover, the structure using the conditional expression of events other than event A3 may be sufficient. Further, the communication quality is not limited to the downlink communication quality, and may be configured to use the uplink communication quality.

<Simulation>
The inventors of the present application performed a simulation on the operation of the radio base station apparatus according to the first embodiment of the present invention. Hereinafter, the contents and results of this simulation will be described in detail.

FIG. 26 is a diagram showing radio environment parameters in the radio communication system to be simulated.

Referring to FIG. 26, the radio environment parameters of the radio communication system to be the target of this simulation are “number of base stations / number of sectors”, “distance between base stations”, “path loss”, that is, radio transmitted by the radio base station apparatus. The difference between the transmission power of the signal and the reception power of the radio signal in the radio terminal device, the “base station antenna gain”, that is, the gain by directivity when the non-directivity is 0 dB, “terminal antenna gain”, “shadowing” "That is, the amount of time fluctuation of the reception power of the radio signal in the wireless terminal device 202," the shadowing correlation distance ", that is, the distance between the two points when the correlation between the two points of shadowing is 0.5, “Correlation value of shadowing”, “Base station antenna directivity pattern”, “Carrier frequency / band”, “Total transmission power of base station”, “Ante Configuration "and" base station - the minimum distance "between terminals.

Specifically, the number of macro base stations in this wireless communication system is 19, the total number of sectors is 57, assuming that the macro base station has three sectors, the number of pico base stations is 1, and the pico base station Has one sector and the total number of sectors is one. The distance between the macro base stations is 500 m, and the distance between the macro base station and the pico base station is 250 m. The path loss for the macro base station is 15.3 + 37.6 × log ₁₀ (d) [dB] where the distance between the macro base station and the wireless terminal device is d [m], and the path loss for the pico base station is pico The distance between the base station and the wireless terminal device is 30.6 + 36.7 × log ₁₀ (d) [dB] where d [m] is the distance. The antenna gain of the macro base station is 15 dBi, and the antenna gain of the pico base station is 5 dBi. The antenna gain of the wireless terminal device 202 is 0 dBi in both the macro base station and the pico base station. The standard deviation of shadowing for the macro base station is 8 dB, and the standard deviation of shadowing for the pico base station is 10 dB. The shadowing interphase distance for the macro base station is 25 m, and the shadowing interphase distance for the pico base station is 25 m. The shadowing correlation value for a macro base station is 0.5 between cells and 1 between sectors, and the shadowing correlation value for a pico base station is 0.5 between cells. The directivity pattern of the macro base station antenna is a three-dimensional pattern, and the pico base station antenna is omnidirectional. The carrier frequency and band on the transmission side of the macro base station are 2.0 GHz and 10 MHz, respectively, and the carrier frequency and band on the transmission side of the pico base station are 2.0 GHz and 10 MHz, respectively. The total transmission power of the macro base station is 46 dBm, and the total transmission power of the pico base station is 30 dBm. The macro base station has one transmission antenna, the pico base station has one transmission antenna, and the wireless terminal device 202 has two reception antennas. Other parameters such as the minimum distance between the radio base station apparatus and the radio terminal apparatus conform to 3GPP TR 36.814.

FIG. 27 is a diagram illustrating parameters of power measurement processing (Measurement) in the wireless communication system to be simulated.

Referring to FIG. 27, in this simulation, set 1 to set 5 are provided as profiles. In the order from set 1 to set 5, the timing of the handover operation is advanced, and in set 5, the timing of the handover operation is the earliest. The parameters of the power measurement process are the terminal moving speed, the base station load factor, TTT, the offset OST of the event A3, the power measurement interval, that is, the measurement result notification update cycle, and the filtering coefficient α.

Here, the filtering coefficient α will be described. For example, the wireless terminal device 202 receives the received power M (t−1) measured at time (t−1), the received power M (t) measured at time t after time (t−1), and the filtering coefficient α. From this, the received power MR (t) expressed by the following equation is calculated.
MR (t) = (1-2− ^{α / 4} ) × MR (t−1) + 2− ^{α / 4} × M (t)

The wireless terminal device 202 transmits a measurement result notification indicating the received power MR (t) to the wireless base station device.

When the filtering coefficient α is increased, the past received power is reflected in the measurement result notification, so the timing of the handover operation is delayed. On the other hand, when the filtering coefficient α is reduced, the more recent received power is reflected in the measurement result notification, so that the timing of the handover operation is advanced.

In set 1 to set 5, the moving speed of the wireless terminal device 202 is 3 km, 30 km, 60 km, and 120 km per hour, and the base station load factor is 100%. In the set 1, the TTT is 480 ms, the offset OST is 3 dB, the power measurement interval is 200 ms, and the filtering coefficient α is 4. In set 2, the TTT is 160 ms, the offset OST is 3 dB, the power measurement interval is 200 ms, and the filtering coefficient α is 4. In set 3, the TTT is 160 ms, the offset OST is 2 dB, the power measurement interval is 200 ms, and the filtering coefficient α is 1. In set 4, the TTT is 80 ms, the offset OST is 1 dB, the power measurement interval is 200 ms, and the filtering coefficient α is 1. In set 5, TTT is 40 ms, offset OST is −1 dB, power measurement interval is 200 ms, and filtering coefficient α is 0.

Here, in the radio base station apparatus according to the first embodiment of the present invention, an operation for completing the handover operation preparation process prior to the handover operation execution determination is referred to as “HO preparation shortening”.

In this simulation, the radio base station apparatus selects the radio base station apparatus with the highest received power as the handover destination in the newest measurement result notification. Further, the radio base station apparatus receives a measurement result notification from the radio terminal apparatus 202 once every 200 ms.

In addition, the handover operation preparation processing time when the HO preparation shortening is performed is 10 ms, and the handover operation preparation processing time when the HO preparation shortening is not performed is as shown in FIG. 2 without using the X2 interface. Assuming a handover operation using the S1 interface, it is 100 ms.

FIG. 28 is a diagram showing a simulation result of a handover failure probability.

Referring to FIG. 28, in the configuration in which HO preparation shortening is performed, the probability of occurrence of handover failure (HOF) can be reduced in most cases compared to the configuration in which HO preparation shortening is not performed.

FIG. 29 is a diagram showing a simulation result of the occurrence probability of “Ping Pong HO”.

Referring to FIG. 29, in the configuration in which the HO preparation is shortened, the occurrence probability of “Ping Pong HO” is slightly increased as compared with the configuration in which the HO preparation is not shortened. This is because handover failure (HOF) is avoided.

FIG. 30 is a diagram showing the sum of the handover failure probability shown in FIG. 28 and the occurrence probability of “Ping Pong HO” shown in FIG.

Referring to FIG. 30, in the configuration in which the HO preparation shortening is performed, the sum of the handover failure probability and the occurrence probability of “Ping Pong HO” is decreased in most cases as compared with the configuration in which the HO preparation shortening is not performed.

FIG. 31 is a diagram illustrating an improvement target by the radio base station apparatus according to the first embodiment of the present invention.

FIG. 31 shows a breakdown of the elapsed time from when the radio wave environment in the surrounding cells becomes better than that in the serving cell until the handover operation is actually completed.

The time required for the handover operation is, for example, a time T211 corresponding to an interval of power measurement processing in the wireless terminal device 202, a time T212 corresponding to TTT, a preparation time T213 for handover operation, and an execution time of the handover operation, that is, RRC This is the sum of the time T214 from when the connection reconfiguration instruction is transmitted to when the handover completion notification is transmitted.

Note that, as described above, TTT is a period for the wireless terminal device 202 to transmit measurement result notifications at regular intervals after transition to the report-on state. For this reason, time T211 and time T212 may overlap. For the sake of simplicity, FIG. 31 shows a case where a handover operation is performed based on a measurement result notification first transmitted by the wireless terminal device 202 after transition to the report-on state.

The time T211 is, for example, 200 ms, and is 5 ms at the shortest when the CQI report is used. The time T212 is 40 ms to 1000 ms, for example. The time T213 is, for example, 40 ms to 100 ms. The time T214 is 50 ms, for example.

The improvement target by “HO preparation shortening” in the radio base station apparatus according to the first embodiment of the present invention is time T213.

Note that the preparation process for the handover operation is performed after the execution of the handover operation is determined. For this reason, even if the HO preparation is shortened, the effect of reducing the occurrence of “Ping Pong HO”, that is, reducing the number of unnecessary handover operations is not directly obtained.

As described above, from this simulation, the handover operation of the radio terminal apparatus is appropriately controlled by the radio base station apparatus according to the first embodiment of the present invention, and the communication in the radio communication system can be stabilized. Was confirmed.

Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Second Embodiment>
In the first embodiment described above, the case where the communication connection destination of the wireless terminal device 202 is switched from the wireless base station device 101A to the wireless base station device 101B in the handover operation has been described. On the other hand, in the second embodiment, a case will be described in which not only the radio

base station devices

101A and 101B but also higher-level devices in the core network are switched. The contents other than those described below are the same as those of the wireless communication system according to the first embodiment. Examples of the host device include MME (Mobility Management Entity) or S-GW (Serving Gateway).

Hereinafter, as a second embodiment of the present invention, switching of MME is required in handover operation, switching of S-GW is required in handover operation, and switching of MME and S-GW in handover operation. The explanation is divided into cases where necessary.

(A) When MME switching is required [Configuration and basic operation]
FIG. 32 is a diagram illustrating an example of a configuration of a wireless communication system according to the second embodiment of the present invention.

Referring to FIG. 32, a radio communication system 401 is a mobile communication system according to LTE (Long Term Evolution) standardized by 3GPP, for example, and includes radio

base station apparatuses

101A and 101B. Here, when the wireless terminal device 202 moves from a state where it is communicating with the wireless base station device 101A, a handover operation is performed in which the communication partner, that is, the communication connection destination is switched from the wireless base station device 101A to the wireless base station device 101B. Is assumed. That is, it is assumed that the radio base station apparatus 101A corresponds to a serving base station and the radio base station apparatus 101B corresponds to a peripheral base station (also referred to as a target base station).

FIG. 32 representatively shows two radio

base station apparatuses

101A and 101B, but a larger number of radio base station apparatuses may be provided. The wireless communication system 401 further includes an S-GW 161 (gateway device),

MMEs

162A and 162B (communication control device), and a P-GW (Packet Data Network Gateway) 163 provided in the core network 301.

The wireless terminal device 202 establishes a communication connection with a server or the like in the IP network 302 (upper network) via the wireless

base station devices

101A and 101B, the S-GW 161, and the P-GW 163, for example, an IP (Internet Protocol) packet. Communication data including

The S-GW 161 is connected between the radio

base station apparatuses

101A and 101B and the IP network 302. The S-GW 161 transmits communication data received from the wireless terminal device 202 via the wireless

base station devices

101A and 101B to the IP network 302 via the P-GW 163, and also received via the P-GW 163 from a server or the like in the IP network 302. The transmitted communication data is transmitted to the wireless terminal device 202 via the wireless

base station devices

101A and 101B.

The MME 162A manages the wireless base station device 101A, the wireless terminal device 202, and the like in the wireless communication system 401. The MME 162A transmits and receives control messages to and from the radio base station apparatus 101A. Further, the MME 162B manages the radio base station apparatus 101B and the radio terminal apparatus 202 in the radio communication system 401. The MME 162B transmits and receives control messages to and from the radio base station apparatus 101B.

Radio

base station apparatuses

101A and 101B transmit and receive communication data to and from IP network 302 via S-GW 161 and P-GW 163. The radio

base station apparatuses

101A and 101B and the S-GW 161 exchange various data with each other via the S1-U interface by transmitting and receiving communication data according to the S1-U interface which is a logical interface.

The radio base station apparatus 101A and the MME 162A exchange various data via the S1-MME interface by transmitting and receiving communication data according to the S1-MME interface, which is a logical interface, as indicated by a dotted line. Similarly, wireless base station apparatus 101B and MME 162B exchange various data via the S1-MME interface by transmitting and receiving communication data according to the S1-MME interface, which is a logical interface, as indicated by dotted lines. .

The

MMEs

162A, 162B and the S-GW 161 exchange various data with each other via the S11 interface by transmitting and receiving communication data according to the S11 interface which is a logical interface.

The S-GW 161 and the P-GW 163 exchange various data with each other via the S5 interface by transmitting and receiving communication data according to the S5 interface which is a logical interface.

The MME 162A and the MME 162B mutually exchange various information via the S10 interface by transmitting and receiving communication data according to the S10 interface which is a logical interface.

[Operation]
Next, the flow of the handover operation in the wireless communication system 401 according to the second embodiment of the present invention will be described separately when the handover operation execution condition is satisfied and when the handover operation execution condition is not satisfied. To do.

(I) When Execution Conditions are Satisfied FIG. 33 is a sequence of handover operations in a situation where the execution conditions for handover operations are satisfied in the wireless communication system according to the second embodiment of the present invention.

Referring to FIG. 33, first, wireless terminal apparatus 202 transmits a measurement result notification indicating a measurement result of received power to wireless base station apparatus 101A. For example, the wireless terminal device 202 periodically measures the received power, when the communication state with the wireless base station device 101A deteriorates, and with other wireless base station devices other than the wireless base station device 101A When the state becomes better, a measurement result notification is transmitted to the radio base station apparatus 101A (step S321).

Next, based on the measurement result notification received from the radio terminal apparatus 202, the radio base station apparatus 101A acquires measurement information indicating the measurement result for each cell ID and stores it in a storage unit (not shown). Then, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A acquires the communication quality between itself and the wireless terminal device 202. Then, when the acquired communication quality satisfies a predetermined handover preparation condition, the radio base station apparatus 101A determines that a handover preparation process should be performed, and refers to neighboring cell information, for example, the radio base station apparatus 101B is determined as the handover destination (step S322).

Next, the radio base station apparatus 101A transmits a handover request indicating the radio base station apparatus 101B to the MME 162A that is a corresponding higher-level apparatus (step S323).

Next, the MME 162A determines whether it is necessary to switch the MME based on the handover request received from the radio base station apparatus 101A. Specifically, the MME 162A determines whether or not the radio base station apparatus 101B indicated in the handover request is its management target (step S324).

Next, since the radio base station apparatus 101B is not a management target, the MME 162A transmits a handover request indicating the radio base station apparatus 101B to the MME 162B that manages the radio base station apparatus 101B (step S325).

Next, the MME 162B determines whether it is necessary to switch the S-GW 161 based on the handover request received from the MME 162A. Specifically, the MME 162B includes an S-GW 161 connected between the radio base station apparatus 101A and the IP network 302, and an S-GW 161 connected between the radio base station apparatus 101B and the IP network 302. Whether or not is different. Here, the S-GW 161 connected between the radio base station apparatus 101A and the IP network 302 and the S-GW 161 connected between the radio base station apparatus 101B and the IP network 302 are the same. Therefore, the MME 162B determines that there is no need to switch the S-GW 161 (step S326).

Next, the MME 162B transmits a handover request to the radio base station apparatus 101B (step S327).

Next, the radio base station apparatus 101B receives the handover request from the MME 162B and transmits a handover response to the handover request to the MME 162B (Step S328).

Next, the MME 162B transfers the handover response received from the radio base station apparatus 101B to the MME 162A (step S329).

Here, when the target packet that is a packet addressed to the wireless terminal device 202 is accumulated in the wireless base station device 101A during the preparation period for the handover operation of the wireless terminal device 202, or the target packet is newly received from the S-GW 161. In this case, data forwarding is performed in which the radio base station apparatus 101A transfers the target packet to the radio base station apparatus 101B.

Therefore, when the MME 162A receives the handover response from the MME 162B, the MME 162A sends a request for establishing a communication path for performing data forwarding via the S1-U interface, that is, a logical path (hereinafter also referred to as a data forwarding path) to the S-GW 161. Transmit (step S330).

Next, upon receiving a data forwarding path establishment request from the MME 162A, the S-GW 161 establishes a data forwarding path. That is, S-GW 161 establishes a logical path between radio base station apparatus 101A and radio base station apparatus 101B through itself. Then, the S-GW 161 transmits a data forwarding path establishment response to the MME 162A (step S331).

Next, the MME 162A transmits a handover instruction to the radio base station apparatus 101A. When the above-described handover operation preparation processing is executed and the radio base station apparatus 101A receives a handover instruction from the MME 162A, the radio base station apparatus 101A starts data forwarding via the S1-U interface. That is, the radio base station apparatus 101A transfers the target packet, which is a packet addressed to the radio terminal apparatus 202 that is stored in itself or newly received from the S-GW 161, to the radio base station apparatus 101B via the S-GW 161. (Step S332).

Next, the radio base station apparatus 101A determines whether or not the communication quality between itself and the radio terminal apparatus 202 satisfies a predetermined handover execution condition. When the communication quality satisfies the handover execution condition, the radio base station apparatus 101A determines that the handover operation of the radio terminal apparatus 202 should be executed (step S333). Note that the communication quality indicated by the preparation condition described above is better than the communication quality indicated by the execution condition.

Next, the radio base station apparatus 101A transmits an RRC connection reconfiguration instruction (RRC Connection Reconfiguration) to the radio terminal apparatus 202 (step S334).

Next, the radio base station apparatus 101A transmits a status notification indicating its own communication status and the like to the MME 162A (step S335). This state notification includes information such as the serial number of the packet for the radio base station apparatus 101B to process the transfer packet in data forwarding.

Next, the MME 162A transfers the status notification received from the radio base station apparatus 101A to the MME 162B (step S336).

Next, the MME 162B transmits a status notification response to the status notification transferred from the MME 162A to the MME 162A (step S337).

Next, the MME 162B transmits a status notification indicating communication contents and the like with the wireless terminal device 202 to the wireless base station device 101B (step S338).

Next, when the RRC connection is established between the wireless terminal device 202 and the wireless base station device 101B, the wireless terminal device 202 transmits an RRC connection reconfiguration completion notification (RRC Connection Reconfiguration Complete) to the wireless base station device 101B. (Step S339).

Then, the radio base station apparatus 101B receives the RRC connection reconfiguration completion notification from the radio terminal apparatus 202, and transmits the packet transferred from the radio base station apparatus 101A to the radio terminal apparatus 202. Here, radio base station apparatus 101B performs packet sequence control using the serial number or the like indicated by the status notification received from radio base station apparatus 101A.

Further, the wireless terminal device 202 transmits a packet to the wireless base station device 101B, and the wireless base station device 101B transmits the target packet to the S-GW 161.

Next, the radio base station apparatus 101B receives the RRC connection reconfiguration completion notification from the radio terminal apparatus 202, and transmits a handover completion notification to the MME 162B (step S340). This handover completion notification includes a path switching request to the S-GW 161.

Next, the MME 162B transfers the handover completion notification received from the radio base station apparatus 101B to the MME 162A (step S341).

Next, the MME 162A transmits a handover completion notification response to the handover completion notification received from the MME 162B to the MME 162B (step S342).

Next, the MME 162B transmits a bearer change request including the path switching request to the S-GW 161 (step S343).

The S-GW 161 receives the bearer change request from the MME 162B, and performs path switching processing. That is, the transmission destination of the target packet addressed to the wireless terminal device 202 is changed from the wireless base station device 101A to the wireless base station device 101B. Switch to.

Next, the S-GW 161 transmits a bearer change response including a path switch response to the bearer change request to the MME 162B (step S344).

Then, the S-GW 161 transmits the target packet with the end marker attached to the radio base station apparatus 101A, ends the transmission of the target packet to the radio base station apparatus 101A, and then transmits the target packet to the radio base station apparatus 101B. Start sending.

Also, the radio base station apparatus 101B suspends and accumulates transmission of the target packet from the S-GW 161 not via the radio base station apparatus 101A to the radio terminal apparatus 202.

Then, the wireless base station device 101A transfers the target packet with the end marker received from the S-GW 161 to the wireless base station device 101B via the S-GW 161. At this time, the radio base station apparatus 101A sets the end of the target packet to be transferred to the radio base station apparatus 101B as the target packet with the end marker.

Then, the radio base station apparatus 101B receives the target packet with the end marker from the radio base station apparatus 101A, and recognizes that the data forwarding to itself by the radio base station apparatus 101A has been completed. The radio base station apparatus 101B transmits all the target packets transferred from the radio base station apparatus 101A to the radio terminal apparatus 202, and then transmits the accumulated target packets from the S-GW 161 to the radio terminal apparatus 202. To start.

Next, the MME 162A transmits a terminal information release instruction to the radio base station apparatus 101A (step S345).

Next, the radio base station apparatus 101A receives a terminal information release instruction from the MME 162A, releases information related to the radio terminal apparatus 202, and transmits a terminal information release completion notification to the MME 162A (step S346).

Next, upon receiving the terminal information release completion notification from the radio base station apparatus 101A, the MME 162A transmits a data forwarding path deletion request to the S-GW 161 (step S347).

Next, when receiving the data forwarding path deletion request, the S-GW 161 deletes the data forwarding path and transmits a data forwarding path deletion response to the MME 162A (step S348).

(Ii) Case where Execution Condition is Not Satisfied FIG. 34 is a sequence of a handover operation in a situation where the execution condition for the handover operation is not satisfied in the radio communication system according to the second embodiment of the present invention.

Referring to FIG. 34, the operation from step S351 to step S362 is the same as the operation from step S321 to step S332 shown in FIG. 33, and therefore detailed description will not be repeated here.

Next, upon receiving a handover instruction from the MME 162A, the radio base station apparatus 101A determines whether or not the communication quality between itself and the radio terminal apparatus 202 satisfies a predetermined handover execution condition. If the communication quality does not satisfy the handover execution condition, the radio base station apparatus 101A should not execute the handover operation of the radio terminal apparatus 202 and should stop the handover operation for which the preparation process has been performed. It is determined that there is (step S363).

Next, the radio base station apparatus 101A transmits a handover cancel notification for canceling the handover operation to the MME 162A (step S364).

Next, the MME 162A transfers the handover cancellation notification received from the radio base station apparatus 101A to the MME 162B (step S365).

Next, when the MME 162B receives the handover cancellation notification, the MME 162B transmits a terminal information release instruction to the radio base station apparatus 101B (step S366).

Next, the radio base station apparatus 101B receives a terminal information release instruction from the MME 162B, releases information related to the radio terminal apparatus 202, and transmits a terminal information release completion notification to the MME 162B (step S367).

Next, when receiving the terminal information release completion notification from the radio base station apparatus 101B, the MME 162B transmits a handover stop response to the MME 162A (step S368).

Next, the MME 162A transmits the handover stop response received from the MME 162B to the radio base station apparatus 101A (step S369).

Next, the MME 162A transmits a data forwarding path deletion request to the S-GW 161 (step S370).

Next, when receiving the data forwarding path deletion request, the S-GW 161 deletes the data forwarding path and transmits a data forwarding path deletion response to the MME 162A (step S371).

(B) When switching of S-GW is necessary [Configuration and basic operation]
FIG. 35 is a diagram illustrating an example of a configuration of a wireless communication system according to the second embodiment of the present invention.

35, radio communication system 402 is a mobile communication system according to LTE standardized by 3GPP, for example, similar to radio communication system 401 shown in FIG. 32, and includes radio base station apparatus 101A and radio base station A station apparatus 101B. Here, as in the case shown in FIG. 32, the wireless terminal device 202 moves from a state where it is communicating with the wireless base station device 101A, and the communication partner, that is, the communication connection destination is changed from the wireless base station device 101A to the wireless base station device. Assume that a handover operation is performed so as to switch to 101B.

The wireless communication system 402 further includes S-

GWs

161A and 161B (gateway devices), an MME 162 (communication control device), and a P-GW 163 provided in the core network 301.

The S-GW 161A is connected between the radio base station apparatus 101A and the IP network 302. The S-GW 161A transmits communication data received from the wireless terminal device 202 via the wireless base station device 101A to the IP network 302 via the P-GW 163, and communication received from the server in the IP network 302 via the P-GW 163. Data is transmitted to the wireless terminal device 202 via the wireless base station device 101A.

The S-GW 161B is connected between the radio base station apparatus 101B and the IP network 302. The S-GW 161B transmits the communication data received from the wireless terminal device 202 via the wireless base station device 101B to the IP network 302 via the P-GW 163, and the communication received via the P-GW 163 from a server or the like in the IP network 302. Data is transmitted to the wireless terminal device 202 via the wireless base station device 101B.

The MME 162 manages the radio

base station apparatuses

101A and 101B and the radio terminal apparatus 202 in the radio communication system 402. The MME 162 transmits and receives control messages to and from the radio

base station apparatuses

101A and 101B.

The radio base station apparatus 101A transmits / receives communication data to / from the IP network 302 via the S-GW 161A and the P-GW 163. The radio base station apparatus 101B transmits / receives communication data to / from the IP network 302 via the S-GW 161B and the P-GW 163.

The radio base station apparatus 101A and the S-GW 161A exchange various data with each other via the S1-U interface by transmitting and receiving communication data according to the S1-U interface which is a logical interface. The radio base station apparatus 101B and the S-GW 161B exchange various data with each other via the S1-U interface by transmitting and receiving communication data according to the S1-U interface which is a logical interface.

The radio

base station apparatuses

101A and 101B and the MME 162 exchange various data with each other via the S1-MME interface by transmitting and receiving communication data according to the S1-MME interface, which is a logical interface, as indicated by a dotted line. .

The MME 162 and the S-

GWs

161A and 161B exchange various pieces of information with each other via the S11 interface by transmitting and receiving communication data according to the S11 interface, which is a logical interface.

The S-

GWs

161A and 161B and the P-GW 163 exchange various data with each other via the S5 interface by transmitting and receiving communication data according to the S5 interface which is a logical interface.

[Operation]
Next, the flow of the handover operation in the wireless communication system 402 according to the second embodiment of the present invention will be described separately when the handover operation execution condition is satisfied and when the handover operation execution condition is not satisfied. To do.

(I) When Execution Condition is satisfied FIG. 36 is a sequence of a handover operation in a situation where the execution condition for the handover operation is satisfied in the wireless communication system according to the second embodiment of the present invention.

Referring to FIG. 36, the operation from step S381 to step S383 is the same as the operation from step S321 to step S323 shown in FIG. 33, and therefore detailed description will not be repeated here.

Next, the MME 162 determines whether it is necessary to switch the MME 162 based on the handover request received from the radio base station apparatus 101A. Specifically, the MME 162 determines whether or not the radio base station apparatus 101B indicated in the handover request is its own management target. Here, since the radio base station apparatus 101B is the management target of the MME 162, the MME 162 determines that there is no need to switch the MME (step S384).

Next, the MME 162 determines whether or not it is necessary to perform S-GW switching based on the handover request received from the radio base station apparatus 101A. Specifically, the MME 162 includes an S-GW connected between the radio base station apparatus 101A and the IP network 302, and an S-GW connected between the radio base station apparatus 101B and the IP network 302. Whether or not is different (step S385).

Next, the MME 162 includes an S-GW 161A connected between the radio base station apparatus 101A and the IP network 302, and an S-GW 161B connected between the radio base station apparatus 101B and the IP network 302. Because of the difference, the P-GW 163 and the radio base station apparatus are configured so that downlink packets addressed to the radio terminal apparatus 202 from the upper network and uplink packets from the radio terminal apparatus 202 to the upper network can pass through the S-GW 161B. The S-GW 161B is requested to create a communication path with the 101B (step S386).

Next, the S-GW 161B receives the communication path creation request from the MME 162, creates a communication path between the P-GW 163 and the radio base station apparatus 101B passing through the S-GW 161B, and sends a communication path creation response to the MME 162. (Step S387).

Next, the MME 162 transmits a handover request to the radio base station apparatus 101B (step S388).

Next, the radio base station apparatus 101B receives the handover request from the MME 162, and transmits a handover response to the handover request to the MME 162 (step S389).

Next, when receiving a handover response from the radio base station apparatus 101B, the MME 162 issues a request for establishing a communication path for performing data forwarding via the S1-U interface, that is, a logical path (hereinafter also referred to as a data forwarding path). The data is transmitted to the S-GW 161B (step S390).

Next, upon receiving a data forwarding path establishment request from the MME 162, the S-GW 161B establishes a data forwarding path. That is, S-GW 161B establishes a logical communication path between S-GW 161A and S-GW 161B, and a logical communication path between S-GW 161B and radio base station apparatus 101B. Then, the S-GW 161B transmits a data forwarding path establishment response to the MME 162 (step S391).

Next, the MME 162 transmits a request for establishing a communication path for performing data forwarding via the S1-U interface to the S-GW 161A (step S392).

Next, upon receiving a data forwarding path establishment request from the MME 162, the S-GW 161A establishes a data forwarding path. That is, S-GW 161A establishes a logical communication path between S-GW 161A and radio base station apparatus 101A. Then, the S-GW 161A transmits a data forwarding path establishment response to the MME 162 (step S393).

Next, the MME 162 transmits a handover instruction to the radio base station apparatus 101A. Then, the base transceiver station 101A starts data forwarding via the S1-U interface (step S394).

Next, the radio base station apparatus 101A determines whether or not the communication quality between itself and the radio terminal apparatus 202 satisfies a predetermined handover execution condition. When the communication quality satisfies the handover execution condition, the radio base station apparatus 101A determines that the handover operation of the radio terminal apparatus 202 should be executed (step S395).

Next, the radio base station apparatus 101A transmits an RRC connection reconfiguration instruction to the radio terminal apparatus 202 (step S396).

Next, the wireless base station device 101A transmits a state notification indicating its own communication state and the like to the MME 162 (step S397). This state notification includes information such as the serial number of the packet for the radio base station apparatus 101B to process the transfer packet in data forwarding.

Next, the MME 162 transmits a status notification indicating communication contents and the like with the wireless terminal device 202 to the wireless base station device 101B (step S398).

Next, when the RRC connection is established between the wireless terminal device 202 and the wireless base station device 101B, the wireless terminal device 202 transmits an RRC connection reconfiguration completion notification to the wireless base station device 101B (step S399).

Also, the wireless terminal device 202 transmits a packet to the wireless base station device 101B, and the wireless base station device 101B transmits the target packet to the S-GW 161B.

Next, the radio base station apparatus 101B receives the RRC connection reconfiguration completion notification from the radio terminal apparatus 202 and transmits a handover completion notification to the MME 162 (step S400). This handover completion notification includes a path switching request for the S-GW 161B.

Next, the MME 162 transmits a bearer change request including the path switching request to the S-GW 161B (step S401).

The S-GW 161B receives the bearer change request from the MME 162, and performs path switching processing. That is, the transmission destination of the target packet addressed to the wireless terminal device 202 is changed from the wireless base station device 101A to the wireless base station device 101B. Switch to.

Next, the S-GW 161B transmits a bearer change response including a path switching response to the bearer change request to the MME 162 (step S402).

Then, the S-GW 161A transmits the target packet with the end marker attached thereto to the radio base station apparatus 101A, terminates the transmission of the target packet to the radio base station apparatus 101A, and transmits the target packet to the radio base station apparatus 101B. Start sending.

Also, the radio base station apparatus 101B suspends and accumulates transmission of the target packet from the S-GW 161B not via the radio base station apparatus 101A to the radio terminal apparatus 202.

Then, the radio base station apparatus 101A transfers the target packet with the end marker received from the S-GW 161A to the radio base station apparatus 101B via the S-GW 161A and the S-GW 161B. At this time, the radio base station apparatus 101A sets the end of the target packet to be transferred to the radio base station apparatus 101B as the target packet with the end marker.

Then, the radio base station apparatus 101B receives the target packet with the end marker from the radio base station apparatus 101A, and recognizes that the data forwarding to itself by the radio base station apparatus 101A has been completed. The radio base station apparatus 101B transmits all the target packets transferred from the radio base station apparatus 101A to the radio terminal apparatus 202, and then transmits the accumulated target packets from the S-GW 161B to the radio terminal apparatus 202. To start.

Next, the MME 162 requests the S-GW 161A to delete the communication path between the P-GW 163 and the radio base station apparatus 101A (step S403).

Next, the MME 162 transmits a terminal information release instruction to the radio base station apparatus 101A (step S404).

Next, the radio base station apparatus 101A receives a terminal information release instruction from the MME 162, releases information related to the radio terminal apparatus 202, and transmits a terminal information release completion notification to the MME 162 (step S405).

Next, the S-GW 161A receives the communication path deletion request from the MME 162, deletes the communication path between the P-GW 163 and the radio base station apparatus 101A, and transmits a communication path deletion response to the MME 162 ( Step S406).

Next, when the MME 162 receives the terminal information release completion notification from the radio base station apparatus 101A, the MME 162 deletes the logical communication path between the S-GW 161A and the radio base station apparatus 101A, that is, the data forwarding path, from the S-GW 161A. (Step S407).

Next, when receiving the data forwarding path deletion request, the S-GW 161A deletes the logical communication path between the S-GW 161A and the radio base station apparatus 101A, and sends a data forwarding path deletion response to the MME 162. Transmit (step S408).

Next, the MME 162 deletes the logical communication path between the S-GW 161A and the S-GW 161B and the logical communication path between the S-GW 161B and the radio base station apparatus 101B, that is, the deletion of the data forwarding path. -Request to GW 161B (step S409).

Next, when the S-GW 161B receives the data forwarding path deletion request, the logical communication path between the S-GW 161A and the S-GW 161B and the logical communication path between the S-GW 161B and the radio base station apparatus 101B. The communication path is deleted, and a data forwarding path deletion response is transmitted to the MME 162 (step S410).

(Ii) Case where Execution Condition is Not Satisfied FIG. 37 is a sequence of handover operation in a situation where the execution condition for handover operation is not satisfied in the radio communication system according to the second embodiment of the present invention.

Referring to FIG. 37, the operation from step S411 to step S424 is the same as the operation from step S381 to step S394 shown in FIG. 36, and therefore detailed description will not be repeated here.

Next, when receiving the handover instruction from the MME 162, the radio base station apparatus 101A determines whether or not the communication quality between itself and the radio terminal apparatus 202 satisfies a predetermined handover execution condition. If the communication quality does not satisfy the handover execution condition, the radio base station apparatus 101A should not execute the handover operation of the radio terminal apparatus 202 and should stop the handover operation for which the preparation process has been performed. It is determined that there is (step S425).

Next, the radio base station apparatus 101A transmits a handover cancellation notification to the MME 162 (step S426).

Next, upon receiving the handover cancellation notification, the MME 162 transmits a terminal information release instruction to the radio base station apparatus 101B (step S427).

Next, the radio base station apparatus 101B receives a terminal information release instruction from the MME 162, releases information related to the radio terminal apparatus 202, and transmits a terminal information release completion notification to the MME 162 (step S428).

Next, the MME 162 requests the S-GW 161B to delete the communication path between the P-GW 163 and the radio base station apparatus 101B (step S429).

Next, the S-GW 161B receives the communication path deletion request from the MME 162, deletes the communication path between the P-GW 163 and the radio base station apparatus 101B, and transmits a communication path deletion response to the MME 162 ( Step S430).

Next, when receiving a communication path deletion response from the S-GW 161B, the MME 162 transmits a handover stop response to the radio base station apparatus 101A (step S431).

Then, the operations from step S432 to step S435 are executed. Since the operations from step S432 to step S435 are the same as the operations from step S407 to step S410 shown in FIG. 36, detailed description will not be repeated here.

(C) When switching between MME and S-GW is necessary [Configuration and basic operation]
FIG. 38 is a diagram illustrating an example of a configuration of a wireless communication system according to the second embodiment of the present invention.

Referring to FIG. 38, radio communication system 403 is a mobile communication system according to LTE standardized by, for example, 3GPP, similar to radio communication system 401 shown in FIG. A station apparatus 101B. Here, similarly to the case shown in FIG. 32, the wireless terminal device 202 moves from a state in which it is communicating with the wireless base station device 101A, and the communication partner, that is, the communication connection destination is changed from the wireless base station device 101A to the wireless base station Assume that a handover operation is performed so as to switch to the apparatus 101B.

The wireless communication system 403 further includes S-

GWs

161A and 161B (gateway devices),

MMEs

162A and 162B (communication control devices), and a P-GW 163 provided in the core network 301.

The radio base station apparatus 101A and the MME 162A exchange various data via the S1-MME interface by transmitting and receiving communication data according to the S1-MME interface, which is a logical interface, as indicated by a dotted line.

The radio base station apparatus 101B and the MME 162B exchange various kinds of information with each other via the S1-MME interface by transmitting and receiving communication data according to the S1-MME interface, which is a logical interface, as indicated by a dotted line.

The MME 162A and the S-GW 161A exchange various data with each other via the S11 interface by transmitting and receiving communication data according to the S11 interface which is a logical interface. The MME 162B and the S-GW 161B exchange various data with each other via the S11 interface by transmitting and receiving communication data according to the S11 interface which is a logical interface.

The S-

GWs

[Operation]
Next, the flow of the handover operation in the wireless communication system 403 according to the second embodiment of the present invention will be described separately when the handover operation execution condition is satisfied and when the handover operation execution condition is not satisfied. To do.

(I) When Execution Conditions are Satisfied FIG. 39 is a sequence of handover operations in a situation where the execution conditions for handover operations are satisfied in the wireless communication system according to the second embodiment of the present invention.

39, the operation from step S441 to step S445 is the same as the operation from step S321 to step S325 shown in FIG. 33, and therefore detailed description will not be repeated here.

Next, the MME 162B determines whether it is necessary to switch the S-GW based on the handover request received from the MME 162A. Specifically, the MME 162B includes an S-GW connected between the radio base station apparatus 101A and the IP network 302, and an S-GW connected between the radio base station apparatus 101B and the IP network 302. Whether or not is different (step S446).

Next, the MME 162B includes an S-GW 161A connected between the radio base station apparatus 101A and the IP network 302, and an S-GW 161B connected between the radio base station apparatus 101B and the IP network 302. Because of the difference, the P-GW 163 and the radio base station apparatus 101B are configured so that downlink packets addressed to the radio terminal apparatus 202 from the higher level network and uplink packets from the radio terminal apparatus 202 to the higher level network can pass through the S-GW 161B. A request is made to the S-GW 161B to create a communication path between them (step S447).

Next, the S-GW 161B receives a communication path creation request from the MME 162B, creates a communication path between the P-GW 163 and the radio base station apparatus 101B passing through the S-GW 161B, and sends a communication path creation response to the MME 162B. (Step S448).

Next, the MME 162B transmits a handover request to the radio base station apparatus 101B (step S449).

Next, radio base station apparatus 101B receives the handover request from MME 162B, and transmits a handover response to the handover request to MME 162B (step S450).

Next, when receiving a handover response from the radio base station apparatus 101B, the MME 162B issues a request for establishing a communication path for performing data forwarding via the S1-U interface, that is, a logical path (hereinafter also referred to as a data forwarding path). The data is transmitted to the S-GW 161B (step S451).

Next, upon receiving a data forwarding path establishment request from the MME 162B, the S-GW 161B establishes a data forwarding path. That is, S-GW 161B establishes a logical communication path between S-GW 161A and S-GW 161B, and a logical communication path between S-GW 161B and radio base station apparatus 101B. Then, the S-GW 161B transmits a data forwarding path establishment response to the MME 162B (step S452).

Next, the MME 162B transfers the handover response received from the radio base station apparatus 101B to the MME 162A (step S453).

Next, the MME 162A transmits a request for establishing a logical communication path for performing data forwarding via the S1-U interface to the S-GW 161A (step S454).

Next, upon receiving a data forwarding path establishment request from the MME 162A, the S-GW 161A establishes a data forwarding path. That is, S-GW 161A establishes a logical communication path between S-GW 161A and radio base station apparatus 101A. Then, the S-GW 161A transmits a data forwarding path establishment response to the MME 162A (step S455).

Next, the MME 162A transmits a handover instruction to the radio base station apparatus 101A. Then, the radio base station apparatus 101A starts data forwarding via the S1-U interface (step S456).

Next, the radio base station apparatus 101A determines whether or not the communication quality between itself and the radio terminal apparatus 202 satisfies a predetermined handover execution condition. When the communication quality satisfies the handover execution condition, the radio base station apparatus 101A determines that the handover operation of the radio terminal apparatus 202 should be executed (step S457).

Next, the radio base station apparatus 101A transmits an RRC connection reconfiguration instruction to the radio terminal apparatus 202 (step S458).

Next, the radio base station apparatus 101A transmits a status notification indicating its own communication status and the like to the MME 162A (step S459). This state notification includes information such as the serial number of the packet for the radio base station apparatus 101B to process the transfer packet in data forwarding.

Next, the MME 162A transfers the status notification received from the radio base station apparatus 101A to the MME 162B (step S460).

Next, the MME 162B transmits a status notification response to the status notification transferred from the MME 162A to the MME 162A (step S461).

Next, the MME 162B transmits a status notification indicating the communication contents and the like with the wireless terminal device 202 to the wireless base station device 101B (step S462).

Next, when the RRC connection is established between the wireless terminal device 202 and the wireless base station device 101B, the wireless terminal device 202 transmits an RRC connection reconfiguration completion notification (RRC Connection Reconfiguration Complete) to the wireless base station device 101B. (Step S463).

Next, the radio base station apparatus 101B receives the RRC connection reconfiguration completion notification from the radio terminal apparatus 202 and transmits a handover completion notification to the MME 162B (step S464). This handover completion notification includes a path switching request for the S-GW 161B.

Next, the MME 162B transfers the handover completion notification received from the radio base station apparatus 101B to the MME 162A (step S465).

Next, the MME 162A transmits a handover completion notification response to the handover completion notification received from the MME 162B to the MME 162B (step S466).

Next, the MME 162B transmits a bearer change request including the above path switching request to the S-GW 161B (step S467).

Then, the S-GW 161B receives the bearer change request from the MME 162B, and performs a path, that is, a logical communication path switching process, that is, sets the transmission destination of the target packet addressed to the wireless terminal device 202 to the wireless base station device 101A To the radio base station apparatus 101B.

Next, the S-GW 161B transmits a bearer change response including a path switching response to the bearer change request to the MME 162B (step S468).

Next, the MME 162A requests the S-GW 161A to delete the communication path between the P-GW 163 and the radio base station apparatus 101A (step S469).

Next, the MME 162A transmits a terminal information release instruction to the radio base station apparatus 101A (step S470).

Next, the radio base station apparatus 101A receives a terminal information release instruction from the MME 162A, releases information related to the radio terminal apparatus 202, and transmits a terminal information release completion notification to the MME 162A (step S471).

Next, the S-GW 161A receives a communication path deletion request from the MME 162A, deletes the communication path between the P-GW 163 and the radio base station apparatus 101A, and transmits a communication path deletion response to the MME 162A ( Step S472).

Next, when the MME 162A receives the terminal information release completion notification from the radio base station apparatus 101A, the MME 162A deletes the logical communication path between the S-GW 161A and the radio base station apparatus 101A, that is, the data forwarding path, from the S-GW 161A. (Step S473).

Next, when receiving the data forwarding path deletion request, the S-GW 161A deletes a logical communication path between the S-GW 161A and the radio base station apparatus 101A, and sends a data forwarding path deletion response to the MME 162A. Transmit (step S474).

Next, the MME 162B deletes the logical communication path between the S-GW 161A and the S-GW 161B and the logical communication path between the S-GW 161B and the radio base station apparatus 101B, that is, the deletion of the data forwarding path. -Request to GW 161B (step S475).

Next, when the S-GW 161B receives the data forwarding path deletion request, the logical communication path between the S-GW 161A and the S-GW 161B and the logical communication path between the S-GW 161B and the radio base station apparatus 101B. The communication path is deleted, and a data forwarding path deletion response is transmitted to the MME 162B (step S476).

(Ii) Case where Execution Condition is Not Satisfied FIG. 40 is a sequence of handover operation in a situation where the execution condition for the handover operation is not satisfied in the radio communication system according to the second embodiment of the present invention.

Referring to FIG. 40, the operation from step S481 to step S496 is the same as the operation from step S441 to step S456 shown in FIG. 39, and therefore detailed description will not be repeated here.

Next, upon receiving a handover instruction from the MME 162A, the radio base station apparatus 101A determines whether or not the communication quality between itself and the radio terminal apparatus 202 satisfies a predetermined handover execution condition. If the communication quality does not satisfy the handover execution condition, the radio base station apparatus 101A should not execute the handover operation of the radio terminal apparatus 202 and should stop the handover operation for which the preparation process has been performed. It is determined that there is (step S497).

Next, the radio base station apparatus 101A transmits a handover cancellation notification to the MME 162A (step S498).

Next, the MME 162A transfers the handover cancellation notification received from the radio base station apparatus 101A to the MME 162B (step S499).

Next, when the MME 162B receives the handover cancellation notification, the MME 162B transmits a terminal information release instruction to the radio base station apparatus 101B (step S500).

Next, the radio base station apparatus 101B receives a terminal information release instruction from the MME 162B, releases information related to the radio terminal apparatus 202, and transmits a terminal information release completion notification to the MME 162B (step S501).

Next, the MME 162B requests the S-GW 161B to delete the communication path between the P-GW 163 and the radio base station apparatus 101B (step S502).

Next, the S-GW 161B receives the communication path deletion request from the MME 162B, deletes the communication path between the P-GW 163 and the radio base station apparatus 101B, and transmits a communication path deletion response to the MME 162B ( Step S503).

Next, when receiving the terminal information release completion notification from the radio base station apparatus 101B, the MME 162B transmits a handover stop response to the MME 162A (step S504).

Next, the MME 162A transmits the handover stop response received from the MME 162B to the radio base station apparatus 101A (step S505).

Then, the operations from step S506 to step S509 are executed. Since the operations from step S506 to step S509 are the same as the operations from step S473 to step S476 shown in FIG. 39, detailed description will not be repeated here.

Incidentally, when an inappropriate handover operation as described in Non-Patent Document 1 is performed, various problems such as communication interruption and increase in communication traffic occur in the wireless communication system.

On the other hand, in the radio communication system 401 according to the second embodiment of the present invention, the radio base station apparatus 101A issues a handover request for performing a handover operation of the radio terminal apparatus 202 from itself to the radio base station apparatus 101B. It transmits to corresponding MME162A. Further, when the handover destination radio base station apparatus 101B indicated by the handover request is not the management target of the MME 162A, the MME 162A transmits the handover request to the MME 162B that manages the radio base station apparatus 101B. In addition, the MME 162B transmits the received handover request to the radio base station apparatus 101B, and when receiving a response to the handover request from the radio base station apparatus 101B, transmits a response to the MME 162A. Further, the MME 162A receives the response from the MME 162B, and transmits a handover instruction to the radio base station apparatus 101A. The radio base station apparatus 101A receives the handover instruction, determines whether or not a predetermined execution condition regarding communication quality with the radio terminal apparatus 202 is satisfied, and if the execution condition is not satisfied, The provision of an instruction for performing a handover operation to the wireless terminal device 202 is stopped or suspended.

With such a configuration, even when the MME 162A that manages the radio base station apparatus 101A and the MME 162B that manages the radio base station apparatus 101B are different, the preparation process for the handover operation is completed prior to determining whether to perform the handover operation. Therefore, for example, “Too Late HO” in which the timing of handover by the wireless terminal device 202 is too late can be suppressed. Also, unlike when adjusting parameters for handover operation, even if “Too Late HO” is suppressed, the timing of handover by wireless terminal device 202 is too early to prevent an increase in the occurrence probability of “Too Early HO”. it can. That is, an inappropriate handover operation can be suppressed and a good wireless communication system can be constructed. Therefore, the communication can be stabilized by appropriately controlling the handover operation of the wireless terminal device 202.

Also, in the radio communication system 401 according to the second embodiment of the present invention, the radio base station apparatus 101A issues a handover request when a predetermined preparation condition regarding communication quality with the radio terminal apparatus 202 is satisfied. The communication quality transmitted to the radio base station apparatus 101B and indicated by the preparation condition is better than the communication quality indicated by the execution condition.

With such a configuration, the preparation process for the handover operation can be performed in advance under conditions that are milder than the communication quality that is the basis for determining whether to execute the handover operation. In addition, the time required for the handover operation can be significantly shortened by performing transmission / reception of information necessary for switching the MME 162 in advance as a preparation process for the handover operation.

Also, in the radio communication system 402 according to the second embodiment of the present invention, the radio base station apparatus 101A transmits a handover request for performing a handover operation of the radio terminal apparatus 202 from itself to the radio base station apparatus 101B to the MME 162. To do. In addition, the MME 162 is configured when the S-GW 161A connected between the radio base station apparatus 101A and the upper network is different from the S-GW 161B connected between the radio base station apparatus 101B and the upper network. Transmits a communication path creation request to the S-GW 161B. In addition, when the S-GW 161B receives the communication path creation request, the S-GW 161B can relay communication data addressed to the wireless terminal device 202 transmitted from the upper network and communication data transmitted from the wireless terminal device 202 to the upper network. A route is created, and a communication route creation response to the communication route creation request is transmitted to the MME 162. Further, when the MME 162 receives the communication path creation response, the MME 162 transmits a handover request to the radio base station apparatus 101B, and when receiving a response to the handover request from the radio base station apparatus 101B, transmits a handover instruction to the radio base station apparatus 101A. When the radio base station apparatus 101A receives the handover instruction, the radio base station apparatus 101A determines whether or not a predetermined execution condition regarding communication quality with the radio terminal apparatus 202 is satisfied, and the execution condition is not satisfied. In this case, the provision of an instruction for performing a handover operation to the wireless terminal device 202 is stopped or suspended.

With such a configuration, the S-GW 161A connected between the radio base station apparatus 101A and the upper network is different from the S-GW 161B connected between the radio base station apparatus 101B and the upper network. However, since the preparation process for the handover operation can be completed prior to the determination of the execution of the handover operation, for example, it is possible to suppress “Too Late HO” in which the timing of the handover by the wireless terminal device 202 is too late. it can. Also, unlike when adjusting parameters for handover operation, even if “Too Late HO” is suppressed, the timing of handover by wireless terminal device 202 is too early to prevent an increase in the occurrence probability of “Too Early HO”. it can. That is, an inappropriate handover operation can be suppressed and a good wireless communication system can be constructed. Therefore, the communication can be stabilized by appropriately controlling the handover operation of the wireless terminal device 202.

Also, in the radio communication system 402 according to the second embodiment of the present invention, the radio base station apparatus 101A performs the handover request when a predetermined preparation condition regarding communication quality with the radio terminal apparatus 202 is satisfied. Is transmitted to the MME 162, and the communication quality indicated by the preparation condition is better than the communication quality indicated by the execution condition.

With such a configuration, the preparation process for the handover operation can be performed in advance under conditions that are milder than the communication quality that is the basis for determining whether to execute the handover operation. In addition, the time required for the handover operation can be significantly shortened by performing transmission / reception of information necessary for switching the S-GW 161 in advance as a preparation process for the handover operation.

<Third Embodiment>
In the first embodiment described above, the case where the communication connection destination of the wireless terminal device 202 is switched from the wireless base station device 101A to the wireless base station device 101B in the handover operation has been described. On the other hand, in the third embodiment, a case will be described in which there are a plurality of switching destinations, that is, handover destination candidates in addition to the radio base station apparatus 101B. The contents other than those described below are the same as those of the radio base station apparatus according to the first embodiment.

(A) Problems when there are a plurality of handover destination candidates First, problems when there are a plurality of radio base station apparatuses that are handover destination candidates will be described. 41 is a diagram for explaining an example of a situation where there are a plurality of radio base station apparatuses that are handover destination candidates, and FIG. 42 is a diagram showing an example of a sequence of handover operations in the situation shown in FIG. is there.

Referring to FIG. 41, radio base station apparatus 101A can communicate with radio terminal apparatus 202 by forming cell CA and transmitting / receiving radio signals to / from radio terminal apparatus 202 existing in cell CA. It is. The radio base station apparatus 101B can communicate with the radio terminal apparatus 202 by forming a cell CB and transmitting and receiving radio signals to and from the radio terminal apparatus 202 existing in the cell CB. The radio base station apparatus 101C can communicate with the radio terminal apparatus 202 by forming a cell CC and transmitting and receiving radio signals to and from the radio terminal apparatus 202 existing in the cell CC.

Here, it is assumed that the wireless terminal device 202 is located in the cell CA, moves to the overlapping area of the cell CA, the cell CB, and the cell CC after selecting the wireless base station device 101A as a communication connection destination. That is, the radio base station apparatus 101A corresponds to a serving base station, the radio

base station apparatuses

101B and 101C correspond to peripheral base stations, and the radio

base station apparatuses

101B and 101C serve as handover destination candidates. Assume the case.

42, first, radio terminal apparatus 202 transmits a measurement result notification indicating a measurement result of received power to radio base station apparatus 101A. This measurement result includes the measurement results of the received power of the radio signals transmitted from the radio

base station apparatuses

101B and 101C in the neighboring cells and the cell IDs of the radio

base station apparatuses

101B and 101C (step S511).

Next, based on the measurement result notification received from the radio terminal apparatus 202, the radio base station apparatus 101A acquires measurement information indicating the measurement result for each cell ID and stores it in a storage unit (not shown). Then, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A acquires the communication quality between itself and the wireless terminal device 202. Then, radio base station apparatus 101A determines that the handover preparation process should be performed when the acquired communication quality satisfies a predetermined handover preparation condition.

At this time, the measurement result regarding the radio signal transmitted from the radio base station apparatus 101B and the measurement result regarding the radio signal transmitted from the radio base station apparatus 101C may both satisfy the handover preparation condition. In such a case, the radio base station apparatus 101A determines, as a handover destination radio base station apparatus, that the communication quality with the radio terminal apparatus 202 is better among the radio

base station apparatuses

101B and 101C that are candidates for the handover destination. Select (step S512).

Next, when the radio base station apparatus 101B is selected as a handover destination in step S512, for example, the radio base station apparatus 101A sends a handover request indicating the radio base station apparatus 101B to an MME (Mobility Management Entity) 162 that is a higher-level apparatus. Transmit (step S513).

Next, the MME 162 receives the handover request from the radio base station apparatus 101A, and transmits the handover request to the radio base station apparatus 101B (step S514).

Next, the radio base station apparatus 101B receives the handover request from the MME 162, and transmits a handover response to the handover request to the MME (step S515).

Next, the MME 162 receives the handover response from the radio base station apparatus 101B, and transmits a handover instruction to the radio base station apparatus 101A (step S516). As described above, the preparation process for the handover operation is completed (step S517).

Next, the wireless terminal device 202 transmits a new measurement result notification to the wireless base station device 101A (step S518).

Next, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A newly acquires communication quality between itself and the wireless terminal device 202. Then, the radio base station apparatus 101A determines that the handover operation of the radio terminal apparatus 202 should be executed when the newly acquired communication quality satisfies a predetermined handover execution condition (step S519).

Then, the operations from step S520 to step S526 are executed. Since the operations from step S520 to step S526 are the same as the operations from step S174 to step S180 shown in FIG. 21, detailed description will not be repeated here.

43 is a diagram for explaining a problem in an example of a situation where there are a plurality of radio base station apparatuses that are handover destination candidates, and FIG. 44 shows an example of a sequence of a handover operation in the situation shown in FIG. 43. FIG.

Referring to FIG. 43, handover operation to radio base station apparatus 101B having the best communication quality with radio terminal apparatus 202 when radio terminal apparatus 202 is located in the overlapping area of cell CA, cell CB and cell CC Assume that the wireless terminal device 202 enters the cell CC after the preparation process is completed. In this case, an operation as shown in FIG. 44 is executed.

Referring to FIG. 44, first, operations from step S531 to step S538 are executed. Since the operations from step S531 to step S538 are the same as the operations from step S511 to step S518 shown in FIG. 42, detailed description will not be repeated here.

Next, the wireless base station device 101A newly acquires communication quality based on the measurement result notification received from the wireless terminal device 202. At this time, the wireless terminal device 202 has entered the cell CC, and the communication quality between the wireless base station device 101B and the wireless terminal device 202 newly acquired by the wireless base station device 101A satisfies a predetermined handover execution condition. Suppose that it does not meet. In this case, the radio base station apparatus 101A determines that the handover operation of the radio terminal apparatus 202 to the radio base station apparatus 101B should be stopped (step S539).

Next, the radio base station apparatus 101A transmits a handover cancellation notification for canceling the handover operation to the radio base station apparatus 101B to the MME 162 (step S540). Then, the MME 162 receives the handover cancellation notification from the radio base station apparatus 101B, and transmits a terminal information release instruction to the radio base station apparatus 101B (step S541).

Next, the radio base station apparatus 101B receives a terminal information release instruction from the MME 162, releases information related to the radio terminal apparatus 202, and transmits a terminal information release completion notification to the MME 162 (step S542). Then, the MME 162 receives the terminal information release completion notification from the radio base station apparatus 101B, and transmits a handover stop response to the radio base station apparatus 101A (step S543).

Next, the wireless base station device 101A selects a handover destination wireless base station device based on the newly acquired measurement result. At this time, since the wireless terminal device 202 has entered the cell CC, the wireless base station device 101C is newly selected as a handover destination wireless base station device (step S544). Then, a handover operation preparation process (steps S545 to S549) is performed again. Since the operations from step S545 to step S549 are the same as the operations from step S513 to step S517 shown in FIG. 42, detailed description will not be repeated here.

As described above, it is conceivable that the radio terminal apparatus 202 related to the peripheral base station deteriorates due to the movement of the wireless terminal apparatus 202 after the completion of the preparation process for the handover operation to a certain peripheral base station. In such a case, the handover operation preparation process and the handover operation stop process are repeated.

(B) Radio communication system according to the third embodiment of the present invention Next, with respect to the radio communication system 404 according to the third embodiment of the present invention, there are a plurality of radio base station apparatuses that are handover destination candidates. The case where the handover source radio base station apparatus 101A selects the handover destination radio base station apparatus and the case where the radio terminal apparatus 202 selects the handover destination radio base station apparatus will be described separately.

Referring to FIG. 41 again, in the third embodiment of the present invention, after radio terminal apparatus 202 is located in cell CA and selects radio base station apparatus 101A as a communication connection destination, cell CA, It is assumed that the radio

base station apparatuses

101B and 101C satisfy the preparation conditions for the handover operation in a situation where the radio

base station apparatuses

101B and 101C have moved to the overlapping area of the cell CB and the cell CC.

(I) When the handover source radio base station apparatus selects the handover destination [Configuration and Basic Operation]
FIG. 45 is a diagram showing a configuration of a wireless communication system according to the third embodiment of the present invention.

Referring to FIG. 45, radio communication system 404 according to the third embodiment of the present invention is a mobile communication system according to LTE (Long Term Evolution) standardized by 3GPP, for example, and includes radio base station apparatus 101A. , 101B, 101C. In FIG. 45, three radio base station apparatuses are representatively shown, but a larger number of radio base station apparatuses may be provided. The wireless communication system 404 further includes an S-GW (Serving Gateway) 161 (gateway device), an MME (Mobility Management Entity) 162 (communication control device) provided in the core network 301, and a P-GW (Packet Data Network). Gateway) 163.

The wireless terminal device 202 establishes a communication connection with a server or the like in the IP network 302 via the wireless

base station devices

101A, 101B, and 101C, the S-GW 161, and the P-GW 163, for example, an IP (Internet Protocol) packet. Send and receive communication data.

The S-GW 161 is connected between the radio

base station apparatuses

101A, 101B, and 101C and the IP network 302. The S-GW 161 transmits communication data received from the wireless terminal device 202 via the wireless

base station devices

101A, 101B, and 101C to the IP network 302 via the P-GW 163, and from the server in the IP network 302 via the P-GW 163. The communication data received in (1) is transmitted to the wireless terminal device 202 via the wireless

base station devices

101A, 101B, 101C.

The MME 162 manages the radio

base station apparatuses

101A, 101B, 101C, the radio terminal apparatus 202, and the like in the radio communication system 401. The MME 162 transmits and receives control messages to and from the radio

base station apparatuses

101A, 101B, and 101C.

The radio

base station apparatuses

101A, 101B, and 101C transmit and receive communication data to and from the IP network 302 via the S-GW 161 and the P-GW 163.

The radio

base station apparatuses

101A, 101B, 101C and the S-GW 161 exchange various data with each other via the S1-U interface by transmitting and receiving communication data according to the S1-U interface which is a logical interface.

The radio

base station apparatuses

101A, 101B, 101C and the MME 162 transmit and receive communication data according to the S1-MME interface, which is a logical interface, to each other via the S1-MME interface, as indicated by dotted lines. Communicate.

The MME 162 and the S-GW 161 exchange various data with each other via the S11 interface by transmitting and receiving communication data according to the S11 interface which is a logical interface.

(Detailed configuration of radio base station device)
Also, the radio

base station apparatuses

101A, 101B, and 101C of the radio communication system 404 are all the same as the radio base station apparatus 101 according to the first embodiment of the present invention. That is, with reference to FIG. 19 and FIG. 20, the radio

base station apparatuses

101A, 101B, and 101C include an antenna 91, a circulator 92, a radio reception unit 93, a radio transmission unit 94, a signal processing unit 95, and a control. Part 98.

Further, the control unit 98 of the radio

base station apparatuses

101A, 101B, and 101C includes a handover request unit 11, a handover instruction unit 12, a handover condition adjustment unit 13, a handover information acquisition unit 14, and a terminal measurement result acquisition unit 15. Have

The handover request unit 11 transmits a handover request to a plurality of other radio base station apparatuses. For example, the handover request unit 11 of the radio base station apparatus 101A determines that both the radio

base station apparatuses

101B and 101C have a handover preparation condition between the radio terminal apparatus 202 and the radio

base station apparatuses

101B and 101C. A handover request is transmitted to.

The handover instruction unit 12 receives a response from another radio base station apparatus to the handover request, and selects a handover destination radio base station apparatus from among the other radio base station apparatuses corresponding to this response. For example, the handover request unit 11 of the radio base station apparatus 101A transmits a handover request to the radio

base station apparatuses

101B and 101C, and the radio

base station apparatuses

101B and 101C can execute a handover operation to the radio base station apparatus 101A. Is transmitted, the handover instructing unit 12 of the radio base station apparatus 101A sets the radio

base station apparatuses

101B and 101C as handover destination candidates, and selects the handover destination radio base station from the radio

base station apparatuses

101B and 101C. Select a station device.

Specifically, the handover instructing unit 12 acquires the measurement result of the received power in the radio terminal device 202 of the radio signal transmitted from the radio

base station devices

101B and 101C, and based on the measurement result, the radio terminal device The radio base station apparatus with the better communication state with 202 is selected as the handover destination radio base station apparatus.

Further, the handover instruction unit 12 transmits an RRC connection reconfiguration instruction for instructing a handover operation to the selected handover destination radio base station apparatus to the radio terminal apparatus 202.

Similarly to the first embodiment of the present invention, the handover instructing unit 12 receives the response and executes handover related to the communication quality between its own radio

base station apparatuses

101A, 101B, 101C and the radio terminal apparatus 202. If the condition is not satisfied, the assignment of the instruction to the wireless terminal device 202 is stopped or suspended. For example, when a predetermined handover execution condition is not satisfied, the handover instruction unit 12 does not transmit an RRC connection reconfiguration instruction to the radio terminal apparatus 202, and sends a handover cancellation notification to another radio base station apparatus. Send.

Further, after receiving the response from the radio

base station apparatuses

101B and 101C, the handover instruction unit 12 can exclude other radio base station apparatuses corresponding to the measurement results that cannot be acquired for a predetermined period from the handover destination candidates. is there.

That is, for example, after the reception power is measured by the wireless terminal device 202 and the preparation for the handover operation to the wireless

base station devices

101B and 101C is started, the wireless terminal It is assumed that the device 202 moves to a position away from the radio base station device 101C to such an extent that the received power with the radio base station device 101C cannot be measured. In this case, the measurement result notification received from the wireless terminal device 202 within a predetermined period after the wireless base station device 101A receives the response indicates the communication state between the wireless base station device 101B and the wireless terminal device 202. Although information related to the measurement result of the received power is included, information related to the measurement result of the received power indicating the communication state between the radio base station apparatus 101C and the radio terminal apparatus 202 may not be included. In such a case, the handover instructing unit 12 can remove the radio base station apparatus 101C from the handover destination candidates.

Further, after the handover operation is completed, the handover instructing unit 12 notifies the other base transceiver station other than the handover destination base transceiver station among the other base transceiver stations corresponding to the response to stop the handover operation. Send.

That is, for example, the handover request unit 11 of the radio base station apparatus 101A transmits a handover request to the radio

base station apparatuses

101B and 101C, and the radio

base station apparatuses

101B and 101C can execute a handover operation to the radio base station apparatus 101A. A case is assumed where a response indicating that there is a transmission and the handover instruction unit 12 selects the radio base station apparatus 101B as a handover destination. In this case, when the radio base station apparatus 101A receives, for example, a notification indicating that the handover is completed from the radio base station apparatus 101B via the higher-level apparatus, the handover instruction unit 12 of the radio base station apparatus 101A A handover operation stop notification is transmitted to the base station apparatus 101C.

[Operation]
Next, a flow of a handover operation when the handover source radio base station apparatus 101A selects a handover destination in the radio communication system 404 according to the third embodiment of the present invention will be described. FIG. 46 is a sequence of the handover operation when the handover source radio base station apparatus selects the handover destination in the radio communication system according to the third embodiment of the present invention.

46, first, radio terminal apparatus 202 transmits a measurement result notification indicating a measurement result of received power to radio base station apparatus 101A. This measurement result notification includes the measurement result of the received power of the radio signal transmitted from the radio

base station apparatuses

101B and 101C in the neighboring cells (step S551).

Next, based on the measurement result notification received from the radio terminal apparatus 202, the radio base station apparatus 101A acquires measurement information indicating the measurement result for each cell ID and stores it in a storage unit (not shown). Then, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A acquires the communication quality between itself and the wireless terminal device 202. Then, radio base station apparatus 101A determines that the preparation process for the handover operation should be performed when the acquired communication quality satisfies a predetermined handover preparation condition.

At this time, the measurement result regarding the radio signal transmitted from the radio base station apparatus 101B and the measurement result regarding the radio signal transmitted from the radio base station apparatus 101C may both satisfy the handover preparation condition. In such a case, the radio base station apparatus 101A sets the radio base station apparatus 101B and the radio base station apparatus 101C as handover destination candidates (step S552).

Next, the radio base station apparatus 101A transmits a handover request indicating the radio base station apparatus 101B to the MME 162 (step S553). Also, the radio base station device 101A transmits a handover request indicating the radio base station device 101C to the MME 162 (step S554).

Next, the MME 162 receives the handover request from the radio base station apparatus 101A, and transmits the handover request to the radio base station apparatus 101B (step S555). Further, the MME 162 receives the handover request from the radio base station apparatus 101A, and transmits the handover request to the radio base station apparatus 101C (step S556).

Next, the radio base station apparatus 101B receives a handover request from the MME 162, and transmits a handover response to the handover request to the MME 162 (step S557). Also, the radio base station apparatus 101C receives a handover request from the MME 162, and transmits a handover response to the handover request to the MME 162 (Step S558).

Next, the MME 162 receives the handover response from the radio base station apparatus 101B, and transmits a handover instruction with the radio base station apparatus 101B as the handover destination to the radio base station apparatus 101A (step S559). Also, the MME 162 receives the handover response from the radio base station apparatus 101C, and transmits a handover instruction with the radio base station apparatus 101C as the handover destination to the radio base station apparatus 101A (step S560). As described above, the preparation process for the handover operation to the radio

base station apparatuses

101B and 101C is completed (step S561).

Next, the wireless terminal device 202 transmits a new measurement result notification to the wireless base station device 101A (step S562).

Next, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A newly acquires communication quality between itself and the wireless terminal device 202. Then, the radio base station apparatus 101A determines that the handover operation of the radio terminal apparatus 202 should be executed when the newly acquired communication quality satisfies a predetermined handover execution condition.

At this time, the radio base station apparatus 101A determines, for example, the one with the better communication quality with the radio terminal apparatus 202 from the radio

base station apparatuses

101B and 101C for which the handover operation preparation process has been completed. Select as a radio base station device. In 3rd Embodiment, the case where the wireless base station apparatus 101B is selected is assumed (step S563).

Next, the radio base station apparatus 101A transmits an RRC connection reconfiguration instruction with the radio base station apparatus 101B as a handover destination to the radio terminal apparatus 202 (step S564).

Next, the radio base station apparatus 101A transmits a status notification indicating its own communication status and the like to the MME 162 (step S565).

Next, the MME 162 receives the status notification from the radio base station device 101A, and transmits a status notification indicating the communication content with the radio terminal device 202 to the radio base station device 101B (step S566).

Further, when the RRC connection is established between the wireless terminal device 202 and the wireless base station device 101B, the wireless terminal device 202 transmits an RRC connection reconfiguration completion notification to the wireless base station device 101B (step S567).

Next, the radio base station apparatus 101B receives the RRC connection reconfiguration completion notification from the radio terminal apparatus 202 and transmits a handover completion notification to the MME 162 (step S568).

Next, the MME 162 receives the handover completion notification from the radio base station apparatus 101B, and transmits a terminal information release instruction to the radio base station apparatus 101A (step S569).

Next, the radio base station apparatus 101A receives the terminal information release instruction from the MME 162, and performs a handover operation to the radio base station apparatus other than the radio base station apparatus 101B selected as the handover destination, that is, the radio base station apparatus 101C. A handover cancel notification for canceling is transmitted to the MME 162 (step S570).

Next, the MME 162 receives the handover cancellation notification from the radio base station apparatus 101A, and transmits a terminal information release instruction to the radio base station apparatus 101C (step S571).

Next, the radio base station apparatus 101C receives a terminal information release instruction from the MME 162, releases information related to the radio terminal apparatus 202, and transmits a terminal information release completion notification to the MME 162 (step S572).

Then, the MME 162 receives the terminal information release completion notification from the radio base station apparatus 101C, and transmits a handover stop response to the radio base station apparatus 101A (step S573).

Next, the radio base station apparatus 101A receives a handover stop response from the MME 162, releases information related to the radio terminal apparatus 202, and transmits a terminal information release completion notification to the MME 162 (step S574).

In the operation flow described above, the handover operation to the radio base station apparatus 101B is completed (step S568), and after the radio base station apparatus 101A receives the terminal information release instruction from the MME 162 (step S569), the radio base station The apparatus 101A transmits a handover cancellation notification to the MME 162 (step S570). However, the operation flow is not necessarily limited to this. For example, the radio base station apparatus 101A sends a handover operation stop notification to the radio base station apparatus 101C before the handover operation to the radio base station apparatus 101B is completed. May be sent to. In this case, for example, the operations from step S570 to step S573 are performed before step S567.

As described above, in the radio communication system 404 according to the third embodiment of the present invention, the handover request unit 11 of the radio

base station devices

101A, 101B, and 101C sends a handover request to a plurality of other radio base station devices. Do it.

It can be considered that the radio terminal device 202 related to the neighboring base station deteriorates due to the movement of the wireless terminal device 202 after the completion of the preparation process for the handover operation to a certain neighboring base station. Even in such a case, since the preparation process for the handover operation with another neighboring base station is completed, the handover operation to the other neighboring base station can be performed in a short time. It is possible to prevent the communication between the device 202 and the radio base station device from being interrupted.

Further, as described above, even when the radio wave condition of the wireless terminal device 202 related to the neighboring base station deteriorates, the handover operation preparation processing with other neighboring base stations is completed, so the handover operation It is possible to prevent the transmission / reception of information for the preparation process and the handover operation stop process from being repeated, and to reduce the load on the wireless communication system.

Also, in the radio communication system 404 according to the third embodiment of the present invention, the handover instruction unit 12 receives a handover response, and receives a handover destination radio from other radio base station apparatuses corresponding to this response. A base station apparatus is selected, and an instruction to perform a handover operation to the handover destination radio base station apparatus is given to the radio terminal apparatus 202.

Thus, by selecting a handover destination radio base station apparatus and giving an instruction for a handover operation to the radio terminal apparatus 202, the information is compared with the case where a plurality of radio base station apparatuses are presented in the instruction. The amount can be reduced, and the contents of the instruction can be simplified.

Moreover, in the radio communication system 404 according to the third embodiment of the present invention, after receiving the handover response, the handover instructing unit 12 transmits a radio signal transmitted from another radio base station apparatus corresponding to this response. A measurement result of the received power in the radio terminal device 202 is acquired, and a handover destination radio base station device is selected based on the measurement result.

With such a configuration, it is possible to select an appropriate radio base station apparatus as a handover destination according to the radio wave environment in the radio terminal apparatus 202 after completion of preparation for the handover operation.

Also, in the radio communication system 404 according to the third embodiment of the present invention, the handover instruction unit 12 receives another radio base station apparatus corresponding to a measurement result that cannot be acquired for a predetermined period after receiving the handover response as the handover destination. Remove from the candidate.

With such a configuration, for example, a radio base station apparatus that is far away from the radio terminal apparatus 202 to such an extent that the radio terminal apparatus 202 cannot measure received power can be excluded from handover destination candidates. A suitable radio base station apparatus can be selected.

Also, in the radio communication system 404 according to the third embodiment of the present invention, the handover instruction unit 12 performs handover target radio base station among other radio base station apparatuses corresponding to the handover response after the handover operation is completed. A request for canceling the handover operation is transmitted to a radio base station apparatus other than the station apparatus.

Here, for example, after the handover operation to the radio base station apparatus other than the radio base station apparatus selected as the handover destination is canceled before the handover operation is completed, the radio terminal apparatus 202 may When moving in a direction approaching the apparatus, the radio base station apparatus to be canceled may be an optimal handover destination. In this case, it is necessary to perform the handover operation to the radio base station apparatus to be canceled again.

On the other hand, the handover instruction unit 12 in the wireless communication system 404 performs the handover operation to the wireless base station device other than the wireless base station device selected as the handover destination as described above. Stop after completion. As a result, even when the wireless terminal device 202 moves and the radio wave state changes before the handover operation is completed, and the handover operation to another neighboring base station is performed, the preparation process for the handover operation is performed again. There is no need to do it.

(Ii) When the wireless terminal device selects a handover destination [Configuration and basic operation]
Next, a case where the radio terminal apparatus 202 selects a handover destination from a plurality of handover destination candidates will be described. Here, differences from radio communication system 404 in “(i) When the handover source radio base station apparatus selects a handover destination” will be described.

(Detailed configuration of radio base station device)
Referring to FIGS. 19 and 20 again, radio

base station apparatuses

101A, 101B, and 101C of radio communication system 405 according to the third embodiment include antenna 91, circulator 92, radio receiver 93, and radio A transmission unit 94, a signal processing unit 95, and a control unit 98 are provided.

Further, the control unit 98 of the radio

base station apparatuses

101A, 101B, and 101C includes a handover request unit 11, a handover instruction unit 12, a handover condition adjustment unit 13, a handover information acquisition unit 14, and a terminal measurement result acquisition unit 15. including.

The handover instruction unit 12 receives a response from another radio base station apparatus to the handover request, sets another radio base station apparatus corresponding to this response as a handover destination candidate, and indicates the radio base station apparatus that is the candidate Information is transmitted to the wireless terminal device 202.

For example, the handover request unit 11 of the radio base station apparatus 101A transmits a handover request to the radio

base station apparatuses

101B and 101C, and the radio

base station apparatuses

101B and 101C can execute a handover operation to the radio base station apparatus 101A. Is transmitted, the handover instruction unit 12 of the radio base station apparatus 101A instructs the radio

base station apparatuses

101B and 101C to perform a handover operation using the radio

base station apparatuses

101B and 101C as handover destination candidates. The RRC connection reconfiguration instruction is transmitted to the wireless terminal device 202.

Here, FIG. 47 is a diagram illustrating a comparative example of the message structure of the RRC connection reconfiguration instruction, and FIG. 48 is transmitted from the handover request unit in the wireless communication system according to the third embodiment of the present invention. It is a figure which shows an example of the message structure of a RRC connection reconfiguration instruction | indication.

As shown in FIG. 47, for example, when the radio base station apparatus 101A selects the radio base station apparatus 101B as a handover destination and transmits an RRC connection reconfiguration instruction to the radio terminal apparatus 202, the radio base station apparatus 101A Includes only the information of the radio base station apparatus 101B in the “Mobility Control Info” of the RRC connection reconfiguration instruction (see “Info1” in FIG. 47).

On the other hand, when the radio terminal apparatus 202 selects a handover destination radio base station apparatus, for example, as illustrated in FIG. 48, the radio base station apparatus 101A performs “Mobility Control Info” in an RRC connection reconfiguration instruction. The information (“Target Cell List”) of a plurality of radio base station devices is enumerated and transmitted to the radio terminal device 202 (see “Info2” in FIG. 48). Thereby, the radio | wireless terminal apparatus 202 can grasp | ascertain the some radio base station apparatus which is a candidate of a handover destination from the received RRC connection reconfiguration | reconfiguration instruction | indication.

Then, the wireless terminal device 202 receives the RRC connection reconfiguration instruction and selects a handover destination wireless base station device. The handover instructing unit 12 receives information indicating the handover destination radio base station apparatus selected by the radio terminal apparatus 202 and sends a status notification indicating the communication state of its own radio base station apparatus to the handover destination radio base station apparatus Send to.

(Detailed configuration of wireless terminal device)
FIG. 49 is a diagram illustrating a configuration of a wireless terminal apparatus of the wireless communication system according to the third embodiment of the present invention.

49, the wireless terminal device 202 of the wireless communication system 405 includes an antenna 21, a circulator 22, a receiving unit 23, a transmitting unit 24, and a signal processing unit 25. The signal processing unit 25 includes a reception signal processing unit 26, a selection unit 27, and a communication control unit 28.

The circulator 22 outputs the radio signals from the radio

base station apparatuses

101A, 101B, and 101C received at the antenna 21 to the reception unit 23 and outputs the radio signals received from the transmission unit 24 to the antenna 21.

The receiving unit 23 outputs the radio signal received from the circulator 22 to the signal processing unit 25. The received signal processing unit 26 performs various signal processing such as despreading in a CDMA (Code Division Multiple Access) system on the radio signal output from the receiving unit 23.

For example, based on the RRC connection reconfiguration instruction received from the radio

base station apparatuses

101A, 101B, and 101C that are communication connection destinations of the radio terminal apparatus 202, the selection unit 27 determines whether the radio base station apparatus is a handover destination candidate. To select a handover destination radio base station apparatus.

Specifically, the selection unit 27 of the wireless terminal device 202 acquires a measurement result of the received power in the wireless terminal device 202 of the wireless signal transmitted from the wireless

base station devices

101B and 101C, and based on the measurement result Then, the radio base station apparatus with the better communication state with the radio terminal apparatus 202 is selected as the handover destination radio base station apparatus.

The communication control unit 28 uses, for example, an IFFT (Inverse Fast Fourier Transform) in an OFDM (Orthogonal Frequency Division Multiplex) method for information indicating the handover destination radio base station apparatus selected by the selection unit 27 or information generated by itself. Various signal processing is performed, and the signal after this signal processing is output to the transmitter 24.

The transmission unit 24 outputs the signal received from the communication control unit 28 to the circulator 22. For example, the transmission unit 24 transmits information indicating the handover destination radio base station device selected by the selection unit 27, that is, a handover destination notification via the circulator 22 and the antenna 21, as a wireless connection destination of the radio terminal device 202. Transmit to base station apparatus 101A.

[Operation]
Next, the flow of a handover operation when the radio terminal apparatus 202 selects a handover destination in the radio communication system 405 according to the third embodiment of the present invention will be described. FIG. 50 is a sequence of the handover operation when the radio terminal apparatus selects the handover destination in the radio communication system according to the third embodiment of the present invention.

Referring to FIG. 50, the operations from step S581 to step S592 are executed. Since the operations from step S581 to step S592 are the same as the operations from step S551 to step S562 shown in FIG. 46, detailed description will not be repeated here.

Next, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A newly acquires communication quality between itself and the wireless terminal device 202. Then, the radio base station apparatus 101A determines that the handover operation of the radio terminal apparatus 202 should be executed when the newly acquired communication quality satisfies a predetermined handover execution condition (step S593).

Next, radio base station apparatus 101A issues an RRC connection reconfiguration instruction to instruct radio terminal apparatus 202 to perform a handover operation to radio

base station apparatuses

101B and 101C determined as a handover destination candidate based on the measurement result notification. It transmits to the wireless terminal device 202 (step S594).

Next, the wireless terminal device 202 receives the RRC connection reconfiguration instruction for instructing the handover operation from the wireless base station device 101A to the wireless

base station devices

101B and 101C, and the handover operation preparation process is completed. A handover destination radio base station apparatus is selected from the existing radio

base station apparatuses

101B and 101C. In the third embodiment, it is assumed that the radio base station apparatus 101B is selected (step S595).

Next, the radio terminal apparatus 202 transmits information indicating the selected handover destination radio base station apparatus 101B, that is, a handover destination notification to the radio base station apparatus 101A (step S596).

Next, the radio base station apparatus 101A receives information indicating the handover destination radio base station apparatus 101B selected by the radio terminal apparatus 202, and sends a status notification indicating the communication status of the radio base station apparatus 101A to the MME 162. Send. This state notification includes, for example, information indicating the radio base station apparatus 101B selected as the handover destination (step S597).

Then, the operations from step S598 to step S606 are executed. Since the operations from step S598 to step S606 are the same as the operations from step S566 to step S574 shown in FIG. 46, detailed description will not be repeated here.

As described above, in the radio communication system 405 according to the third embodiment of the present invention, the handover instruction unit 12 receives the handover response, and designates another radio base station apparatus corresponding to this response as a handover destination candidate. Is transmitted to the wireless terminal device 202.

As described above, the configuration in which the wireless terminal device 202 selects the handover destination wireless base station device makes it possible to select the handover destination wireless base station according to the latest radio wave environment as compared with the case where the handover source wireless base station device selects. A device can be selected.

Also, in the radio communication system 405 according to the third embodiment of the present invention, the handover instruction unit 12 receives and receives information indicating the handover destination radio base station apparatus selected by the radio terminal apparatus 202 Predetermined information is transmitted to the handover destination radio base station apparatus indicated by the information.

With such a configuration, the handover source radio base station apparatus grasps the handover destination radio base station apparatus selected by the radio terminal apparatus 202, and then transmits information necessary for the handover operation to the handover destination radio base station apparatus. Since it is transmitted to the apparatus, it is possible to transmit and receive information without waste.

<Fourth embodiment>
In the first embodiment described above, the case where the communication connection destination of the wireless terminal device 202 is switched from the wireless base station device 101A to the wireless base station device 101B in the handover operation has been described. On the other hand, in the fourth embodiment, a case will be described in which there are a plurality of switching destinations, that is, handover destination candidates, and the host device in the core network is also switched. The contents other than those described below are the same as those of the radio base station apparatus according to the first embodiment. As the host device, for example, MME (Mobility Management Entity) or S-GW (Serving Gateway) can be cited as in the second embodiment.

Hereinafter, as a fourth embodiment of the present invention, a case where MME switching is required in a handover operation and a case where S-GW switching is required in a handover operation will be described separately.

(A) When MME switching is required [Configuration and basic operation]
FIG. 51 is a diagram illustrating an example of a configuration of a wireless communication system according to the fourth embodiment of the present invention.

Referring to FIG. 51, a radio communication system 406 according to the fourth embodiment is a mobile communication system according to LTE (Long Term Evolution) standardized by 3GPP, for example, and includes radio

base station apparatuses

101A, 101B, 101C is provided.

Referring to FIG. 41 and FIG. 43, as shown in FIG. 41, the radio base station apparatus 101A forms a cell CA, and transmits and receives radio signals to and from the radio terminal apparatus 202 existing in the cell CA. Communication with the wireless terminal device 202 is possible. The radio base station apparatus 101B can communicate with the radio terminal apparatus 202 by forming a cell CB and transmitting and receiving radio signals to and from the radio terminal apparatus 202 existing in the cell CB. The radio base station apparatus 101C can communicate with the radio terminal apparatus 202 by forming a cell CC and transmitting and receiving radio signals to and from the radio terminal apparatus 202 existing in the cell CC.

base station apparatuses

101B and 101C correspond to peripheral base stations, and the radio

base station apparatuses

101B and 101C serve as handover destination candidates. Assume the case.

Referring again to FIG. 51, the wireless communication system 406 further includes an S-GW 161 (gateway device),

MME

162A, 162B, 162C (communication control device), and P-GW (Packet Data) provided in the core network 301. Network Gateway) 163.

base station devices

101A, 101B, and 101C, the S-GW 161, and the P-GW 163. Protocol) Communication data including packets is transmitted and received.

The S-GW 161 is connected between the radio

base station apparatuses

base station devices

101A, 101B, 101C.

The MME 162A manages the wireless base station device 101A, the wireless terminal device 202, and the like in the wireless communication system 401. The MME 162A transmits and receives control messages to and from the radio base station apparatus 101A. Further, the MME 162B manages the radio base station apparatus 101B and the radio terminal apparatus 202 in the radio communication system 401. The MME 162B transmits and receives control messages to and from the radio base station apparatus 101B. The MME 162C manages the wireless base station device 101C, the wireless terminal device 202, and the like in the wireless communication system 401. The MME 162C transmits and receives control messages to and from the radio base station apparatus 101C.

The radio

base station apparatuses

The radio base station apparatus 101A and the MME 162A exchange various data via the S1-MME interface by transmitting and receiving communication data according to the S1-MME interface, which is a logical interface, as indicated by a dotted line. Similarly, wireless base station apparatus 101B and MME 162B exchange various data via the S1-MME interface by transmitting and receiving communication data according to the S1-MME interface, which is a logical interface, as indicated by dotted lines. . Similarly, the wireless base station apparatus 101C and the MME 162C exchange various pieces of information with each other via the S1-MME interface by transmitting and receiving communication data according to the S1-MME interface, which is a logical interface, as indicated by a dotted line. .

The

MMEs

162A, 162B, 162C and the S-GW 161 exchange various data with each other via the S11 interface by transmitting and receiving communication data according to the S11 interface which is a logical interface.

The MME 162A, MME 162B, and MME 162C exchange various data with each other via the S10 interface by transmitting and receiving communication data according to the S10 interface that is a logical interface.

[Operation]
FIG. 52 is a sequence of a handover operation in the radio communication system according to the fourth embodiment of the present invention.

52, first, radio terminal apparatus 202 transmits a measurement result notification indicating a measurement result of received power to radio base station apparatus 101A. For example, the wireless terminal device 202 periodically measures the received power, when the communication state with the wireless base station device 101A becomes worse, and with other wireless base station devices other than the wireless base station device 101A. When the state becomes better, a measurement result notification is transmitted to the radio base station apparatus 101A (step S611).

At this time, the measurement result regarding the radio signal transmitted from the radio base station apparatus 101B and the measurement result regarding the radio signal transmitted from the radio base station apparatus 101C may both satisfy the handover preparation condition. In such a case, the radio base station apparatus 101A sets the radio base station apparatus 101B and the radio base station apparatus 101C as handover destination candidates (step S612).

Next, the radio base station apparatus 101A transmits a handover request indicating the radio base station apparatus 101B to the MME 162A (step S613). Also, the radio base station apparatus 101A transmits a handover request indicating the radio base station apparatus 101C to the MME 162A (step S614).

Next, the MME 162A determines whether it is necessary to switch the MME based on the handover request received from the radio base station apparatus 101A. Specifically, the MME 162A determines whether or not the radio

base station devices

101B and 101C indicated in the handover request are their management targets (step S615).

Next, the MME 162A transmits a handover request indicating the radio base station apparatus 101B to the MME 162B that manages the radio base station apparatus 101B because the radio base station apparatus 101B is not a management target of the MME 162A (step S616).

Next, the MME 162B determines whether it is necessary to switch the S-GW 161 based on the handover request received from the MME 162A. Specifically, the MME 162B includes an S-GW connected between the radio base station apparatus 101A and the IP network 302, and an S-GW connected between the radio base station apparatus 101B and the IP network 302. Whether or not is different. Here, the S-GW connected between the radio base station apparatus 101A and the IP network 302 is the same as the S-GW connected between the radio base station apparatus 101B and the IP network 302. Therefore, the MME 162B determines that there is no need to switch the S-GW 161 (step S617).

Next, the MME 162B transmits a handover request to the radio base station apparatus 101B (step S618).

Next, the radio base station apparatus 101B receives the handover request from the MME 162B and transmits a handover response to the handover request to the MME 162B (step S619).

Next, the MME 162B transfers the handover response received from the radio base station apparatus 101B to the MME 162A (step S620).

Here, when a target packet that is a packet addressed to the wireless terminal device 202 is accumulated in the wireless base station device 101A during the preparation period of the handover operation of the wireless terminal device 202, or a new target packet is received from the S-GW 161. When received, data forwarding is performed in which the radio base station apparatus 101A transfers this target packet to the radio base station apparatus 101B.

Therefore, when the MME 162A receives the handover response from the MME 162B, the MME 162A sends a request for establishing a communication path for performing data forwarding via the S1-U interface, that is, a logical path (hereinafter also referred to as data forwarding path) to the S-GW 161. Transmit (step S621).

Next, upon receiving a data forwarding path establishment request from the MME 162A, the S-GW 161 establishes a data forwarding path. That is, S-GW 161 establishes a logical path between radio base station apparatus 101A and radio base station apparatus 101B through itself. Then, the S-GW 161 transmits a data forwarding path establishment response to the MME 162A (step S622).

Next, the MME 162A transmits a handover instruction to the radio base station apparatus 101A. When the above-described handover operation preparation processing is executed and the radio base station apparatus 101A receives a handover instruction from the MME 162A, the radio base station apparatus 101A starts data forwarding via the S1-U interface. That is, the radio base station apparatus 101A transfers the target packet, which is a packet addressed to the radio terminal apparatus 202 that is stored in itself or newly received from the S-GW 161, to the radio base station apparatus 101B via the S-GW 161. (Step S623).

Also, the MME 162A transmits a handover request indicating the radio base station apparatus 101C to the MME 162C that manages the radio base station apparatus 101C because the radio base station apparatus 101C is not a management target of itself (step S624).

Next, the MME 162C determines whether or not it is necessary to switch the S-GW 161 based on the handover request received from the MME 162A. Specifically, the MME 162C includes an S-GW connected between the radio base station apparatus 101A and the IP network 302, and an S-GW connected between the radio base station apparatus 101C and the IP network 302. Whether or not is different. Here, the S-GW connected between the radio base station apparatus 101A and the IP network 302 is the same as the S-GW connected between the radio base station apparatus 101C and the IP network 302. Therefore, the MME 162C determines that there is no need to switch the S-GW 161 (step S625).

Next, the MME 162C transmits a handover request to the radio base station apparatus 101C (step S626).

Next, the radio base station apparatus 101C receives a handover request from the MME 162C and transmits a handover response to the handover request to the MME 162C (step S627).

Next, the MME 162C transfers the handover response received from the radio base station apparatus 101C to the MME 162A (step S628).

Next, when receiving a handover response from the MME 162C, the MME 162A transmits a request for establishing a communication path for performing data forwarding via the S1-U interface, that is, a logical path, to the S-GW 161 (step S629).

Next, upon receiving a data forwarding path establishment request from the MME 162A, the S-GW 161 establishes a data forwarding path. That is, S-GW 161 establishes a logical path between radio base station apparatus 101A and radio base station apparatus 101C through itself. Then, the S-GW 161 transmits a data forwarding path establishment response to the MME 162A (step S630).

Next, the MME 162A transmits a handover instruction to the radio base station apparatus 101A. Then, the radio base station apparatus 101A starts data forwarding via the S1-U interface. That is, the wireless base station device 101A transfers the target packet, which is a packet addressed to the wireless terminal device 202 stored in itself or newly received from the S-GW 161, to the wireless base station device 101C via the S-GW 161. (Step S631).

As described above, the preparation process for the handover operation to the radio

base station apparatuses

101B and 101C is completed (step S632). Note that the operations from step S616 to step S623 as described above and the operations from step S624 to step S631 are performed in parallel.

Next, the wireless terminal device 202 transmits a new measurement result notification to the wireless base station device 101A (step S633).

Next, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A newly acquires communication quality between itself and the wireless terminal device 202. Then, the radio base station apparatus 101A determines that the handover operation of the radio terminal apparatus 202 should be executed when the newly acquired communication quality satisfies a predetermined handover execution condition. Note that the communication quality indicated by the preparation condition described above is better than the communication quality indicated by the execution condition.

base station apparatuses

101B and 101C for which the handover operation preparation process has been completed. Select as a radio base station device. In the fourth embodiment, it is assumed that the radio base station apparatus 101B is selected (step S634).

Next, the radio base station apparatus 101A transmits an RRC connection reconfiguration instruction with the radio base station apparatus 101B as a handover destination to the radio terminal apparatus 202 (step S635).

Next, the radio base station apparatus 101A transmits a status notification indicating its own communication status to the MME 162A (step S636). This state notification includes information such as the serial number of the packet for the radio base station apparatus 101B to process the transfer packet in data forwarding.

Next, the MME 162A transfers the status notification received from the radio base station apparatus 101A to the MME 162B (step S637).

Next, the MME 162B transmits a status notification response to the status notification transferred from the MME 162A to the MME 162A (step S638).

Next, the MME 162B transmits a status notification indicating communication contents and the like with the wireless terminal device 202 to the wireless base station device 101B (step S639).

Next, when the RRC connection is established between the wireless terminal device 202 and the wireless base station device 101B, the wireless terminal device 202 transmits an RRC connection reconfiguration completion notification to the wireless base station device 101B (step S640).

Next, the radio base station apparatus 101B receives the RRC connection reconfiguration completion notification from the radio terminal apparatus 202 and transmits a handover completion notification to the MME 162B. This handover completion notification includes a path switching request for the S-GW 161 (step S641).

Next, the MME 162B transfers the handover completion notification received from the radio base station apparatus 101B to the MME 162A (step S642).

Next, the MME 162A transmits a handover completion notification response to the handover completion notification received from the MME 162B to the MME 162B (step S643).

Next, the MME 162B transmits a bearer change request including the path switching request to the S-GW 161 (step S644).

Next, the S-GW 161 receives the bearer change request from the MME 162B, and performs path switching processing. That is, the transmission destination of the target packet addressed to the wireless terminal device 202 is changed from the wireless base station device 101A to the wireless base station device. Switch to 101B. Then, the S-GW 161 transmits a bearer change response including a path switch response to the bearer change request to the MME 162B (step S645).

Then, the S-GW 161 transmits the target packet with the end marker attached to the radio base station apparatus 101A, ends the transmission of the target packet to the radio base station apparatus 101A, and then transmits the target packet to the radio base station apparatus 101B. Start sending. In addition, the radio base station apparatus 101B suspends and stores the transmission of the target packet from the S-GW 161 that does not pass through the radio base station apparatus 101A to the radio terminal apparatus 202.

Next, when the data forwarding as described above is completed, the MME 162A transmits a terminal information release instruction to the radio base station apparatus 101A (step S646).

Next, the radio base station apparatus 101A receives the terminal information release instruction from the MME 162A, and is selected as the handover destination and notifies the radio base station apparatus other than the radio base station apparatus 101B, that is, the radio base station apparatus 101C. Is transmitted to the MME 162A (step S647).

Next, the MME 162A transfers the handover cancellation notice to the radio base station apparatus 101C received from the radio base station apparatus 101A to the MME 162C (step S648).

Next, the MME 162C receives the handover cancellation notification from the MME 162A, and transmits a terminal information release instruction to the radio base station apparatus 101C (step S649).

Next, the radio base station apparatus 101C receives a terminal information release instruction from the MME 162C, releases information related to the radio terminal apparatus 202, and transmits a terminal information release completion notification to the MME 162C (step S650).

Next, the MME 162C receives the terminal information release completion notification from the radio base station apparatus 101C, and transmits a handover stop response to the MME 162A (step S651).

Next, the MME 162A transmits the handover stop response received from the MME 162C to the radio base station apparatus 101A (step S652).

Next, the radio base station apparatus 101A receives a handover stop response from the MME 162A, releases information related to the radio terminal apparatus 202, and transmits a terminal information release completion notification to the MME 162A (step S653).

Next, when the MME 162A receives the terminal information release completion notification from the radio base station apparatus 101A, the MME 162A issues a request to delete the data forwarding path between the radio base station apparatus 101A and the radio base station apparatus 101B via the S-GW 161. It transmits to GW161 (step S654).

Next, when the S-GW 161 receives the data forwarding path deletion request, the S-GW 161 deletes the data forwarding path between the radio base station apparatus 101A and the radio base station apparatus 101B via itself, and the data forwarding path deletion response. Is transmitted to the MME 162A (step S655).

When the MME 162A receives the terminal information release completion notification from the radio base station apparatus 101A, the MME 162A issues a request to delete the data forwarding path between the radio base station apparatus 101A and the radio base station apparatus 101C via the S-GW 161. (Step S656).

Next, when the S-GW 161 receives the data forwarding path deletion request, the S-GW 161 deletes the data forwarding path between the radio base station apparatus 101A and the radio base station apparatus 101C via the data transmission path, and receives a data forwarding path deletion response. Is transmitted to the MME 162A (step S657).

In the above-described operation flow, after the handover operation to the radio base station apparatus 101B is completed and the radio base station apparatus 101A receives the terminal information release instruction from the MME 162 (step S646), the radio base station apparatus 101A performs the MME 162. The handover stop notification is transmitted to (step S647). However, the operation flow is not necessarily limited to this. For example, the radio base station apparatus 101A sends a handover operation stop notification to the radio base station apparatus 101C before the handover operation to the radio base station apparatus 101B is completed. May be sent to. In this case, for example, the operations from step S647 to step S652 are performed before step S640.

As described above, in the wireless communication system 406 according to the fourth embodiment of the present invention, the MME 162A receives the handover request indicating the wireless

base station devices

101B and 101C as the handover destination from the wireless base station device 101A, and receives the handover request. Is determined for each of the radio

base station apparatuses

101B and 101C. If the radio

base station apparatuses

101B and 101C are not their own management targets, a handover request is sent to the

MMEs

162B and 162C that manage the radio

base station apparatuses

101B and 101C. Send.

It can be considered that the radio terminal device 202 related to the neighboring base station deteriorates due to the movement of the wireless terminal device 202 after the completion of the preparation process for the handover operation to a certain neighboring base station. Even in such a case, since the preparation process for the handover operation with another neighboring base station is completed, the handover operation to the other neighboring base station can be performed in a short time. It is possible to prevent communication between the device 202 and the radio

base station devices

101A, 101B, and 101C from being interrupted.

(B) When switching of S-GW is necessary [Configuration and basic operation]
FIG. 53 is a diagram illustrating an example of a configuration of a wireless communication system according to the fourth embodiment of the present invention.

Referring to FIG. 53, radio communication system 407 according to the fourth embodiment is a mobile communication system according to LTE standardized by 3GPP, for example, similarly to radio communication system 406 shown in FIG.

Base station apparatuses

101A, 101B, and 101C are provided. Here, it is assumed that radio terminal apparatus 202 is located in cell CA, selects radio base station apparatus 101A as a communication connection destination, and then moves to an overlapping area of cell CA, cell CB, and cell CC. That is, the radio base station apparatus 101A corresponds to a serving base station, the radio

base station apparatuses

101B and 101C correspond to peripheral base stations, and the radio

base station apparatuses

101B and 101C serve as handover destination candidates. Assume the case.

Referring to FIG. 53 again, the wireless communication system 407 further includes S-

GWs

161A, 161B, 161C (gateway devices), an MME 162 (communication control device), and a P-GW 163 provided in the core network 301. .

The S-GW 161C is connected between the radio base station apparatus 101C and the IP network 302. The S-GW 161C transmits communication data received from the wireless terminal device 202 via the wireless base station device 101B to the IP network 302 via the P-GW 163, and communication received via the P-GW 163 from a server or the like in the IP network 302. Data is transmitted to the wireless terminal device 202 via the wireless base station device 101C.

The MME 162 manages the radio

base station apparatuses

101A, 101B, 101C, the radio terminal apparatus 202, and the like in the radio communication system 402. The MME 162 transmits and receives control messages to and from the radio

base station apparatuses

101A, 101B, and 101C.

The radio base station apparatus 101A and the S-GW 161A exchange various data with each other via the S1-U interface by transmitting and receiving communication data according to the S1-U interface which is a logical interface. The radio base station apparatus 101B and the S-GW 161B exchange various data with each other via the S1-U interface by transmitting and receiving communication data according to the S1-U interface which is a logical interface. The radio base station apparatus 101C and the S-GW 161C exchange various pieces of information with each other via the S1-U interface by transmitting and receiving communication data according to the S1-U interface which is a logical interface.

The radio

base station apparatuses

The MME 162 and the S-

GWs

161A, 161B, and 161C exchange various pieces of information with each other via the S11 interface by transmitting and receiving communication data according to the S11 interface that is a logical interface.

The S-

GW

161A, 161B, 161C and the P-GW 163 exchange various data with each other via the S5 interface by transmitting and receiving communication data according to the S5 interface which is a logical interface.

[Operation]
FIG. 54 is a sequence of a handover operation in the radio communication system according to the fourth embodiment of the present invention.

54, the operation from step S661 to step S664 is the same as the operation from step S611 to step S614 shown in FIG. 52, and therefore, detailed description thereof will not be repeated here.

Next, the MME 162 determines whether it is necessary to switch the MME 162 based on the handover request received from the radio base station apparatus 101A. Specifically, the MME 162 determines whether or not the radio

base station apparatuses

101B and 101C indicated in the handover request are their management targets. Here, since the radio

base station apparatuses

101B and 101C are the management targets of the MME 162, the MME 162 determines that there is no need to switch the MME (step S665).

Next, the MME 162 determines whether or not it is necessary to perform S-GW switching based on the handover request received from the radio base station apparatus 101A. Specifically, the MME 162 includes an S-GW connected between the radio base station apparatus 101A and the IP network 302, and an S-GW connected between the radio base station apparatus 101B and the IP network 302. Whether or not is different. Further, in the MME 162, the S-GW connected between the radio base station apparatus 101A and the IP network 302 is different from the S-GW connected between the radio base station apparatus 101C and the IP network 302. It is determined whether or not (step S666).

Next, the MME 162 includes an S-GW 161A connected between the radio base station apparatus 101A and the IP network 302, and an S-GW 161B connected between the radio base station apparatus 101B and the IP network 302. Due to the difference, the downstream packet addressed to the wireless terminal device 202 from the higher level network and the upstream packet from the wireless terminal device 202 to the higher level network are connected between the wireless base station device 101B and the IP network 302. The S-GW 161B is requested to create a communication path between the P-GW 163 and the radio base station apparatus 101B so as to be able to pass through the GW 161B (step S667).

Next, the S-GW 161B receives the communication path creation request from the MME 162, creates a communication path between the P-GW 163 and the radio base station apparatus 101B passing through the S-GW 161B, and sends a communication path creation response to the MME 162. (Step S668).

Next, the MME 162 transmits a handover request to the radio base station apparatus 101B (step S669).

Next, the radio base station apparatus 101B receives the handover request from the MME 162, and transmits a handover response to the handover request to the MME 162 (Step S670).

Next, when receiving a handover response from the radio base station apparatus 101B, the MME 162 transmits a communication path for performing data forwarding via the S1-U interface, that is, a logical path establishment request to the S-GW 161B (step S671). ).

Next, upon receiving a data forwarding path establishment request from the MME 162, the S-GW 161B establishes a data forwarding path. That is, S-GW 161B establishes a logical communication path between S-GW 161A and S-GW 161B, and a logical communication path between S-GW 161B and radio base station apparatus 101B. Then, the S-GW 161B transmits a data forwarding path establishment response to the MME 162 (step S672).

Next, the MME 162 transmits a request for establishing a communication path for performing data forwarding via the S1-U interface to the S-GW 161A (step S673).

Next, upon receiving a data forwarding path establishment request from the MME 162, the S-GW 161A establishes a data forwarding path. That is, S-GW 161A establishes a logical communication path between S-GW 161A and radio base station apparatus 101A. Then, the S-GW 161A transmits a data forwarding path establishment response to the MME 162 (step S674).

Next, the MME 162 transmits a handover instruction to the radio base station apparatus 101A. Then, the radio base station apparatus 101A starts data forwarding via the S1-U interface. That is, the radio base station apparatus 101A transfers the target packet, which is a packet addressed to the radio terminal apparatus 202 that is stored in itself or newly received from the S-GW 161, to the radio base station apparatus 101B via the S-GW 161. (Step S675).

The MME 162 is different in S-GW 161A connected between the radio base station apparatus 101A and the IP network 302 and S-GW 161B connected between the radio base station apparatus 101C and the IP network 302. Therefore, the S-GW 161C in which the downstream packet addressed to the wireless terminal device 202 from the higher level network and the upstream packet from the wireless terminal device 202 to the higher level network are connected between the wireless base station device 101C and the IP network 302. Is requested to the S-GW 161C to create a communication path between the P-GW 163 and the radio base station apparatus 101C (step S676).

Next, the S-GW 161C receives the communication path creation request from the MME 162, creates a communication path between the P-GW 163 and the radio base station apparatus 101C passing through the S-GW 161C, and sends a communication path creation response to the MME 162. (Step S677).

Next, the MME 162 transmits a handover request to the radio base station apparatus 101C (step S678).

Next, the radio base station apparatus 101C receives a handover request from the MME 162, and transmits a handover response to the handover request to the MME 162 (step S679).

Next, when receiving a handover response from the radio base station apparatus 101B, the MME 162 transmits a request for establishing a communication path for performing data forwarding via the S1-U interface, that is, a logical path, to the S-GW 161C (step S680). ).

Next, upon receiving a data forwarding path establishment request from the MME 162, the S-GW 161C establishes a data forwarding path. That is, S-GW 161C establishes a logical communication path between S-GW 161A and S-GW 161C, and a logical communication path between S-GW 161C and radio base station apparatus 101C. Then, the S-GW 161C transmits a data forwarding path establishment response to the MME 162 (step S681).

Next, the MME 162 transmits a request for establishing a communication path for data forwarding via the S1-U interface to the S-GW 161A (step S682).

Next, the MME 162 transmits a handover instruction to the radio base station apparatus 101A. Then, the radio base station apparatus 101A starts data forwarding via the S1-U interface. That is, the wireless base station device 101A transfers the target packet, which is a packet addressed to the wireless terminal device 202 stored in itself or newly received from the S-GW 161, to the wireless base station device 101C via the S-GW 161. (Step S684).

base station apparatuses

101B and 101C is completed (step S685). Note that the operations from step S667 to step S675 as described above and the operations from step S676 to step S684 are performed in parallel.

Next, the wireless terminal device 202 transmits a new measurement result notification to the wireless base station device 101A (step S686).

base station apparatuses

101B and 101C for which the handover operation preparation process has been completed. Select as a radio base station device. In the fourth embodiment, it is assumed that the radio base station apparatus 101B is selected (step S687).

Next, the radio base station apparatus 101A transmits an RRC connection reconfiguration instruction with the radio base station apparatus 101B as a handover destination to the radio terminal apparatus 202 (step S688).

Next, the radio base station apparatus 101A transmits a status notification indicating its own communication status and the like to the MME 162 (step S689). This state notification includes information such as the serial number of the packet for the radio base station apparatus 101B to process the transfer packet in data forwarding.

Next, the MME 162 transmits a status notification indicating the content of communication with the wireless terminal device 202 to the wireless base station device 101B (step S690).

Next, the wireless terminal device 202 transmits an RRC connection reconfiguration completion notification to the wireless base station device 101B (step S691).

Next, the radio base station apparatus 101 B receives the RRC connection reconfiguration completion notification from the radio terminal apparatus 202 and transmits a handover completion notification to the MME 162. This handover completion notification includes a path switching request for the S-GW 161B (step S6492).

Next, the MME 162 transmits a bearer change request including the path switching request to the S-GW 161B (step S693).

The S-GW 161B receives the bearer change request from the MME 162, and performs path switching processing. That is, the transmission destination of the target packet addressed to the wireless terminal device 202 is changed from the wireless base station device 101A to the wireless base station device 101B. Switch to. Then, the S-GW 161B transmits a bearer change response including a path switching response to the bearer change request to the MME 162 (Step S694).

Then, the S-GW 161A transmits the target packet with the end marker attached thereto to the radio base station apparatus 101A, terminates the transmission of the target packet to the radio base station apparatus 101A, and transmits the target packet to the radio base station apparatus 101B. Start sending. Also, the radio base station apparatus 101B suspends and stores the transmission of the target packet from the S-GW 161B that does not pass through the radio base station apparatus 101A to the radio terminal apparatus 202.

Next, the MME 162 requests the S-GW 161A to delete the communication path between the P-GW 163 and the radio base station apparatus 101A (Step S695).

Next, the S-GW 161A receives the communication path deletion request from the MME 162, deletes the communication path between the P-GW 163 and the radio base station apparatus 101A, and transmits a communication path deletion response to the MME 162 ( Step S696).

Next, the MME 162 transmits a terminal information release instruction to the radio base station apparatus 101A (step S697).

Next, the radio base station apparatus 101A receives the terminal information release instruction from the MME 162, and is selected as the handover destination and notifies the radio base station apparatus other than the radio base station apparatus 101B, that is, the radio base station apparatus 101C. Is transmitted to the MME 162 (step S698).

Next, the MME 162 requests the S-GW 161C to delete the communication path between the P-GW 163 and the radio base station apparatus 101C (Step S699).

Next, the S-GW 161C receives a communication path deletion request from the MME 162, deletes the communication path between the P-GW 163 and the radio base station apparatus 101C, and transmits a communication path deletion response to the MME 162 ( Step S700).

Next, the MME 162 receives a communication path deletion response from the S-GW 161C, and transmits a terminal information release instruction to the radio base station apparatus 101C (step S701).

Next, the wireless base station device 101C receives a terminal information release instruction from the MME 162, releases information related to the wireless terminal device 202, and transmits a terminal information release completion notification to the MME 162 (step S702).

Next, the MME 162 receives the terminal information release completion notification from the radio base station apparatus 101C, and transmits a handover stop response to the radio base station apparatus 101A (step S703).

Next, the wireless base station device 101A receives a handover stop response from the MME 162, releases information related to the wireless terminal device 202, and transmits a terminal information release completion notification to the MME 162 (step S704).

Next, the MME 162 requests the S-GW 161A to delete the communication path between the P-GW 163 and the radio base station apparatus 101A (step S705).

Next, the MME 162 requests the S-GW 161B to delete the logical communication path between the S-GW 161B and the radio base station apparatus 101B, that is, the data forwarding path (step S706).

Next, the S-GW 161A receives the communication path deletion request from the MME 162, deletes the communication path between the P-GW 163 and the radio base station apparatus 101A, and transmits a communication path deletion response to the MME 162 ( Step S707).

Next, upon receiving a data forwarding path deletion request from the MME 162, the S-GW 161B deletes a logical communication path between the S-GW 161B and the radio base station apparatus 101B, and sends a data forwarding path deletion response. It transmits to MME162 (step S708).

Also, the MME 162 requests the S-GW 161A to delete the logical communication path between the S-GW 161A and the radio base station apparatus 101A, that is, the data forwarding path (Step S709).

Also, the MME 162 requests the S-GW 161C to delete the logical communication path between the S-GW 161C and the radio base station apparatus 101C, that is, the data forwarding path (Step S710).

Next, when the S-GW 161A receives the data forwarding path deletion request from the MME 162, it deletes the logical communication path between the S-GW 161A and the radio base station apparatus 101A, and sends a data forwarding path deletion response. It transmits to MME162 (step S711).

When the S-GW 161C receives the data forwarding path deletion request from the MME 162, the S-GW 161C deletes the logical communication path between the S-GW 161C and the radio base station apparatus 101C, and sends a data forwarding path deletion response to the MME 162. (Step S712).

Thus, in the wireless communication system 407 according to the fourth embodiment of the present invention, the MME 162A receives the handover request indicating the radio

base station devices

101B and 101C as the handover destination from the radio base station device 101A, and receives the handover request. For each of the wireless

base station devices

101B and 101C shown in FIG. 1, the gateway device 161A connected between the wireless base station device 101A and the upper network, and the wireless

base station devices

101B and 101C and the upper network are connected. It is determined whether or not the existing

gateway devices

161B and 161C are different, and a communication path creation request is transmitted to the

gateway devices

161B and 161C determined to be different.

base station devices

101A, 101B, and 101C from being interrupted.

In the fourth embodiment of the present invention, the case where MME switching is required in the handover operation and the case where S-GW switching is required in the handover operation have been described. However, the radio communication system according to the present invention is described. Can cope with the case where switching between MME and S-GW is necessary in the handover operation.

In the fourth embodiment of the present invention, the case where the radio base station apparatus 101A, which is the communication connection destination of the radio terminal apparatus 202, selects a handover destination from a plurality of handover destination candidates has been described. The apparatus 202 may receive information indicating a plurality of handover destination candidates from the radio base station apparatus 101A, and the radio terminal apparatus 202 may select a handover destination from the plurality of handover destination candidates.

It should be noted that some or all of the components and operations of each device according to the first to fourth embodiments of the present invention can be arbitrarily combined.

It should be considered that the above embodiment is illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 11 Handover request part 12 Handover instruction part 13 Handover condition adjustment part 14 Handover information acquisition part 15 Terminal measurement result acquisition part 21 Antenna 22 Circulator 23 Reception part 24 Transmission part 25 Signal processing part 26 Reception signal processing part 27 Selection part 28 Communication control part 91 antenna 92 circulator 93 wireless receiving unit 94 wireless transmitting unit 95 signal processing unit 96 received signal processing unit 97 transmission signal processing unit 98

control unit

101A, 101B, 101C wireless

base station apparatus

161, 161A, 161B, 161C S-GW (gateway apparatus)
162, 162A, 162B, 162C MME (communication control device)
163 P-GW
202 Wireless terminal device 301 Core network 302 IP network (upper network)
401, 402, 403, 404, 405, 406, 407 Wireless communication system

Claims

In a communication system capable of communicating with a plurality of radio base station apparatuses by performing a handover operation, the radio terminal apparatus is a radio base station apparatus for transmitting and receiving radio signals to and from the radio terminal apparatus,
A handover request unit for making a request to perform a handover operation of a radio terminal device from its own radio base station device to another radio base station device, to the other radio base station device;
In response to a response from the other radio base station apparatus to the request, a handover for giving an instruction to perform a handover operation from the radio base station apparatus to the other radio base station apparatus to the radio terminal apparatus An instruction unit,
In response to the response, the handover instruction unit gives the instruction to the radio terminal device when a predetermined execution condition relating to communication quality between the own radio base station device and the radio terminal device is not satisfied. A radio base station apparatus that cancels or puts on hold.
In response to the response, if the execution condition is not satisfied, the handover instruction unit does not give the instruction to the wireless terminal device, and cancels the handover operation. The radio base station apparatus according to claim 1, which is notified to the station apparatus.
In response to the response, if the execution condition is not satisfied, the handover instruction unit waits until the execution condition is satisfied, and when the execution condition is satisfied, the instruction to the wireless terminal device The radio base station apparatus according to claim 1, wherein:
The handover instruction unit indicates that the handover operation is stopped without giving the instruction to the wireless terminal device when a predetermined stop condition is satisfied before the execution condition is satisfied. The radio base station apparatus according to claim 3, which is notified to the radio base station apparatus.
The handover request unit makes the request to the other radio base station apparatus when a predetermined preparation condition regarding communication quality between the own radio base station apparatus and the radio terminal apparatus is satisfied,
The radio base station apparatus according to any one of claims 1 to 4, wherein the communication quality indicated by the preparation condition is better than the communication quality indicated by the execution condition.
The handover request unit makes the request to the other radio base station apparatus when a predetermined preparation condition regarding communication quality between the own radio base station apparatus and the radio terminal apparatus is satisfied,
The radio base station apparatus according to any one of claims 1 to 4, wherein the communication quality indicated by the preparation condition is equivalent to the communication quality indicated by the execution condition.
The handover request unit makes the request to the other radio base station apparatus when a predetermined preparation condition regarding communication quality between the own radio base station apparatus and the radio terminal apparatus is satisfied,
The cancellation condition is a condition related to communication quality between its own radio base station apparatus and the radio terminal apparatus,
The communication quality indicated by the preparation condition is equal to or better than the communication quality indicated by the execution condition, and the communication quality indicated by the stop condition is good quality compared with the communication quality indicated by the preparation condition. The radio base station apparatus according to claim 4, wherein
When the handover instruction unit notifies the other radio base station apparatus of the cancellation of the handover operation, it is determined that the communication quality between the own radio base station apparatus and the radio terminal apparatus does not satisfy the condition. The radio base station apparatus according to claim 2, 4 or 7, which is notified to the radio base station apparatus.
The radio base station device further includes:
The radio base station apparatus according to claim 5, further comprising a handover condition adjustment unit for adjusting a difference between communication quality indicated by the execution condition and communication quality indicated by the preparation condition.
The handover request unit makes the request to the other radio base station apparatus when a predetermined preparation condition regarding communication quality between the own radio base station apparatus and the radio terminal apparatus is satisfied,
The radio base station device further includes:
The difference between the communication quality indicated by the execution condition and the communication quality indicated by the preparation condition is adjusted, and the difference is adjusted based on the number of times the handover instruction unit is notified of the cancellation of the handover operation to another radio base station apparatus. The radio base station apparatus according to claim 2, 4 or 7, further comprising a handover condition adjustment unit for performing
The radio base station device further includes:
A handover information acquisition unit for acquiring the number of times the handover operation from the own radio base station apparatus to another radio base station apparatus by the radio terminal apparatus is inappropriate,
The radio base station apparatus according to claim 9 or 10, wherein the handover condition adjustment unit adjusts the difference based on the number of times acquired by the handover information acquisition unit.
A communication control method in a radio base station apparatus for transmitting and receiving radio signals to and from a radio terminal apparatus in a communication system capable of communicating with a plurality of radio base station apparatuses by performing a handover operation of the radio terminal apparatus,
Performing a request to perform a handover operation of a radio terminal device from itself to another radio base station device to the other radio base station device;
Determining whether to give an instruction to perform a handover operation from itself to the other radio base station apparatus in response to a response from the other radio base station apparatus to the request; Including
In the step of determining whether or not to give the instruction, if a predetermined execution condition regarding communication quality between the own radio base station apparatus and the radio terminal apparatus is not satisfied, the radio terminal apparatus A communication control method for notifying the other radio base station apparatus that the handover operation is to be stopped without giving the instruction.
A communication control program used in a radio base station apparatus for transmitting / receiving a radio signal to / from a radio terminal apparatus in a communication system in which the radio terminal apparatus performs communication with a plurality of radio base station apparatuses by performing a handover operation. To the computer
Performing a request to perform a handover operation of a radio terminal device from itself to another radio base station device to the other radio base station device;
Determining whether to give an instruction to perform a handover operation from itself to the other radio base station apparatus in response to a response from the other radio base station apparatus to the request; Is a program for executing
In the step of determining whether or not to give the instruction, if a predetermined execution condition regarding communication quality between the own radio base station apparatus and the radio terminal apparatus is not satisfied, the radio terminal apparatus A communication control program for notifying the other radio base station apparatus that the handover operation is to be stopped without giving the instruction.
The radio base station apparatus according to claim 1, wherein the handover request unit makes the request to a plurality of the other radio base station apparatuses.
The handover instruction unit receives the response, selects a handover destination radio base station device from the other radio base station devices corresponding to the response, and transmits the handover destination to the radio terminal device. The radio base station apparatus according to claim 14, which gives an instruction to perform a handover operation to the radio base station apparatus.
The handover instruction unit obtains a measurement result of the received power in the radio terminal device of a radio signal transmitted from the other radio base station device corresponding to the response after receiving the response, and the measurement result 16. The radio base station apparatus according to claim 15, wherein the radio base station apparatus of the handover destination is selected based on
The radio base station according to claim 16, wherein the handover instruction unit removes the other radio base station apparatus corresponding to the measurement result that cannot be acquired for a predetermined period after receiving the response from the handover destination candidates. Station equipment.
15. The range according to claim 14, wherein the handover instruction unit receives the response and transmits information indicating the other radio base station apparatus corresponding to the response as a handover destination candidate to the radio terminal apparatus. Wireless base station equipment.
The handover instruction unit receives information indicating the handover destination radio base station apparatus selected by the radio terminal apparatus, and transmits predetermined information to the handover destination radio base station apparatus indicated by the received information The radio base station apparatus according to claim 18.
After the handover operation is completed, the handover instruction unit cancels the handover operation to the other radio base station device other than the handover destination radio base station device among the other radio base station devices corresponding to the response. The radio base station apparatus according to any one of claims 14 to 19, wherein the request is transmitted.
A radio terminal apparatus capable of communicating with a plurality of radio base station apparatuses by transmitting and receiving radio signals to and from a radio base station apparatus and performing a handover operation,
A receiving unit for receiving information indicating a plurality of other radio base station devices as handover destination candidates from a serving base station that is a radio base station device that establishes a communication connection with itself;
A selection unit for selecting a handover destination radio base station device from among the plurality of other radio base station devices indicated by the information received by the reception unit;
A communication control unit configured to transmit information indicating the handover destination radio base station device selected by the selection unit to the serving base station and newly establish a communication connection with the handover destination radio base station device; A wireless terminal device.
A plurality of wireless base station devices for transmitting and receiving wireless signals to and from wireless terminal devices;
A communication system comprising a plurality of communication control devices for managing one or a plurality of the radio base station devices,
The radio base station apparatus transmits a handover request for performing a handover operation of the radio terminal apparatus from itself to another radio base station apparatus to a corresponding communication control apparatus,
The corresponding communication control device, when the other radio base station device to be handed over indicated by the handover request is not a management target of itself, to the other communication control device that manages the other radio base station device Send a handover request,
The other communication control apparatus transmits the received handover request to the other radio base station apparatus, and receives a response to the handover request from the other radio base station apparatus, the response to the corresponding communication control apparatus Send
The corresponding communication control apparatus receives the response from the other communication control apparatus, and transmits a handover instruction to the radio base station apparatus that is the transmission source of the handover request,
The radio base station apparatus receives the handover instruction, determines whether or not a predetermined execution condition relating to communication quality with the radio terminal apparatus is satisfied, and the execution condition is not satisfied A communication system for canceling or holding an instruction to perform a handover operation on the wireless terminal device.
The radio base station apparatus transmits the handover request to the corresponding communication control apparatus when a predetermined preparation condition regarding communication quality with the radio terminal apparatus is satisfied,
The communication system according to claim 22, wherein the communication quality indicated by the preparation condition is better than the communication quality indicated by the execution condition.
The corresponding communication control apparatus receives the handover request indicating a plurality of the other radio base station apparatuses as handover destinations from the radio base station apparatus, and self-corresponds to each other radio base station apparatus indicated by the handover request. The handover request is transmitted to another communication control apparatus that manages the other radio base station apparatus if it is not a management target of the self radio terminal station apparatus. Or the communication system according to Item 23.
A plurality of wireless base station devices for transmitting and receiving wireless signals to and from wireless terminal devices;
A communication control device for managing one or a plurality of the radio base station devices;
Connected between one or a plurality of the radio base station apparatuses and the upper network, and transmits communication data received from the radio terminal apparatus via the radio base station apparatus to the upper network and received from the upper network A communication system comprising a plurality of gateway devices for transmitting communication data to the wireless terminal device via the wireless base station device,
The radio base station apparatus transmits a handover request for performing a handover operation of the radio terminal apparatus from itself to another radio base station apparatus to the communication control apparatus,
The communication control apparatus includes a gateway apparatus connected between the radio base station apparatus and the upper network, and the other radio base station apparatus at the handover destination indicated by the handover request and the upper network. When the connected gateway device is different, a communication path creation request is transmitted to the gateway device connected between the other radio base station device and the upper network,
When the gateway device receives the communication path creation request, the gateway device can relay the communication data addressed to the wireless terminal device transmitted from the upper network and the communication data transmitted from the wireless terminal device to the upper network. Create a communication path, send a communication path creation response to the communication path creation request to the communication control device,
When the communication control apparatus receives the communication path creation response, the communication control apparatus transmits the handover request to the other radio base station apparatus, and receives the response to the handover request from the other radio base station apparatus, the handover request A handover instruction to the wireless base station device of the transmission source of
The radio base station apparatus receives the handover instruction, determines whether or not a predetermined execution condition relating to communication quality with the radio terminal apparatus is satisfied, and the execution condition is not satisfied A communication system that stops or suspends giving an instruction to perform a handover operation on the wireless terminal device.
The radio base station apparatus transmits the handover request to the communication control apparatus when a predetermined preparation condition relating to communication quality with the radio terminal apparatus is satisfied,
26. The communication system according to claim 25, wherein the communication quality indicated by the preparation condition is better than the communication quality indicated by the execution condition.
The communication control apparatus receives the handover request indicating a plurality of other radio base station apparatuses as handover destinations from the radio base station apparatus, and transmits the radio request for each of the other radio base station apparatuses indicated by the handover request. Determining whether a gateway device connected between a base station device and the upper network is different from a gateway device connected between the other radio base station device and the upper network; 27. The communication system according to claim 25 or 26, wherein the communication path creation request is transmitted to the gateway device determined to be different.
A plurality of wireless base station devices for transmitting and receiving wireless signals to and from wireless terminal devices;
A communication control method in a communication system comprising a plurality of communication control devices for managing one or a plurality of the radio base station devices,
The radio base station device transmitting a handover request for performing a handover operation of the radio terminal device from itself to another radio base station device to the corresponding communication control device;
When the other radio base station apparatus that is the handover destination indicated by the handover request is not a management target of the corresponding communication control apparatus, the corresponding communication control apparatus is directed to another communication control apparatus that manages the other radio base station apparatus. Sending a handover request;
When the other communication control apparatus transmits the received handover request to the other radio base station apparatus and receives a response to the handover request from the other radio base station apparatus, the response is sent to the corresponding communication control apparatus. A step of sending
The corresponding communication control apparatus receiving the response from the other communication control apparatus and transmitting a handover instruction to the radio base station apparatus that is the transmission source of the handover request;
When the radio base station apparatus receives the handover instruction, determines whether or not a predetermined execution condition regarding communication quality with the radio terminal apparatus is satisfied, and the execution condition is not satisfied Includes a step of canceling or suspending the provision of an instruction for performing a handover operation on the wireless terminal device.
A plurality of wireless base station devices for transmitting and receiving wireless signals to and from wireless terminal devices;
A communication control device for managing one or a plurality of the radio base station devices;
Connected between one or a plurality of the radio base station apparatuses and the upper network, and transmits communication data received from the radio terminal apparatus via the radio base station apparatus to the upper network and received from the upper network A communication control method in a communication system comprising a plurality of gateway devices for transmitting communication data to the wireless terminal device via the wireless base station device,
The radio base station device transmitting a handover request for performing a handover operation of the radio terminal device from itself to another radio base station device to the communication control device;
The communication control device is connected between the gateway device connected between the radio base station device and the upper network, and the other radio base station device of the handover destination indicated by the handover request and the upper network. If the connected gateway device is different, transmitting a communication path creation request to the gateway device connected between the other radio base station device and the upper network;
When the gateway device receives the communication path creation request, the gateway device can relay the communication data addressed to the wireless terminal device transmitted from the upper network and the communication data transmitted from the wireless terminal device to the upper network. Creating a communication path and transmitting a communication path creation response to the communication path creation request to the communication control device;
When the communication control device receives the communication path creation response, transmits the handover request to the other radio base station device, and receives the response to the handover request from the other radio base station device, the handover request Transmitting a handover instruction to the radio base station apparatus of the transmission source of
When the radio base station apparatus receives the handover instruction, determines whether or not a predetermined execution condition regarding communication quality with the radio terminal apparatus is satisfied, and the execution condition is not satisfied Includes a step of canceling or suspending the provision of an instruction for performing a handover operation on the wireless terminal device.
A plurality of wireless base station devices for transmitting and receiving wireless signals to and from wireless terminal devices;
A communication control program used in a communication system including a plurality of communication control devices for managing one or a plurality of the radio base station devices,
On the computer,
The radio base station device transmitting a handover request for performing a handover operation of the radio terminal device from itself to another radio base station device to the corresponding communication control device;
When the other radio base station apparatus that is the handover destination indicated by the handover request is not a management target of the corresponding communication control apparatus, the corresponding communication control apparatus is directed to another communication control apparatus that manages the other radio base station apparatus. Sending a handover request;
When the other communication control apparatus transmits the received handover request to the other radio base station apparatus and receives a response to the handover request from the other radio base station apparatus, the response is sent to the corresponding communication control apparatus. A step of sending
The corresponding communication control apparatus receiving the response from the other communication control apparatus and transmitting a handover instruction to the radio base station apparatus that is the transmission source of the handover request;
When the radio base station apparatus receives the handover instruction, determines whether or not a predetermined execution condition regarding communication quality with the radio terminal apparatus is satisfied, and the execution condition is not satisfied A communication control program for executing a step of canceling or suspending the provision of an instruction for performing a handover operation on the wireless terminal device.
A plurality of wireless base station devices for transmitting and receiving wireless signals to and from wireless terminal devices;
A communication control device for managing one or a plurality of the radio base station devices;
Connected between one or a plurality of the radio base station apparatuses and the upper network, and transmits communication data received from the radio terminal apparatus via the radio base station apparatus to the upper network and received from the upper network A communication control program used in a communication system including a plurality of gateway devices for transmitting communication data to the wireless terminal device via the wireless base station device,
On the computer,
The radio base station device transmitting a handover request for performing a handover operation of the radio terminal device from itself to another radio base station device to the communication control device;
The communication control device is connected between the gateway device connected between the radio base station device and the upper network, and the other radio base station device of the handover destination indicated by the handover request and the upper network. If the connected gateway device is different, transmitting a communication path creation request to the gateway device connected between the other radio base station device and the upper network;
When the gateway device receives the communication path creation request, the gateway device can relay the communication data addressed to the wireless terminal device transmitted from the upper network and the communication data transmitted from the wireless terminal device to the upper network. Creating a communication path and transmitting a communication path creation response to the communication path creation request to the communication control device;
When the communication control device receives the communication path creation response, transmits the handover request to the other radio base station device, and receives the response to the handover request from the other radio base station device, the handover request Transmitting a handover instruction to the radio base station apparatus of the transmission source of
When the radio base station apparatus receives the handover instruction, determines whether or not a predetermined execution condition regarding communication quality with the radio terminal apparatus is satisfied, and the execution condition is not satisfied A communication control program for executing a step of canceling or suspending the provision of an instruction for performing a handover operation on the wireless terminal device.