JP2013118588A - Radio base station device, communication control method, and communication control program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio base station device, communication control method, communication control program that can stabilize communication by adequately controlling the movement operation of a radio terminal device.SOLUTION: In a communication system in which a radio terminal device 202 is able to communicate with a plurality of radio base station devices by performing movement operation, a radio base station device 101 transmits and receives a radio signal to/from the radio terminal device 202. The radio base station device 101 comprises: a movement operation detection unit 14 for detecting occurrence of prescribed movement operation among movement operation from another radio base station device to the own radio base station device by the radio terminal device 202; and an avoidance processing unit 16 for adjusting operation of the own radio base station device such that the occurrence of the prescribed movement operation is restrained if the movement operation detection unit 14 has detected the prescribed movement operation.

Description

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

  Since the radius of the femto cell (Femto Cell) formed by this small base station (hereinafter also referred to as a femto base station) is as small as about 10 meters, the femto base station is the macro cell (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.

  In addition, 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 having 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)).

3GPP TR 36.902 V9.3.1 2011.3

  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.

  This invention was made in order to solve the above-mentioned subject, The objective is a radio base station apparatus which can aim at stabilization of communication by controlling the movement operation of a radio | wireless terminal apparatus appropriately, A communication control method and a communication control program are provided.

  (1) In order to solve the above problems, a radio base station apparatus according to an aspect of the present invention is a radio terminal in a communication system in which a radio terminal apparatus can communicate with a plurality of radio base station apparatuses by performing a moving operation. A radio base station device for transmitting and receiving radio signals to and from a device, wherein a predetermined movement operation is generated among movement operations from another radio base station device to its own radio base station device by a radio terminal device. When the predetermined movement operation is detected by the movement operation detection unit for detecting and the movement operation detection unit, the operation of the radio base station apparatus is controlled so that the generation of the predetermined movement operation is suppressed. And an avoidance processing unit for adjustment.

  As described above, since it is possible to execute inappropriate movement detection and avoidance processing in the destination radio base station apparatus, other radio base station apparatuses are allowed to adjust parameters used for timing control of the movement operation. Even when it is impossible, it is possible to suppress the occurrence of the predetermined movement operation and construct a good communication system. Therefore, communication can be stabilized by appropriately controlling the movement operation of the wireless terminal device.

  (2) Preferably, the avoidance processing unit adjusts the timing of the movement operation from the other radio base station device to the own radio base station device by adjusting the operation of the own radio base station device.

  In this way, by adjusting the operation of its own radio base station apparatus that is the destination radio base station apparatus, it is possible to adjust the timing of the movement operation and suppress the occurrence of an inappropriate movement operation.

  (3) More preferably, the avoidance processing unit notifies the other radio base station device that the mobile terminal device is permitted to move from the other radio base station device to its own radio base station device. Adjust timing.

  In this way, by adjusting the timing for notifying the other radio base station apparatus that the mobile terminal apparatus is permitted to move from the other radio base station apparatus to its own radio base station apparatus, It is possible to adjust the timing of the moving operation from the station apparatus to the own radio base station apparatus.

  (4) More preferably, the moving operation detection unit is configured such that the moving operation from the other wireless base station device to the own wireless base station device by the wireless terminal device is too early, and the second moving operation is too late. When the first movement operation is detected, the avoidance processing unit delays the permission notification timing, and when the second movement operation is detected, the avoidance processor detects the permission. Make the notification timing earlier.

  In this way, by adjusting the timing of notifying the other radio base station device that the mobile terminal device is permitted to move from the other radio base station device to its own radio base station device, It is possible to appropriately adjust the timing of the moving operation from the wireless base station device to the own wireless base station device.

  (5) Preferably, the avoidance processing unit adjusts a condition for permitting a movement operation from the other radio base station apparatus to the own radio base station apparatus by the radio terminal apparatus.

  With such a configuration, it is possible to suppress the occurrence of inappropriate movement operation by adjusting the conditions for permitting the movement operation from another wireless base station device to the own wireless base station device by the wireless terminal device. it can.

  (6) More preferably, the radio base station apparatus further includes a received power information acquisition unit for acquiring received power information indicating a measurement result of a received power of a radio signal from each radio base station apparatus in the radio terminal apparatus. The avoidance processing unit adjusts the condition based on the received power of the radio signal from the other radio base station apparatus indicated by the received power information and the received power of the radio signal from the own radio base station apparatus. To do.

  With such a configuration, it is possible to appropriately adjust the conditions for permitting the mobile terminal device to move from another radio base station device to its own radio base station device based on the received power in the radio terminal device.

  (7) More preferably, the moving operation detection unit is configured such that the moving operation from another wireless base station device to another wireless base station device by the wireless terminal device is too early, and the second moving operation is too late. The avoidance processing unit detects a movement operation, and the avoidance processing unit has a difference between a reception power of the radio signal from the other radio base station apparatus and a reception power of the radio signal from the own radio base station apparatus less than a predetermined threshold Or when the reception quality of the other radio base station apparatus based on the reception power of the radio signal from the other radio base station apparatus and the reception power of the radio signal from the own radio base station apparatus is poor. The terminal device permits the movement operation from the other radio base station device to the own radio base station device, and when the first movement operation is detected, the threshold value is decreased and the second operation is performed. When movement is detected It is to increase the above-mentioned threshold.

  In this way, by adaptively adjusting the threshold value for performing the determination based on the reception power or the reception quality in the wireless terminal device, the wireless terminal device can change its own wireless base station device from other wireless base station devices. It is possible to more appropriately adjust the conditions for permitting the movement operation to.

  (8) Preferably, the avoidance processing unit adjusts a radio signal transmission operation from its own radio base station apparatus to the radio terminal apparatus.

  With such a configuration, by adjusting the reception state of the radio signal transmitted from the own radio base station apparatus in the radio terminal apparatus, it is possible to suppress the occurrence of an inappropriate movement operation.

  (9) More preferably, the avoidance processing unit adjusts the transmission power of the radio signal from the own radio base station apparatus to the radio terminal apparatus.

  In this way, by adjusting the transmission power of the radio signal transmitted from its own radio base station apparatus, the magnitude relationship of the received power in the radio terminal apparatus of the radio signal transmitted by each radio base station apparatus is appropriately controlled. be able to.

  (10) More preferably, the moving operation detection unit includes a first moving operation in which the moving operation by the wireless terminal device from another wireless base station device to its own wireless base station device is too early, and a second moving operation that is too late. The avoidance processing unit detects a movement operation, and increases the transmission power when the first movement operation is detected, and decreases the transmission power when the second movement operation is detected. To do.

  In this way, by appropriately adjusting the transmission power of the radio signal transmitted from the own radio base station apparatus, the reception state in the radio terminal apparatus of the radio signal transmitted by each radio base station apparatus is appropriately set. be able to.

  (11) More preferably, the avoidance processing unit adjusts resources related to transmission of a radio signal from its own radio base station apparatus to the radio terminal apparatus.

  In this way, by adjusting the resources related to the transmission of the radio signal from the own radio base station apparatus to the radio terminal apparatus, the magnitude relationship of the received power in the radio terminal apparatus of the radio signal transmitted by each radio base station apparatus is determined. It can be controlled appropriately.

  (12) More preferably, the moving operation detection unit is configured such that the moving operation from the other radio base station device to the own radio base station device by the wireless terminal device is too early, and the second moving operation is too late. When the first movement operation is detected, the avoidance processing unit detects at least one of predetermined information included in the radio signal, the frequency of the radio signal, and the power of the radio signal when the first movement operation is detected. The period during which one is limited is decreased, and the period is increased when the second moving motion is detected.

  In this way, by adaptively adjusting the period during which at least one of the predetermined information included in the radio signal transmitted from the own radio base station apparatus, the frequency of the radio signal, and the power of the radio signal is limited The reception state of the radio signal transmitted by each radio base station apparatus in the radio terminal apparatus can be set appropriately.

  (13) More preferably, the moving operation detection unit is configured such that the moving operation from the other radio base station device to the own radio base station device by the radio terminal device is too early, and the second moving operation is too late. The moving operation is detected, and the resource is a frequency used for transmission of the radio signal, and the avoidance processing unit decreases the type of the frequency when the first moving operation is detected, and When the second movement operation is detected, the frequency type is increased.

  In this way, by adaptively adjusting the type of frequency used for the radio signal transmitted from its own radio base station apparatus, the reception state of the radio signal transmitted by each radio base station apparatus in the radio terminal apparatus is changed. It can be set appropriately.

  (14) More preferably, the avoidance processing unit adjusts the directivity of an antenna for transmitting a radio signal from its own radio base station device to the radio terminal device, and the mobile motion detection unit is based on the radio terminal device. The avoidance processing unit detects the first movement operation that is too early and the second movement operation that is too late from the other radio base station apparatus to the own radio base station apparatus. When the second moving operation is detected by adjusting the directivity of the antenna to increase the intensity of the transmitted radio wave in the direction toward the other radio base station apparatus. First, by adjusting the directivity of the antenna, the intensity of the transmitted radio wave in the direction toward the other radio base station apparatus is reduced.

  In this way, by adaptively adjusting the directivity of the antenna used for transmitting the radio signal transmitted from its own radio base station apparatus, the radio terminal apparatus receives the radio signal transmitted by each radio base station apparatus. The state can be set appropriately.

  (15) Preferably, the radio base station apparatus further acquires reception quality information indicating a first reception quality that is a reception quality of a radio signal from the radio base station apparatus in the radio terminal apparatus. A reception quality information acquisition unit is provided, and the mobile operation detection unit is acquired first or within a predetermined time after a mobile terminal performs a mobile operation from another radio base station device to its own radio base station device. In addition, when the first reception quality indicated by the reception quality information is poor, a predetermined moving operation in which the timing of the moving operation from the other wireless base station device to the own wireless base station device by the wireless terminal device is too early Is determined to have occurred.

  With such a configuration, even when the own radio base station apparatus is the destination radio base station apparatus and information regarding the predetermined movement operation is not transmitted from the radio terminal apparatus to the own radio base station apparatus, the radio terminal apparatus Based on the received quality, it is possible to appropriately determine the occurrence of the predetermined movement operation.

  (16) More preferably, the reception quality information acquisition unit further acquires reception quality information indicating a second reception quality that is a reception quality of a radio signal from the other radio base station apparatus in the radio terminal apparatus. The mobile operation detector detects the reception quality information obtained first or within a predetermined time after the mobile terminal performs a mobile operation from another radio base station device to its own radio base station device. When the first reception quality shown is poor and the second reception quality is good, the timing of the moving operation by the wireless terminal device from the other wireless base station device to its own wireless base station device is early. It is determined that too much predetermined movement has occurred.

  With such a configuration, it is possible to appropriately determine whether the cause of the predetermined movement operation is an early movement operation by the movement-source radio base station apparatus or the communication environment in the radio terminal apparatus. Can do. Accordingly, it is possible to more appropriately determine the occurrence of the predetermined movement operation based on the reception quality of the wireless terminal device.

  (17) Preferably, the radio base station apparatus further schedules arrival of predetermined information from the radio terminal apparatus, and monitors other radio stations by the monitoring unit for monitoring the arrival of the predetermined information. After the movement operation from the base station apparatus to the own radio base station apparatus is performed until the predetermined information from the radio terminal apparatus does not arrive at the own radio base station apparatus against the schedule of the monitoring unit A time measuring unit for measuring time, and when the time measured by the time measuring unit is less than a predetermined value, the moving operation detecting unit is configured to perform the other radio base station by the radio terminal device. It is determined that a predetermined moving operation has occurred that is too early for the moving operation from the device to its own radio base station device.

  With such a configuration, even when the own radio base station apparatus is the destination radio base station apparatus and information regarding the predetermined movement operation is not transmitted from the radio terminal apparatus to the own radio base station apparatus, the radio terminal apparatus It is possible to appropriately determine the occurrence of the predetermined movement operation based on the time until the predetermined information from the mobile station does not arrive at its own radio base station device against the schedule of the monitoring unit.

  (18) In order to solve the above-described problem, a communication control method according to an aspect of the present invention provides a wireless terminal device in a communication system in which a wireless terminal device can communicate with a plurality of wireless base station devices by performing a moving operation. Is a communication control method in a radio base station apparatus for transmitting and receiving radio signals to and from a radio terminal station, and a predetermined movement operation among movement operations from another radio base station apparatus to its own radio base station apparatus by a radio terminal apparatus And detecting the occurrence of the predetermined movement operation and adjusting the operation of the own radio base station apparatus so that the occurrence of the predetermined movement operation is suppressed.

  As described above, since it is possible to execute inappropriate movement detection and avoidance processing in the destination radio base station apparatus, other radio base station apparatuses are allowed to adjust parameters used for timing control of the movement operation. Even when it is impossible, it is possible to suppress the occurrence of the predetermined movement operation and construct a good communication system. Therefore, communication can be stabilized by appropriately controlling the movement operation of the wireless terminal device.

  (19) In order to solve the above-described problem, a communication control program according to an aspect of the present invention provides a wireless terminal device in a communication system in which a wireless terminal device can communicate with a plurality of wireless base station devices by performing a moving operation. Is a communication control program used in a radio base station apparatus for transmitting and receiving radio signals to and from the computer, and the computer performs a movement operation from another radio base station apparatus to its own radio base station apparatus by the radio terminal apparatus. Among them, a step of detecting the occurrence of a predetermined movement operation, and a step of adjusting the operation of its own radio base station apparatus so that the occurrence of the predetermined movement operation is suppressed when the predetermined movement operation is detected. Is a program for executing

  As described above, since it is possible to execute inappropriate movement detection and avoidance processing in the destination radio base station apparatus, other radio base station apparatuses are allowed to adjust parameters used for timing control of the movement operation. Even when it is impossible, it is possible to suppress the occurrence of the predetermined movement operation and construct a good communication system. Therefore, communication can be stabilized by appropriately controlling the movement operation of the wireless terminal device.

  According to the present invention, communication can be stabilized by appropriately controlling the movement operation of the wireless terminal device.

It is a figure which shows the structure of the radio | wireless communications system which concerns on 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 embodiment of this invention. It is a figure which shows an example of the condition where the inappropriate hand-over operation (Too Late HO) occurred in the radio | wireless communications system which concerns on embodiment of this invention. It is a figure which shows an example of the sequence of the improper handover operation (Too Late HO) and its detection process in the radio | wireless communications system which concerns on embodiment of this invention. It is a figure which shows an example of the condition where the inappropriate hand-over operation (Too Early HO case 1) occurred in the radio | wireless communications system which concerns on embodiment of this invention. It is a figure which shows an example of the sequence of the inappropriate handover operation | movement (Too Early HO case 1) and its detection process in the radio | wireless communications system which concerns on embodiment of this invention. It is a figure which shows an example of the condition where the inappropriate hand-over operation (Too Early HO case 2) occurred in the radio | wireless communications system which concerns on embodiment of this invention. It is a figure which shows an example of the sequence of the improper handover operation (Too Early HO case 2) and its detection process in the radio | wireless communications system which concerns on embodiment of this invention. It is a figure which shows an example of the condition where the inappropriate hand-over operation (HO to Wron Cell) occurred in the radio | wireless communications system which concerns on embodiment of this invention. It is a figure which shows an example of the sequence of the improper handover operation (HO to Wron Cell) and its detection process in the radio | wireless communications system which concerns on embodiment of this invention. It is a figure which shows the structure of the radio base station apparatus which concerns on 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 embodiment of this invention. 5 is a flowchart defining an operation procedure for the radio base station apparatus according to the embodiment of the present invention to identify the cause of an inappropriate handover operation. It is a figure which shows an example of the sequence of an improper handover operation (Too Early HO) and its detection process in the target base station which concerns on embodiment of this invention. It is a figure which shows an example of the sequence of an improper handover operation (Too Early HO) and its detection process in the target base station which concerns on embodiment of this invention. It is a figure which shows an example of the sequence of the operation | movement procedure at the time of the radio base station apparatus which concerns on embodiment of this invention performing timing control of a handover operation. It is a figure which shows the reception power difference of the radio signal measured when the radio | wireless terminal apparatus which concerns on embodiment of this invention moves between radio base station apparatuses, and the change of reception quality. It is a figure which shows an example of the sequence of the operation | movement procedure at the time of the radio base station apparatus which concerns on embodiment of this invention performing timing control of a handover operation. It is a figure which shows an example of the condition which prevents the inappropriate hand-over operation | movement by the target base station which concerns on embodiment of this invention adjusting transmission power. It is a figure which shows an example of the flame | frame contained in the radio signal which the target base station which concerns on embodiment of this invention transmits.

  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 a 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 22.22 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.

  Further, in the femtocell access mode, 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.

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

  The macro base station and the pico base station are wireless base station devices that are under the management of the operator and can communicate with the wireless 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.

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

  Further, the femto base station operates in one of open / hybrid / closed access modes. 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.

[Configuration and basic operation]
FIG. 1 is a diagram showing a configuration of a radio communication system according to an embodiment of the present invention.

  Referring to FIG. 1, the radio communication system is a mobile communication system according to 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 radio base station apparatus 101A can communicate with the radio terminal apparatus 202 by forming a cell CA and transmitting and receiving radio signals to and from the radio terminal apparatus 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 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 showing an exemplary sequence of a handover operation in the radio communication system according to the 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 received power of the wireless signal transmitted from the other wireless base station device that has been set. 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, 101 A of radio base station apparatuses acquire the measurement information which shows the measurement result for every cell ID based on the measurement result notification received from the radio | wireless terminal apparatus 202, and preserve | save it in the memory | storage part which is not shown in figure (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 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 S8).

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

  Next, the higher-level apparatus receives a handover response from the radio base station apparatus 101B, and transmits a handover instruction to the radio base station apparatus 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 radio base station apparatus 101A transmits a status notification indicating its own communication status and the like to the higher level apparatus (step S12).

  Next, the higher-level device receives the state notification from the wireless base station device 101A, and transmits a state notification indicating the communication contents and the like with the wireless terminal device 202 to the wireless base station device 101B (step S13).

  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 (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 higher-level apparatus receives a 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 S16).

  Next, the wireless base station device 101A receives a 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 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 radio base station apparatus that can be a handover destination is also referred to as a peripheral base station. The radio base station apparatus that has determined that the serving base station is suitable for the handover destination and has transmitted the handover request is also referred to as a target 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 embodiment of the present invention.

  With reference to FIG. 3, the wireless communication system further includes a wireless base station device 101 </ b> Z as compared with the wireless communication system shown in FIG. 1. Radio base station apparatus 101Z is, for example, a femto base station, a pico base station, or a macro base station.

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

  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 embodiment of the present invention.

  “Too Late HO” refers to the following cases, for example. That is, before the handover starts or during the handover process, 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 wireless terminal 202 re-establishes a wireless link to the wireless base station 101B after the RLF has occurred for the wireless base station 101A, the wireless terminal 202 sends an RLF report to the wireless base station 101B. Send. Thereby, the radio base station apparatus 101B detects “Too Late HO”.

  Here, as shown in FIG. 3, it is assumed that the wireless terminal device 202 is located in the cell CZ and is in communication with the wireless base station device 101Z and moves into the area of the cell CA (step S50). To do.

  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 the base station apparatus 101Z (step S52).

  Next, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101Z determines whether or not the wireless terminal device 202 should be handed over. If it is determined that the radio terminal apparatus 202 should be handed over, the radio base station apparatus 101Z refers to the neighboring cell information and determines, for example, the radio base station apparatus 101A as a handover destination (step S54).

  Next, the radio base station apparatus 101Z transmits a handover request indicating the radio base station apparatus 101A to the higher-level apparatus (Step S56).

  Next, the higher-level apparatus receives the handover request from the radio base station apparatus 101Z and transmits the handover request to the radio base station apparatus 101A (step S58).

  Next, the wireless base station device 101A receives the handover request from the higher-level device, and transmits a handover response to the handover request to the higher-level device (step S60).

  Next, the higher-level device receives a handover response from the radio base station device 101A, and transmits a handover instruction to the radio base station device 101Z (step S62).

  Next, the radio base station apparatus 101Z receives the handover instruction from the higher-level apparatus and transmits an RRC connection reconfiguration instruction (RRC Connection Reconfiguration) to the radio terminal apparatus 202 (step S64).

  Next, when receiving the RRC connection reconfiguration instruction from the radio base station apparatus 101Z, the radio terminal apparatus 202 acquires the HO time that is the time when the RRC connection reconfiguration instruction is received, and stores it in a storage unit (not shown) (step). S66). At this time, the radio terminal apparatus 202 transmits the ECGI (E-UTRAN Cell Global Identifier) of the radio base station apparatus 101Z that has transmitted the RRC connection reconfiguration instruction and the ECGI of the radio base station apparatus 101A that is the handover destination, which will be described later. The requested cell ID and RLF serving cell ID are stored in a storage unit (not shown).

  Also, the radio base station apparatus 101Z transmits a status notification indicating its own communication status and the like to the higher level apparatus (step S68).

  Next, the higher-level device receives the status notification from the radio base station device 101Z, and transmits a status notification indicating the communication contents and the like with the radio terminal device 202 to the radio base station device 101A (step S70).

  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 to the wireless base station device 101A (step S72).

  Next, the wireless base station device 101A receives the RRC connection reconfiguration completion notification from the wireless terminal device 202 and transmits a handover completion notification to the higher-level device (step S74).

  Next, the higher-level apparatus receives a handover completion notification from the radio base station apparatus 101A, and transmits a terminal information release instruction to the radio base station apparatus 101Z (step S76).

  Next, the radio base station apparatus 101Z receives a terminal information release instruction from the upper apparatus, releases information related to the radio terminal apparatus 202, and transmits a terminal information release completion notification to the upper apparatus (step S78).

  Thus, the handover of the wireless terminal device 202 from the wireless base station device 101Z to the wireless base station device 101A is completed (step S80).

  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 received power of the wireless signal transmitted from the other wireless base station device (step S82). .

  Next, the wireless terminal device 202 receives the measurement start request from the wireless base station device 101A, starts the power measurement process, and measures the received power of the wireless signal transmitted from the other wireless base station device, It moves from the area of the cell CZ to the area of the cell CA (step S84).

  The wireless terminal device 202 periodically measures received power, for example, when the communication state with the wireless base station device 101A deteriorates, and the communication state with other wireless base station devices other than the wireless base station device 101A When the measurement becomes better, a measurement result notification is transmitted to the radio base station apparatus 101A (step S86).

  Next, the wireless terminal device 202 moves to the overlapping area between the cell CA and the cell CB while measuring the received power of the wireless signal transmitted from another wireless base station device within the area of the cell CA (step S88). .

  The wireless terminal device 202 periodically measures received power, for example, when the communication state with the wireless base station device 101A deteriorates, and the communication state with other wireless base station devices other than the wireless base station device 101A When the measurement is improved, a measurement result notification is transmitted to the radio base station apparatus 101A (step S90).

  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 S92).

  Next, the radio base station device 101A transmits a handover request indicating the radio base station device 101B to the higher-level device (step S94).

  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 S96).

  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 S98).

  Next, the higher-level apparatus receives a handover response from the radio base station apparatus 101B, and transmits a handover instruction to the radio base station apparatus 101A (step S100).

  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 via the host apparatus, the radio terminal apparatus 202 Then, the cell moves out of the cell CA and into the cell CB (step S102).

  Due to the movement of the wireless terminal device 202, the RRC connection reconfiguration instruction (step S104) for instructing the handover transmitted from the wireless base station device 101A does not reach the wireless terminal device 202, and RLF occurs (step S104). S106).

  Next, the wireless terminal device 202 stores the following information, for example, in order to identify the cause of RLF occurrence. That is, when detecting the RLF, the wireless terminal device 202 acquires the RLF time that is the time when the RLF has occurred. Next, the wireless terminal device 202 calculates the difference between the acquired RLF time and the HO time described above, thereby obtaining the connection time connected to the wireless base station device 101A serving as the serving base station, and stores the memory (not shown). (Step S108).

  Further, when detecting the RLF, the wireless terminal device 202 measures the received power of the wireless signal from the surrounding wireless base station device when the RLF is generated, and stores it in a storage unit (not shown) (step S110).

  Next, the wireless terminal device 202 searches for a wireless base station device to be reconnected based on a measurement result such as reception power of a wireless signal from a surrounding wireless base station device, and re-connects to the searched wireless base station device 101B. In order to connect, an RRC connection reestablishment request is transmitted to the radio base station apparatus 101B (step S112). At this time, the radio terminal apparatus 202 stores the ECGI of the radio base station apparatus 101B, which is the transmission destination of the RRC connection re-establishment request, in a storage unit (not shown) as a re-establishment destination cell ID described later.

  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 S114). 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 reestablishment completion notification (RRC Connection Reestablishment Complete) to the wireless base station device 101B (step S116).

  This RRC connection re-establishment completion notification includes, for example, a parameter “rlf-InfoAvailable”. 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 S118).

  Next, the wireless terminal device 202 receives a terminal information request from the wireless base station device 101B, and transmits a terminal information response (UE Information Response) including an RLF report to the wireless base station device 101B (step S120).

  The RLF report includes at least reception power and reception quality of radio signals transmitted from the serving base station and the neighboring base stations when the RLF occurs in order to identify the cause of the inappropriate handover operation. The reception quality is, for example, SIR (Signal to Interference Ratio) or SINR (Signal to Interference and Noise power Ratio).

  In addition, the RLF report includes the connection time for connection to the serving base station described above, the serving cell ID (failedPCellID) that is the ECGI of the serving base station at the time of RLF occurrence, and the first RRC connection re-establishment after the occurrence of RLF. Including the reestablishment cell ID (reestablishmentCellID) that is the ECGI of the radio base station apparatus and the HO request cell ID (previousPCellID) that is the ECGI of the radio base station apparatus that has transmitted the last RRC connection reconfiguration instruction before the occurrence of RLF Good. In addition, instead of ECGI indicating the RLF serving cell ID, the RLF report is transmitted by PCI (Physical Cell ID) used to distinguish the radio base station device in the physical layer in network communication and the radio base station device. The frequency of the radio signal may be used. Here, the RLF serving cell ID is the ID of the radio base station device 101A, the re-establishment destination cell ID is the ID of the radio base station device 101B, and the HO request cell ID is the ID of the radio base station device 101Z.

  In addition, when performing the process of reconnecting to the radio terminal apparatus 202 (step S112 to step S120), the radio base station apparatus 101B performs transmission / reception of information used for reconnection with an upper apparatus as necessary.

  Next, the radio base station apparatus 101B moves from the cell CA to the cell CB by following an operation procedure for identifying the cause of an inappropriate handover operation described later based on the RLF report received from the radio terminal apparatus 202. It is determined that “Too Late HO” has occurred (step S122).

  Next, the radio base station apparatus 101B executes an inappropriate handover operation avoidance process so as to suppress the occurrence of “Too Late HO” from the cell CA to the cell CB formed by itself (step S124). .

  FIG. 5 is a diagram illustrating an example of a situation in which an inappropriate handover operation (Too Early HO case 1) occurs in the wireless communication system according to the embodiment of the present invention.

  Referring to FIG. 5, cell CB formed by radio base station apparatus 101B includes cell CB1 including the installation area of radio base station apparatus 101B, and the installation area of radio base station apparatus 101B formed in cell CA. The cell CB2 is not included.

  FIG. 6 is a diagram showing an example of an inappropriate handover operation (Too Early HO case 1) and its detection processing sequence in the wireless communication system according to the embodiment of the present invention.

  “Too Early HO case 1” refers to the following case, for example. That is, the radio terminal device 202 receives an RRC connection reconfiguration instruction from the handover source radio base station device and attempts to connect to the handover destination radio base station device, but RLF occurs in a short time before the connection succeeds. In addition, this is a case where connection re-establishment of the wireless terminal device 202 occurs with respect to the handover destination wireless base station device.

  The detection method of “Too Early HO case 1” is, for example, as follows. That is, the handover destination radio base station apparatus 101B receives the RLF report from the radio terminal apparatus 202, and analyzes the received RLF report to detect “Too Early HO”.

  Here, as shown in FIG. 5, it is assumed that 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 S150). .

  5 and 6, first, radio terminal apparatus 202 measures the reception power of a radio signal transmitted from the radio base station apparatus, and sends a measurement result notification indicating the measurement result of the measured reception power to the serving base. It transmits to the radio base station apparatus 101A which is a station (step S152).

  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 S154).

  Next, the radio base station device 101A transmits a handover request indicating the radio base station device 101B to the higher-level device (step S156).

  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 S158).

  Next, the radio base station apparatus 101B receives the handover request from the upper apparatus and transmits a handover response to the handover request to the upper apparatus (step S160).

  Next, the upper apparatus receives a handover response from the radio base station apparatus 101B, and transmits a handover instruction to the radio base station apparatus 101A (step S162).

  Next, the wireless base station device 101A receives a handover instruction from the higher-level device and transmits an RRC connection reconfiguration instruction to the wireless terminal device 202 (step S164).

  Next, when the radio terminal apparatus 202 receives the RRC connection reconfiguration instruction from the radio base station apparatus 101A, the radio terminal apparatus 202 acquires the HO time that is the time when the RRC connection reconfiguration instruction is received, and saves it in a storage unit (not shown) (step) S166). At this time, the radio terminal apparatus 202 uses the ECGI of the radio base station apparatus 101A that has transmitted the RRC connection reconfiguration instruction and the ECGI of the radio base station apparatus 101B that is the handover destination as the HO request cell ID and the RLF serving cell ID, respectively. Save in a storage unit (not shown).

  Here, the wireless terminal device 202 moves within the cell CA and out of the cell CB2 (step S168).

  Then, since the wireless terminal device 202 cannot communicate with the wireless base station device 101B, RLF occurs (step S170).

  Next, the wireless terminal device 202 stores the following information, for example, in order to identify the cause of RLF occurrence. That is, when detecting the RLF, the wireless terminal device 202 acquires the RLF time that is the time when the RLF has occurred. Next, the wireless terminal device 202 calculates the difference between the acquired RLF time and the HO time described above, thereby obtaining the connection time connected to the wireless base station device 101A serving as the serving base station, and stores the memory (not shown). (Step S172).

  Here, the wireless terminal device 202 moves outside the cell CA and within the cell CB1 (step S174).

  In addition, the wireless terminal device 202 measures the reception power, reception quality, and the like of the wireless signal transmitted from the surrounding wireless base station device when the RLF occurs, and stores it in a storage unit (not shown) (step S176).

  Next, the wireless terminal device 202 searches for a wireless base station device to be reconnected based on a measurement result such as reception power of a wireless signal from a surrounding wireless base station device, and re-connects to the searched wireless base station device 101B. In order to establish a connection, an RRC connection re-establishment request is transmitted to the radio base station apparatus 101B (step S178). At this time, the radio terminal apparatus 202 stores the ECGI of the radio base station apparatus 101B, which is the transmission destination of the RRC connection re-establishment request, in a storage unit (not shown) as the re-establishment destination cell ID.

  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 S180). 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 to the wireless base station device 101B (step S182).

  This RRC connection re-establishment completion notification includes, for example, a parameter “rlf-InfoAvailable”. 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 to the radio terminal apparatus 202 in order to acquire detailed information on the RLF (step S184).

  Next, the wireless terminal device 202 receives the terminal information request from the wireless base station device 101B, and transmits a terminal information response including the RLF report to the wireless base station device 101B (step S186). In this RLF report, the RLF serving cell ID is the ID of the radio base station device 101B, the re-establishment destination cell ID is the ID of the radio base station device 101B, and the HO request cell ID is the ID of the radio base station device 101A. .

  In addition, when performing the process of reconnecting to the radio terminal apparatus 202 (step S178 to step S186), the radio base station apparatus 101B performs transmission / reception of information used for reconnection with an upper apparatus as necessary.

  Next, based on the RLF report received from the radio terminal apparatus 202, the radio base station apparatus 101B forms itself from the cell CA by following an operation procedure for identifying the cause of an inappropriate handover operation described later. It is determined that “Too Early HO” has occurred in the cell CB (step S188).

  Next, the radio base station apparatus 101B executes an inappropriate handover operation avoidance process so as to suppress the occurrence of “Too Early HO” from the cell CA to the cell CB (step S190).

  FIG. 7 is a diagram illustrating an example of a situation where an inappropriate handover operation (Too Early HO case 2) occurs in the wireless communication system according to the embodiment of the present invention.

  Referring to FIG. 7, cell CB formed by radio base station apparatus 101B includes cell CB1 including the installation area of radio base station apparatus 101B, and the installation area of radio base station apparatus 101B formed in cell CA. The cell CB2 is not included.

  FIG. 8 is a diagram showing an example of an inappropriate handover operation (Too Early HO case 2) and its detection processing sequence in the wireless communication system according to the embodiment of the present invention.

  “Too Early HO case 2” refers to the following case, 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 case 2” is, for example, as follows. That is, the handover source radio base station apparatus 101A receives the RLF report from the radio terminal apparatus 202 and analyzes the received RLF report, thereby detecting “Too Early HO case 2”. In addition to receiving the RLF report from the radio base station apparatus 101A, the handover destination radio base station apparatus 101B detects “Too Early HO case 2” by an operation procedure described later.

  Here, as shown in FIG. 7, 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 S250). .

  7 and 8, first, radio terminal apparatus 202 measures the reception power of a radio signal transmitted from the radio base station apparatus, and sends a measurement result notification indicating the measurement result of the measured reception power to the serving base. It transmits to the radio base station apparatus 101A, which is a station (step S252).

  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 S254).

  Next, the radio base station device 101A transmits a handover request indicating the radio base station device 101B to the higher-level device (step S256).

  Next, the higher-level 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 S258).

  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 S260).

  Next, the higher-level apparatus receives a handover response from the radio base station apparatus 101B, and transmits a handover instruction to the radio base station apparatus 101A (step S262).

  Next, the radio base station apparatus 101A receives a handover instruction from the higher-level apparatus and transmits an RRC connection reconfiguration instruction to the radio terminal apparatus 202 (step S264).

  Next, when the radio terminal apparatus 202 receives the RRC connection reconfiguration instruction from the radio base station apparatus 101A, the radio terminal apparatus 202 acquires the HO time that is the time when the RRC connection reconfiguration instruction is received, and saves it in a storage unit (not shown) (step) S266). At this time, the radio terminal apparatus 202 uses the ECGI of the radio base station apparatus 101A that has transmitted the RRC connection reconfiguration instruction and the ECGI of the radio base station apparatus 101B that is the handover destination as the HO request cell ID and the RLF serving cell ID, respectively. Save in a storage unit (not shown).

  Also, the radio base station device 101A transmits a status notification indicating its own communication status to the higher-level device (step S268).

  Next, the higher-level device receives the status notification from the radio base station device 101A, and transmits a status notification indicating communication contents and the like with the radio terminal device 202 to the radio base station device 101B (step S270).

  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 S272).

  Next, the radio base station apparatus 101B transmits to the radio terminal apparatus 202 a measurement start request for causing the radio terminal apparatus 202 to measure the reception power of radio signals transmitted from other radio base station apparatuses (step S274). .

  Next, the wireless terminal device 202 receives a measurement start request from the wireless base station device 101B, starts power measurement processing, and receives received power of a wireless signal transmitted from another wireless base station device within the cell CB2. Is measured (step S278).

  Next, the wireless terminal device 202 transmits a measurement result notification indicating measurement of received power to the wireless base station device 101B (step S280).

  Also, 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 S276).

  Next, the higher-level apparatus receives a 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 S282).

  Next, the wireless base station device 101A receives a terminal information release instruction from the higher-level device, releases information (UE Context) regarding the wireless terminal device 202, and transmits a terminal information release completion notification to the higher-level device (step S284). ).

  Thus, 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 S286).

  Here, the wireless terminal device 202 moves out of the cell CB2 and into the cell CA (step S288).

  Then, since the wireless terminal device 202 cannot communicate with the wireless base station device 101B, RLF occurs (step S290).

  Next, the wireless terminal device 202 stores the following information, for example, in order to identify the cause of RLF occurrence. That is, when detecting the RLF, the wireless terminal device 202 acquires the RLF time that is the time when the RLF has occurred. Next, the wireless terminal device 202 calculates the difference between the acquired RLF time and the HO time described above, thereby obtaining the connection time connected to the wireless base station device 101A serving as the serving base station, and stores the memory (not shown). (Step S292).

  In addition, the wireless terminal device 202 measures the reception power, reception quality, and the like of the wireless signal transmitted from the surrounding wireless base station device when the RLF occurs, and stores it in a storage unit (not shown) (step S294).

  Next, the wireless terminal device 202 searches for a wireless base station device to be reconnected based on the measurement result such as the received power of the wireless signal from the surrounding wireless base station device, and reconnects to the searched wireless base station device 101A. In order to establish a connection, an RRC connection re-establishment request is transmitted to the radio base station apparatus 101A (step S296). At this time, the wireless terminal device 202 stores the ECGI of the wireless base station device 101A, which is the transmission destination of the RRC connection re-establishment request, as a re-establishment destination cell ID in a storage unit (not shown).

  Next, since the wireless base station device 101A has released and does not hold the information (UE Context) regarding the wireless terminal device 202, the wireless base station device 101A can accept the RRC connection re-establishment request from the wireless terminal device 202. If it cannot be performed (step S298), an RRC connection re-establishment rejection is transmitted to the wireless terminal device 202 (step S300).

  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 S302).

  That is, first, the wireless terminal device 202 transmits an RRC connection request to the wireless base station device 101A (step S304).

  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 S306).

  Next, the wireless terminal device 202 receives RRC connection information from the wireless base station device 101A, and transmits an RRC connection completion notification (RRC Connection Setup Complete) (step S308).

  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 S310).

  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 S312).

  Next, the radio base station apparatus 101A transmits an RRC connection reconfiguration instruction to the radio terminal apparatus 202 (step S314).

  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 to the wireless base station device 101A (step S316).

  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 to the wireless terminal device 202 in order to acquire detailed information of the RLF (step S318).

  Next, the wireless terminal device 202 receives the terminal information request from the wireless base station device 101A, and transmits a terminal information response including the RLF report to the wireless base station device 101A (step S320). In this RLF report, the RLF serving cell ID is the ID of the radio base station device 101B, the re-establishment destination cell ID is the ID of the radio base station device 101A, and the HO request cell ID is the ID of the radio base station device 101A. .

  In addition, when performing the process of reconnecting to the radio terminal apparatus 202 (step S304 to step S320), the radio base station apparatus 101B performs transmission / reception of information used for reconnection with an upper apparatus as necessary.

  Next, based on the RLF report received from the radio terminal apparatus 202, the radio base station apparatus 101A follows an operation procedure for identifying the cause of an inappropriate handover operation described later, from the cell CA formed by itself. It is determined that “Too Early HO” has occurred in the cell CB (step S322).

  Next, the radio base station apparatus 101A performs a handover operation optimizing process so that the occurrence of “Too Early HO” from the cell CA to the cell CB is suppressed (step S324).

  FIG. 9 is a diagram illustrating an example of a situation in which an inappropriate handover operation (HO to Wron Cell) occurs in the wireless communication system according to the embodiment of the present invention.

  Referring to FIG. 9, the wireless communication system further includes a wireless base station device 101 </ b> C compared to 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. 10 is a diagram illustrating an example of an improper handover operation (HO to Wron Cell) and its detection processing sequence in the wireless communication system according to the embodiment of the present invention.

  “HO to Wong Cell” refers to the following case, 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.

  A detection method of “HO to Wong Cell” is, for example, as follows. That is, the reconnection-destination radio base station apparatus 101C receives the RLF report from the radio terminal apparatus 202 and analyzes the received RLF report, thereby confirming that the radio base station apparatus 101A is “HO to Wong Cell”. Detect.

  Here, as shown in FIG. 9, 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 ( Step S350) is assumed. The virtual cell CBV is a virtual cell that is expanded from the cell CB according to an offset 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 is a parameter held by the radio base station apparatus 101A.

  Referring to FIG. 9 and FIG. 10, 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 S352).

  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. If 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 S354).

  Next, the radio base station device 101A transmits a handover request indicating the radio base station device 101B to the higher-level device (step S356).

  Next, the higher-level 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 S358).

  Next, the radio base station apparatus 101B receives the handover request from the upper apparatus and transmits a handover response to the handover request to the upper apparatus (step S360).

  Next, the higher-level apparatus receives a handover response from the radio base station apparatus 101B, and transmits a handover instruction to the radio base station apparatus 101A (step S362).

  Next, the wireless base station device 101A receives a handover instruction from the higher-level device and transmits an RRC connection reconfiguration instruction to the wireless terminal device 202 (step S364).

  Next, when the radio terminal apparatus 202 receives the RRC connection reconfiguration instruction from the radio base station apparatus 101A, the radio terminal apparatus 202 acquires the HO time that is the time when the RRC connection reconfiguration instruction is received, and stores the HO time in a storage unit (not shown) (step). S366). At this time, the radio terminal apparatus 202 uses the ECGI of the radio base station apparatus 101A that has transmitted the RRC connection reconfiguration instruction and the ECGI of the radio base station apparatus 101B that is the handover destination as the HO request cell ID and the RLF serving cell ID, respectively. Save in a storage unit (not shown).

  Also, the radio base station device 101A transmits a status notification indicating its own communication status and the like to the higher-level device (step S368).

  Next, the higher-level device receives the state notification from the wireless base station device 101A, and transmits a state notification indicating the communication contents and the like with the wireless terminal device 202 to the wireless base station device 101B (step S370).

  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 S372).

  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 S374).

  Next, the higher-level apparatus receives a 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 S376).

  Next, the wireless base station device 101A receives a 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 S378).

  Thus, 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 S380).

  Here, before the wireless terminal device 202 receives the measurement result start request from the wireless base station device 101B, the wireless terminal device 202 moves out of the cell CB and into the virtual cell CBV and cell CC (step S382).

  Then, the radio terminal apparatus 202 has a large interference of radio signals transmitted from the radio base station apparatus 101C and cannot communicate with the radio base station apparatus 101B, so that RLF occurs (step S384).

  Next, the wireless terminal device 202 stores the following information, for example, in order to identify the cause of RLF occurrence. That is, when detecting the RLF, the wireless terminal device 202 acquires the RLF time that is the time when the RLF has occurred. Next, the wireless terminal device 202 calculates the difference between the acquired RLF time and the HO time described above, thereby obtaining the connection time connected to the wireless base station device 101B serving as the serving base station, and stores the memory (not shown). (Step S386).

  In addition, the wireless terminal device 202 measures the reception power and reception quality of the wireless signal transmitted from the surrounding wireless base station device when the RLF is generated, and stores it in a storage unit (not shown) (step S388).

  Next, the wireless terminal device 202 searches for a wireless base station device to be reconnected based on a measurement result such as reception power of a wireless signal from a surrounding wireless base station device, and re-connects to the searched wireless base station device 101C. In order to establish a connection, an RRC connection re-establishment request is transmitted to the radio base station apparatus 101C (step S390). At this time, the radio terminal apparatus 202 stores the ECGI of the radio base station apparatus 101C, which is the transmission destination of the RRC connection re-establishment request, as a re-establishment destination cell ID in a storage unit (not shown).

  Next, since the wireless base station device 101C does not hold the 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 S392). ), RRC connection re-establishment rejection is transmitted to the wireless terminal device 202 (step S394).

  Next, the radio terminal apparatus 202 receives the 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 S396).

  That is, first, the wireless terminal device 202 transmits an RRC connection request to the wireless base station device 101C (step S398).

  Next, the wireless base station device 101C receives the RRC connection request from the wireless terminal device 202, and transmits RRC connection information to the wireless terminal device 202 (step S400).

  Next, the wireless terminal device 202 receives RRC connection information from the wireless base station device 101C and transmits an RRC connection completion notification (step S402).

  Next, the wireless base station device 101C receives the RRC connection completion notification from the wireless terminal device 202, and transmits security information to the wireless terminal device 202 (step S404).

  Next, the wireless terminal device 202 receives the security information from the wireless base station device 101C, and transmits a security completion notification to the wireless base station device 101C (step S406).

  Next, the radio base station apparatus 101C transmits an RRC connection reconfiguration instruction to the radio terminal apparatus 202 (step S408).

  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 to the wireless base station device 101C (step S410).

  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 to the wireless terminal device 202 in order to acquire detailed information of the RLF (step S412).

  Next, the wireless terminal device 202 receives the terminal information request from the wireless base station device 101C, and transmits a terminal information response including the RLF report to the wireless base station device 101C (step S414). In this RLF report, the RLF serving cell ID is the ID of the radio base station device 101B, the re-establishment destination cell ID is the ID of the radio base station device 101C, and the HO request cell ID is the ID of the radio base station device 101A. .

  In addition, when performing the process of reconnecting to the wireless terminal apparatus 202 (steps S398 to S414), the radio base station apparatus 101C performs transmission / reception of information used for reconnection with a higher-level apparatus as necessary.

  Next, the radio base station apparatus 101C moves from the cell CA to the cell CB by following an operation procedure for identifying the cause of an inappropriate handover operation described later based on the RLF report received from the radio terminal apparatus 202. It is determined that “HO to Wong Cell” has occurred (step S416).

  Next, the radio base station device 101C transmits a handover report to the higher-level device (step S418). This handover report includes, for example, a parameter “Handover Report Type”. The radio base station apparatus 101C notifies the radio base station apparatus 101A of “HO to Wong Cell” via the host apparatus by setting this parameter to a predetermined value.

  Next, the higher-level apparatus receives the handover report from the radio base station apparatus 101C and transmits the handover report to the radio base station apparatus 101A (step S420).

  Next, the radio base station apparatus 101A receives the handover report from the radio base station apparatus 101C via the host apparatus, and confirms that the “HO to Wron Cell” from the cell CA to the cell CB that it forms has occurred. Recognize (step S422) and execute the optimization process of the handover operation so that the occurrence of “HO to Wong Cell” is suppressed (step S424).

[Radio base station equipment]
FIG. 11 is a diagram showing a configuration of a radio base station apparatus according to the embodiment of the present invention.
Referring to FIG. 11, radio base station apparatus 101 includes antenna 91, circulator 92, radio reception unit 93, radio transmission unit 94, signal processing unit 95, and 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 antenna 91 has directivity at least for transmission, and can change the direction in which the beam intensity of the radio signal becomes strong.

  Radio receiving section 93 converts the radio signal received from 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 received signal processing section 96.

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

  The transmission signal processing unit 97 performs IFFT (Inverse Fast Fourier Transform) in the OFDMA (Orthogonal Frequency Division Multiple Access) method on communication data obtained by converting communication data received from the core network side into a predetermined frame format or communication data generated by itself. ) And the like, and the digital signal after this signal processing is output to the wireless transmission unit 94.

  The radio transmission unit 94 converts the digital signal received from the transmission signal processing unit 97 into an analog signal, frequency-converts the converted analog signal into a radio signal, performs amplification by an amplifier, and outputs the amplified 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.

  FIG. 12 is a diagram showing a configuration of a control unit in the radio base station apparatus according to the embodiment of the present invention.

  Referring to FIG. 12, the control unit 98 includes a monitoring unit 11, a time measurement unit 12, a reception quality information acquisition unit 13, a movement operation detection unit 14, a reception power information acquisition unit 15, and an avoidance processing unit 16. Including.

  The monitoring unit 11 schedules the arrival of a measurement result notification or CQI (Channel Quality Indicator) report from the wireless terminal device 202, and monitors the arrival of the measurement result notification or CQI report.

  After receiving the RRC connection reconfiguration completion notification indicating that the handover has been completed from the wireless terminal device 202, the time measurement unit 12 has the measurement result notification or CQI report from the wireless terminal device 202 contrary to the schedule of the monitoring unit 11. Then, the time until the wireless base station device does not arrive is measured. Then, the time measuring unit 12 notifies the moving operation detecting unit 14 of the measured duration.

  The reception quality information acquisition unit 13 obtains the reception quality based on the measurement result notification or CQI report transmitted by the wireless terminal device 202. Then, the reception quality information acquisition unit 13 notifies the mobile operation detection unit 14 of the obtained reception quality.

  Based on the RLF report transmitted by the wireless terminal device 202, the reception quality notified by the reception quality information acquisition unit 13 or the duration notified by the time measurement unit 12, the mobile operation detection unit 14 may, for example, “Too Early HO”. The occurrence of an inappropriate handover operation such as “Too Late HO” is detected. Then, the movement operation detection unit 14 outputs a detection result indicating the detection result to the avoidance processing unit 16.

  The received power information acquisition unit 15 performs the following operation when the received power measured by the wireless terminal device 202 is included in the handover request transmitted from the serving base station. That is, the reception power information acquisition unit 15 calculates a reception power difference, which is a difference between the reception power of the radio signal transmitted by the serving base station and the reception power of the radio signal transmitted by the own radio base station device, in the wireless terminal device 202. Ask.

  Further, the reception power information acquisition unit 15 may obtain the reception quality at the wireless terminal device 202 of the wireless signal transmitted by the serving base station. Next, the reception power information acquisition unit 15 outputs the obtained reception power difference or reception quality to the avoidance processing unit 16.

  The avoidance processing unit 16 is a process for avoiding an inappropriate handover operation based on the detection result received from the movement operation detection unit 14 or the reception power difference or reception quality received from the reception power information acquisition unit 15. I do.

  For example, when the avoidance processing unit 16 receives a handover request from the radio base station apparatus 101 that has caused an inappropriate handover operation, the avoidance processing unit 16 changes the timing of transmitting a handover response, which is a response to the handover request, to the radio base station apparatus 101. .

  In addition, when the avoidance processing unit 16 receives a reception power difference or reception quality obtained when the mobile motion detection unit 14 receives a handover request, for example, the avoidance processing unit 16 has a reception power difference equal to or greater than a predetermined threshold or good reception quality Determines that the handover is not permitted, and does not transmit a handover response. On the other hand, the avoidance processing unit 16 determines that the handover should be permitted if the received power difference is less than the predetermined threshold value or the reception quality is poor, and transmits a handover response.

  In addition, the avoidance processing unit 16 changes the predetermined threshold according to the occurrence state of “Too Early HO” or “Too Late HO” detected by the moving motion detection unit 14.

  When the avoidance processing unit 16 performs handover of the radio terminal device 202 from the cell formed by the radio base station device 101 that has caused an inappropriate handover operation to the cell formed by the own radio base station device 101, the avoidance processing unit 16 The radio terminal apparatus 202 controls interference of radio signals transmitted by the radio base station apparatus 101.

  For example, the avoidance processing unit 16 adjusts the transmission power of the wireless signal transmitted by itself by increasing or decreasing the amplification factor of the amplifier in the wireless transmission unit 94, and the wireless terminal device 202 of the wireless signal transmitted by its own wireless base station. Control interference in

  Further, the avoidance processing unit 16 generates a subframe to be an ABS (Almost Blank Sub-frame), which will be described later, when the transmission signal processing unit 97 creates one frame by converting communication data into a predetermined frame format, for example. Is adjusted to control interference in the radio terminal apparatus 202 of radio signals transmitted by the own radio base station.

  Further, for example, when the transmission signal processing unit 97 divides resources related to radio signal transmission in the time axis direction and the frequency axis direction in the transmission signal processing unit 97 in the time axis direction and the frequency axis direction, the avoidance processing unit 16 will be described later. By adjusting the amount of the carrier (Blank Carrier), the interference in the wireless terminal device 202 of the wireless signal transmitted by the own wireless base station is controlled.

  In addition, the avoidance processing unit 16 controls interference in the wireless terminal device 202 of a wireless signal transmitted by its own wireless base station, for example, by adjusting the directivity of the antenna 91.

[Identification of the cause of inappropriate handover]
Next, the operation when the radio base station apparatus according to the embodiment of the present invention specifies the cause of an inappropriate handover operation will be described in detail.

  FIG. 13 is a flowchart defining an operation procedure for the radio base station apparatus according to the embodiment of the present invention to identify the cause of an inappropriate handover operation.

  After the RLF occurs, the wireless terminal device 202 transmits an RLF report to the wireless base station device 101 that is reconnected first. When the RLF report includes the connection time, the RLF serving cell ID, the re-establishment destination cell ID, and the HO request cell ID, the radio base station apparatus 101 that has received the RLF report causes an inappropriate handover operation according to the following operation procedure. Identify.

  Receiving the RLF report, if the radio base station apparatus 101 determines that the connection time is greater than the predetermined threshold (NO in step S452), the radio base station apparatus 101 is re-established from the cell formed by the serving base station indicated by the RLF serving cell ID. It is specified as “Too Late HO” to the cell formed by the target base station indicated by the destination cell ID (step S454).

  Further, the wireless terminal device 202 transmits an RLF report to the wireless terminal device 101 that is reconnected first after the occurrence of RLF, that is, the wireless terminal device 101 indicated by the re-establishment destination cell ID. Therefore, the radio base station apparatus 101 that has received the RLF report specifies “Too Late HO” from the cell formed by the serving base station indicated by the RLF serving cell ID to the cell formed by itself.

  For example, in the case shown in FIG. 3 and FIG. 4, the connection time is the time that the wireless terminal device 202 stayed in the cell CA. In this case, the wireless terminal device 202 has stayed within the cell CA for a time longer than the threshold value. The RLF serving cell ID indicates the ID of the radio base station device 101A, the re-establishment destination cell ID indicates the ID of the radio base station device 101B, and the HO request cell ID indicates the ID of the radio base station device 101Z. Therefore, the radio base station apparatus 101B receives the RLF report from the radio terminal apparatus 202 after the occurrence of RLF, and determines that it is “Too Late HO” from the cell CA to the cell CB formed by itself.

  In addition, when the connection time is smaller than the predetermined threshold (YES in step S452), the radio base station apparatus 101 that has received the RLF report determines whether the re-establishment destination cell ID and the HO request cell ID are the same. (Step S456).

  When the radio base station apparatus 101 that has received the RLF report determines that the re-establishment destination cell ID and the HO request cell ID are the same (YES in step S456), the serving base station indicated by the HO request cell ID forms. The cell is identified as “Too Early HO case 2” from the cell to the cell formed by the target base station indicated by the serving cell ID at the time of RLF (step S458).

  In addition, the wireless terminal device 202 transmits an RLF report to the wireless terminal device 101 indicated by the re-establishment destination cell ID. In this case, since the radio base station apparatus 101 that has received the RLF report has the same re-establishment destination cell ID and the HO request cell ID, the target base station indicated by the RLF serving cell ID is formed from the cell formed by itself. Specify “Too Early HO case 2” for the cell.

  For example, in the case shown in FIG. 7 and FIG. 8, the connection time is the time during which the wireless terminal device 202 stays in the area of the cell CB2. In this case, the wireless terminal device 202 has stayed in the area of the cell CB2 for a time shorter than the threshold value. The RLF serving cell ID indicates the ID of the radio base station device 101B, the re-establishment destination cell ID indicates the ID of the radio base station device 101A, and the HO request cell ID indicates the ID of the radio base station device 101A. Therefore, the radio base station apparatus 101A receives the RLF report from the radio terminal apparatus 202 after the occurrence of RLF, and determines that it is “Too Early HO” from the cell CA to the cell CB formed by itself.

  In addition, when the radio base station apparatus 101 that has received the RLF report determines that the re-establishment destination cell ID and the HO request cell ID are not the same (NO in step S456), the re-establishment destination cell ID and the RLF serving cell ID are the same. Is determined (step S460).

  When the radio base station apparatus 101 that has received the RLF report determines that the re-establishment destination cell ID and the RLF serving cell ID are the same (YES in step S460), the serving base station indicated by the HO request cell ID forms. The cell is identified as “Too Early HO case 1” to the cell formed by the target base station indicated by the re-establishment destination cell ID (step S462).

  In addition, the wireless terminal device 202 transmits an RLF report to the wireless terminal device 101 indicated by the re-establishment destination cell ID. Therefore, the radio base station apparatus 101 that has received the RLF report specifies “Too Early HO case 1” from the cell formed by the serving base station indicated by the HO request cell ID to the cell formed by itself.

  For example, in the case shown in FIG. 5 and FIG. 6, the connection time is the time during which the wireless terminal device 202 stays in the cell CB2. In this case, the wireless terminal device 202 has stayed in the area of the cell CB2 for a time shorter than the threshold value. The RLF serving cell ID indicates the ID of the radio base station device 101B, the re-establishment destination cell ID indicates the ID of the radio base station device 101B, and the HO request cell ID indicates the ID of the radio base station device 101A. Therefore, the radio base station apparatus 101B receives the RLF report from the radio terminal apparatus 202 after the occurrence of the RLF, and determines that it is “Too Early HO” from the cell CA to the cell CB formed by itself.

  When the radio base station apparatus 101 that has received the RLF report determines that the re-establishment destination cell ID and the RLF serving cell ID are not the same (NO in step S460), the serving base station indicated by the HO request cell ID is formed. To the cell formed by the target base station indicated by the serving cell ID at the time of RLF (step S464).

  For example, in the case shown in FIGS. 9 and 10, the connection time is the time during which the wireless terminal device 202 stays in the cell CBV. In this case, the wireless terminal device 202 has stayed within the cell CBV for a time shorter than the threshold. The RLF serving cell ID indicates the ID of the radio base station device 101B, the re-establishment destination cell ID indicates the ID of the radio base station device 101C, and the HO request cell ID indicates the ID of the radio base station device 101A. Accordingly, the radio base station apparatus 101C receives the RLF report from the radio terminal apparatus 202 after the occurrence of RLF, and determines that it is “HO to Wron Cell” from the cell CA to the cell CB.

  With the above operation, the radio base station apparatus 101 that has received the RLF report from the radio terminal apparatus 202 after the occurrence of RLF can identify the cause of an inappropriate handover operation.

  Also, when the connection time, the RLF serving cell ID, the re-establishment destination cell ID, and the HO request cell ID are not included in the received RLF report, the radio base station apparatus 101 performs the following analysis. That is, the cause of an inappropriate handover operation is specified using the reception power or reception quality of the radio signal transmitted from the serving base station and the neighboring base station when the RLF occurs, included in the RLF report.

  For example, when the reception power of the serving base station in the RLF report is larger than the reception power of the target base station, the wireless terminal device 202 uses the reception power larger than the radio signal transmitted by the target base station when the RLF occurs. The radio signal to be transmitted was received. From this, the radio base station apparatus 101 identifies “Too Early HO” from the cell formed by the serving base station to the cell formed by the target base station.

  Further, for example, when the reception power of the serving base station in the RLF report is smaller than the reception power of the target base station, the radio terminal device 202 uses the serving base station with a smaller reception power than the radio signal transmitted by the target base station when RLF occurs. This means that a radio signal transmitted by the station has been received. From this, the radio base station apparatus 101 identifies “Too Late HO” from the cell formed by the serving base station to the cell formed by the target base station.

  For example, when the reception quality of the serving base station in the RLF report is better than the reception quality of the target base station, the wireless terminal device 202 has a better reception quality than the radio signal transmitted by the target base station when the RLF occurs. The radio signal to be transmitted was received. From this, the radio base station apparatus 101 identifies “Too Early HO” from the cell formed by the serving base station to the cell formed by the target base station.

  Further, for example, when the reception quality of the serving base station in the RLF report is worse than the reception quality of the target base station, the wireless terminal device 202 has a lower reception quality than the wireless signal transmitted by the target base station when the RLF occurs. This means that a radio signal transmitted by the station has been received. From this, the radio base station apparatus 101 identifies “Too Late HO” from the cell formed by the serving base station to the cell formed by the target base station.

  By the way, since the femto base station is connected to the core network via, for example, the HeNB-GW, there are cases where the X2 interface for directly exchanging information between the radio base station apparatuses cannot be used.

  In this case, the femto base station cannot cause other radio base station devices to adjust parameters used for timing control of the handover operation.

  For this reason, there arises a problem in that the serving base station cannot perform handover optimization processing.

  Further, for example, in the case of “Too Early HO case 2” shown in FIG. 7 and FIG. 8, the femto base station cannot detect an inappropriate handover operation because the RLF report is not transmitted to the femto base station. There's a problem.

  Therefore, when the radio base station apparatus 101 is the target base station in an inappropriate handover operation, the radio base station apparatus 101 can detect the inappropriate handover operation and take appropriate measures even if the RLF report is not transmitted to itself. Therefore, it is desirable that inappropriate handover operations can be suppressed.

  For example, in “Too Late HO” shown in FIG. 3 and FIG. 4, the wireless terminal device 202 transmits an RLF report to the wireless base station device 101B that is the target base station first after the occurrence of RLF. Based on the received RLF report, the radio base station apparatus 101B specifies “Too Late HO” from the cell CA to the cell CB formed by itself.

  In a situation where the X2 interface cannot be used, the radio base station apparatus 101B suppresses the occurrence of an inappropriate handover operation by adjusting its own operation as described later. Thereby, the radio base station apparatus 101B can suppress the occurrence of an inappropriate handover operation without using the X2 interface.

  Also, the radio base station apparatus 101B may transmit parameters or RLF reports necessary for timing control of the handover operation to the radio base station apparatus 101A in a situation where the X2 interface can be used. Then, the radio base station apparatus 101A controls the timing of the handover operation, thereby suppressing the occurrence of an inappropriate handover operation.

  For example, in “Too Early HO case 1” illustrated in FIG. 5 and FIG. 6, the wireless terminal device 202 first transmits an RLF report to the wireless base station device 101B, which is the target base station, after the RLF is generated. Based on the received RLF report, the radio base station apparatus 101B specifies “Too Early HO” from the cell CA to the cell CB formed by itself.

  In a situation where the X2 interface cannot be used, the radio base station apparatus 101B suppresses the occurrence of an inappropriate handover operation by adjusting its own operation as described later. Thereby, the radio base station apparatus 101B can suppress the occurrence of an inappropriate handover operation without using the X2 interface.

  Also, the radio base station apparatus 101B may transmit parameters or RLF reports necessary for timing control of the handover operation to the radio base station apparatus 101A in a situation where the X2 interface can be used. Then, the radio base station apparatus 101A controls the timing of the handover operation, thereby suppressing the occurrence of an inappropriate handover operation.

  For example, in “Too Early HO case 2” illustrated in FIG. 7 and FIG. 8, the wireless terminal device 202 transmits an RLF report to the wireless base station device 101A serving as a serving base station first after the RLF is generated. Based on the received RLF report, the radio base station apparatus 101A identifies “Too Early HO” from the cell CA to the cell CB formed by itself.

  The radio base station apparatus 101A suppresses occurrence of an inappropriate handover operation by performing timing control of the handover operation by parameter adjustment. At this time, the radio base station apparatus 101B, which is the target base station, detects “Too Early HO” from the cell formed by the serving base station to the cell formed by itself using the following detection method, The occurrence of an inappropriate handover operation may be suppressed. Thereby, the radio base station apparatus 101B can suppress the occurrence of an inappropriate handover operation.

[Detection of “Too Early HO” at the target base station]
In the case of “Too Early HO case 2” illustrated in FIG. 7 and FIG. 8, the radio base station apparatus 101B that is the target base station cannot receive the RLF report from the radio terminal apparatus 202 after the occurrence of RLF. For this reason, the radio base station apparatus 101B detects an inappropriate handover operation by using the measurement result notification or the CQI report instead of the RLF report.

  FIG. 14 is a diagram showing an example of an inappropriate handover operation (Too Early HO) and its detection processing sequence in the target base station according to the embodiment of the present invention.

  Referring to FIG. 14, first, similarly to steps S250 to S272 in FIGS. 7 and 8, radio terminal apparatus 202 that has communicated with radio base station apparatus 101A receives an RRC reconfiguration instruction from radio base station apparatus 101A. Accordingly, an RRC connection is established with the radio base station apparatus 101B, and an RRC connection reconfiguration completion notification is transmitted to the radio base station apparatus 101B.

  Next, the radio terminal apparatus 202 transmits an RRC connection reconfiguration completion notification to the radio base station apparatus 101B (step S502).

  Next, when receiving the RRC connection reconfiguration completion notification from the wireless terminal device 202, the wireless base station device 101B measures whether or not the measurement result notification is transmitted from the wireless terminal device 202 within a predetermined standby time. Then, a timer is started (step S504). Further, the standby time is set to, for example, about a few percent of the periodic measurement cycle performed by the wireless terminal device 202.

  Next, the radio base station apparatus 101B transmits to the radio terminal apparatus 202 a measurement start request for causing the radio terminal apparatus 202 to periodically measure the reception power of radio signals transmitted from other radio base station apparatuses, for example. (Step S506). Note that the periodic measurement cycle performed by the wireless terminal device 202 may be specified by the wireless base station device 101B or may be a cycle normally used in the communication system.

  Also, 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 S508).

  Next, the higher-level apparatus receives a 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 S510).

  Next, the wireless base station device 101A receives a terminal information release instruction from the higher-level device, releases information (UE Context) regarding the wireless terminal device 202, and transmits a terminal information release completion notification to the higher-level device (step S512). ).

  At this time, the radio terminal device 202 starts a power measurement process that is periodically performed based on the measurement start request received from the radio base station device 101B, and reduces the received power of radio signals transmitted from other radio base station devices. Measurement is performed (step S514).

  Next, the wireless terminal device 202 transmits a measurement result notification indicating the periodic measurement result of the received power to the wireless base station device 101B (step S516).

  Further, the wireless terminal device 202 may periodically measure the reception quality instead of the reception power in step S514 of measuring the reception power. At this time, the radio terminal apparatus 202 measures the reception quality of radio signals transmitted from other radio base station apparatuses.

At this time, the wireless terminal device 202 indicates the measured reception quality by a value expressed in 16 steps of 0 to 15 by the following formula using CQI, that is, SINR. For example, 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)

  Next, radio terminal apparatus 202 transmits a CQI report including CQI indicating reception quality to radio base station apparatus 101B.

  Next, when receiving a periodic measurement result notification or CQI report from the wireless terminal device 202, the wireless base station device 101B checks the timer that has been started. When the timer is operating, that is, when the standby time has not elapsed since the timer was started, the radio base station apparatus 101B records the elapsed time since the timer was first started. At this time, the radio base station apparatus 101B resets the timer because the measurement result notification or CQI report from the radio terminal apparatus 202 can be received within the standby time, and the next periodic transmission transmitted from the radio terminal apparatus 202 is performed. In preparation for receiving a typical measurement result notification or CQI report (step S518).

  Next, the radio base station apparatus 101B determines that the radio terminal apparatus 202 is connected to itself by receiving a measurement result notification or a CQI report from the radio terminal apparatus 202 (step S520).

  Also, the wireless terminal device 202 starts a reception power or reception quality measurement process that is periodically performed, and measures the reception power or reception quality of a wireless signal transmitted from another wireless base station device (step S522).

  Next, the wireless terminal device 202 transmits a periodic measurement result notification or CQI report indicating the measurement result to the wireless base station device 101B (step S524).

  Next, when receiving a periodic measurement result notification or CQI report from the wireless terminal device 202, the wireless base station device 101B checks the timer that has been started. When the timer is operating, that is, when the standby time has not elapsed since the timer was reset, radio base station apparatus 101B adds the elapsed time since the timer was reset to the duration. At this time, if the duration is less than the predetermined value, the radio base station apparatus 101B resets the timer and receives the next periodic measurement result notification or CQI report transmitted from the radio terminal apparatus 202. Provided (step S526). The predetermined value is set, for example, for a plurality of times of measurement result notification or CQI report transmission cycle.

  Next, the radio base station apparatus 101B determines that the radio terminal apparatus 202 is connected to itself by receiving a measurement result notification or a CQI report from the radio terminal apparatus 202 (step S528).

  In addition, the wireless terminal device 202 starts a reception power or reception quality measurement process that is periodically performed, and measures reception power or reception quality of a radio signal transmitted from another wireless base station device (step S530).

  At this time, the wireless terminal device 202 moves outside the cell CB2 and within the cell CA, similarly to step S288 shown in FIG. 7 (step S532).

  Then, since the wireless terminal device 202 cannot communicate with the wireless base station device 101B, RLF occurs. In this case, “Too Early HO” occurs (step S534).

  Since the RLF has occurred, the wireless terminal device 202 cannot transmit a periodic measurement result notification or CQI report to the wireless base station device 101B during the timer operation (step S536).

  Next, when the radio base station apparatus 101B receives a measurement end notification from the timer because the standby time has elapsed, the radio base station apparatus 101B adds the timer standby time to the duration (step S538).

  Next, the radio base station apparatus 101B determines that communication with the radio terminal apparatus 202 has been interrupted when the measurement result notification or the CQI report cannot be received within the waiting time of the timer, that is, when the radio base station apparatus 101B cannot receive the measurement result contrary to the schedule. To do. If the duration is less than the predetermined value, the radio base station apparatus 101B determines that “Too Early HO” has occurred from the cell CA to the cell CB formed by itself (step S540).

  The radio base station apparatus 101B determines that “Too Early HO” has not occurred when the radio terminal apparatus 202 is connected to the radio terminal apparatus 202 when the duration time continues to a predetermined value or more, and the detection process Exit.

  Next, the radio base station apparatus 101B performs an inappropriate handover operation avoidance process so as to suppress the occurrence of “Too Early HO” (step S542).

  With the above operation, after receiving the RRC connection reconfiguration completion notification, the radio base station apparatus 101B has a duration for receiving a measurement result notification or CQI report periodically transmitted from the radio terminal apparatus 202 is less than a predetermined value. In this case, the occurrence of “Too Early HO” can be detected.

  FIG. 15 is a diagram showing an example of an inappropriate handover operation (Too Early HO) and its detection processing sequence in the target base station according to the embodiment of the present invention.

  Referring to FIG. 15, first, similarly to steps S250 to S272 in FIG. 7 and FIG. 8, radio terminal apparatus 202 communicating with radio base station apparatus 101A receives an RRC reconfiguration instruction from radio base station apparatus 101A. Accordingly, an RRC connection is established with the radio base station apparatus 101B, and an RRC connection reconfiguration completion notification is transmitted to the radio base station apparatus 101B.

  Next, the wireless terminal device 202 transmits an RRC connection reconfiguration completion notification to the wireless base station device 101B (step S552).

  Next, when the radio base station apparatus 101B receives the RRC connection reconfiguration completion notification from the radio terminal apparatus 202, in order to measure whether the measurement result notification is transmitted from the radio terminal apparatus 202 within a predetermined time, A timer is started (step S554).

  Next, the radio base station apparatus 101B transmits to the radio terminal apparatus 202 a measurement start request for causing the radio terminal apparatus 202 to periodically measure the reception power of radio signals transmitted from other radio base station apparatuses, for example. (Step S556). Note that the periodic measurement cycle performed by the wireless terminal device 202 may be specified by the wireless base station device 101B, or may be a cycle normally used in the wireless communication system.

  Also, 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 S558).

  Next, the higher-level apparatus receives a 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 S560).

  Next, the wireless base station device 101A receives a terminal information release instruction from the higher-level device, releases information (UE Context) regarding the wireless terminal device 202, and transmits a terminal information release completion notification to the higher-level device (step S562). ).

  At this time, the radio terminal device 202 starts a power measurement process that is periodically performed based on the measurement start request received from the radio base station device 101B, and reduces the received power of radio signals transmitted from other radio base station devices. Measurement is performed (step S564).

  Next, the wireless terminal device 202 transmits a measurement result notification indicating the periodic measurement result of the received power to the wireless base station device 101B (step S566).

  In addition, the wireless terminal device 202 may periodically measure reception quality instead of reception power in step S564 of measuring reception power. At this time, the radio terminal apparatus 202 measures the reception quality of radio signals transmitted from other radio base station apparatuses.

  Next, radio terminal apparatus 202 transmits a CQI report indicating the measured reception quality to radio base station apparatus 101B.

  Next, when receiving a periodic measurement result notification or CQI report from the wireless terminal device 202, the wireless base station device 101B checks the timer that has been started, and if the timer is operating, that is, starts the timer. If the predetermined time has not passed since the measurement, the measurement result notification or the CQI report is scrutinized (step S568).

  Also, the radio base station apparatus 101B closely examines the measurement result notification or CQI report transmitted first after the handover by the radio terminal apparatus 202 whose communication destination has been changed to self by handover, regardless of the predetermined time.

  Radio terminal apparatus 202 first transmits a measurement result notification or CQI report recording reception power or reception quality measured during or immediately after handover to handover-target radio base station apparatus 101B after handover. For this reason, the radio base station apparatus 101B can obtain information on the communication state of the radio terminal apparatus 202 close to the time of handover.

  When the radio base station apparatus 101B receives the measurement result notification, the radio base station apparatus 101B obtains reception quality represented by, for example, SINR based on the reception power of the radio signal transmitted from each radio base station apparatus included in the measurement result notification. .

  Next, in the measurement result notification or the CQI report, the radio base station apparatus 101B determines that “Too Early HO” has occurred from the cell CA to the cell CB formed by itself when the reception quality is poor (step S1). S570).

  More preferably, when the radio base station apparatus 101B has a poor reception quality and a good reception quality of the radio base station apparatus 101A in the measurement result notification or CQI report, the radio base station apparatus 101B forms a cell CB formed by the cell CA. It is determined that “Too Early HO” has occurred.

  Next, the radio base station apparatus 101B performs an inappropriate handover operation avoidance process so as to suppress the occurrence of “Too Early HO” (step S572).

  With the above operation, the radio base station apparatus 101B receives the RRC connection reconfiguration completion notification from the radio terminal apparatus 202, and then the radio terminal apparatus 202 transmits first after handover or within a predetermined time. The occurrence of “Too Early HO” can be detected based on the received quality included in the measurement result notification or the CQI report.

[Radio link disconnection (RLF) avoidance processing]
Next, operations performed when the radio base station apparatus according to the embodiment of the present invention avoids radio link disconnection (RLF) will be described in detail.

  Hereinafter, the timing of the handover operation is controlled by controlling the timing at which the radio base station apparatus 101B transmits a handover response (Handover Preparation ACK) that is a response to the handover request (Handover Preparation) received from the radio base station apparatus 101A. An example of control is shown.

  FIG. 16 is a diagram illustrating an example of a sequence of operation procedures when the radio base station apparatus according to the embodiment of the present invention performs timing control of a handover operation.

  Referring to FIG. 16, first, radio terminal apparatus 202 measures the received power of radio signals transmitted from radio base station apparatuses including radio base station apparatus 101A and radio base station apparatus 101B (step S652).

  Next, the wireless terminal device 202 transmits a measurement result notification indicating the measurement result of the measured received power to the wireless base station device 101A (step S654).

  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 S656).

  Next, the radio base station device 101A transmits a handover request indicating the radio base station device 101B to the higher-level device (step S658).

  Next, the higher-level 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 S660).

  Next, when receiving the handover request from the higher-level device, the radio base station device 101B determines whether it is necessary to change the timing of the handover operation (step S662).

  That is, the radio base station apparatus 101B detects, for example, that the number of occurrences of “Too Early HO” is large in the handover of the radio terminal apparatus 202 from the cell formed by the radio base station apparatus 101A to the cell formed by itself. If it is, it is determined that the timing of the handover operation should be delayed.

  Also, the radio base station apparatus 101B detects, for example, that the number of occurrences of “Too Late HO” is large in the handover of the radio terminal apparatus 202 from the cell formed by the radio base station apparatus 101A to the cell formed by itself. If it is, it is determined that the timing of the handover operation should be advanced.

  Next, when determining that the timing of the handover operation should be delayed in step S662, the radio base station device 101B delays the timing of transmitting the handover response to the higher-level device (step S664).

  If the radio base station apparatus 101B determines that the timing of the handover operation should be advanced in step S662, the radio base station apparatus 101B advances the timing of transmitting the handover response to the upper apparatus.

  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 S666).

  Next, the radio base station apparatus 101A receives the handover instruction from the host apparatus, determines the handover of the radio terminal apparatus 202 (step S668), and transmits the RRC connection reconfiguration instruction to the radio terminal apparatus 202 (step S668). S690).

  With the above operation, the radio base station apparatus 101B that is the target base station controls the transmission timing of the handover response that is a response to the handover request from the radio base station apparatus 101A that is the serving base station. The timing of handover in can be adjusted.

  For example, if the radio base station apparatus 101B delays the timing at which the handover response is transmitted to the upper apparatus in step S664 shown in FIG. 16, a handover instruction is transmitted from the upper apparatus to the radio base station apparatus 101A (step S666 shown in FIG. 16). ) Subsequent processing can be slowed down. Thereby, the radio base station apparatus 101B can delay the handover timing of the radio terminal apparatus 202 from the cell formed by the radio base station apparatus 101A to the cell formed by itself.

  Therefore, the radio base station apparatus 101B delays the timing of transmitting a handover response to the host apparatus when "Too Early HO" has occurred from the cell formed by the radio base station apparatus 101A to the cell formed by itself. Thus, the occurrence of “Too Early HO” can be suppressed.

  Further, for example, when the radio base station apparatus 101B advances the timing of transmitting a handover response to the upper apparatus in step S664 illustrated in FIG. 16, transmission of a handover instruction transmitted from the upper apparatus to the radio base station apparatus 101A (shown in FIG. 16). Processing subsequent to step S666) can be accelerated. Thereby, the radio base station apparatus 101B can accelerate the handover timing of the radio terminal apparatus 202 from the cell formed by the radio base station apparatus 101A to the cell formed by itself.

  Therefore, when the “Too Late HO” from the cell formed by the wireless base station device 101A to the cell formed by the wireless base station device 101A has occurred, the wireless base station device 101B advances the timing for transmitting the handover response to the host device. Thus, the occurrence of “Too Late HO” can be suppressed.

  FIG. 17 is a diagram illustrating a difference in reception power difference and reception quality of radio signals measured when the radio terminal apparatus according to the embodiment of the present invention moves between radio base station apparatuses.

  Referring to FIG. 17, the vertical axis represents the difference in received power between the radio signal transmitted by radio base station apparatus 101A and the radio signal transmitted by radio base station apparatus 101B in radio terminal apparatus 202. Further, the vertical axis may take reception quality represented by SIR or SINR of a radio signal transmitted by the radio base station apparatus 101A in the radio terminal apparatus 202.

  The horizontal axis represents the position of the wireless terminal device 202 with respect to the wireless base station device 101A when the wireless terminal device 202 moves from the wireless base station device 101A to the wireless base station device 101B.

  For example, when the wireless terminal device 202 moves from the wireless base station device 101A to the wireless base station device 101B, other wireless base station devices including the wireless base station device 101A and the wireless base station device 101B from the position A to the position M Measures the received power of the radio signal transmitted from the terminal and transmits a measurement result notification including the measured result of the received power to the radio base station apparatus 101A.

  Based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A receives the received power of the wireless signal transmitted by itself and the received power of the wireless signal transmitted by the wireless base station device 101B. Or the reception quality of the radio signal transmitted by itself.

  The obtained reception power difference or reception quality is greatest at the position A where the wireless terminal device 202 is closest to the wireless base station device 101A, and decreases when the wireless terminal device 202 moves away from the wireless base station device 101A and approaches the wireless base station device 101B. Also, the received power difference or the received quality is such that the radio terminal apparatus 202 cannot perform radio communication at a position M farthest from the radio base station apparatus 101A due to interference by radio signals from the radio base station apparatus 101B, that is, RLF. It is bad enough to occur.

  Therefore, the radio base station apparatus 101A needs to hand over the radio terminal apparatus 202 from itself to the radio base station apparatus 101B between the position A and the position M.

  For example, a threshold value serving as a reference for determining that the radio base station apparatus 101A can satisfactorily hand over the radio terminal apparatus 202 from itself to the radio base station apparatus 101B is defined as a threshold value ThHOU.

  At this time, radio base station apparatus 101A determines that handover of radio terminal apparatus 202 should be performed at position G where the received power difference or received quality falls below threshold value ThHOU.

  On the other hand, for example, when the radio base station apparatus 101B detects that the number of occurrences of “Too Early HO” from the cell CA formed by the radio base station apparatus 101A to the cell CB formed by itself is large, the radio terminal apparatus A threshold value serving as a reference for determining that 202 can be successfully handed over from the radio base station apparatus 101A to itself is set to a threshold value ThHO lower than the threshold value ThHOU.

  At this time, radio base station apparatus 101B determines that handover of radio terminal apparatus 202 should be performed at position I where the received power difference or the received quality is below threshold value ThHO.

  That is, when the radio base station apparatus 101B determines that the timing of the handover operation performed by the radio base station apparatus 101A is early, the radio base station apparatus 101B reduces the threshold value serving as a reference for determining that the handover can be performed satisfactorily, The timing of handover can be delayed.

  Hereinafter, the radio base station apparatus 101B determines whether or not to perform handover based on the threshold value, and transmits a handover response that is a response to the handover request received from the radio base station apparatus 101A based on the determination. An example is shown in which the timing of the handover operation is controlled by controlling.

  FIG. 18 is a diagram illustrating an example of a sequence of operation procedures when the radio base station apparatus according to the embodiment of the present invention performs timing control of a handover operation.

  Radio terminal apparatus 202 measures the reception power or reception quality of a radio signal transmitted from each radio base station apparatus while moving from position G to position I, and transmits the measurement result to radio base station apparatus 101A.

  Note that the wireless terminal device 202 measures the received power of the radio signal transmitted from each radio base station device, obtains the received power difference from the difference from the received power of the radio signal transmitted from the radio base station device 101A, The received power difference may be transmitted to the radio base station apparatus 101A.

  Referring to FIG. 18, first, radio terminal apparatus 202 measures the received power of radio signals transmitted from radio base station apparatuses including radio base station apparatus 101A and radio base station apparatus 101B at position G (step). S752).

  Next, the wireless terminal device 202 transmits a measurement result notification indicating the measurement result of the measured received power to the wireless base station device 101A (step S754).

  Next, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A receives the wireless signal received power of the wireless terminal device 202 and the wireless signal transmitted by the wireless base station device 101B. The reception quality of the radio signal transmitted by itself is obtained. Based on the received power difference or reception quality, radio base station apparatus 101A determines whether or not to perform handover of radio terminal apparatus 202. If the radio base station apparatus 101A determines that the reception power difference or the reception quality has fallen below the threshold value ThHOU, and that the radio terminal apparatus 202 should be handed over, the radio base station apparatus 101A refers to the neighboring cell information, for example, the radio base station The apparatus 101B is determined as a handover destination (step S756).

  Next, the radio base station device 101A transmits a handover request indicating the radio base station device 101B to the higher-level device (step S758). At this time, the radio base station apparatus 101A transmits the handover request including the content of the measurement result notification.

  Next, the higher-level 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 S760).

  Next, the radio base station apparatus 101B receives a handover request from the host apparatus. Next, based on the measurement result notification included in the handover request, the radio base station apparatus 101B receives the reception power of the radio signal transmitted by the radio base station apparatus 101A and the reception of the radio signal transmitted by itself in the radio terminal apparatus 202. The difference from the power or the reception quality of the radio signal transmitted by the radio base station apparatus 101A is obtained. The radio base station apparatus 101B determines whether the timing of the handover operation is appropriate based on the obtained reception power difference or reception quality. The radio base station apparatus 101B determines that the handover request is not permitted because the received power difference or the received quality does not fall below the threshold value ThHO (step S762).

  At this time, the radio base station apparatus 101B notifies the radio base station apparatus 101A of non-permission of the handover request via the host apparatus. Therefore, the handover operation is not performed any more.

  In addition, the wireless terminal device 202 measures the received power of the wireless signal transmitted from each wireless base station device including the wireless base station device 101A and the wireless base station device 101B at the position H (step S764).

  Next, the wireless terminal device 202 transmits a measurement result notification indicating the measurement result of the measured received power to the wireless base station device 101A (step S766).

  Next, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A receives the wireless signal received power of the wireless terminal device 202 and the wireless signal transmitted by the wireless base station device 101B. The reception quality of the radio signal transmitted by itself is obtained. Based on the received power difference or reception quality, radio base station apparatus 101A determines whether or not to perform handover of radio terminal apparatus 202. When the radio base station apparatus 101A determines that the radio terminal apparatus 202 should be handed over because the received power difference or the reception quality is lower than the threshold value ThHOU, the radio base station apparatus 101A refers to neighboring cell information, for example, the radio base station The station apparatus 101B is determined as a handover destination (step S768).

  Next, the radio base station device 101A transmits a handover request indicating the radio base station device 101B to the higher-level device (step S770). At this time, the radio base station apparatus 101A transmits the handover request including the content of the measurement result notification.

  Next, the higher-level 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 S772).

  Next, the radio base station apparatus 101B receives a handover request from the host apparatus. Next, based on the measurement result notification included in the handover request, the radio base station apparatus 101B receives the reception power of the radio signal transmitted by the radio base station apparatus 101A and the reception of the radio signal transmitted by itself in the radio terminal apparatus 202. The difference from the power or the reception quality of the radio signal transmitted by the radio base station apparatus 101A is obtained. The radio base station apparatus 101B determines whether the timing of the handover operation is appropriate based on the obtained reception power difference or reception quality. The radio base station apparatus 101B determines that the handover request is not permitted because the received power difference or the received quality does not fall below the threshold value ThHO (step S774).

  At this time, the radio base station apparatus 101B notifies the radio base station apparatus 101A of non-permission of the handover request via the host apparatus. Therefore, the handover operation is not performed any more.

  Further, the wireless terminal device 202 measures the received power of the wireless signal transmitted from each wireless base station device including the wireless base station device 101A and the wireless base station device 101B at the position I (step S776).

  Next, the wireless terminal device 202 transmits a measurement result notification indicating the measurement result of the measured received power to the wireless base station device 101A (step S778).

  Next, based on the measurement result notification received from the wireless terminal device 202, the wireless base station device 101A receives the wireless signal received power of the wireless terminal device 202 and the wireless signal transmitted by the wireless base station device 101B. The reception quality of the radio signal transmitted by itself is obtained. Based on the received power difference or reception quality, radio base station apparatus 101A determines whether or not to perform handover of radio terminal apparatus 202. When the radio base station apparatus 101A determines that the radio terminal apparatus 202 should be handed over because the received power difference or the reception quality is lower than the threshold value ThHOU, the radio base station apparatus 101A refers to neighboring cell information, for example, the radio base station The station apparatus 101B is determined as a handover destination (step S780).

  Next, the radio base station device 101A transmits a handover request indicating the radio base station device 101B to the higher-level device (step S782). At this time, the radio base station apparatus 101A transmits the handover request including the content of the measurement result notification.

  Next, the higher-level 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 S784).

  Next, the radio base station apparatus 101B receives a handover request from the host apparatus. Next, based on the measurement result notification included in the handover request, the radio base station apparatus 101B receives the reception power of the radio signal transmitted by the radio base station apparatus 101A and the reception of the radio signal transmitted by itself in the radio terminal apparatus 202. The difference from the power or the reception quality of the radio signal transmitted by the radio base station apparatus 101A is obtained. The radio base station apparatus 101B determines whether the timing of the handover operation is appropriate based on the obtained reception power difference or reception quality. The radio base station apparatus 101B determines that the handover request is permitted because the received power difference or the received quality falls below the threshold value ThHO (step S786).

  Next, the radio base station apparatus 101B transmits a handover response to the handover request to the higher-level apparatus (Step S788).

  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 S790).

  Next, the wireless base station device 101A receives the handover instruction from the host device, and decides to hand over the wireless terminal device 202 from itself to the wireless base station device 101B (step S792).

  Next, the radio base station apparatus 101A transmits an RRC connection reconfiguration instruction to the radio terminal apparatus 202 based on the determination (step S794).

  Referring again to FIG. 17, for example, it is assumed that radio base station apparatus 101B determines to change the communication destination of radio terminal apparatus 202 to itself based on threshold value ThHOL that is smaller than threshold value ThHO.

  At this time, the radio base station apparatus 101B receives the handover request including the measurement result of the received power measured at the position K where the radio terminal apparatus 202 has passed the position I, and then transmits a handover response to the higher-level apparatus.

  If such a setting is made, the timing of the handover operation of the wireless terminal device 202 from the wireless base station device 101A to the wireless base station device 101B is delayed, so that the number of occurrences of “Too Late HO” has increased. To do.

  When the radio base station apparatus 101B detects that the number of occurrences of “Too Late HO” from the cell CA formed by the radio base station apparatus 101A to the cell CB formed by itself is large, the radio base station apparatus 101B performs the following operation. That is, radio base station apparatus 101B sets a threshold value that serves as a reference for determining that radio terminal apparatus 202 can be successfully handed over from radio base station apparatus 101A to itself, for example, a threshold value greater than threshold value ThHOL. Set to ThHO.

  Thereby, after receiving the handover request including the measurement result of the received power measured at the position I, the radio base station device 101B transmits a handover response to the higher-level device (step S788 shown in FIG. 18).

  That is, the radio base station apparatus 101B increases the threshold value used as a criterion for determining that the handover can be favorably performed when the handover operation timing is delayed according to its own criterion. The timing can be advanced.

  Through the above operation, the radio base station apparatus 101B, which is the target base station, sets a threshold value serving as a reference for determining that the handover can be performed satisfactorily to a predetermined value, thereby performing handover in the radio terminal apparatus 202. The timing can be adjusted.

  For example, when the radio base station apparatus 101B detects that the number of occurrences of “Too Early HO” of the radio terminal apparatus 202 from the cell CA formed by the radio base station apparatus 101A to the cell CB formed by itself is large, Set the threshold value smaller.

  Thereby, the radio base station apparatus 101B determines handover permission at a timing delayed from the handover permission determination by the radio base station apparatus 101A. As a result, since the radio base station apparatus 101B transmits a handover response to the host apparatus at a later timing, handover of the radio terminal apparatus 202 from the cell CA formed by the radio base station apparatus 101A to the cell CB formed by itself is performed. Timing can be delayed.

  Accordingly, when the radio base station apparatus 101B detects that the number of occurrences of “Too Early HO” from the cell CA formed by the radio base station apparatus 101A to the cell CB formed by itself is large, the threshold value is set. By setting a small value, the occurrence of “Too Early HO” can be suppressed.

  Further, for example, the radio base station apparatus 101B detects that the number of occurrences of “Too Late HO” of the radio terminal apparatus 202 from the cell CA formed by the radio base station apparatus 101A to the cell CB formed by itself is large. If so, set a larger threshold.

  Thereby, the radio base station apparatus 101B determines the handover permission at a timing earlier than the determination of the handover permission by itself before setting the threshold value large. As a result, since the radio base station apparatus 101B transmits a handover response to the host apparatus at an earlier timing, handover of the radio terminal apparatus 202 from the cell CA formed by the radio base station apparatus 101A to the cell CB formed by itself is performed. The timing can be advanced.

  Therefore, when the radio base station apparatus 101B detects that the number of occurrences of “Too Late HO” from the cell CA formed by the radio base station apparatus 101A to the cell CB formed by itself is large, the threshold value is set. By setting a large value, the occurrence of “Too Late HO” can be suppressed.

  FIG. 19 is a diagram illustrating an example of a situation in which an inappropriate handover operation is prevented by the target base station according to the embodiment of the present invention adjusting transmission power.

  Referring to FIG. 19, radio terminal apparatus 202 is moving from cell CA formed by radio base station apparatus 101A toward cell CB formed by radio base station apparatus 101B, and cell CA and cell CB overlap each other. Suppose that an appropriate handover operation can be performed.

  That is, the radio base station apparatus 101A can prevent an inappropriate handover operation by handing over the radio terminal apparatus 202 at the position Q to the radio base station apparatus 101B.

  For example, radio base station apparatus 101A determines that radio terminal apparatus 202 at position P can be appropriately handed over to radio base station apparatus 101B. At this time, the wireless terminal device 202 is located within the cell CA, but not within the cell CB. Therefore, when the handover operation is started, an inappropriate handover operation, in this case, “Too Early HO” occurs. End up.

  For example, when the radio base station apparatus 101B detects that the number of occurrences of “Too Early HO” is large, the radio base station apparatus 101B forms a cell CBL larger than the cell CB by increasing the power of the radio signal to be transmitted.

  That is, since the interference at the position P of the radio signal transmitted by the radio base station apparatus 101A is relatively weak, the radio base station apparatus of the radio terminal apparatus 202 is located at the position P within the cell CA and within the cell CBL. An appropriate handover is performed from 101A to the radio base station apparatus 101B.

  Thereby, the radio base station apparatus 101B can avoid the occurrence of “Too Early HO”.

  Also, the radio base station apparatus 101A determines, for example, that the radio terminal apparatus 202 at the position R can be appropriately handed over to the radio base station apparatus 101B. At this time, although the wireless terminal device 202 is located within the cell CA, but is an end of the cell CA, an inappropriate handover operation, in this case, “Too Late HO” occurs when the handover operation is started. .

  For example, when it is detected that the number of occurrences of “Too Late HO” is large, the radio base station apparatus 101B forms a cell CBS smaller than the cell CB by reducing the power of the radio signal to be transmitted.

  That is, since the interference at the position R of the radio signal transmitted by the radio base station apparatus 101B is relatively weak, the radio base station apparatus of the radio terminal apparatus 202 is located at the position R within the cell CA and within the cell CBS. An appropriate handover is performed from 101A to the radio base station apparatus 101B.

  Thereby, the radio base station apparatus 101B can avoid the occurrence of “Too Late HO”.

  FIG. 20 is a diagram illustrating an example of a frame included in a radio signal transmitted by the target base station according to the embodiment of the present invention. (A), (B), and (C) in FIG. 20 show one frame composed of, for example, 10 subframes.

  The radio base station apparatus 101 controls interference in the radio terminal apparatus 202 of the radio signal by controlling resources related to the radio signal to be transmitted.

  When the radio base station apparatus 101 controls the degree of freedom in the time axis direction of resources, a period in which at least one of information included in the radio signal, the frequency of the radio signal, and the power of the radio signal is limited, For example, by increasing / decreasing the ABS (Almost Blank Sub-frame), the radio terminal apparatus 202 controls the interference of the radio signal transmitted by itself. A method for controlling interference in the time domain using ABS is described in 3GPP TS 36.423 v. 10.2.0. This is called eICIC (enhanced Inter-Cell Interference Coordination).

  Specifically, the radio base station apparatus 101 converts communication data to be transmitted to the radio terminal apparatus 202 into a predetermined frame format, creates a frame, and transmits the frame using a radio signal. The transmitted frame includes, for example, an ABS that hardly contains information. The radio base station apparatus 101 adjusts the number of subframes serving as ABSs in order to control interference in the radio terminal apparatus 202 of radio signals transmitted by itself.

  Referring to FIG. 20, the target base station transmits a frame indicated by (B) in FIG. When the target base station detects that the number of occurrences of “Too Early HO” from the cell formed by the serving base station to the cell formed by the target base station is large, an ABS as shown in FIG. Send the reduced frame.

  The cause of “Too Early HO” is that the radio signal transmitted from the serving base station in the radio terminal apparatus 202 interferes with the radio signal transmitted from the target base station. Therefore, the target base station can relatively weaken the interference in the radio terminal apparatus 202 of the radio signal transmitted by the serving base station by reducing the number of ABSs in the frame transmitted by the target base station.

  Also, the target base station can easily retransmit by HRQ (Hybrid Repeat reQuest) by reducing the ABS. Thereby, the radio | wireless terminal apparatus 202 can reduce the error which arises at the time of the reception of the radio signal from a target base station. As a result, the occurrence of “Too Early HO” can be suppressed.

  Further, for example, when the target base station detects that the number of occurrences of “Too Late HO” from the cell formed by the serving base station to the cell formed by the target base station is large, the target base station is illustrated in FIG. A frame with increased ABS is transmitted.

  The cause of “Too Late HO” is that the radio signal transmitted from the target base station in the wireless terminal device 202 interferes with the radio signal transmitted from the serving base station. Therefore, the target base station can relatively weaken the interference in the radio terminal apparatus 202 of the radio signal transmitted by the target base station by increasing the number of ABSs in the frame transmitted by the target base station. As a result, the occurrence of “Too Late HO” can be suppressed.

  Also, the radio base station apparatus 101 controls interference in the radio terminal apparatus 202 of radio signals transmitted by itself by controlling the degree of freedom in the frequency axis direction of resources.

  Specifically, when the target base station transmits a radio signal to the radio terminal apparatus 202 by the OFDMA method, the target base station divides resources related to radio signal transmission in the time axis direction and the frequency axis direction, and uses the radio signal. Effective use of resources by allocating resources divided according to needs.

  The target base station is, for example, an ICIC (Inter-Cell Interference Coordination) that adjusts the amount of blank resource blocks (Blank Resource Blocks) containing almost no information in resource block units of a bandwidth of 180 kHz allocated to individual users. By performing the above, interference in the wireless terminal device 202 of the wireless signal transmitted by itself is controlled.

  When the target base station detects that the number of occurrences of “Too Early HO” is large, the target base station relatively reduces the interference in the radio terminal apparatus 202 of the radio signal transmitted by the serving base station by reducing the blank resource block. Can weaken.

  Further, when the target base station detects that the number of occurrences of “Too Late HO” is large, the target base station relatively increases the interference in the wireless terminal device 202 of the wireless signal transmitted by increasing the number of blank resource blocks. Can weaken.

  In addition, the target base station performs CA based ICIC (Carrier Aggregation based ICIC) that adjusts the amount of blank carrier that hardly contains information in a carrier unit of a bandwidth of several tens of MHz that bundles resource blocks. You may control the interference in the radio | wireless terminal apparatus 202 of the radio signal which self transmits.

  Also, the radio base station apparatus 101 controls interference in the radio terminal apparatus 202 of radio signals transmitted by itself by controlling the degree of freedom in the radio signal transmission direction.

  Specifically, the target base station controls the directivity of the antenna 91 that transmits a radio signal, thereby controlling interference in the radio terminal device 202 of the radio signal transmitted by the target base station. For example, when the target base station detects that the number of occurrences of “Too Early HO” is large, the target base station increases the directivity of the antenna 91 so that the beam intensity of the radio signal transmitted by itself increases toward the serving base station. Control.

  Thereby, the target base station can relatively weaken the interference due to the radio signal transmitted by the serving base station in the radio terminal device 202 located in the region where the number of occurrences of “Too Early HO” is large.

  Further, when the target base station detects that the number of occurrences of “Too Late HO” is large, for example, the directivity of the antenna 91 is set so that the beam intensity of the radio signal transmitted by the target base station becomes weaker toward the serving base station. To control.

  Thereby, the target base station can relatively weaken the interference caused by the radio signal transmitted by itself in the radio terminal apparatus 202 located in the area where the number of occurrences of “Too Late HO” is large.

  By the way, 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.

  On the other hand, in the radio base station apparatus according to the embodiment of the present invention, the mobile operation detection unit 14 performs a handover operation from another radio base station apparatus to its own radio base station apparatus by the radio terminal apparatus 202. A predetermined handover operation is detected. Further, the avoidance processing unit 16 adjusts the operation of its own radio base station apparatus so that the occurrence of the predetermined handover operation is suppressed when the predetermined handover operation is detected by the movement operation detection unit 14. .

  As described above, since the target base station can detect and avoid an inappropriate handover operation such as “Too Early HO” or “Too Late HO” and perform a handover operation to another radio base station apparatus. Even when the parameters used for the timing control cannot be adjusted, the occurrence of 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 embodiment of the present invention, communication can be stabilized by appropriately controlling the handover operation of the radio terminal apparatus.

  Also, in the radio base station apparatus according to the embodiment of the present invention, the avoidance processing unit 16 adjusts the operation of its own radio base station apparatus to change from its own radio base station apparatus to its own radio base station apparatus. The timing of the handover operation is adjusted.

  In this way, by adjusting the operation of its own radio base station apparatus that is the target base station, it is possible to adjust the timing of the handover operation and suppress the occurrence of an inappropriate handover operation.

  Also, in the radio base station apparatus according to the embodiment of the present invention, the avoidance processing unit 16 includes permission to allow the radio terminal apparatus 202 to perform a handover operation from another radio base station apparatus to its own radio base station apparatus. The timing for transmitting the handover response to another radio base station apparatus is adjusted.

  In this way, by adjusting the timing of transmitting a handover response to be notified to another radio base station device, the timing of the handover operation from the other radio base station device to the own radio base station device can be adjusted. .

  Further, in the radio base station apparatus according to the embodiment of the present invention, the mobile operation detection unit 14 performs “Too Early HO” from the other radio base station apparatus to its own radio base station apparatus by the radio terminal apparatus 202, And “Too Late HO” is detected. The avoidance processing unit 16 delays the transmission timing of the handover response when “Too Early HO” is detected, and accelerates the transmission timing of the handover response when “Too Late HO” is detected.

  In this way, by appropriately adjusting the timing of transmitting a handover response to be notified to another radio base station apparatus, the timing of the handover operation from the other radio base station apparatus to its own radio base station apparatus is appropriately set. Can be adjusted.

  Further, in the radio base station apparatus according to the embodiment of the present invention, the avoidance processing unit 16 adjusts conditions for permitting a handover operation from another radio base station apparatus to its own radio base station apparatus by the radio terminal apparatus 202. To do.

  With such a configuration, it is possible to suppress the occurrence of an inappropriate handover operation by adjusting the conditions for allowing the wireless terminal device 202 to perform a handover operation from another wireless base station device to its own wireless base station device. it can.

  In the radio base station apparatus according to the embodiment of the present invention, the received power information acquisition unit 15 sends a measurement result notification indicating the measurement result of the received power of the radio signal from each radio base station apparatus in the radio terminal apparatus 202. Receive. Further, the avoidance processing unit 16 adjusts the condition based on the received power of the radio signal from the other radio base station apparatus and the received power of the radio signal from the own radio base station apparatus in the received measurement result notification.

  With such a configuration, it is possible to appropriately adjust the conditions for allowing the wireless terminal device 202 to perform a handover operation from another wireless base station device to its own wireless base station device based on the received power in the wireless terminal device 202. it can.

  Further, in the radio base station apparatus according to the embodiment of the present invention, the mobile operation detection unit 14 performs “Too Early HO” from the other radio base station apparatus to its own radio base station apparatus by the radio terminal apparatus 202 and “Too Late HO” is detected. Further, the avoidance processing unit 16 determines whether the difference between the reception power of the radio signal from another radio base station device and the reception power of the radio signal from its own radio base station device is less than a predetermined threshold, or When the reception quality of the other radio base station apparatus based on the reception power of the radio signal from the other radio base station apparatus and the reception power of the radio signal from the own radio base station apparatus 10 is poor, When a handover operation from the radio base station apparatus to its own radio base station apparatus is permitted, and “Too Early HO” is detected, the above threshold value is decreased, and when “Too Late HO” is detected Increases the threshold.

  In this way, by adaptively adjusting the threshold value for making a determination based on the reception power or reception quality in the wireless terminal device 202, the wireless terminal device 202 can change its own wireless base station from other wireless base station devices. The conditions for permitting the handover operation to the station apparatus can be adjusted more appropriately.

  Further, in the radio base station apparatus according to the embodiment of the present invention, avoidance processing unit 16 adjusts the radio signal transmission operation from its own radio base station apparatus to radio terminal apparatus 202.

  With such a configuration, it is possible to suppress the occurrence of an inappropriate handover operation by adjusting the reception state in the wireless terminal device 202 of the wireless signal transmitted from the own wireless base station device.

  Further, in the radio base station apparatus according to the embodiment of the present invention, avoidance processing unit 16 adjusts the transmission power of radio signals from its own radio base station apparatus to radio terminal apparatus 202.

  In this way, by adjusting the transmission power of the radio signal transmitted from its own radio base station apparatus, the magnitude relationship of the received power at the radio terminal apparatus 202 of the radio signal transmitted by each radio base station apparatus is appropriately controlled. can do.

  Further, in the radio base station apparatus according to the embodiment of the present invention, the mobile operation detection unit 14 performs “Too Early HO” from the other radio base station apparatus to its own radio base station apparatus by the radio terminal apparatus 202 and “Too Late HO” is detected. Further, the avoidance processing unit 16 increases the transmission power when “Too Early HO” is detected, and decreases the transmission power when “Too Late HO” is detected.

  In this way, by appropriately adjusting the transmission power of the radio signal transmitted from the own radio base station apparatus, the reception state in the radio terminal apparatus 202 of the radio signal transmitted by each radio base station apparatus is appropriately set. can do.

  Further, in the radio base station apparatus according to the embodiment of the present invention, avoidance processing unit 16 adjusts resources related to transmission of radio signals from its own radio base station apparatus to radio terminal apparatus 202.

  In this way, by adjusting the resources related to the transmission of the radio signal from the own radio base station apparatus to the radio terminal apparatus 202, the magnitude of the received power of the radio signal transmitted by each radio base station apparatus at the radio terminal apparatus 202 is increased or decreased. The relationship can be controlled appropriately.

  Further, in the radio base station apparatus according to the embodiment of the present invention, the mobile operation detection unit 14 performs “Too Early HO” from the other radio base station apparatus to its own radio base station apparatus by the radio terminal apparatus 202 and “Too Late HO” is detected. In addition, when “Too Early HO” is detected, the avoidance processing unit 16 sets a period during which at least one of the predetermined information included in the radio signal, the frequency of the radio signal, and the power of the radio signal is limited. If “Too Late HO” is detected, the period is increased.

  In this way, by adaptively adjusting the period during which at least one of the predetermined information included in the radio signal transmitted from the own radio base station apparatus, the frequency of the radio signal, and the power of the radio signal is limited The reception state of the radio signal transmitted by each radio base station apparatus in the radio terminal apparatus 202 can be appropriately set.

  Further, in the radio base station apparatus according to the embodiment of the present invention, the mobile operation detection unit 14 performs “Too Early HO” from the other radio base station apparatus to its own radio base station apparatus by the radio terminal apparatus 202 and “Too Late HO” is detected. Further, the resource is a frequency used for transmitting a radio signal, and the avoidance processing unit 16 reduces the type of frequency when “Too Early HO” is detected, and “Too Late HO” is detected. In some cases, the frequency type is increased.

  In this way, by adaptively adjusting the type of frequency used for the radio signal transmitted from the own radio base station apparatus, the reception state of the radio signal transmitted by each radio base station apparatus in the radio terminal apparatus 202 Can be set appropriately.

  Further, in the radio base station apparatus according to the embodiment of the present invention, avoidance processing unit 16 adjusts the directivity of an antenna for transmitting a radio signal from its own radio base station apparatus to radio terminal apparatus 202. In addition, the mobile operation detection unit 14 detects “Too Early HO” and “Too Late HO” from another wireless base station device to its own wireless base station device by the wireless terminal device 202. When “Too Early HO” is detected, the avoidance processing unit 16 adjusts the directivity of the antenna to increase the intensity of the transmitted radio wave in the direction toward the other radio base station apparatus. When "Late HO" is detected, the beam intensity of the transmission radio wave in the direction to the other radio base station apparatus is reduced by adjusting the directivity of the antenna.

  In this way, by adaptively adjusting the directivity of the antenna used for transmitting the radio signal transmitted from the own radio base station apparatus, the radio terminal apparatus 202 transmits the radio signal transmitted by each radio base station apparatus. The reception state can be set appropriately.

  For example, in the case of “Too Early HO case 2” shown in FIG. 7 and FIG. 8, the femto base station cannot detect an inappropriate handover because the RLF report is not transmitted to itself. .

  Therefore, in the radio base station apparatus according to the embodiment of the present invention, reception quality information acquisition section 13 obtains the first reception quality that is the reception quality of the radio signal from its own radio base station apparatus in radio terminal apparatus 202. Received reception quality information is acquired. In addition, the mobile operation detection unit 14 receives the reception quality information acquired first or within a predetermined time after a handover operation from another radio base station device to its own radio base station device by the radio terminal device 202 is performed. When the first reception quality indicated by is poor, it is determined that “Too Early HO” has occurred from another radio base station apparatus to its own radio base station apparatus by the radio terminal apparatus 202.

  With such a configuration, even when the own radio base station apparatus is the target base station and the RLF report is not transmitted from the radio terminal apparatus 202 to the own radio base station apparatus, it is based on the reception quality of the radio terminal apparatus 202. Thus, the occurrence of “Too Early HO” can be appropriately determined.

  Further, in the radio base station apparatus according to the embodiment of the present invention, reception quality information acquisition section 13 further receives a second reception that is the reception quality of a radio signal from another radio base station apparatus in radio terminal apparatus 202. Receive quality information indicating quality is acquired. In addition, the mobile operation detection unit 14 receives the reception quality information acquired first or within a predetermined time after the handover operation from another radio base station device to its own radio base station device by the radio terminal device 202 is performed. When the first reception quality shown is poor and the second reception quality is good, a “Too Early HO” has occurred from the other wireless base station device to its own wireless base station device 1 by the wireless terminal device 202 Judge.

  With such a configuration, it is possible to appropriately determine whether the cause of “Too Early HO” is an early handover operation by the serving base station or the communication environment in the wireless terminal device 202. it can. Accordingly, it is possible to more appropriately determine the occurrence of “Too Early HO” based on the reception quality of the wireless terminal device.

  In the radio base station apparatus according to the embodiment of the present invention, monitoring section 11 schedules the arrival of a measurement result notification or CQI report from radio terminal apparatus 202, and monitors the arrival of the measurement result notification or CQI report. . In addition, the time measurement unit 12 monitors the measurement result notification or CQI report from the wireless terminal device 202 after the wireless terminal device 202 performs a handover operation from another wireless base station device to its own wireless base station device. The time until the wireless base station apparatus stops arriving against the schedule of the unit 11 is measured. When the time measured by the time measurement unit 12 is less than the predetermined value, the movement operation detection unit 14 performs “Too Early HO” from another radio base station device to its own radio base station device by the radio terminal device 202. Is determined to have occurred.

  With such a configuration, even when the own radio base station apparatus is the target base station and the RLF report is not transmitted from the radio terminal apparatus 202 to the own radio base station apparatus, the measurement result notification from the radio terminal apparatus 202 is notified. Alternatively, the occurrence of “Too Early HO” can be appropriately determined based on the time until the CQI report does not arrive at its own radio base station apparatus against the schedule of the monitoring unit 11.

  In the embodiment of the present invention, the handover operation of the wireless terminal device has been specifically described. However, in the inter-base station movement (inter-cell movement) operation performed by the wireless terminal device in communication with the wireless base station device. The present invention is applied not only to a certain handover but also to an inter-base station movement (inter-cell movement) operation performed by an idle wireless terminal device. That is, in the embodiment of the present invention, the present invention is also applied to a configuration and operation in which “handover” is replaced with “movement”.

  The above embodiment should be considered as 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 Monitoring part 12 Time measurement part 13 Reception quality information acquisition part 14 Moving motion detection part 15 Reception power information acquisition part 16 Avoidance process part 91 Antenna 92 Circulator 93 Radio | wireless reception part 94 Radio | wireless transmission part 95 Signal processing part 96 Reception signal process part 97 Transmission signal processing unit 98 Control unit 101A, 101B, 101C, 101Z Wireless base station apparatus

Claims (19)

In a communication system capable of communicating with a plurality of radio base station devices by performing a mobile operation of the radio terminal device, a radio base station device for transmitting and receiving radio signals to and from the radio terminal device,
Among the movement operations from another wireless base station device to its own wireless base station device by the wireless terminal device, a moving operation detection unit for detecting the occurrence of a predetermined movement operation,
When the predetermined movement operation is detected by the movement operation detection unit, an avoidance processing unit for adjusting the operation of its own radio base station apparatus is provided so that occurrence of the predetermined movement operation is suppressed. Wireless base station equipment.   The avoidance processing unit adjusts the timing of the movement operation from the other radio base station device to the own radio base station device by adjusting the operation of the own radio base station device. Wireless base station device.   The avoidance processing unit adjusts a timing for notifying the other radio base station device that a movement operation from the other radio base station device to the own radio base station device by the radio terminal device is permitted. The radio base station apparatus according to 2. The moving operation detection unit detects a first moving operation that is too early and a second moving operation that is too late from the other radio base station device to the own radio base station device by the radio terminal device,
The avoidance processing unit delays the permission notification timing when the first movement operation is detected, and accelerates the permission notification timing when the second movement operation is detected. The radio base station apparatus according to claim 3.   The radio base station apparatus according to claim 1, wherein the avoidance processing unit adjusts a condition for permitting a movement operation from the other radio base station apparatus to the own radio base station apparatus by the radio terminal apparatus. The radio base station device further includes:
A reception power information acquisition unit for acquiring reception power information indicating a measurement result of reception power of a radio signal from each radio base station device in a radio terminal device,
The avoidance processing unit adjusts the condition based on reception power of a radio signal from the other radio base station apparatus indicated by the reception power information and reception power of a radio signal from its own radio base station apparatus, Item 6. The radio base station apparatus according to Item 5. The moving operation detection unit detects a first moving operation that is too early and a second moving operation that is too late from the other radio base station device to the own radio base station device by the radio terminal device,
The avoidance processing unit is configured such that the difference between the received power of the radio signal from the other radio base station device and the received power of the radio signal from the own radio base station device is less than a predetermined threshold, or the other When the reception quality of the other radio base station apparatus based on the reception power of the radio signal from the radio base station apparatus and the reception power of the radio signal from the own radio base station apparatus is poor, the other radio by the radio terminal apparatus Permitting the movement operation from the base station device to its own wireless base station device,
The avoidance processing unit decreases the threshold value when the first moving motion is detected, and increases the threshold value when the second moving motion is detected. 6. The radio base station apparatus according to 6.   The radio base station apparatus according to claim 1, wherein the avoidance processing unit adjusts a radio signal transmission operation from the radio base station apparatus to the radio terminal apparatus.   The radio base station apparatus according to claim 8, wherein the avoidance processing unit adjusts transmission power of a radio signal from the radio base station apparatus to the radio terminal apparatus. The moving operation detection unit detects a first moving operation that is too early and a second moving operation that is too late from the other radio base station device to the own radio base station device by the radio terminal device,
The avoidance processing unit increases the transmission power when the first movement operation is detected, and decreases the transmission power when the second movement operation is detected. The radio base station apparatus described.   The radio base station apparatus according to claim 8, wherein the avoidance processing unit adjusts resources related to transmission of radio signals from the radio base station apparatus to the radio terminal apparatus. The moving operation detection unit detects a first moving operation that is too early and a second moving operation that is too late from the other radio base station device to the own radio base station device by the radio terminal device,
When the first movement operation is detected, the avoidance processing unit restricts at least one of predetermined information included in the radio signal, a frequency of the radio signal, and power of the radio signal. The radio base station apparatus according to claim 11, wherein the period is decreased and the period is increased when the second movement operation is detected. The moving operation detection unit detects a first moving operation that is too early and a second moving operation that is too late from the other radio base station device to the own radio base station device by the radio terminal device,
The resource is a frequency used for transmission of the radio signal,
The avoidance processing unit decreases the type of the frequency when the first movement operation is detected, and increases the type of the frequency when the second movement operation is detected. 11. A radio base station apparatus according to 11. The avoidance processing unit adjusts the directivity of an antenna for transmitting a radio signal from its own radio base station apparatus to a radio terminal apparatus,
The moving operation detection unit detects a first moving operation that is too early and a second moving operation that is too late from the other radio base station device to the own radio base station device by the radio terminal device,
When the first movement operation is detected, the avoidance processing unit increases the beam intensity of the transmission radio wave in the direction to the other radio base station apparatus by adjusting the directivity of the antenna. 9. When the second moving operation is detected, the beam intensity of the transmission radio wave in the direction to the other radio base station apparatus is reduced by adjusting the directivity of the antenna. The radio base station apparatus described. The radio base station device further includes:
A reception quality information acquisition unit for acquiring reception quality information indicating a first reception quality that is a reception quality of a radio signal from its own radio base station apparatus in the radio terminal apparatus;
The mobile operation detection unit indicates the reception quality information acquired first or within a predetermined time after a mobile terminal device performs a mobile operation from another radio base station device to its own radio base station device. When the first reception quality is poor, it is determined that a predetermined movement operation has occurred that is too early for a movement operation from the other radio base station apparatus to the own radio base station apparatus by the radio terminal apparatus. The radio base station apparatus according to any one of claims 1 to 14. The reception quality information acquisition unit further acquires reception quality information indicating a second reception quality that is a reception quality of a radio signal from the other radio base station apparatus in the radio terminal apparatus,
The mobile operation detection unit indicates the reception quality information acquired first or within a predetermined time after a mobile terminal device performs a mobile operation from another radio base station device to its own radio base station device. When the first reception quality is poor and the second reception quality is good, the timing of the moving operation from the other radio base station apparatus to the radio base station apparatus by the radio terminal apparatus is too early. The radio base station apparatus according to claim 15, wherein it is determined that a movement operation has occurred. The radio base station device further includes:
A monitoring unit for scheduling arrival of the predetermined information from the wireless terminal device and monitoring the arrival of the predetermined information;
After the wireless terminal device performs a moving operation from another wireless base station device to its own wireless base station device, the predetermined information from the wireless terminal device is not the schedule of the monitoring unit. With a time measurement unit for measuring the time until it stops arriving at the station device,
When the time measured by the time measurement unit is less than a predetermined value, the movement operation detection unit is configured to detect a movement operation from the other radio base station device to the own radio base station device by the radio terminal device. The radio base station apparatus according to any one of claims 1 to 14, wherein the radio base station apparatus determines that a predetermined movement operation that is too early has occurred. 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 mobile operation of the radio terminal apparatus,
A step of detecting occurrence of a predetermined movement operation among movement operations from another wireless base station device to the own wireless base station device by the wireless terminal device;
Adjusting the operation of its own radio base station apparatus so that occurrence of the predetermined movement operation is suppressed when the predetermined movement operation is detected. A communication control program used 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 moving operation of the radio terminal apparatus. To the computer
A step of detecting occurrence of a predetermined movement operation among movement operations from another wireless base station device to the own wireless base station device by the wireless terminal device;
A communication control program for executing the step of adjusting the operation of its own radio base station apparatus so that the occurrence of the predetermined movement operation is suppressed when the predetermined movement operation is detected.

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