JP2017163415A - Base station device, terminal device, control method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the time required for handover.SOLUTION: A base station device performs a control to cause a terminal device to perform a handover to another base station device, on the basis of a measurement report of radio wave from other base station in the terminal device which is received from the terminal device connected to the base station itself. The base station device transmits a signal indicating that a predetermined connection process is unnecessary to the terminal device, in at least a part of handover of the terminal device to another base station device in which time synchronization is established with the base station device.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a handover process in cellular communication.

  In general, in a cellular communication system, it is assumed that a terminal device moves across cells developed by a plurality of base station devices, and a handover process for maintaining a connection is also defined at that time. . For example, Non-Patent Document 1 and Non-Patent Document 2 describe a handover process in 3GPP long-term evolution (LTE). In LTE handover, in order to establish uplink synchronization, a predetermined random access process using a random access channel (RACH) is executed between the terminal apparatus and the handover destination base station apparatus.

3GPP TS36.300 v9.0.0, June 2009 3GPP TS36.213 v9.0.0, December 2009

  The connection process such as the predetermined random access process described above requires a certain time to complete. At this time, the terminal device cannot perform data communication during execution of this process. Due to such a period during which data communication cannot be performed, for example, the quality of communication with high real-time characteristics can be significantly degraded. Further, when the wireless environment is not good, this process is further prolonged, and this quality deterioration can be remarkable.

  The present invention has been made in view of the above-described problems, and an object thereof is to shorten the period required for handover.

  In order to achieve the above object, a base station apparatus according to the present invention is based on a measurement report received from a terminal apparatus connected to the base station apparatus from another base station apparatus. And control means for performing control to hand over the terminal apparatus to the other base station apparatus, and the control means establishes time synchronization with the base station apparatus for a signal indicating that predetermined connection processing is not required. The terminal device is transmitted to at least a part of the case where the terminal device is handed over to another base station device.

  In order to achieve the above object, a terminal device according to the present invention transmits a measurement report of a signal transmitted from another base station device to the base station device to which the terminal device is connected. When receiving a signal indicating that a predetermined random access process is unnecessary after transmitting the report from the transmission unit and the base station apparatus, the other base station apparatus does not perform the predetermined connection process. Execution means for executing a handover to.

  According to the present invention, the period required for handover can be shortened.

The figure which shows the structural example of a radio | wireless communications system. The figure which shows the hardware structural example of each apparatus. The block diagram which shows the function structural example of a base station apparatus. The block diagram which shows the function structural example of a terminal device. The figure which shows the example of the flow of the process performed in a radio | wireless communications system.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(Wireless communication system)
FIG. 1 shows a configuration example of a wireless communication system according to this embodiment. This radio | wireless communications system is comprised including the base station apparatus (eNB) and terminal device of long term evolution (LTE), for example. Note that the base station device may be a communication device in which an area (cell) provided by each of the plurality of base station devices is expanded and a movable terminal device is connected to one of them. For example, the base station apparatus may be a base station apparatus of another wireless communication standard such as a past or future cellular communication system. In the example of FIG. 1, two base station devices and one terminal device are shown, but the present invention is not limited to this. That is, as in a general cellular communication system, a large number of base station apparatuses are arranged so as to provide a seamless communication area to terminal apparatuses, and a large number of terminal apparatuses can be connected to any of the base station apparatuses. .

  Here, it is assumed that the terminal apparatus moves from a cell deployed by a certain base station apparatus to a cell deployed by another base station apparatus, as indicated by an arrow in FIG. At this time, if the terminal device moves away from the base station device to which it originally connected, the received power of the radio wave received from the base station device is reduced, and the radio wave received by itself is received by the base station device. Since power is reduced, communication cannot be performed as it is. For this reason, in order to perform communication with sufficient radio quality at the destination, the terminal apparatus executes a handover process for switching the connection to the base station apparatus having the destination as the coverage area.

  Here, at the time of handover, the terminal device needs to establish time synchronization with the base station device to which the connection is switched. In LTE, in an uplink in which a signal is transmitted from a terminal apparatus to a base station apparatus, the terminal apparatus transmits a physical random access channel (PRACH) to the base station apparatus, and the timing advance (TA) command is transmitted from the base station apparatus. Receive. With the TA command, a timing correction value when a signal is transmitted from the terminal apparatus to the base station apparatus is notified to the terminal apparatus. The terminal apparatus corrects the transmission timing of the uplink signal using this timing correction value (for example, the signal is transmitted earlier than the frame timing by the timing correction value). Thus, the base station apparatus does not collide with other uplink signals, that is, the transmitted signal reaches the base station apparatus at the scheduled timing. As for the downlink, since the base station device transmits a synchronization signal at a constant period, the terminal device can establish downlink time synchronization at the timing of receiving the synchronization signal.

  In conventional cellular radio communication systems, in many cases, FDD (Frequency Division Duplex) using different frequency bands for uplink and downlink has been adopted. In the FDD system, it is allowed not to synchronize the time between base stations. On the other hand, in recent years, TDD (Time Division Duplex) has attracted attention and is expected to be adopted. In TDD, it is necessary to establish time synchronization between base stations. For this reason, in a radio communication system using TDD, it is considered that frame synchronization is established between a plurality of base station apparatuses. That is, frames are started at the same timing among a plurality of base station apparatuses, and the plurality of base station apparatuses can transmit at least signals at the same timing. Even in a wireless communication system using FDD, the same can be said when time synchronization between base station apparatuses is established.

  As described above, when time synchronization is established between base station apparatuses, the terminal apparatus can appropriately transmit signals in the uplink without performing random access processing using the random access channel as described above. Specific timing can be specified (or estimated). That is, the terminal apparatus estimates the propagation delay between each base station apparatus and the terminal apparatus from the reception timing of signals (for example, synchronization signals, reference signals, etc.) transmitted from the plurality of base station apparatuses at a predetermined timing. can do. Here, the terminal device is connected to one of the base station devices, and when transmitting a signal to the base station device, the terminal device uses the timing correction value (for example, obtained by the above TA command) to Assume that the transmission timing of the link signal is corrected. In this case, the terminal device uses the reception timing difference between the synchronization signal from the connected base station device and the synchronization signal from the handover destination base station device and the currently used timing correction value at the handover destination. The timing correction value to be used can be estimated.

  For example, ΔT is a value obtained by subtracting the value of the synchronization signal reception timing from the currently connected base station apparatus from the value of the synchronization signal reception timing from the handover destination base station apparatus. ΔT takes a negative value when the synchronization signal from the handover destination base station apparatus is received by the terminal apparatus earlier than the synchronization signal from the currently connected base station apparatus. Similarly, ΔT takes a positive value when the synchronization signal from the currently connected base station apparatus is received by the terminal apparatus earlier than the synchronization signal from the handover destination base station apparatus. The terminal device can specify the timing correction value to be used at the handover destination by adding the value of ΔT to the currently used timing correction value. That is, if the synchronization signal from the handover destination base station device is received by the terminal device earlier than the synchronization signal from the currently connected base station device, the timing correction value becomes smaller, so it is slower A signal is transmitted at the timing. In addition, when the synchronization signal from the currently connected base station device is received by the terminal device earlier than the synchronization signal from the handover destination base station device, the value of the timing correction value becomes larger. A signal is transmitted at an early timing.

  In this way, on the assumption that the time synchronization is established between the base station devices, the terminal device does not perform a predetermined connection process (for example, a random access process) with the base station apparatus that is the handover destination, Time synchronization in the uplink can be established. In this embodiment, paying attention to this, when the terminal device performs handover, the handover source base station device randomly selects the terminal device if it has established time synchronization with the handover destination base station device. Control to execute the access process. Here, the random access process will be described, but the present invention is not limited to this. If the terminal apparatus can be connected to the handover destination base station apparatus without performing another predetermined connection process, the predetermined process is performed. There is no need to execute the connection process. Therefore, it should be noted that the following “random access process” can be read as an arbitrary “predetermined connection process”.

  For example, a handover source base station apparatus does not need random access processing for a terminal apparatus when time synchronization is established between the handover source base station apparatus and the handover destination base station apparatus. Send a signal to indicate that there is. Note that the signal indicating that the random access process is not required may be a signal indicating that time synchronization is established between the handover source base station apparatus and the handover destination base station apparatus. That is, if time synchronization is established, it can be said that it is not necessary to execute the random access process, and therefore it is possible to notify whether or not the execution of the random access process is unnecessary by notification of the presence or absence of time synchronization. The base station apparatus to be handed over can be determined by the radio station measurement report from the peripheral base station apparatus from the terminal apparatus. Therefore, the base station apparatus determines the handover destination base station apparatus in response to receiving the measurement report from the terminal apparatus, and time synchronization is established with the handover destination base station apparatus. Can be notified that the random access processing is unnecessary.

  When receiving a signal indicating that the execution of the random access process is unnecessary from the connected base station apparatus, the terminal apparatus executes the handover process without performing the random access process. In this case, as described above, the terminal apparatus performs post-handover from the timing at which the signal transmitted from the handover source and handover destination base station apparatuses is received at a predetermined timing and the currently used timing correction value. The timing correction value can be specified. In addition, when the handover without the random access process fails, the terminal apparatus can execute the conventional handover process with the random access process, for example, under the control of the base station apparatus or independently.

  In addition, when the base station apparatus notifies the terminal apparatus that the execution of the random access process is unnecessary, the base station apparatus acquires information on whether or not the terminal apparatus has succeeded in the handover without the random access process. Also good. For example, the base station device collects information on success or failure of handover for a plurality of terminal devices that have performed handover processing using the same base station device as a handover destination, and then performs random access processing based on the success rate of handover. No can be determined. For example, if the success rate of handover executed without random access processing is lower than a predetermined value, the base station device performs normal random access even if it is time-synchronized with the handover destination base station device. The terminal apparatus is caused to execute a handover process involving the process. For example, if the handover source base station apparatus and the handover destination base station apparatus employ FDD and the propagation environment differs between the uplink and the downlink, it is specified that the random access processing is not performed. The timing correction value may not be appropriate. In such a case, the terminal device may fail to perform handover. Therefore, the base station apparatus can cause the terminal apparatus to execute a conventional handover process with a random access process for a handover destination where such handover failures frequently occur.

Moreover, the base station apparatus can specify whether time synchronization with the other base station apparatus which provides an adjacent cell can be established based on the information contained in the list | wrist of the adjacent cell hold | maintained beforehand. The base station device establishes time synchronization between the base station devices from the handover destination base station device, for example, after identifying the handover destination base station device based on the measurement report from the terminal device. Information indicating whether or not there is can be received. This information can be transmitted / received by communication between base station apparatuses via a backbone network, for example. If each base station device supports time synchronization between base station devices,
In the following, a configuration of a base station device and a terminal device that perform such processing, and an embodiment of a flow of processing performed by these devices will be described in detail.

(Hardware configuration)
FIG. 2 shows a hardware configuration example of the base station device and the terminal device. For example, the base station apparatus and the terminal apparatus have a hardware configuration as shown in FIG. 2, and include, for example, a CPU 201, a ROM 202, a RAM 203, an external storage device 204, and a communication device 205. In the base station device and the terminal device, for example, the CPU 201 executes a program that realizes each function of each device as described above, which is recorded in any of the ROM 202, the RAM 203, and the external storage device 204.

  And a base station apparatus and a terminal device control the communication apparatus 205 by CPU201, for example, and communicate with another apparatus. The communication device 205 of the base station device communicates with the terminal device via a cellular wireless communication interface such as an LTE wireless interface, and communicates with other base station devices via a wired or wireless communication interface. Yes. The communication device 205 of the terminal device can perform communication with the base station device. In the configuration of FIG. 2, the base station device and the terminal device are schematically illustrated as having one communication device 205, but are not limited thereto. For example, the base station device can include a first communication device for communication with another base station device and a second communication device between the terminal devices. The terminal device includes, for example, a cellular communication device and a wireless LAN communication device.

  Note that the base station device and the terminal device may be provided with dedicated hardware for executing each function, or a part of the base station device and the terminal device may be executed by the hardware, and the other part may be executed by a computer that operates the program. . All functions may be executed by a computer and a program.

(Functional configuration of base station equipment)
FIG. 3 shows a functional configuration example of the base station apparatus. As an example, the base station apparatus includes a wireless communication unit 301, a wired communication unit 302, a handover control unit 303, and a synchronization determination unit 304. The wireless communication unit 301 performs LTE communication with the terminal device. The wired communication unit 302 performs communication with other base station devices, for example. The base station apparatus can also communicate with other base station apparatuses, for example, wirelessly. In this case, the wired communication unit 302 is omitted, and the wireless communication unit 301 is used for communication with other base station apparatuses. Alternatively, the wired communication unit 302 may be replaced with a second wireless communication unit.

  The handover control unit 303 identifies another base station device to be handed over in response to the measurement report received from the terminal device via the wireless communication unit 301 from the base station device around the terminal device. Then, the terminal device is caused to execute a handover process. At this time, when time synchronization is established between the base station apparatus and another base station apparatus to which the handover is performed, the handover control unit 303 performs a handover process without a random access process on the terminal apparatus. May be directed to do so. Synchronization determination section 304 determines whether the base station apparatus has established time synchronization with another handover destination base station apparatus. Note that this determination may be performed based on information included in the neighboring cell list held in the base station device, for example, or other bases of the handover destination via the wired communication unit 302, for example. You may perform based on the information acquired from the station apparatus.

  Note that the handover control unit 303 can acquire information indicating whether or not the handover has succeeded for the terminal device that has instructed the handover process without the random access process. In this case, based on the information, the handover control unit 303 can statistically determine, for example, for each other handover destination base station apparatus, whether to continue the handover process without the random access process. That is, the handover control unit 303 can determine that the handover process without the random access process is not continued, for example, when the probability that the handover process without the random access process fails is greater than or equal to a predetermined value. As a result, for a handover destination that has a high probability that the handover process without the random access process will fail, it is possible to cause the terminal device to execute the conventional handover process and prevent the handover process from being disabled. In addition, when the probability of failure is high, the time required for the total handover can be reduced by preventing the handover process without the random access process from being performed.

(Functional configuration of terminal device)
FIG. 4 shows a functional configuration example of the terminal device. As an example, the terminal device includes a wireless communication unit 401, a measurement report unit 402, a handover execution unit 403, and a timing correction value specifying unit 404. The wireless communication unit 401 performs wireless communication with the base station apparatus according to the LTE standard. The measurement report unit 402 measures a reference signal (radio wave) transmitted by a surrounding base station device, for example, according to the LTE standard, and reports the measurement result to the base station device. The handover execution unit 403 executes a handover for switching the connection destination base station apparatus in accordance with an instruction from the base station apparatus. Note that the handover execution unit 403 executes the handover process without executing the random access process or by executing the random access process according to an instruction from the base station apparatus.

  The timing correction value specifying unit 404 specifies a timing correction value to be used for transmission of an uplink signal after handover when executing a handover without a random access process. For example, as described above, the timing correction value specifying unit 404 performs timing correction after handover from the reception timing of the signal transmitted from the handover source and handover destination base station apparatuses at a predetermined timing and the current timing correction value. The value can be specified. Note that the timing correction value specifying unit 404 is, for example, when there is a base station device that is not a connected base station device that is a transmission source of a radio wave measured at a predetermined power level or higher in the measurement report unit 402. A timing correction value can be specified in advance for the base station apparatus. In this case, the timing correction value specifying unit 404 should use the timing correction value specified in advance after the handover when instructed by the connected base station apparatus to execute a handover without random access processing. It can be specified as a timing correction value. The wireless communication unit 401 transmits an uplink signal at a timing earlier by the timing correction value specified from the frame timing. The terminal device operates in accordance with the conventional LTE standard when establishing an initial connection. Therefore, the terminal apparatus can initially specify the timing correction value according to the TA command received from the connection destination base station apparatus when the connection is established.

(Process flow)
Subsequently, a flow of processing executed between the base station apparatus and the terminal apparatus will be described with reference to FIG. Hereinafter, a case will be described in which the handover source base station apparatus determines that the random access process is unnecessary. Note that the handover process accompanied by the random access process can be executed, for example, as defined in the conventional LTE standard.

  In this process, as an initial state, the terminal device has established a connection with the handover source base station device, and adjusts the uplink signal transmission timing according to the TA command received from the base station device, for example. It is assumed that data communication is performed (S501). The base station apparatus transmits a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) at a predetermined specific timing and frequency in the frame (S502). PSS and SSS may be signals defined in the conventional LTE standard. Here, the example of FIG. 5 shows an example in which only the handover destination base station apparatus transmits the PSS and SSS, but the handover source base station apparatus also transmits the PSS and SSS only, not shown. Send. Here, all of the plurality of base station apparatuses transmit PSS and SSS at the same timing.

  When receiving the PSS and SSS from the surrounding base station apparatuses (candidates for handover destination), the terminal apparatus specifies a timing correction value when it is assumed that the base station apparatus is handed over from the reception timing (S503). ). The timing correction value can be specified, for example, when the received intensity of a signal from a surrounding base station apparatus is equal to or higher than a predetermined value, targeting the base station apparatus that is the transmission source of the signal. That is, the timing correction value does not have to be specified for the base station apparatus that is the transmission source of the signal whose reception intensity is less than the predetermined value.

  On the other hand, the terminal device measures, for example, a reference signal transmitted by surrounding base station devices (S504), and transmits the measurement report (Measurement Report) to the currently connected base station device (S505). When the base station apparatus that has received the measurement report determines that the terminal apparatus is in a state to execute handover, it confirms whether time synchronization is established between itself and the base station apparatus that is the handover destination (not (Illustrated). And the base station apparatus transmits the instruction | indication of execution of a handover to a terminal device, for example by a RRCConnectionReconfiguration message (S506). When time synchronization is established between the handover source base station apparatus and the handover destination base station apparatus, this message includes information indicating that random access processing is not required in addition to the handover execution instruction. Is included. Information indicating that the random access process is not required may be transmitted separately from the handover execution instruction.

  Upon receiving the message of S506, the terminal device transmits a message for confirming that the handover is completed to the handover destination base station device without executing the conventional random access process (S507). This message can be, for example, an RRCConnectionReconfigurationComplete message.

  If random access processing is required, the terminal device transmits a physical random access channel to the handover destination base station device and receives a TA command from the base station device before the message of S507. It is necessary to perform such processing. On the other hand, according to the process according to the present embodiment, since these processes are omitted, the time required for the handover is shortened. Therefore, for example, it is possible to prevent deterioration of the quality of communication with high real-time property, and it is possible to prevent the time required for the handover process from being prolonged even when the wireless environment is not good.

  In addition, when the terminal device cannot obtain an appropriate timing correction value because the random access process is not executed, the terminal apparatus can execute a handover process with a conventional random access process. As a result, the handover itself can be prevented from failing, and stable communication can be realized. Further, the handover source base station apparatus collects information on whether or not the handover without the random access process is successful. For example, in the handover to the base station apparatus in which the handover process is likely to fail, On the other hand, the conventional handover process can be instructed. As a result, it is possible to prevent the time required for the handover process from being prolonged by attempting a handover without an unnecessary (high probability of failure) random access process.

  The embodiment of the present invention has been described above. This embodiment is merely an example, and is clearly not intended to limit the present invention to the form of the embodiment, and the present invention is within the scope defined by the appended claims. Various modifications to the embodiments are allowed.

Claims (11)

A base station device,
Control for handing over the terminal device to the other base station device based on a measurement report received by the terminal device connected to the base station device from the other base station device. Control means for performing
In at least a part of the case where the control means hands over the terminal device to the other base station device in which time synchronization with the base station device is established, a signal indicating that predetermined connection processing is unnecessary , Transmit to the terminal device,
A base station apparatus. The signal is a signal indicating that time synchronization is established between the base station apparatus and the other base station apparatus,
The base station apparatus according to claim 1. An acquisition means for acquiring information as to whether or not a handover by the terminal device to the other base station device is successful when the signal is transmitted to the terminal device;
A determination unit that determines whether or not the predetermined connection process is unnecessary in a handover from the base station device to the other base station device, based on information acquired by the acquisition unit from a plurality of terminal devices;
The base station apparatus according to claim 1, further comprising: A terminal device,
Transmitting means for transmitting a measurement report in the terminal device of a signal transmitted from another base station device to the base station device to which the terminal device is connected;
When a signal indicating that a predetermined connection process is unnecessary is transmitted from the base station apparatus after transmitting the report, a handover is performed to the other base station apparatus without performing the predetermined connection process Execution means;
The terminal device characterized by having. A timing at which a signal transmitted at a predetermined timing from each of the base station apparatus and the other base station apparatus is received, and a first timing correction value used in uplink communication with the base station apparatus. Based on the second timing correction value used in the uplink communication with the other base station apparatus,
The terminal device according to claim 4. The signal is a signal indicating that time synchronization is established between the base station apparatus and the other base station apparatus,
The terminal device according to claim 4 or 5, wherein When a handover to the other base station apparatus executed without the predetermined connection process is not successful, a handover to the other base station apparatus with the predetermined connection process is executed.
The terminal device according to claim 4, wherein the terminal device is a device. A control method for a base station apparatus,
Control for handing over the terminal device to the other base station device based on a measurement report received by the terminal device connected to the base station device from the other base station device. A control process for performing
In the control step, a signal indicating that a predetermined connection process is unnecessary is at least partly when the terminal device is handed over to the other base station device in which time synchronization with the base station device is established. , Transmitted to the terminal device,
A control method characterized by that. A terminal device control method,
A transmission step of transmitting a measurement report in the terminal device of a signal transmitted from another base station device to the base station device to which the terminal device is connected;
When a signal indicating that a predetermined connection process is unnecessary is transmitted from the base station apparatus after transmitting the report, a handover is performed to the other base station apparatus without performing the predetermined connection process Execution process;
A control method characterized by comprising: In the computer provided in the base station device,
Control for handing over the terminal device to the other base station device based on a measurement report received by the terminal device connected to the base station device from the other base station device. A program for executing a control process for performing
In the control step, a signal indicating that a predetermined connection process is unnecessary is at least partly when the terminal device is handed over to the other base station device in which time synchronization with the base station device is established. , Transmitted to the terminal device,
A program characterized by that. In the computer equipped with the terminal device,
A transmission step of transmitting a measurement report in the terminal device of a signal transmitted from another base station device to the base station device to which the terminal device is connected;
When a signal indicating that a predetermined connection process is unnecessary is transmitted from the base station apparatus after transmitting the report, a handover is performed to the other base station apparatus without performing the predetermined connection process Execution process;
A program for running

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