WO2014033813A1

WO2014033813A1 - Wireless communication system and base station

Info

Publication number: WO2014033813A1
Application number: PCT/JP2012/071595
Authority: WO
Inventors: 大介実川
Original assignee: 富士通株式会社
Priority date: 2012-08-27
Filing date: 2012-08-27
Publication date: 2014-03-06
Also published as: WO2014034679A1

Abstract

A base station: receives, from a peripheral base station, resource information pertaining to a plurality of resources which can be allocated to a mobile terminal, and interpreted data for the resource information; notifies the peripheral base station of the resource to be used in coordinated multiple point transmission, and which was selected on the basis of the resource information when the interpreted data has a value meaning that the resource information indicates a resource capable of being used in the coordinated multiple point transmission; and executes a process for conducting coordinated multiple point transmission with a peripheral base station to a mobile terminal by using the selected resource.

Description

Wireless communication system and base station

The present disclosure relates to a wireless communication system and a base station.

Commercial service for LongLTerm Evolution (LTE (Release 8)), a new mobile communication system, has started. The International Standards Organization 3GPP has already developed LTE-Advanced IV (Release IV 10) with greatly expanded functions. Currently, active discussions are taking place to further expand the functionality in the next release, Release 11.

As a countermeasure for inter-cell interference for the downlink shared channel (PDSCH), a partial frequency reuse (FFR) technique has already been put into practical use. A specific mechanism of FFR will be described with reference to FIG.

In FIG. 1, relative narrowband transmission power (Relative Narrow-band Tx Power: RNTP) is defined as an information element exchanged on the interface between base stations (X2 interface). RNTP indicates a frequency resource (Resource Block: RB) of transmission power exceeding a threshold value by “1”, and indicates RB of transmission power (including transmission power zero) below the threshold value by “0”. The base station indicates an RB whose transmission power is equal to or less than the threshold value by RNTP and declares it to the base station of the neighboring cell.

By receiving RNTP, the base station can know the RB whose transmission power in the adjacent cell is equal to or less than the threshold. The user scheduler in the base station of the adjacent cell allocates the RB to a mobile station (User Equipment: UE) at the adjacent cell boundary. By such FFR, interference with the mobile station is suppressed.

3GPP is studying to introduce a technology called Coordinated Multiplex Point (CoMP) to Release 11 as another countermeasure against inter-cell interference. One form of CoMP is joint transmission (JT).

In normal cellular communication, the UE receives a signal from a cell adjacent to the connected cell as an interference signal. In contrast, in joint transmission (CoMP JT) in coordinated transmission between base stations, a plurality of base stations cooperate to transmit a downlink shared channel (PDSCH) based on the same data to a specific UE. As a result, the UE can receive not only a signal from the connected cell but also a signal from an adjacent cell as a desired signal. For this reason, inter-cell interference is reduced.

Fig. 2 shows the CoMP JT system model. As downlink signal transmission stations (base stations), there are forms such as a macro base station, a pico base station, and RRH (Remote Radio Head), but in FIG. 2, they are represented as TP (Transmission Point) without distinguishing the transmission stations. ing. 2 is a transmitting station (TP) of a connected cell with which the UE exchanges control signals and the like, and transmits a data signal s1 to the UE.

TP2 is a transmitting station (TP) of the coordinated cell, and includes a scheduler connected to the scheduler of TP1 via the X2 interface. The scheduler of TP2 transmits the same data signal s1 as the data signal s1 transmitted from TP1 to the UE in cooperation with TP1.

As a cooperative cell selection method, for example, based on the downlink received power measurement value (Reference Signal Received Power: RSRP) fed back from the UE, a cell that falls within the RSRP threshold with the connected cell is selected. The method is known.

JP 2010-178237 A JP 2011-49617 A JP 2011-87009 A JP 2011-151779 A JP 2011-155501 A JP 2010-283632 A

In the standardization of Release IV 11, CoMP in a form of cooperation between different sectors in the same base station apparatus or a form of cooperation between the base station apparatus and its associated RRH is being studied. These forms can be regarded as cooperative control closed in the same device.

On the other hand, in order to realize CoMP using different base station apparatuses, as shown in FIG. 2, the scheduling information and information necessary for cooperative control in each base station of the connected cell and the cooperative cell are exchanged on the X2 interface. It is required to do. Information elements exchanged on the X2 interface have already been defined for conventional releases. For this reason, from the viewpoint of overhead of control information, it is desirable that CoMP can be realized without greatly expanding existing information elements.

The purpose of the present disclosure is to provide a technology capable of realizing inter-base station cooperative transmission while suppressing the expansion range of existing information elements.

One aspect of the embodiment of the present invention is that communication is possible with the first base station, the second base station that is a peripheral base station of the first base station, and the first base station and the second base station. Including mobile stations,
The first base station is
A receiving device that receives resource information about a plurality of resources that can be allocated to the mobile station, and predetermined data used to interpret the resource information;
Used for inter-base station cooperative transmission selected based on the resource information when the predetermined data has a first value that means that the resource information indicates a resource that can be used for inter-base station cooperative transmission And a control device that performs processing for performing inter-base station cooperative transmission with the second base station using the selected resource to the second base station. ,
When the second base station notifies the first base station of resources that can be used for inter-base station cooperative transmission, the second base station sends the resource information and the predetermined data having the first value to the first base station. Means that when transmitting a resource whose transmission power is equal to or less than a threshold to the first base station, the resource information and the resource information indicate a resource whose transmission power is equal to or less than the threshold. A transmission device for transmitting the predetermined data having a value of 1 to the first base station,
The mobile station is a wireless communication system including a receiving device capable of receiving signals transmitted from the first base station and the second base station by coordinated transmission between base stations.

According to the present disclosure, inter-base station cooperative transmission can be realized while suppressing the expansion range of existing information elements.

FIG. 1 shows a usage example of the control information RNTP. FIG. 2 shows a CoMP JT system model. It is explanatory drawing in case the value of the RNTP replacement instruction | indication in embodiment is "1". It is explanatory drawing when the value of the RNTP replacement instruction | indication in embodiment is "0". FIG. 4 is a diagram illustrating a configuration example of a mobile station (UE) applied to the embodiment. FIG. 5 is a diagram illustrating a configuration example of a base station that can be used as a base station (TP1) of a connected cell and a base station (TP2) of a cooperative cell (neighboring cell) in the embodiment. FIG. 6 is a sequence diagram illustrating an example of processing (cooperative transmission between base stations) in the embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The configuration of the embodiment is an exemplification, and the present invention is not limited to the configuration of the embodiment.

The embodiment provides a method for efficiently exchanging information on resources that can be used for CoMP (cooperative transmission between base stations) between base stations. The base station reserves a frequency resource (RB) for CoMP (that is, in an unallocated state) and notifies the neighboring base station of information on the RB. This initiates a procedure for combined transmission (JT).

Here, focusing on the relative narrowband transmission power (RNTP) described with reference to FIG. 1, the RNTP can indicate an RB with limited transmission power, but an unallocated (zero transmission power) RB Cannot be shown. Therefore, new control information (RNTP replacement instruction) is provided and exchanged between base stations. Based on the RNTP replacement instruction notified by the neighboring base stations, the base station replaces the RNTP information with information on resources that can be used for CoMP transmission. The RNTP replacement instruction is a flag having a binary value of “0” or “1”. The RNTP is an example of resource information regarding a plurality of resources that can be allocated to the mobile station, and the RNTP replacement instruction is an example of predetermined data used for interpreting the resource information, and the first value (“1”) and the first value It has a value of 2 (“0”).

FIG. 3A is an explanatory diagram when the value of the RNTP replacement instruction is “1” (RNTP replacement instruction = 1). The base station declares that the RB with RNTP = 0 can be used for CoMP transmission by notifying the other base station of the RNTP replacement instruction “1”. That is, an RB with RNTP = 0 represents an unassigned RB and an RB that can be used for partial frequency reuse (FFR).

FIG. 3B is an explanatory diagram when the value of the RNTP replacement instruction is “0” (RNTP replacement instruction = 0). The base station declares that the RNTP = 0 RB cannot be used for CoMP transmission by notifying the neighboring cell base station of the RNTP replacement instruction “0”. For example, it can be assumed that the RB is used for data transmission with low transmission power. That is, an RB with RNTP = 0 can represent an RB that can be used for FFR.

The base station (peripheral base station) of the neighboring cell that receives the RNTP replacement instruction and the RNTP of each RB performs the following interpretation. That is, if the value of the RNTP replacement instruction is “1” (RNTP replacement instruction = 1), the base station of the neighboring cell interprets that the RB with RNTP = 0 can be used for CoMP transmission. On the other hand, if the value of the RNTP replacement instruction is “0” (RNTP replacement instruction = 0), the base station of the neighboring cell interprets that the RB with RNTP = 0 can be used for FFR.

According to the above configuration, the resource information (RB) that can be used for CoMP transmission is transmitted to the base station of the neighboring cell only by adding a control information element (RNTP replacement instruction) of a small size (1 bit). You can be notified. In addition, since the definition of RNTP itself is not changed, by setting the RNTP read instruction to “0”, the FFR function using RNTP can be supported as usual. The meaning indicated by the bit value indicating the RNTP replacement instruction may be opposite to the above. Further, the number of bits for indicating the first and second values is not limited to one bit, and may be two or more bits.

FIG. 4 is a diagram illustrating a configuration example of a mobile station (UE) applied to the embodiment. FIG. 4 shows, as an example, a configuration of a UE in a mobile communication system in which an orthogonal frequency division multiple access (OFDMA) scheme is applied to a radio access scheme.

In FIG. 4, a UE 10 includes a radio (RF) transmission / reception circuit 11, a DSP (Digital Signal Processor) 12 that functions as a part of a baseband processing unit, and an LSI (Large Scale Integrated) that functions as a part of a baseband processing unit. circuit) 13.

The RF transmission / reception circuit 11 manages processing related to a radio (RF) signal. The RF transceiver circuit 11 includes a reception RF circuit (wireless receiver) 15 connected to the reception antenna 14 and a transmission RF circuit (wireless transmitter) 17 connected to the transmission antenna 16. The reception RF circuit 15 connected to the reception antenna 14 is an example of a reception device included in the mobile station.

The DSP 12 is an example of a processor, and the processor can include a CPU. The DSP 12 loads a program stored in a storage device (auxiliary storage device) (not shown) into the main storage device (main memory) and executes it. As a result, the DSP 12 performs fast Fourier transform (FFT) processing 18, channel estimation processing 19, control signal demodulation processing 20, reference signal received power (RSRP) calculation processing 21, and uplink control signal. The generation process 22 is executed.

The LSI 13 is an example of an integrated circuit, and includes a data signal demodulation circuit 23 that performs data signal demodulation processing. Each process executed by the DSP 12 can be realized by using one or more integrated circuits such as an LSI, an ASIC (Application Specific Specific Integrated Circuit), or a programmable logic device such as an FPGA.

The reception RF circuit performs radio frequency-to-baseband conversion, quadrature demodulation, and analog-digital (A / D) conversion on a signal (downlink received signal) from the base station (TP) received by the receiving antenna 14. .

In FFT processing 18, FFT timing detection, CP (Cyclic prefix) removal, and FFT are performed on the received signal (output signal of reception RF circuit 15). Moreover, in the channel estimation process 18, the reference signal for every base station (TP) is extracted from the received signal after FFT (the signal generated by the FFT process 18). Next, the cross-correlation between the extracted reference signal and the known reference signal of each base station is calculated. As a result, a channel estimation value of the radio channel represented by a complex number is obtained for each base station.

RSRP calculation processing 21 calculates the RSRP of each base station. In the control signal demodulation process 20, a control signal is extracted from the received signal after FFT (the signal generated by the FFT process 18). In the demodulation process 20, control information (resource allocation information) is restored from the control signal by performing channel compensation, data demodulation, and error correction decoding using the channel estimation value for the control signal.

The data signal demodulation circuit 23 extracts the data signal from the received signal after FFT (the signal generated by the FFT process 18) based on the resource allocation information obtained by the demodulation process 20. Further, the demodulation circuit 23 restores information bits from the data signal by performing channel compensation, data demodulation, and error correction decoding using the channel estimation value obtained by the channel estimation processing 19.

In the uplink control signal generation process 22, a control signal is generated by encoding, data modulation, or the like with respect to control information including RSRP of each base station. The transmission RF circuit 17 performs conversion from baseband to radio frequency by performing digital-analog (D / A) conversion and quadrature modulation on the control signal. The radio frequency signal is transmitted from the transmission antenna 16 as an upstream transmission signal.

FIG. 5 shows a configuration example of the base station TP1 of the connected cell that exchanges signals with the UE 10 shown in FIG. 4 and the base station TP2 of the cooperative cell located around the connected cell. Since the base station TP1 and the base station TP2 have the same configuration, the configuration of the base station TP1 will be described. “Base station” means a downlink transmission station, and includes, for example, a macro base station, a pico base station, an RRH, and the like.

The base station TP1 includes an RF transmission / reception circuit 31, a DSP 32 functioning as a baseband processing unit, and a wired interface circuit (wired I / F) 33.

The RF transmission / reception circuit 31 manages processing related to a radio (RF) signal. The RF transceiver circuit 31 includes a reception RF circuit (wireless receiver) 35 connected to the reception antenna 34 and a transmission RF circuit (wireless transmitter) 37 connected to the transmission antenna 36.

The DSP 32 is an example of a processor, and the processor can include a CPU. The DSP 32 loads a program stored in a storage device (auxiliary storage device) (not shown) into the main storage device (main memory) and executes it. As a result, the DSP 32 performs an uplink control signal demodulation process 38, a cooperative transmission control process 39, a process (scheduling) as a scheduler 40, an RNTP information generation process 41, a data signal generation process 42, and a control signal. Generation processing 43, reference signal generation processing 44, physical channel multiplexing processing 45, and inverse fast Fourier transform (IFFT) processing 46 are executed.

Each process executed by the DSP 32 can be realized by using one or more integrated circuits such as IC, LSI, and ASIC, or a programmable logic device such as FPGA.

The wired I / F 33 is connected to the wired I / F 33 of the base station TP2 via a wired interface. In FIG. 5, the DSP 32 and the RF transmission / reception circuit 31 in the base station TP2 are not shown.

The reception RF circuit 35 performs radio frequency-to-baseband conversion, orthogonal demodulation, and A / D conversion on the uplink received signal from the UE 10 (FIG. 4). In the uplink control signal demodulation process 38, an uplink control signal demodulation process is performed, and control information (RSRP of each cell) is extracted.

In the cooperative transmission control process 39, based on RSRP or the like, determination of a base station (for example, base station TP2) to be coordinated, setting of a resource (RB) for CoMP, determination of whether or not cooperation is possible, and joint transmission (JT) An execution instruction and a decision to cancel cooperation are made.

In the RNTP information generation process 41, setting of RNTP and RNTP replacement instruction is performed. In the scheduler 40, allocation of frequency resources to UEs, selection of transmission parameters, and the like are performed. The wired I / F 33 performs data transfer (transfer of RNTP and RNTP replacement instruction, UE data, etc.) to and from the base station TP2 of the cooperative cell.

In the data signal generation process 42, error correction coding, data modulation, and the like are performed on the data information. In the control signal generation process 43, a control signal is generated by executing error correction coding, data modulation, and the like for control information such as resource allocation information. In the reference signal generation process 44, the reference signal of the base station TP1 is generated. In the physical channel multiplexing process 45, each physical channel is frequency-multiplexed.

After that, the same processing as the typical OFDM method is executed. That is, IFFT processing 46 executes IFFT on the signal multiplexed by multiplexing processing 45, and CP is added to the signal obtained by IFFT. The transmission RF circuit 37 performs D / A conversion and quadrature modulation on the signal to which the CP is added. Thereby, the conversion from the baseband to the radio frequency is performed. The radio signal generated in this way is transmitted from the transmission antenna 36 as a downlink transmission signal.

FIG. 6 is a sequence diagram illustrating a processing example in the embodiment. In FIG. 6, first, the base station TP1 of the connected cell of the UE 10 and the base station TP2 which is a neighboring base station transmit a downlink (DL) reference signal (pilot signal) to the UE 10 (<1> in FIG. 6). .

The UE 10 measures the RSRP of each cell using the reference signal received from the base stations TP1 and TP2 of the connected cell (<2> in FIG. 6). Specifically, the DSP 12 of the UE 10 measures the RSRP of each cell using the reference signal. Specifically, the DSP 12 calculates a channel estimation value from the correlation between the known reference signal and the received reference signal by the channel estimation processing 19. Furthermore, the DSP 12 measures RSRP by averaging the power value of the received reference signal over time by the RSRP calculation process 21. Further, the DSP 12 generates an uplink control signal including an RSRP measurement result by the generation process 22. The transmission RF circuit 17 generates a radio signal (uplink transmission signal) of the uplink control signal and transmits it from the transmission antenna 16 to the base station TP1 (<3> in FIG. 6).

In the base station TP1, the uplink transmission signal of the UE is received as the uplink reception signal, and the uplink control signal is demodulated by the demodulation process 38 of the DSP 32. Further, the DSP 32 determines a cooperation target base station for the UE 10 based on the RSRP measurement result included in the uplink control signal by the cooperative transmission control process 39 (<4> in FIG. 6). In the example illustrated in FIG. 6, the base station TP2 is determined as a cooperation target.

In the base station TP2, the coordinated transmission control processing 39 sets, for example, that some resources (RB) are not used for transmission when the amount of data traffic under the cell of the own station is small. Such an RB is referred to as a “no transmission RB”. In the base station TP2, in the RNTP information generation process 41, the value corresponding to the non-transmission RB in RNTP is set to “0”, and the value of the RNTP replacement instruction is set to “1” (<5> in FIG. 6). ). The RNTP and the RNTP replacement instruction (= 1) are transmitted to the peripheral cells through, for example, the wired I / F 33 (<6> in FIG. 6).

The base station TP1 recognizes the RNTP and RNTP replacement instruction from the base station TP2 by the cooperative transmission control process 39 by the DSP 32. Thereby, the base station TP1 can know the RBs that the base station TP2 can use for CoMP. That is, the DSP 32 is suitable for CoMP among non-transmission RBs based on the recognition that the RB with the value “0” is a non-transmission RB (RB usable for CoMP) according to the RNTP replacement instruction (= 1). One or more RBs are selected, and the selected RBs are determined as CoMP RBs (<7> in FIG. 6). Information on the RB for CoMP is transmitted to the base station TP2 using the wired I / F 33 (<8> in FIG. 6).

The base station TP2 reserves the CoMP RB for CoMP JT based on the information on the CoMP RB received from the base station TP1, and updates the RNTP (FIG. 6 <9>). Specifically, the DSP 32 sets the value of the RB in the RNTP corresponding to the CoMP RB to “1” by the RNTP information generation process 41. With such a setting, it is possible to prevent a base station of a neighboring cell from misinterpreting that “the non-transmission RB can be used for CoMP” in the next RNTP transmission. The base station TP2 transmits a notification indicating that cooperation is possible (that is, the CoMP RB notified from the base station TP1 is reserved) to the base station TP1 by the cooperative transmission control processing 39 (FIG. 6). <10>).

When the base station TP1 receives a notification indicating that cooperation is possible from the base station TP2, the coordinated transmission control processing 39 transmits data for the UE 10 transmitted by CoMP JT, control information (transmission parameters such as a modulation scheme), and the like. Is transferred to the base station TP2 through the wired I / F 33 (<11> in FIG. 6).

The base station TP1 and the base station TP2 perform user scheduling of the UE 10 that transmits by CoMPJT based on the exchanged CoMP RB information (FIG. 6 <12>, <13>). The PDSCH is transmitted by CoMP JT (FIG. 6 <14>, <15>). Thereby, the same data is transmitted from the base station TP1 and the base station TP2.

Thereafter, the base station TP1 monitors the channel state for the UE 10 used for CoMP JT transmission based on the regularly reported RSRP, and serves as the base station of the cooperative cell that performs CoMP JT for the UE 10 If it is determined that TP2 is inappropriate, a notification of cancellation of cooperation is transmitted to the base station TP2 via the wired I / F 33 (<16> in FIG. 6).

When the base station TP1 receives the RNTP together with the RNTP replacement instruction (= 0), the DSP 32 is information indicating that the RNTP has a resource (RB) whose original transmission power is equal to or less than a threshold, that is, each RB. The corresponding value (0 or 1) is interpreted as a value indicating whether or not the transmission power is less than or equal to the threshold value. Then, the base station TP1 assigns an RB having a value of “0” to the UE located at the cell boundary with the base station TP2.

Thus, according to the embodiment, the CoMP JT is transmitted by transmitting the RNTP in which the value of the free RB (RB usable for CoMP) is set to 0 and the RNTP replacement instruction “1” to the neighboring cells. It is possible to inform the base station of the neighboring cell of the resource information that can be used.

In this way, for information elements transmitted and received between base stations, by adding a minimum (at least 1 bit) that defines an RNTP replacement instruction, resources (RB) that can be used for CoMP transmission (cooperative transmission between base stations) A mechanism to notify information can be constructed.

TP1, TP2 ... Base station 10 ... UE
32 ... DSP

Claims

A first base station;
A second base station that is a peripheral base station of the first base station;
A mobile station capable of communicating with the first base station and the second base station,
The first base station is
A receiving device that receives resource information about a plurality of resources that can be allocated to the mobile station, and predetermined data used to interpret the resource information;
When the predetermined data has a first value that means that the resource information indicates a resource that can be used for coordinated transmission between base stations, the coordinated transmission between base stations selected based on the resource information A control device for notifying the second base station of the resource to be used, and for executing processing for performing inter-base station cooperative transmission with the second base station for the mobile station using the selected resource; Including
The second base station is
When notifying the first base station of resources that can be used for coordinated transmission between base stations, the resource information and the predetermined data having the first value are transmitted to the first base station. When notifying the first base station of a resource whose power is less than or equal to a threshold, the resource information and the predetermined data having the second value indicating that the resource information indicates a resource whose transmission power is less than or equal to the threshold Including a transmission device for transmitting to the first base station,
The mobile station
Including a receiving device capable of receiving signals transmitted from the first base station and the second base station by cooperative transmission between base stations,
Wireless communication system.
The wireless communication system according to claim 1, wherein the control device determines whether the predetermined data has the first value or the second value.
The first base station moves at a cell boundary with the second base station based on the resource information when the resource information and the predetermined data having the second value are received. The radio communication system according to claim 1 or 2, wherein a resource whose transmission power is equal to or less than a threshold is allocated to a station.
The wireless communication system according to any one of claims 1 to 3, wherein the resource information is RNTP (Relative Narrow-band Tx Power).
A receiving device that receives resource information about a plurality of resources that can be allocated to a mobile station and predetermined data used for interpretation of the resource information from a neighboring base station;
Resources used for inter-base station cooperative transmission selected based on the resource information when the predetermined data has a value meaning that the resource information indicates a resource that can be used for inter-base station cooperative transmission A control device that performs processing for performing inter-base station cooperative transmission for the mobile station with the neighboring base station using the selected resource, and
Including base stations.
When notifying neighboring base stations of resources that can be used for coordinated transmission between base stations, resource information regarding a plurality of resources that can be allocated to mobile stations, and the resource information indicates resources that can be used for coordinated transmission between base stations The resource information and the resource information are transmitted when notifying the neighboring base station of a resource whose transmission power is not more than a threshold while transmitting predetermined data having a first value that means Transmitting the predetermined data having a second value, which means that transmission power indicates a resource having a threshold value or less, to the neighboring base station;
Inter-base station cooperative transmission with respect to the mobile station is performed with the neighboring base stations using information indicating resources for cooperative transmission between base stations selected based on the resource information received from the neighboring base stations. A base station including a control device that executes processing for performing.
When the predetermined data used for interpretation of resource information regarding a plurality of assignable resources has a first value that means that the resource information indicates a resource that can be used for coordinated transmission between base stations, the resource A first base station that notifies the neighboring base station of resources used for coordinated transmission between base stations selected based on information, and a resource that can be used for coordinated transmission between base stations to the first base station In addition, when transmitting the resource information and the predetermined data having the first value to the first base station while notifying the first base station of a resource whose transmission power is equal to or less than a threshold, A second base station that transmits information and the predetermined data having a second value, which means that the resource information indicates a resource whose transmission power is less than or equal to a threshold, or Mobile station comprising a receiver for receiving a signal transmitted by cooperative transmission between base stations using the selected resources.
Receiving resource information about a plurality of resources that can be allocated to a mobile station, and predetermined data used for interpretation of the resource information from neighboring base stations;
Resources used for inter-base station cooperative transmission selected based on the resource information when the predetermined data has a value meaning that the resource information indicates a resource that can be used for inter-base station cooperative transmission To the neighboring base station, and using the selected resource to perform a process for performing inter-base station cooperative transmission with the neighboring base station for the mobile station,
The inter-base station cooperative transmission method.