JP2014143734A - Radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize data transmission control in which base stations cooperate in consideration of efficient use of radio resources.SOLUTION: A radio communication system comprises: a first base station; a second base station connected to a wired network; and radio communication terminals which perform single data transmission for transmitting data by at least one of the base stations and cooperative data transmission for transmitting data by cooperation of the plurality of base stations. The base stations notify the radio communication terminals of a condition for cooperative data transmission. When communication quality of transmission path satisfies the condition, the radio communication terminal transmits necessary information for the cooperative data transmission to the base stations.

Description

  The present invention relates to a radio communication system having a plurality of base stations, and more particularly to a radio communication system in which a plurality of base stations cooperate to perform data transmission with one or more radio communication terminals.

  In wireless communication, the wireless communication terminal at the cell edge has a sufficient signal degradation due to the signal attenuation of the desired signal power from the base station to which it belongs and the interference to the adjacent base station. I can't get the rate. As a technique for solving this problem and improving the user rate of the cell edge wireless communication terminal, a base station cooperation technique is known in which base stations cooperate with each other to perform data transmission with the wireless communication terminal. It is the successor of 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) (Non-Patent Documents 1 and 2), which is widely adopted as the 9th generation wireless communication system in the world, and the 4th generation wireless communication. Base station cooperation technology is also expected to be included in the standard in LTE-A (Long Term Evolution-Advanced) (Non-patent Document 3), which is one of the system candidates.

  In 3GPP, base station cooperation technologies are classified into two types: Coordinated Scheduling and Joint Processing. Coordinated Scheduling uses BF (Beam Forming) for each base station to give strong directivity to transmitted signals, avoiding interference between adjacent base stations, and improving SINR Technology. On the other hand, Joint Processing is a technology that improves the transmission rate by allowing one terminal to transmit data to multiple base stations simultaneously. The transmission method when data transmission is performed simultaneously with a plurality of base stations includes site diversity in which a plurality of base stations transmit the same signal and improve desired signal power at the terminal, and a plurality of antennas possessed by the plurality of base stations. There is multi-point MIMO using MIMO transmission. Here, the operation of multipoint MIMO includes SU transmission (Single User transmission: select one wireless communication terminal and perform data transmission to that wireless communication terminal), MU-MIMO transmission (Multi User-MIMO transmission: MIMO Are used for data transmission to a plurality of wireless communication terminals). In the following description, OFDMA (Orthogonal Frequency Division Multiple Access) adopted in LTE downlink (downlink) as a radio resource multiplexing scheme is assumed. However, in the present specification, TDMA is not limited to OFDMA. (Time Division Multiple Access), CDMA (Code Division Multiple Access), and other multiplexing schemes are also applicable.

In SU transmission, a wireless communication terminal receives a pilot signal from a base station to which the wireless communication terminal belongs and an adjacent base station, and performs channel estimation. Further, based on the channel estimation result, the channel quality when using multipoint MIMO transmission, the number of MIMO ranks, and the desired precoding matrix are calculated. The wireless communication terminal transmits at least one of these and a list of base stations participating in the cooperative transmission to the base station to which the wireless communication terminal belongs by using an uplink (uplink) control signal. The base station that has received the information notifies the cooperation scheduler unit that is responsible for radio resource allocation in cooperation with the base station. Based on these pieces of information, the cooperative scheduler unit selects an optimum wireless communication terminal, data transmission method, subcarrier to be used, and the like, and notifies the result to the base station that performs cooperative transmission. The optimum wireless communication terminal can be selected separately for each OFDMA subcarrier. For example, when performing network MIMO transmission between the base stations 1 and 2 and the wireless communication terminals 1 and 2, in the subcarriers 1 to 12, both base stations perform multipoint MIMO communication to the wireless communication terminal 1, In the subcarriers 13 to 24, it can be considered that both base stations perform multipoint MIMO communication with the radio communication terminal 2.

Multi-point MIMO transmission methods for SU transmission include: (1) Open-Loop MIMO transmission that does not require precoding matrix specification from wireless communication terminals, and wireless communication terminals use MMSE (Minimum Mean) in the same way as normal MIMO Reception is performed by Square Error) or MLD (Maximum Likelihood Detection). (2) Use Closed-Loop MIMO transmission such as E-SDM (Eigen Space Division Multiplexing). (3) Transmit diversity using STTD (Space Time Transmit Diversity) can be used. In any case, each base station generates a signal based on each method after exchanging necessary data between base stations that perform cooperative transmission before transmission to the wireless communication terminal. Transmit to the wireless communication terminal. The wireless communication terminal decodes the signal based on the method selected by the base station and receives data. In any of the above methods (1) to (3), the wireless communication terminal subject to multipoint MIMO transmission receives its desired signal instead of interference from the base stations participating in the cooperation. Thus, the channel capacity is greatly improved.

  On the other hand, in MU-MIMO transmission, similarly to one wireless communication terminal transmission, a wireless communication terminal receives a pilot signal from a base station to which the wireless communication terminal belongs and an adjacent base station, and performs channel estimation. Furthermore, based on the channel estimation result, the channel quality when using multipoint MIMO transmission, the number of MIMO ranks, the desired precoding matrix, and the channel matrix with multiple base stations are calculated. The wireless communication terminal transmits at least one of these and a list of base stations participating in the cooperative transmission to the base station to which the wireless communication terminal belongs by using an uplink control signal. The base station that has received the information notifies the cooperation scheduler unit that is responsible for radio resource allocation in cooperation with the base station. Based on these pieces of information, the cooperative scheduler unit selects an optimal combination of wireless communication terminals, a data transmission method, a subcarrier to be used, and the like, and notifies the base station that performs cooperative transmission. The optimum combination of wireless communication terminals can be selected separately for each OFDMA subcarrier. For example, when performing network MIMO transmission between the base stations 1 and 2 and the wireless communication terminals 1, 2, and 3, both base stations perform network MIMO communication with the wireless communication terminals 1 and 2 in the subcarriers 1 to 12. In subcarriers 13 to 24, both base stations may perform network MIMO communication with the wireless communication terminals 2 and 3.

  As a multipoint MIMO transmission method in MU-MIMO transmission, (1) a ZF (Zero Forcing) method that performs precoding using an inverse matrix of a channel matrix on the transmission side is used (Non-patent Document 4). (2) Use DPC (Dirty Paper Coding), which improves channel capacity by utilizing information on interference signals. Etc. are considered. ZF can be realized with a simple principle, but depending on the inverse of the channel matrix, amplification exceeding the upper limit of the transmission power is required and there is a problem that the channel capacity deteriorates. On the other hand, DPC is superior to ZF in terms of channel capacity, but has the problem of a large amount of calculation. Therefore, a method using LQ decomposition is known as one of the DPC implementation methods. In this method, a channel matrix is decomposed into a product of a lower triangular matrix and a unitary matrix, and precoding by pre-equalization processing based on the lower triangular matrix and Hermitian transposition of the unitary matrix is performed on the transmission side. This procedure is a calculation amount that can be actually implemented, and a unitary matrix is used for precoding, so that the signal amplitude is not greatly amplified as in the case of ZF. As a result, in the wireless communication terminal, interference from the adjacent cell is canceled, so that the channel capacity is improved.

3GPP TS36.201 v8.1.0 (2007-11) 3GPP TS36.211, TS36.212, TS36.212 v8.4.0 (2008-9) 3GPP TR36.814 V0.0.1 (2008-9) Laurence Mailaender, "Indoor Network MIMO Performance with Regularized Zero-Forcing Transmission", IEEE ISSSTA 2008, pp.124-128, '08 / 8

  In general, a wireless communication terminal periodically transmits a control signal for notifying the base station of channel quality with the base station to which the wireless communication terminal belongs. Also, when performing MIMO transmission, it is necessary to transmit the number of MIMO ranks and the index of the desired precoding matrix. In addition, in order for base stations to perform data transmission in cooperation with each other, each wireless communication terminal uplinks the channel quality, the number of MIMO ranks, and the index of the desired precoding matrix when performing cooperative transmission. Must be periodically transmitted to the base station using the radio resources. Furthermore, when transmission to a plurality of radio communication terminals is performed, a channel matrix between the radio communication terminal and all base stations participating in the coordinated transmission must be transmitted to the base station using uplink radio resources. In this way, each wireless communication terminal consumes uplink wireless resources to transmit information necessary for the above-described cooperation to the base station. Therefore, as the number of wireless communication terminals belonging to the base station increases, the consumption of uplink radio resources used for information transmission necessary for cooperation increases, and as a result, the radio resources that can be used for uplink user data transmission are compressed. .

  In addition, in order to perform coordinated data transmission, the calculation amount required for radio resource allocation between base stations increases, that is, the processing amount of the cooperative scheduler unit increases. As an example, consider radio resource allocation to one resource block. Here, the resource block is a unit used for radio resource allocation, and is a set of continuous subcarriers. In data transmission by a single base station that does not use cooperation, an optimal wireless communication terminal for SU transmission, an optimal wireless communication terminal combination for MU-MIMO transmission, and a wireless communication terminal belonging to the base station You can choose from. On the other hand, in data transmission in which base stations cooperate with each other, an optimal wireless communication terminal or a combination thereof must be selected from all wireless communication terminals belonging to a plurality of base stations participating in the cooperation. In addition, there are multiple combinations of base stations that participate in cooperation and which of the above-described cooperation methods is adopted, and compared to radio resource allocation in a single base station, the complexity of radio resource allocation in cooperative transmission is Increase dramatically. Furthermore, since there are actually many resource blocks (for example, the maximum number of resource blocks in LTE is 110), radio resource allocation is complicated.

  In order to solve at least one of the above problems, a wireless communication system according to one embodiment of the present invention includes a first base station, a second base station connected by a wired network, and data transmission from one base station. A wireless communication terminal that performs at least one of single data transmission that is performed and cooperative data transmission that is performed in cooperation with a plurality of base stations, and the base station The wireless communication terminal is notified of the conditions shown, and when the communication quality of the propagation path matches the conditions, the wireless communication terminal transmits information necessary for cooperative data transmission to the base station.

  Here, the condition is, for example, that the communication quality of the propagation path is less than a certain threshold value.

  According to an aspect of the present invention, it is possible to allocate resources for transmission of other user data without being used as communication resource for information necessary for cooperative data transmission.

It is a sequence diagram until a wireless communication terminal transmits cooperation information with reference to a threshold value. It is a network block diagram which shows a radio | wireless communications system. It is a figure which shows the apparatus structural example of a base station. It is a figure which shows the apparatus structural example of a radio | wireless communication terminal. It is a figure which shows the structural example of a gateway apparatus. It is a figure which shows the flow (at the time of scheduling request reception) of the scheduler in a station. It is a figure which shows the flow (at the time of cooperation scheduling request | requirement reception) of the scheduler in a station. It is a figure which shows the flow (at the time of single transmission information reception) of the control signal process part in a base station. It is a figure which shows the flow (at the time of resource allocation result reception) of the control signal process part in a base station. It is a figure which shows the flow (at the time of resource allocation request reception) of the control signal process part in a base station. It is a figure which shows the flow (at the time of a cooperation information notification signal reception) of the control signal process part in a base station. It is a figure which shows the flow (at the time of resource allocation result reception) of the data signal processing part in a base station. It is a figure which shows the flow (at the time of user data reception) of the data signal processing part in a base station. It is a figure which shows the flow (at the time of resource allocation signal reception) of the control signal process part in a terminal. It is a figure which shows the flow (at the time of threshold value notification signal reception) of the control signal process part in a terminal. It is a figure which shows the flow of a cooperation scheduler part. It is a figure which shows the packet format of a threshold value notification signal. It is a figure which shows the packet format of a resource allocation signal. It is a figure which shows the packet format of a cooperation information notification signal. It is a figure which shows the packet format (for MU-MIMO) of a cooperation information notification signal. It is a figure which shows the sequence of the cooperative transmission by MU-MIMO. It is a figure which shows the sequence of the cooperation transmission using SU transmission. It is a figure which shows the sequence by Coordinated Scheduling. It is a figure which shows the sequence at the time of using spreading | diffusion for a cooperation information notification signal. It is a figure which shows the packet format example of the option part of a threshold value notification signal. 6 is a graph showing how the number of bits used for one feedback change per wireless communication terminal when the cooperative wireless communication terminal rate is changed in the first embodiment. 6 is a graph showing the uplink radio resource bandwidth in bits per radio communication terminal used for one feedback when the cooperative radio communication terminal rate is changed. It is a figure which shows the database used for cooperation scheduling. It is a figure which shows a CQI distribution table. It is a figure which shows a network block diagram when a certain Backhaul line cannot be used.

  The following examples are based on the assumption that OFDMA is used for multiplexing in downlink data transmission and SC-FDMA (Single Carrier-Frequency Division Multiple Access) is used for multiplexing in uplink data transmission with reference to 3GPP LTE. However, the scope of application of the present invention is not limited to a wireless communication system using these systems, and can be applied to other multiplex communication systems such as CDMA and TDMA.

  In the present embodiment, based on information necessary for single base station transmission periodically transmitted by a wireless communication terminal (hereinafter referred to as single transmission information), data transmission in which bases cooperate ( Hereinafter, it will be described as cooperative transmission.) A sequence for determining the presence / absence threshold value and notifying the result to the wireless communication terminal will be described. Regarding the determination of the threshold value for the presence / absence of cooperative transmission, a process for determining that the total amount of information necessary for cooperative transmission (hereinafter referred to as cooperative information) transmitted by the wireless communication terminal does not exceed a predetermined value. Also explained.

  Prior to the description of the sequence, an overall network configuration and a block diagram of the base station and the wireless communication terminal will be described first.

  FIG. 2 shows a network configuration corresponding to the wireless communication system of the present embodiment. In the wireless communication system, a plurality of base stations 100 are arranged to constitute cells, and wireless communication terminals 200 belonging to each base station 100 are scattered in the cells. Each base station 100 is connected to the core network 1 via the gateway device 2. It is assumed that the base station 100 and the gateway device 2 are wired using an optical fiber or the like (however, even if the connection between the base station 100 and the gateway device 2 is wireless, application of this embodiment is hindered) Absent). In addition, the gateway device 2 includes a cooperative scheduler unit 190 responsible for radio resource allocation in cooperative transmission, and each base station 100 includes a communication IF (Interface) with the cooperative scheduler unit. In the following description, the cooperative scheduler unit 190 will be described as being disposed in the gateway device 2. However, the cooperative scheduler unit 190 may be installed separately as an individual device or in any one of the base stations 100. It can be installed, and in any case, application of this embodiment is not hindered.

  FIG. 3 is a diagram illustrating a device configuration example of the base station 100. As illustrated in FIG. The user data addressed to the radio communication terminal 200 received from the gateway device 2 is accumulated in the buffer of the data signal processing unit 101, and transferred to the signal transmission unit 110 as soon as radio resources are allocated. On the other hand, the user data transferred from the signal receiving unit 120 to the data signal processing unit 101 is transferred to the core network 1 via the gateway device 2. Further, the control signal processing unit 102 transmits and receives control signals between the base station 100 and the radio communication terminal 200 via the signal transmission unit 110 and the signal reception unit 120 as necessary. The in-station scheduler 105 manages radio resource allocation for single base station transmission, performs scheduling based on information from the data signal processing unit 101 and the control signal processing unit 102, and notifies the result. Further, in order to realize cooperative transmission, the intra-station scheduler 105 includes a cooperative scheduler unit IF (Interface) 106 that is an interface with the cooperative scheduler unit 190, and the data signal processing unit 101 is another base station that performs cooperative transmission. A coordinated base station IF107, which is an interface with 100, is provided.

  When the signal transmission unit 110 receives the data signal from the data signal processing unit 101 or the control signal from the control signal processing unit 102, the signal generation unit 111 first performs processing such as error correction coding, modulation, precoding, etc. Generate symbols to be transmitted from the antenna. Subcarrier map section 112 allocates this symbol to any subcarrier in any OFDMA symbol. Next, pilot insertion section 113 inserts pilot symbols used by radio communication terminal 200 for downlink channel estimation at appropriate positions. Finally, the OFDM modulator 114 performs IDFT (Inverse Discrete Fourier Transform) processing and CP (Cyclic Prefix) insertion, and outputs a baseband OFDM signal. The baseband OFDM signal output from the signal transmission unit 110 is sent to the RF processing unit 103, and is independently subjected to digital-analog conversion, up-conversion, and amplification processing, and transmitted from the antenna 104 to the radio communication terminal 200.

  On the other hand, when antenna 104 receives a signal from radio communication terminal 200, RF processing section 103 performs amplification processing, down-conversion, and analog-digital conversion processing, and sends the result to SC-FDMA demodulator 124. SC-FDMA demodulator 124 performs CP removal, DFT processing, and IDFT processing for SC-FDM reception, sends the pilot signal portion of the output to channel estimation section 131, and sends the rest to MIMO receiver 123 . Channel estimation section 131 performs uplink channel estimation based on the pilot signal, and sends the estimated channel matrix to MIMO receiver 123 and CQI / PMI / RI calculation section 132. MIMO receiver 123 performs MIMO reception processing using MMSE and MLD on the output of SC-FDMA demodulator 124 based on this channel matrix, and sends the output for each layer to inverse subcarrier map section 122.

Inverse subcarrier map section 122 performs processing opposite to that performed by subcarrier map section 212 in radio communication terminal 200, and outputs a received symbol sequence. The signal decoding unit 121 performs demodulation and error correction decoding processing on this output, and among the signals obtained as a result, the user data signal is sent to the data signal processing unit 101 and the control signal is sent to the control signal processing unit 102. Also, the CQI / PMI / RI calculation unit 132 performs uplink CQI (Channel Quality Indication: Channel Quality), PMI (Precoding Matrix Indicator: precoding matrix desired by the wireless communication terminal), RI (Rank) based on the channel matrix. Indication: rank in MIMO transmission) is calculated and notified to the control signal processing unit 102. The notified CQI, PMI, and RI are held in the control signal processing unit 102 or held in a memory that can be referred to by the control signal processing unit 102.
Operation flows of the in-station scheduler 105, the control signal processing unit 102, and the data signal processing unit 101 in the base station 100 will be described with reference to FIGS. 6, 7, and 8, respectively.

FIG. 6A shows an operation flow when the in-station scheduler 105 receives a scheduling request (FIG. 7C: 342, FIG. 8B: 362) from the control signal processing unit 102 or the data signal processing unit 101. When the in-station scheduler 105 receives the scheduling request (FIG. 6A: 301), the in-station scheduler 105 first determines whether it is a downlink or uplink scheduling request (302). If it is a downlink scheduling request, the intra-station scheduler 105 determines whether to perform cooperative transmission (303). Specifically, when the cooperation information of the corresponding wireless communication terminal 200 has been acquired and the necessary QoS (Quality of Service) cannot be satisfied without cooperation, it is determined that cooperative transmission is performed. The future operation branches depending on the determination result (304). If it is determined that coordinated transmission is necessary, the intra-station scheduler 105 requests the coordinated scheduler unit 190 for coordinated scheduling via the coordinated scheduler unit IF106 (305). After that, when the intra-station scheduler 105 receives the cooperative scheduling result (FIG. 10: 410) from the cooperative scheduler unit 190 (306), the intra-station scheduler 105 notifies the control signal processing unit 102 and the data signal processing unit 101 of the result. (308, 309), and the process ends (310). On the other hand, if it is determined that the coordinated transmission is unnecessary (No in 304), the in-station scheduler 105 simply determines based on the received data information (eg, data amount, QoS, etc.) and downlink CQI, PMI, RI. Radio resource allocation by one base station transmission is performed (307).
Then, the in-station scheduler 105 sends the radio resource allocation result to the control signal processing unit 102 at 307,
The data signal processing unit 101 is notified (308, 309), and the processing ends (310). On the other hand, if it is an uplink scheduling request at 302, the intra-station scheduler 105 allocates radio resources by single base station transmission based on received data information (for example, QoS) and uplink CQI, PMI, and RI. (307), the result is notified to the control signal processing unit 102 and the data signal processing unit 101 (308, 309), and the processing ends (310).

  FIG. 6B is an operation flow when the in-station scheduler 105 receives the cooperation scheduling result notified by the cooperation scheduler unit 190 (FIG. 10: 410). When the in-station scheduler 105 receives the cooperative scheduling result (FIG. 6B: 311), it notifies the control signal processing unit 102 and the data signal processing unit 101 of the result (312, 313), and ends the processing (314). In FIG. 6A, when it is determined that coordinated transmission is performed in its own base station and a coordinated scheduling request is made (305, 306), the coordinated scheduling result is accepted (305, 306). This is an example (313) of accepting a cooperation scheduling result when a cooperation data transfer is requested from.

  FIG. 7A is an operation flow when the control signal processing unit 102 of the base station receives single transmission information from the radio communication terminal 200. When receiving the single transmission information (321), the control signal processing unit 102 extracts the CQI value in the single transmission included therein. In addition, as CQI, there are Wideband CQI indicating the quality of all bands and subband CQI indicating CQI for each subband. However, in the following explanation, Wideband CQI is targeted, and it is simply described as CQI. . Then, the control signal processing unit 102 updates the CQI distribution table owned by itself based on the CQI value (322).

  Here, the CQI distribution table is the table shown in FIG. This table shows a histogram of CQI values of the wireless communication terminals 200 belonging to the base station 100, and shows the number of wireless communication terminals (562) for each CQI value (561). This CQI distribution table is held in the control signal processing unit 102 or held in a storage medium such as a memory that can be referred to by the control signal processing unit 102 itself.

  That is, at 322 in FIG. 7A, the control signal processing unit 102 increases the number of terminals corresponding to the received CQI value by 1, and updates the CQI distribution table.

  Next, the control signal processing unit 102 refers to the CQI distribution table and determines whether the number of wireless communication terminals 200 satisfying “CQI <cooperative transmission threshold” exceeds a preset default value (323). Specifically, if the number of wireless communication terminals (562) whose CQI value (561) is i is n (i), “Σ_ {i = 0: threshold} n (i)> default value” is satisfied. It is determined whether or not to do. Note that the predetermined value here is determined in advance based on the amount of uplink radio resources allocated to the link information transmission and the allowable amount of interference. If this result is exceeded (Yes in 323), this means that the number of radio communication terminals 200 that transmit the cooperative transmission information notification signal is excessive, and the uplink radio resources are compressed. Therefore, in order to avoid this, the control signal processing unit 102 decreases the value of the cooperative transmission threshold so that the number of wireless communication terminals 200 satisfying “CQI <cooperative transmission threshold” does not exceed a preset default value. (324). Specifically, the maximum I that satisfies “Σ_ {i = 0: I} n (i) <predetermined value” is set as the value of the cooperative transmission threshold. On the other hand, if the determination result of 323 is No (No), this means that there is a margin in uplink radio resources necessary for the cooperative transmission information notification signal. Therefore, in this case, the control signal processing unit 102 increases the number of wireless communication terminals that transmit the cooperative transmission information notification signal by increasing the value of the cooperative transmission threshold (325). It is not always necessary to increase the number, and the current state may be maintained. If the cooperative transmission threshold is updated (326), the control signal processing unit 102 transmits a threshold notification signal to the wireless communication terminal 200 in order to inform the terminal of the update (327). ), The process is terminated (328). On the other hand, if the cooperative transmission threshold is not updated, the process is terminated without transmitting the threshold notification signal.

  In FIG. 7, the threshold value to be transmitted to the terminal is determined with reference to the CQI distribution table. However, the threshold value may be determined by another determination method or set by an external input. May be good.

  FIG. 7B is an operation flow when the control signal processing unit 102 receives an intra-station scheduler resource allocation result (FIG. 6A: 308, FIG. 6B: 312). When the resource allocation result is received (331), the control signal processing unit 102 repeats the following processing for all the wireless communication terminals specified by the resource allocation result (332). First, the control signal processing unit 102 checks whether or not radio resources are allocated to the corresponding radio communication terminal 200 (333), and if so, generates a resource allocation signal (334). Here, the resource allocation signal is a signal for notifying the radio communication terminal 200 of the allocated radio resource, and its packet format will be described later with reference to FIG. 11B. On the other hand, the control signal processing unit 102 suspends data transmission until the next transmission timing for the radio communication terminal 200 to which no resource is allocated (335). If the next transmission timing is LTE, for example, the next subframe transmission may be considered. When the above processing is repeated for all the wireless communication terminals (336), the generated resource allocation signal is transmitted (337), and the processing is terminated (338).

  FIG. 7C is an operation flow when the control signal processing unit 102 receives a resource allocation request signal from the wireless communication terminal 200 (341). At this time, uplink scheduling is requested to the in-station scheduler 105 (342), and the process ends (343).

  FIG. 7D is a flow when the control signal processing unit 102 receives the cooperation information notification signal transmitted by the wireless communication terminal 200 (FIG. 9B 385). Receiving this (346), the control signal processing unit 102 updates the cooperation information to be held (347) and ends the processing (348). Details of the format and the like of the cooperation information notification signal will be described later with reference to FIG.

  FIG. 8A is an operation flow when the data signal processing unit 101 of the base station receives the resource allocation result (FIG. 6A: 309, FIG. 6B: 313) from the in-station scheduler. When the resource allocation result is received (351), first, the data signal processing unit 101 determines whether the resource allocation is for the downlink or the uplink (352). If it is a downlink signal, the data signal processing unit 101 further determines whether or not to perform coordinated transmission (353). If coordinated transmission is performed, the data signal processing unit 101 communicates with other base stations 100 participating in the coordinated transmission. Necessary user data is exchanged (354). Thereafter, the data signal processing unit 101 transfers necessary data from the buffer in the data signal processing unit 101 to the signal transmission unit 110 regardless of whether or not it cooperates (355), and ends the processing (357). On the other hand, if the resource allocation is uplink, the data signal processing unit 101 reserves a buffer in preparation for data reception (356).

  FIG. 8B is an operation flow when the data signal processing unit 101 receives user data addressed to the wireless communication terminal 200 from the gateway device 2. When user data is received (361), downlink scheduling is requested to the in-station scheduler 105 (362), and the process is terminated (363).

  Next, an apparatus configuration diagram of the wireless communication terminal 200 will be described with reference to FIG. User data generated by an upper layer such as a MAC (Medium Access Control) layer in the wireless communication terminal 200 is stored in the buffer of the data signal processing unit 201 and transferred to the signal transmission unit 210 as soon as radio resources are allocated. On the other hand, the user data transferred from the signal receiving unit 220 to the data signal processing unit 201 is passed to the upper layer. In addition, the control signal processing unit 202 transmits and receives control signals between the base station 100 and the wireless communication terminal 200 via the signal transmission unit 210 and the signal reception unit 220 as necessary.

  When the signal transmission unit 210 receives the data signal from the data signal processing unit 201 or the control signal from the control signal processing unit 202, the signal generation unit 211 first performs processing such as error correction coding, modulation, and precoding. A symbol to be transmitted from each antenna is generated. Subcarrier map section 212 allocates the output symbols to any subcarrier in any SC-FDMA symbol. Next, pilot insertion section 213 inserts pilot symbols used by base station 100 for uplink channel estimation at appropriate positions.

  Finally, the SC-FDMA modulator 214 performs SC-FDMA DFT processing, IDFT processing, and CP insertion, and outputs a baseband SC-FDMA signal. The signal transmission unit 210 sends the output baseband SC-FDMA signal to the RF processing unit 203, and the RF processing unit 203 performs digital-analog conversion, up-conversion, and amplification processing of the baseband SC-FDMA signal independently of each other. Transmission is performed from the application antenna 204 toward the base station 100.

  On the other hand, when the antenna 204 receives a signal from the base station 100, the RF processing unit 203 performs amplification processing, down-conversion, and analog-digital conversion processing on the signal, and sends the signal to the OFDM demodulator 224. OFDM demodulator 224 performs CP removal and DFT processing, sends the pilot signal portion of the output to channel estimation section 231, and sends the rest to MIMO receiver 223. The channel estimation unit 231 performs downlink channel estimation based on the pilot signal, and sends the estimated channel matrix to the MIMO receiver 223 and the CQI / PMI / RI calculation unit 232.

  Based on this channel matrix, MIMO receiver 223 performs MIMO reception processing using MMSE or MLD on the output of OFDM demodulator 224, and sends the output for each layer to inverse subcarrier map section 222. Inverse subcarrier map section 222 performs processing opposite to that performed by subcarrier map section 112 in base station 100, and outputs a received symbol sequence. The signal decoding unit 221 performs demodulation and error correction decoding processing on this output, and sends the resulting signal to the data signal processing unit 201 for the user data signal and to the control signal processing unit 202 for the control signal. Also, the CQI / PMI / RI calculation unit 232 calculates downlink CQI, PMI, and RI based on the channel matrix and notifies the control signal processing unit 202 of them.

The threshold included in the threshold notification signal transmitted from the CQI, PMI, RI or base station is the control signal processor
202 is held by itself, or is held in a memory to which the control signal processing unit 202 can refer.

  FIG. 9A is an operation flow when the control signal processing unit 202 in the radio communication terminal 200 receives a resource allocation signal (FIG. 7B: 337) transmitted by the base station 100. When a resource allocation signal is received (371), it is determined whether the resource allocation is downlink or uplink (372). If it is for the downlink, a command for data reception is issued to the data signal processing unit 201 (373), and if it is for the uplink, the data signal processing unit 201 is requested to transmit data (374) and the processing ends. (375).

  FIG. 9B is an operation flow when the control signal processing unit 202 receives the threshold notification signal transmitted by the base station 100 (FIG. 7A: 327). When the threshold notification signal is received (381), the control signal processing unit 202 extracts the cooperative transmission threshold included in the signal (382), and compares the CQI of the wireless communication terminal itself with the notified cooperative transmission threshold (383). ). As a result, if the CQI of the wireless communication terminal itself is smaller than the cooperative transmission threshold value, the control signal processing unit 202 determines that the wireless communication terminal itself is eligible to transmit cooperative information to the base station. Therefore, the control signal processing unit 202 requests an uplink resource for transmitting cooperation information (384), and transmits a cooperation information notification signal using the allocated resource (385). On the other hand, if the comparison result of 382 indicates that its own CQI is equal to or greater than the cooperative transmission threshold, the wireless communication terminal itself determines that it is not qualified to transmit the cooperative information to the base station, and ends the processing as it is (386).

  In FIG. 9B, the control signal processing unit 202 compares the processing of 382 and 383, that is, its own CQI and the threshold at an arbitrary timing of the wireless communication terminal, not when the threshold notification signal is received, and requires cooperation. A determination of NO may be made. For example, the necessity of cooperation may be determined at a timing such as when re-acquiring its own CQI or when acquiring information indicating that the use of uplink resources is low. Further, the threshold value may not be received from the base station, and may be held in advance in the wireless communication terminal.

Next, the cooperative scheduler 190 will be described with reference to FIGS. As shown in FIG. 5, the cooperative scheduler unit 190 is configured in the gateway device 2 and also includes an IF 191. And
The IF 191 is connected to the in-station scheduler via a link scheduler IF 106 in the base station 100). In FIG. 2 and FIG. 5, the base station 100 and the gateway device 2 are connected by wire, but wireless may be used. Further, in this embodiment, the cooperation scheduler unit 190 is configured in the gateway device 2, but other than the gateway device 2, it can be configured as a device that controls the cooperation of a plurality of base stations, or any one of the plurality of base stations. The representative base station may be configured.

  FIG. 19 is an example of a database to be referred to when the cooperative scheduler unit 190 performs radio resource allocation. This database stores the arrival time 552 of user data, the amount of data 553, the instantaneous throughput 554 and the average throughput 555 when cooperative transmission is performed for the wireless communication terminal 200 designated by 551. The cooperation scheduler 190 calculates the amount of wireless resources that require data based on the data arrival time 552 and the data amount 553, and determines the priority of each wireless communication terminal 200 based on the cooperation instantaneous throughput 554 and the average throughput 555. As a method for determining the priority, a method using Proportional Fairness for selecting the radio communication terminal 200 having a large value obtained by dividing the cooperative instantaneous throughput 554 by the average throughput 555 can be considered. Note that the database shown in FIG. 19 is an example, and this database may take other configurations.

  FIG. 10 shows an operation flow when the cooperative scheduler unit 190 receives the cooperative scheduling request requested by the intra-station scheduler 105 (FIG. 6A: 305). Upon receiving the cooperation scheduling request (401), the cooperation scheduler unit 190 first selects one or more wireless communication terminals 200 having a high priority (402). This selection method uses Proportional Fairness using the database of FIG. 19 as described above. The subsequent processing is repeated for all wireless communication terminals that require cooperation (403). First, the cooperative scheduler 190 determines whether or not MU-MIMO transmission is possible (404), and if possible, allocates radio resources by MU-MIMO transmission (407). If the MU-MIMO transmission is not possible, the cooperative scheduler unit 190 determines whether or not radio resource allocation in SU transmission is possible (405), and if possible, allocates radio resources in SU transmission (406). . When the above processing is completed, or when radio resources are not allocated to the corresponding radio communication terminal 200, the coordination scheduler unit 190 gives up radio resource allocation to the radio communication terminal 200, and then determines the priority. One or more expensive wireless communication terminals 200 are selected (408). Then, the cooperation scheduler 190 repeats the above processing until the processing for the corresponding wireless communication terminal 200 is completed or there are no radio resources that can be allocated (409). When this repetition is completed, the cooperation scheduler unit 190 notifies the intra-station scheduler 105 of the radio resource allocation result as a cooperation scheduling result (410), and ends the processing (411). Note that the operation flow of the cooperative scheduler operation 190 is an example, and may be based on another scheduling rule.

  Next, with reference to FIGS. 11 and 12, a packet format necessary for performing data transmission in cooperation between base stations will be described. FIG. 11A shows a packet format of a threshold notification signal that base station 100 transmits to radio communication terminal 200. This packet format defines conditions for data transmission in which base stations cooperate with each other. The format identifier 501 is used for distinction from other control signals. The threshold type 502 is used to specify the type of threshold stored in this signal. Examples of types here include Wideband CQI and subband CQI. In the threshold 503, the cooperative transmission threshold is stored. The cooperative transmission threshold is determined by the flow of FIG. 7A, for example. In this embodiment, the threshold value is determined and updated based on the CQI distribution. However, a value determined in advance may be set instead of the CQI distribution.

  Option 504 is a field that can be used for other extensions.

  FIG. 11B is a packet format of a signal (resource allocation signal) in which base station 100 notifies the result of radio resource allocation to radio communication terminal 200 to which radio resources for coordinated transmission are allocated by coordinated scheduler unit 190. . The format identifier 521 is used to distinguish from other control signals. Allocation resource block designation 522 designates the location of a downlink resource block for base station to perform data transmission in cooperation with the corresponding wireless communication terminal 200. The resource block in this case refers to a plurality of consecutive OFDMA symbols and a plurality of consecutive subcarriers within those OFDMA symbols, and is used as a unit of downlink radio resource allocation. The power control 523 is a field related to power control. The HARQ information 524 notifies a process number in HARQ (Hybrid Automatic Repeat Request) transmission. The transport block-specific information 525 is a field that exists as many as the number of transport blocks to be transmitted, and includes an MCS 525-1 for each transport block and a new HARQ bit 525-2 that distinguishes whether or not HARQ is newly transmitted.

  The cooperative information 526 stores a base station that performs cooperative transmission, a transmission method used for cooperative transmission, and the like. Precoding information 527 stores an index of a precoding matrix used for cooperative transmission or a quantized value.

  FIG. 12 is a packet format of a cooperation information notification signal transmitted from the wireless communication terminal 200 to the cooperation scheduler unit 190 via the base station 100. FIG. 12A is for Open-Loop MIMO, and FIG. The one for MIMO is shown. The cooperation information notification signal according to these packet formats includes information necessary for cooperation.

  First, each field of the packet format in FIG. 12A will be described. The cooperation method 531 is a field for designating a transmission method used for cooperative transmission. Cooperation base station set 532 notifies the set of base stations 100 used for cooperation. The wideband CQI 533 for cooperation notifies CQI in all OFDMA subcarriers when the cooperative transmission designated by the cooperation method 531 is performed. There are as many subband-specific information 534 as there are subbands, and a subband CQI534-1 for cooperation that stores CQI for each subband when cooperative transmission is performed, and for each subband when cooperative transmission is performed. It consists of a coordination subband RI534-2 that stores RI.

  Next, each field of the packet format in FIG. 12B will be described. The cooperation method 541 is a field for designating a transmission method used for cooperative transmission. The cooperation base station set 542 notifies the set of base stations used for cooperation. The wideband CQI 543 for cooperation notifies CQIs for all OFDMA subcarriers when cooperative transmission specified by the cooperation method 541 is performed. The subband-specific information 544 exists as many as the number of subbands, and is a propagation matrix that is a field for storing a value obtained by quantizing the propagation matrix between the base station 100 and the wireless communication terminal 200 specified by the cooperative base station set 542 Includes 544-1.

  Next, a data transmission sequence in which base stations cooperate with each other by MU-MIMO transmission will be described with reference to FIGS. By the time this sequence is started, all the radio communication terminals 200-1 to 200-6 analyze the synchronization signal, and both the synchronization information and cell IDs of the base stations 100-1 and 100-2 with both base stations are analyzed. It is assumed that information necessary for data transmission with the base station has been acquired. Here, radio communication terminals 200-1, 200-2, 200-3 belong to the cell of base station 100-1, and radio communication terminals 200-4, 200-5, 200-6 belong to base station 100-2. Assume that you belong to a cell. Base stations 100-1 and 100-2 regularly transmit pilot signals (601-1 and 601-2), and each wireless communication terminal monitors them and both base stations 100-1 and 100- Calculate the channel matrix from 2. In calculating this channel matrix, interference components from the base station to which it does not belong (for example, the base station 100-2 for the wireless communication terminal 200-1) may be an obstacle. Avoid by some means. Here, as an example of known avoidance means, in a resource in which a certain base station transmits a pilot signal, other base stations refrain from data transmission. After the pilot is spread, the wireless communication terminal performs despreading. Means for improving the SINR are known and any of them may be used.

  Each wireless communication terminal calculates CQI / PMI / RI when performing single base station transmission by the base station to which it belongs based on the channel matrix calculated above, and uses the result as single transmission information. As feedback to the base station to which it belongs using the control signal channel (602-1 to 602-6). Receiving this, the base stations 101 and 102 generate a threshold notification signal and transmit it to the wireless communication terminals according to the flow of FIG. 7A (603-1, 603-2). The wireless communication terminals 200-1 to 200-6 that have received this compare the cooperative transmission threshold (FIG. 11A: 503) included in the threshold notification signal with its own CQI according to the flow of FIG. Decide whether to send

  Hereinafter, it is assumed that the two wireless communication terminals 200-3 and 200-5 transmit the cooperation information notification signal. The wireless communication terminals 200-3 and 200-5 request uplink resources from the base stations 100-1 and 100-2, respectively, in order to transmit the cooperation information notification signal (604-3 and 604-5), Receiving this, base stations 100-1 and 100-2 perform uplink resource allocation according to FIG. 7C (605-3 and 605-5). Thereafter, the wireless communication terminals 200-3 and 200-5 feed back the cooperation information notification signal (using the format of FIG. 12B) to the base stations 100-1 and 100-2 using the allocated resources (606- 3, 606-5).

  FIG. 13 is a sequence from when the user data addressed to the wireless communication terminal arrives at the base station after the sequence of FIG. 1 until actually performing cooperative transmission by MU-MIMO transmission. In the sequence of FIG. 1, since the base stations 100-1 and 100-2 have acquired cooperation information of the wireless communication terminals 200-3 and 200-5, respectively, cooperative transmission is performed for these two wireless communication terminals. Attempts to perform single base station transmission for other wireless communication terminals. First, user data addressed to wireless communication terminals 200-1, 200-2, 200-3 arrives at base station 100-1 (611-1), and wireless communication terminals 200-4, 200-5 arrive at base station 100-2. , 200-6 user data arrives (611-2). In response to this, the in-station scheduler 105 of each base station performs scheduling by single base station transmission for the radio communication terminals 200-1, 200-2, 200-4, and 200-6, respectively. However, at this time, information on BF (Beam Forming) beams such as beam forming patterns may be exchanged with neighboring base stations through the associated base station IF 107 and used for scheduling (612).

  On the other hand, the base stations 100-1 and 100-2 request cooperative scheduling from the cooperative scheduler unit 190 via the cooperative scheduler unit IF106 in order to perform cooperative transmission to the radio communication terminals 200-3 and 200-5. (613-1, 613-2). When the cooperation scheduler unit 190 accepts this request, according to the flow of FIG. 10, radio resources are allocated to the radio communication terminals 200-3 and 200-5 by cooperative transmission, and the result is notified to the base stations 100-1 and 100-2. (614-1, 614-2). Receiving this, the base stations 100-1 and 100-2 exchange user data necessary for the designated cooperative transmission through the cooperative base station IF 107 (615). Thereafter, the base station transmits user data together with a resource allocation signal to the wireless communication terminal. Specifically, base station 100-1 performs user data transmission by single base station transmission to radio communication terminals 200-1 and 200-2 (616-1, 616-2), and base station 100 -2 performs user data transmission by single base station transmission to the radio communication terminals 200-4 and 200-6 (616-4 and 616-6). Furthermore, the base station 100-1 and the base station 100-2 perform user data transmission by cooperative transmission to the line communication terminals 200-3 and 200-5 using MU-MIMO (617). The wireless communication terminals 200-1 to 200-6 that have received this perform user data reception processing according to the resource allocation signal. Thereafter, the wireless communication terminals 200-1 to 200-3 return an ACK signal indicating the reception result to the base station 100-1, and the wireless communication terminals 200-4 to 200-6 return an ACK signal indicating the reception result (618). -1 to 618-6).

  As a result, only the wireless communication terminals 200-3 and 200-5 that require cooperative transmission can perform cooperative transmission by feeding back the cooperative information to the base station. Therefore, uplink radio resources can be saved compared to the case where all the radio communication terminals feed back the cooperation information, and the amount can be used for transmission of other uplink user data.

  In addition, the cooperation scheduler unit 190 only needs to perform the cooperation scheduler processing for the radio communication terminals 200-3 and 200-5, and thus reduces the processing amount of the cooperation scheduling, which has a larger calculation amount than the single base station transmission scheduling. I can do things.

  FIG. 18 shows that when this embodiment is applied, the ratio of wireless communication terminals 200 that perform cooperative transmission to all wireless communication terminals 200 (hereinafter referred to as the cooperative wireless communication terminal rate) It is a graph which shows how the feedback amount to transmit changes. FIG. 18A shows how the number of bits used in one feedback per wireless communication terminal changes when the cooperative wireless communication terminal rate is changed based on the packet format of the cooperation information notification signal in FIG. 12A. It is a graph. However, the linkage method and the linkage base station set (Fig. 12A: 531 and 532) are combined with 4 bits, Wideband CQI for linkage (533) with 4 bits, Subband CQI for linkage and RI for linkage (534-1, 534-2) is combined into 3 bits. 901, 902, 903, and 904 in FIG. 18A indicate the results when the number of subbands is 5, 13, 21, and 28, respectively. When the cooperative wireless communication terminal rate is 1.0, it is equal to the result when this embodiment is not applied, and it can be confirmed that the number of feedback bits is reduced by applying this embodiment.

  FIG. 18B shows, based on the packet format of the cooperation information notification signal of FIG. 12B, when the cooperation wireless communication terminal rate is changed, the uplink wireless resource band used by one feedback per wireless communication terminal in bits. It is a represented graph. However, the cooperative method and the cooperative base station set (Figure 12B: 541, 542) are combined with 4 bits, Wideband CQI for cooperation (543) is 4 bits, and the channel matrix (544-1) is 12 (6 × 2) bits. It is said. In FIG. 21 (b), 911, 912, 913, and 914 indicate the results when the number of subbands is 5, 13, 21, and 28, respectively. When the cooperative wireless communication terminal rate is 1.0, it is equal to the result when this embodiment is not applied, and it can be confirmed that the number of feedback bits is reduced by applying this embodiment.

  As described above, in this embodiment, each wireless communication terminal transmits information necessary for single base station transmission to the base station at a certain timing, but does not transmit information necessary for cooperative transmission at that timing. Each base station determines a threshold used to determine whether or not the wireless communication terminal feeds back information necessary for cooperative transmission based on information necessary for single transmission collected from the wireless communication terminals. This threshold value is dynamically changed by the base station so that uplink radio resources are not compressed by feedback of information necessary for cooperative transmission. The base station notifies the determined threshold to the wireless communication terminal. The wireless communication terminal that has received this compares this communication quality with this threshold, and if the communication quality is inferior to the threshold, the wireless communication terminal determines that it is eligible to participate in cooperative transmission, and information necessary for cooperative transmission. Feedback. On the other hand, if the communication quality of itself exceeds the threshold value, feedback of information necessary for cooperative transmission is not performed, and as a result, data transmission by a single base station is received.

  According to the present embodiment, it is not necessary for all wireless communication terminals to periodically transmit information necessary for cooperative transmission to the base station, and wireless communication terminals that cannot secure sufficient communication quality by single transmission, that is, cooperative transmission is necessary. The wireless communication terminal is transmitting information necessary for cooperative transmission to the base station. In addition, when the base station appropriately sets a threshold value, the number of wireless communication terminals that feed back information necessary for cooperation can be controlled. Therefore, there is an effect that the amount of uplink radio resources used by the cooperation information transmission is reduced, and the amount of radio resources available for uplink transmission of user data is increased.

  In addition, the cooperative scheduler unit does not perform the radio resource allocation process for all radio communication terminals, but may perform radio resource allocation by cooperative transmission for radio communication terminals that require coordinated transmission. There is an effect that the accompanying increase in the processing amount can be reduced.

  In this embodiment, a data transmission sequence in which base stations cooperate with each other by SU transmission will be described with reference to FIG. Prior to the sequence of FIG. 14, the base stations 100-1 and 100-2 acquire the cooperation information notification signals from the radio communication terminals 200-3 and 200-5 according to the sequence of FIG. 1, as in the first embodiment. It shall be. 14, user data arrival to base stations 100-1 and 100-2 (611-1 and 611-2), BF beam information exchange (612), and cooperation schedule request to cooperation scheduler unit 190 (613 -1, 613-2) The process up to this point is the same as in Example 1.

  In this embodiment, as a result of cooperative scheduling, base stations 100-1 and 100-2 perform cooperative transmission by SU transmission to wireless communication terminal 200-3, and give up data transmission to wireless communication terminal 200-5 (actual Is suspended until the next transmission timing.) It is assumed that the base station 100-1 and 100-2 are notified of this decision (621-1, 621-2). In response, the base station 100-1 transfers the user data of the wireless communication terminal 200-3 to the base station 100-2 (622). Further, exactly as in the first embodiment, the base station 100-1 is a resource allocation signal to the radio communication terminals 200-1 and 200-2, and the base station 100-2 is And user data are transmitted by single base station transmission (616-1, 616-2, 616-4, 616-6). Further, the base stations 100-1 and 100-2 transmit user data to the wireless communication terminal 200-3 by cooperative transmission using SU transmission (623). Thereafter, the wireless communication terminals 200-1 to 200-3 return an ACK signal indicating the reception result to the base station 100-1 (618-1 to 618-3), and the wireless communication terminals 200-4 and 200-6 An ACK signal indicating the reception result is returned to the base station 100-2 (618-4, 618-6).

  As a result, as in the first embodiment, uplink radio resources can be saved because only limited radio communication terminals feed back cooperation information.

  In addition, the processing amount required for cooperative scheduling can be reduced.

In addition, although the radio communication terminal 200-5 is deferred in resource allocation until the next transmission timing, the radio communication terminal 200-3 can occupy two base stations 100-1 and 100-2. From the standpoint of -3, the throughput improvement in cooperative transmission is higher than in the first embodiment.

  In this embodiment, a sequence when using BF in which base stations cooperate with each other will be described as an example of Coordinated Scheduling with reference to FIG. Prior to the sequence of FIG. 15, it is assumed that base stations 100-1 and 100-2 have acquired cooperation information from radio communication terminals 200-3 and 200-5 in accordance with the sequence of FIG. However, here, it is assumed that the beam pattern desired by each wireless communication terminal is acquired as the cooperation information. That is, the radio communication terminal 200-3 uses the beam candidate that maximizes the signal component of the base station 100-1 that is the affiliated base station, and the beam that minimizes the signal component of the base station 100-2 that is the interfering base station. Are notified to the base station 100-1 by the cooperation information notification signal. Similarly, the radio communication terminal 200-5 minimizes the beam candidate that maximizes the signal component of the base station 100-2 that is the affiliated base station and the signal component of the base station 100-1 that is the interference base station. The beam candidate is notified to the base station 100-2 by the cooperation information notification signal. The base stations 100-1 and 100-2 make a coordinated scheduling request to the coordinated scheduling function 190 with these pieces of information (FIG. 15: 631-1 and 631-2). Receiving this, the cooperation scheduler 190 determines an optimum beam pattern, and notifies both base stations as a result of the cooperation scheduling (632-1, 632-2). Since Embodiments 1 and 2 were coordinated transmissions using Joint Processing, data exchange between the two base stations was necessary after this, but in principle, this embodiment is unnecessary. Data transmission to the radio communication terminals 200-1, 200-2, 200-4, and 200-6 is normally performed by single base station transmission (616-1, 616-2, 616-4) as in the previous embodiment. 616-6). Furthermore, the base station 100-1 transmits data to the radio communication terminal 200-3 using the beam pattern specified by 632-1 (633-3), and the base station 100-2 is addressed to the radio communication terminal 200-5. Data transmission is performed with the beam pattern specified in 632-2 (633-5). The wireless communication terminals that have received these data return ACKs to the base stations to which they belong (618-1 to 618-6).

As a result, as with Joint Processing, only limited wireless communication terminals
Since feedback necessary for Scheduling is performed, uplink radio resources can be saved, and at the same time, the processing amount required for cooperative scheduling can be reduced. Also Joint Proces
Unlike sing, signal generation is simple and user data transmission between base stations is unnecessary, so although it is inferior to Joint Processing from the viewpoint of maximum throughput, it is excellent from the viewpoint of Backhaul communication volume and signal processing volume. ing.

  In this embodiment, using FIG. 16, when a wireless communication terminal transmits a cooperation information notification signal to a base station, it does not request an uplink resource from the base station each time (sequence in FIG. 1), but reserves it in advance. Shows a sequence to be multiplexed using a spreading code in the assigned resource. The wireless communication terminal receives the pilot from the base station (Fig. 16: 601-1 and 601-2), and feeds back single transmission information to the base station based on it (602-1 to 602-6). 1 is the same as in FIG. 1 until the base station receiving the threshold signal transmits the threshold notification signal (603-1, 603-2). Thereafter, the wireless communication terminal transmits a cooperation information notification signal using the wireless resource determined after spreading the cooperation information without requesting the base station to secure an uplink resource band (641 -3, 641-5). Upon receiving this, the base station performs despreading as appropriate to extract the base signal.

As a result, when the link information notification signal is fed back, the signal for the uplink resource request can be reduced.

In this embodiment, a method for notifying a wireless communication terminal of candidates for another base station that the base station itself desires to cooperate with when transmitting a cooperative transmission threshold to the wireless communication terminal using a threshold notification signal will be described.

  In the present embodiment, the format shown in FIG. 17 is stored in the option field 504 of the threshold notification signal shown in FIG. 11A. A field 591 in FIG. 17 stores a list of other base stations that the base station that transmits the threshold notification signal desires to cooperate with. Reference numeral 592 denotes a field for storing detailed information related to the first base station (referred to as base station xx) that desires cooperation. Specifically, the field (592-1) indicating the amount (congestion amount) of wireless communication terminals in the cell of the base station xx, and the field indicating the throughput and congestion amount of the Backhaul line between the own base station and the base station xx ( 592-2) and a field (592-3) indicating the status of scheduling load in the base station xx. 593 is a field for storing detailed information related to the second base station (referred to as base station xx) that desires cooperation, and the same fields (593-1, 593-2, 593-) as those in base station xx. 3) including. Thereafter, this field is repeated by the number of necessary base stations.

  As shown in FIG. 21, consider a case in which only the Backhaul line between the base station 100-1 and the base station 100-3 is difficult to use (for example, the line is congested for some reason). In this case, the base station 100-1 stores only the base station 100-2 as the cooperation desired base station in the field 591 of the threshold notification signal. Similarly, base station 100-3 stores only base station 100-2. On the other hand, the base station 100-2 stores both the base stations 100-1 and 100-3 as the cooperation desired base stations in the field 591. As a result, the wireless communication terminal belonging to the base station 100-1 feeds back only the cooperation information with the base station 100-2, and the terminal belonging to the base station 100-3 has only the cooperation information with the base station 100-2. Feedback. On the other hand, the terminal belonging to the base station 100-2 feeds back cooperation information with both the base stations 100-1 and 100-3.

According to the present embodiment, the base station can tell the radio communication terminal which base station with which the cooperation information is desired to be fed back. In the above embodiments, for example, Backhaul
Even though the base station 100-1 and the base station 100-3 cannot be linked due to circumstances such as a line, the wireless communication terminal belonging to the base station 100-1 is not connected to the base station 100-3. However, according to the present embodiment, this problem can be avoided, and uplink radio resources can be effectively used.

  The above-described various embodiments have been described using an example related to base station cooperative transmission in accordance with a communication method defined by LTE and LTE-Advanced by 3GPP organizations, but not limited thereto, WiMAX standards by other organizations, etc. The present invention may also be applied to base station cooperative transmission in the above communication method.

1: Core network
2: Gateway device
100: Base station
190: Linked scheduler section
200: Wireless communication terminal

Claims (1)

A wireless communication system,
The first base station,
A second base station connected to the first base station in a wired network;
Radio that selects at least one of single data transmission data transmitted from the first base station and cooperative data transmission data transmitted in cooperation from the first base station and the second base station A communication terminal,
The first base station is
A condition notifying unit for notifying the wireless communication terminal of a condition indicating a case where cooperative data transmission is necessary;
The wireless communication terminal is
A comparison unit that compares the communication quality of the propagation path between the wireless communication terminal and the first base station, and the condition;
A wireless communication system, comprising: a cooperation notification unit that transmits information necessary for cooperative data transmission based on the comparison result.

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