Distributed antenna system, wireless communication method, and wireless communication device

Abstract

This distributed antenna system is provided with a first communication device and a plurality of antennas for performing communication with a plurality of second communication devices by spatial multiplexing in accordance with a control by the first communication device. The first communication device is provided with: an extraction unit that extracts, from among the plurality of second communication devices, a plurality of candidate second communication devices which become candidates for performing spatial multiplexing; and an assignment unit that assigns communication opportunities to, from among the extracted plurality of candidate second communication devices, two or more candidate second communication devices that meet the conditions that the distance between the candidate second communication devices is not less than a first threshold and that an overlapping rate of each of the antennas assigned to the candidate second communication devices is less than a second threshold, as targets for performing communication by spatial multiplexing. Each of the antennas assigned to the two or more candidate second communication devices to which communication opportunities are assigned among the plurality of antennas performs spatial multiplex transmission to the two or more second communication devices.　

Description

[Technical Field]

[0001] The present invention relates to a distributed antenna system, a wireless communication method, and a wireless communication device. [Background technology]

[0002] In wireless communication systems, MIMO (Multiple-Input Multiple-Output) technology is widely used as a technology that can improve frequency utilization efficiency and significantly improve capacity and throughput. MIMO technology uses multiple antennas on the transmitting and receiving sides to perform spatial multiplexing transmission at the same time and frequency. MIMO includes Single-User MIMO (SU-MIMO), which uses multiple antennas in point-to-point communication, and Multi-User MIMO (MU-MIMO), which performs Multiple-Input and Multiple-Output (MIMO) control between multiple terminals when point-to-many or many-to-many communication is performed, such as between a base station (BS) and a terminal (UE: User Equipment).

[0003] When MIMO is performed, channel information (CSI: Channel State Information) between multiple transmitting and receiving antennas is acquired, and precoding is performed on the transmitting side and postcoding on the receiving side to reduce interference between streams. MIMO using a distributed antenna system in which base station antennas are distributed is also being widely studied as a configuration that is expected to reduce spatial correlation between base station antennas and terminal antennas (see, for example, Non-Patent Document 1). In distributed antenna systems, clustering techniques are also being studied to reduce processing load by limiting the range of distributed antennas used by each terminal. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] NTT DOCOMO, INC., “White Paper 5G Evolution and 6G”, 2020 NTT DOCOMO, INC. All Rights Reserved. Summary of the Invention [Problem to be solved by the invention]

[0005] When spatial correlation between transmitting and receiving antennas is high during spatial multiplexing transmission, the effects of noise enhancement due to precoding and postcoding become significant, making it difficult to achieve sufficient communication performance.In a configuration such as a distributed antenna system where a large number of base station antennas are deployed, collecting all CSI between all distributed antennas and each terminal in order to suppress interference between streams using precoding and postcoding or to schedule terminals with low spatial correlation leads to an increase in the bandwidth and processing load between the distributed antennas and the base station, which is undesirable from the perspective of communication efficiency.

[0006] In view of the above circumstances, an object of the present invention is to provide a technology that can reduce spatial correlation when performing spatial multiplexing transmission without acquiring CSI between all antennas, thereby improving communication efficiency. [Means for solving the problem]

[0007] One aspect of the present invention is a distributed antenna system comprising a first communication device and a plurality of antennas that communicate with a plurality of second communication devices using spatial multiplexing under the control of the first communication device, wherein the first communication device comprises an extraction unit that extracts a plurality of candidate second communication devices from the plurality of second communication devices that are candidates for performing spatial multiplexing, and an allocation unit that allocates communication opportunities to two or more candidate second communication devices from the extracted plurality of candidate second communication devices that satisfy the conditions that the distance between the candidate second communication devices is greater than or equal to a first threshold and the overlap rate of each antenna assigned to each candidate second communication device is less than a second threshold, and each antenna assigned to the two or more candidate second communication devices to which communication opportunities have been assigned performs spatial multiplexing transmission to the two or more candidate second communication devices.

[0008] One aspect of the present invention is a wireless communication method in a distributed antenna system having a first communication device and a plurality of antennas that communicate with a plurality of second communication devices using spatial multiplexing in accordance with control of the first communication device, in which the first communication device extracts a plurality of candidate second communication devices from the plurality of second communication devices that are candidates for performing spatial multiplexing, and assigns communication opportunities to two or more candidate second communication devices from the extracted plurality of candidate second communication devices that meet the conditions that the distance between the candidate second communication devices is greater than or equal to a first threshold and the overlap rate of each antenna assigned to each candidate second communication device is less than a second threshold, as targets for communication using spatial multiplexing, and each antenna assigned to the two or more candidate second communication devices to which communication opportunities have been assigned among the plurality of antennas performs spatial multiplexing transmission to the two or more candidate second communication devices.

[0009] One aspect of the present invention is a wireless communication device comprising: a plurality of antennas that perform spatial multiplexing transmission to a plurality of communication devices; an extraction unit that extracts a plurality of candidate communication devices from the plurality of communication devices that are candidates for performing spatial multiplexing; and an allocation unit that allocates communication opportunities to two or more candidate communication devices from the extracted plurality of candidate communication devices that satisfy the conditions that the distance between the candidate communication devices is equal to or greater than a first threshold and the overlap rate of each antenna assigned to each candidate communication device is less than a second threshold, and each antenna assigned to the two or more candidate second communication devices to which communication opportunities have been assigned performs spatial multiplexing transmission to the two or more candidate communication devices. [Effects of the Invention]

[0010] According to the present invention, it is possible to reduce spatial correlation when performing spatial multiplexing transmission without acquiring CSI between all antennas, thereby improving communication efficiency. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating an example of a distributed antenna system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of a base station according to the present embodiment. [Figure 3] FIG. 2 is a diagram illustrating an example of the configuration of a control unit in the present embodiment. [Figure 4] 10 is a flowchart showing a processing flow of a base station in the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a diagram showing an example of a distributed antenna system 100 according to this embodiment. The distributed antenna system 100 includes a base station 10 and a plurality of antennas 20-1 to 20-4. The base station 10 and the plurality of antennas 20-1 to 20-4 are connected by optical transmission paths. Communication between the base station 10 and the plurality of antennas 20-1 to 20-4 is performed by, for example, RoF (Radio over Fiber). The base station 10 and the plurality of antennas 20-1 to 20-4 are one aspect of a wireless communication device.

[0013] In the example shown in Fig. 1, multiple antennas 20-1 to 20-4 are installed on the ceiling within building BL, and perform communication with multiple wireless communication terminals 30-1 to 30-6 located within building BL. The multiple antennas 20-1 to 20-4 are arranged spaced apart from one another as shown in Fig. 1. Each antenna 20 includes multiple subarrays 21. Note that the numbers of antennas 20, wireless communication terminals 30, and subarrays 21 are not limited to those shown in Fig. 1. In the following description, when there is no need to particularly distinguish between the antennas 20-1 to 20-4, they will simply be referred to as antennas 20.

[0014] The base station 10 controls each of the distributed antennas 20 through centralized control. The base station 10 controls each of the antennas 20 to realize simultaneous communication with multiple wireless communication terminals 30 through spatial multiplexing. Specifically, the base station 10 performs MU-MIMO by simultaneously transmitting multiple streams from the multiple antennas 20 to the multiple wireless communication terminals 30.

[0015] Each antenna 20 communicates with each wireless communication terminal 30. Each antenna 20 is configured to include multiple subarrays 21. Each subarray 21 radiates radio waves under control of the base station 10. The antenna 20 communicates with the wireless communication terminal 30 that is the communication target by performing beamforming using multiple array elements to ensure gain in the high frequency band. Note that some of the antennas 20 may not include a subarray 21.

[0016] Each wireless communication terminal 30 has one or more antennas and communicates with each antenna 20. A wireless communication terminal 30 equipped with multiple antennas can also communicate with the antenna 20 using SU-MIMO. The wireless communication terminal 30 may perform beamforming. Each wireless communication terminal 30 has a function for acquiring its own location information, and acquires the location information at a request from the base station 10 or at a predetermined timing. Each wireless communication terminal 30 notifies the base station 10 of the acquired location information via the antenna 20.

[0017] The method by which each wireless communication terminal 30 acquires location information may be any of methods such as a global navigation satellite system (GNSS) such as a global positioning system (GPS), three-point positioning or one-point positioning using communication radio waves, acoustic wave positioning, visible light positioning, etc. Wireless communication using a different frequency band may be used to notify the base station 10 of the location information of each wireless communication terminal 30.

[0018] Next, an overview of the processing of the distributed antenna system 100 will be described using an example of communication (downlink) from a base station 10 to a wireless communication terminal 30, with reference to FIG. 1 . When spatial multiplexing transmission is performed simultaneously between a plurality of wireless communication terminals 30 using the antennas 20 that are distributed as in the distributed antenna system 100, the spatial correlation of the propagation path changes depending on how the wireless communication terminals 30 are selected. Therefore, the communication capacity and throughput also change depending on the selection of the wireless communication terminals 30. Therefore, the distributed antenna system 100 of this embodiment selects wireless communication terminals 30 that are not expected to have high spatial correlation as wireless communication terminals 30 that will simultaneously perform spatial multiplexing, based on the location information of each wireless communication terminal 30. That is, the distributed antenna system 100 of this embodiment allocates communication opportunities to wireless communication terminals 30 that are not expected to have high spatial correlation, as targets for spatial multiplexing.

[0019] Specifically, in the distributed antenna system 100, based on the location information of one selected wireless communication terminal 30, other wireless communication terminals 30 located within a predetermined distance from the selected wireless communication terminal 30 are excluded from allocation of communication opportunities, thereby excluding nearby wireless communication terminals 30 that are likely to have high spatial correlation from selection candidates. In the example shown in FIG. 1, wireless communication terminals 30-1 to 30-6 are located within a building BL, and wireless communication terminals 30-5 and 30-6 are wireless communication terminals 30 that have been allocated communication opportunities. Area 31-1 shown in FIG. 1 represents an area that is a predetermined distance away from wireless communication terminal 30-5, based on the location of wireless communication terminal 30-5. Similarly, area 31-2 shown in FIG. 1 represents an area that is a predetermined distance away from wireless communication terminal 30-6, based on the location of wireless communication terminal 30-6.

[0020] The base station 10 excludes the other wireless communication terminals 30-3 and 30-4 located in the area 31-1 or the area 31-2 from the targets for allocation of communication opportunities. This makes it possible to avoid combinations of wireless communication terminals 30 that have high spatial correlation. As a result, it is possible to reduce the spatial correlation between the wireless communication terminals 30 that are targets for simultaneous communication by spatial multiplexing.

[0021] Furthermore, the distributed antenna system 100 refers to information (hereinafter referred to as "clustering information") regarding the set of antennas 20 assigned to each wireless communication terminal 30, and selects wireless communication terminals 30 with a low overlap rate of antennas 20 assigned to each wireless communication terminal 30 to be spatially multiplexed. The overlap rate is calculated, for example, as the ratio of the number of identical antennas 20 assigned to different wireless communication terminals 30 out of the total number of antennas assigned to each of multiple wireless communication terminals 30 (e.g., two wireless communication terminals 30). Note that when an antenna 20 is configured with multiple subarrays 21, the overlap rate is calculated, for example, as the ratio of the number of identical subarrays 21 assigned to different wireless communication terminals 30 out of the total number of subarrays assigned to each of the two wireless communication terminals 30. This is expected to increase the number of streams assigned per terminal.

[0022] In this way, the base station 10 excludes from selection candidates nearby wireless communication terminals 30 that are likely to have high spatial correlation, and allocates communication opportunities to a plurality of wireless communication terminals 30 that have a low overlap rate of the antennas 20 allocated to each wireless communication terminal 30 that performs spatial multiplexing transmission, as a combination of wireless communication terminals 30 that perform spatial multiplexing transmission. For example, in the example shown in Fig. 1, the base station 10 allocates communication opportunities to wireless communication terminals 30-1, 30-2, 30-5, and 30-6 as a combination of wireless communication terminals 30 that perform spatial multiplexing transmission.

[0023] By performing the above processing, the distributed antenna system 100 can reduce spatial correlation when performing spatial multiplexing transmission without acquiring CSI between all antennas, thereby improving communication efficiency. A specific configuration for realizing the above processing will be described below.

[0024] 2 is a diagram showing an example of the configuration of a base station 10 according to this embodiment. The base station 10 includes a transmission unit 11, a control unit 12, a signal processing unit 13, a MIMO processing unit 14, multiple transmission / reception units 15, and multiple antennas 20.

[0025] The transmission unit 11 transmits signals between a higher-level device on the network and other wireless communication devices.

[0026] The control unit 12 controls the overall operation of the base station 10. For example, the control unit 12 performs scheduling such as allocation of each antenna 20 to each wireless communication terminal 30 for spatial multiplexing transmission.

[0027] The signal processing unit 13 performs signal processing related to wireless communication.

[0028] The MIMO processing unit 14 performs MIMO processing such as precoding and postcoding. Note that the MIMO processing unit 14 may be controlled to perform analog beamforming or hybrid beamforming instead of precoding or postcoding.

[0029] The transmitter / receiver 15 performs processing related to transmission and reception of radio signals. Specifically, the transmitter / receiver 15 controls each antenna 20 to communicate with each wireless communication terminal 30. For example, the transmitter / receiver 15 controls the antenna 20 assigned to a wireless communication terminal 30 (hereinafter referred to as a "candidate terminal station") that is a candidate for spatial multiplexing using MU-MIMO, to communicate with the candidate terminal station.

[0030] 3 is a diagram showing an example of the configuration of the control unit 12 in this embodiment. The control unit 12 includes a location information acquisition unit 121, a terminal station extraction unit 122, and an allocation unit 123.

[0031] The location information acquisition unit 121 acquires location information from each of the multiple wireless communication terminals 30.

[0032] The terminal station extraction unit 122 extracts a plurality of candidate terminal stations from the plurality of wireless communication terminals 30. The method of extracting the candidate terminal stations may be any of the following: a method of selecting candidate terminal stations based on an index such as an RI (Rank Indicator) using various scheduling methods; a method of selecting candidate terminal stations based on a PF (Proportional fair) standard; a method of selecting candidate terminal stations based on received power; and a method of selecting wireless communication terminals 30 that reduce interference between the wireless communication terminals 30 based on their positional relationship or the like. Examples of methods of selecting candidate terminal stations based on received power include a method of checking the received power of each wireless communication terminal 30 and selecting wireless communication terminals 30 in descending order of received power, and a method of selecting wireless communication terminals 30 with similar received power. The terminal station extraction unit 122 is one aspect of the extraction unit.

[0033] The allocation unit 123 allocates an antenna 20 to each wireless communication terminal 30 based on the reception quality, the terminal accommodation status, etc., in the phase in which the wireless communication terminal 30 that has entered the area (for example, building BL) connects to the base station 10. When the antenna 20 is configured to include multiple subarrays 21, the allocation unit 123 allocates a subarray 21 of the antenna 20 to each wireless communication terminal 30 based on the reception quality, the terminal accommodation status, etc., in the phase in which the wireless communication terminal 30 connects to the base station 10. Note that the allocation unit 123 may allocate an antenna 20 that communicates with each candidate terminal station extracted by the terminal station extraction unit 122. Alternatively, the allocation unit 123 may allocate multiple antennas 20 or subarrays 21 of the antenna 20 to the wireless communication terminal 30. When the antenna 20 is configured to include multiple subarrays 21, the allocation unit 123 may allocate a subarray 21 that communicates with each candidate terminal station extracted by the terminal station extraction unit 122.

[0034] Furthermore, the allocation unit 123 allocates communication opportunities to two or more candidate terminal stations as targets for communication by spatial multiplexing. More specifically, the allocation unit 123 allocates communication opportunities to two or more candidate terminal stations as targets for communication by spatial multiplexing, from among the plurality of candidate terminal stations extracted by the terminal station extraction unit 122, that satisfy the conditions that the distance between the candidate terminal stations is equal to or greater than a first threshold and the overlap rate of each antenna allocated to each candidate terminal station is less than a second threshold.

[0035] Fig. 4 is a flowchart showing the flow of processing by the base station 10 in this embodiment. It is assumed that, at the start of the processing in Fig. 4, the base station 10 has acquired location information of each wireless communication terminal 30. For example, each wireless communication terminal 30 may transmit a connection request signal including the location information to the base station 10, thereby allowing the base station 10 to acquire the location information of each wireless communication terminal 30. Furthermore, at the start of the processing in Fig. 4, it is assumed that an antenna 20 has been assigned to each wireless communication terminal 30, and the assignment unit 123 holds, as clustering information, information on a set of one or more antennas 20 or one or more subarrays 21 assigned to each wireless communication terminal 30.

[0036] The terminal station extraction unit 122 extracts candidate terminal stations from among the multiple wireless communication terminals 30 (step S101). The allocation unit 123 assigns a number to each of the extracted candidate terminal stations. For example, the allocation unit 123 assigns numbers in order starting from 1 as candidate terminal station numbers to each candidate terminal station. The allocation unit 123 assigns 1 to candidate terminal station number i (step S102).

[0037] Next, the allocation unit 123 determines whether the location of the i-th candidate terminal station is away from the location of the candidate terminal station to which a communication opportunity has been allocated by a distance equal to or greater than the first threshold value, based on the location information of the i-th candidate terminal station and the location information of the candidate terminal station to which a communication opportunity has been allocated (step S103). At the start of the process, i is 1, so there is no candidate terminal station to which a communication opportunity has been allocated. Therefore, here, the allocation unit 123 determines that the location of the i-th candidate terminal station is away from the location of the candidate terminal station to which a communication opportunity has been allocated by a distance equal to or greater than the first threshold value.

[0038] When the allocation unit 123 determines that the location of the i-th candidate terminal station is away from the location of a candidate terminal station to which a communication opportunity has already been allocated by a distance equal to or greater than the first threshold (step S103-YES), the allocation unit 123 determines whether the overlap rate is less than a second threshold (step S104). Specifically, the allocation unit 123 first refers to the clustering information for each candidate terminal station it holds, and reads out the clustering information of the i-th candidate terminal station and the clustering information of candidate terminal stations to which a communication opportunity has already been allocated. Next, the allocation unit 123 compares the read clustering information to calculate the overlap rate. Here, since i is 1, there is no candidate terminal station to which a communication opportunity has already been allocated. Therefore, the allocation unit 123 determines that the overlap rate is less than the second threshold.

[0039] If the allocation unit 123 determines that the overlap rate is less than the second threshold (step S104-YES), it allocates a communication opportunity to the i-th candidate terminal station (for example, the first candidate terminal station) (step S105). That is, the allocation unit 123 adds the i-th candidate terminal station to the targets for spatial multiplexing. If the allocation unit 123 determines that the overlap rate is equal to or greater than the second threshold (step S104-NO), or after processing step S105, it adds 1 to i (step S106). As a result, if i=1, it becomes i=2 as a result of the processing in step S106.

[0040] Thereafter, the allocation unit 123 determines whether the number of candidate terminal stations to which communication opportunities have been allocated is less than the maximum allocable number (step S107). The maximum allocable number is determined according to, for example, the number of antennas 20 and subarrays 21, the processing capability of the base station 10, or the maximum number of supported MIMO layers.

[0041] If the allocation unit 123 determines that the number of candidate terminal stations to which communication opportunities have been allocated is less than the maximum allocatable number (step S107-YES), it determines whether the value of i is greater than the number of candidate terminal stations (step S108). That is, the allocation unit 123 determines whether allocation determination has been performed for all candidate terminal stations extracted in step S101.

[0042] If the allocation unit 123 determines that the value of i is not greater than the number of candidate terminal stations (step S108-NO), the allocation determination has not been performed for all of the candidate terminal stations extracted in step S101. Therefore, the allocation unit 123 executes the process of step S103. Here, the process of step S103 will be described assuming that i=2 and that a communication opportunity has been allocated to the first candidate terminal station. The allocation unit 123 determines whether the location of the second candidate terminal station is a distance equal to or greater than a first threshold from the location of the candidate terminal station to which a communication opportunity has been allocated, based on the location information of the second candidate terminal station and the location information of the candidate terminal station to which a communication opportunity has been allocated (step S103). Here, the allocation unit 123 determines whether the location of the second candidate terminal station is a distance equal to or greater than a first threshold from the location of the first candidate terminal station, based on the location information of the second candidate terminal station and the location information of the first candidate terminal station.

[0043] If the allocation unit 123 determines that the position of the second candidate terminal station is not far from the position of the first candidate terminal station by a distance equal to or greater than the first threshold (step S103-NO), it adds 1 to i in the processing of step S106 and then executes the processing of step S107.

[0044] On the other hand, in the process of step S103, if the allocation unit 123 determines that the position of the second candidate terminal station is away from the position of the first candidate terminal station by a distance equal to or greater than the first threshold (step S103-YES), it determines whether the overlap rate is less than a second threshold (step S104). Specifically, first, the allocation unit 123 refers to the clustering information for each candidate terminal station that it holds, and reads out the clustering information of the second candidate terminal station and the clustering information of a candidate terminal station to which a communication opportunity has already been allocated (for example, the first candidate terminal station). Next, the allocation unit 123 compares the read clustering information to calculate the overlap rate.

[0045] If the allocation unit 123 determines that the overlap rate is less than the second threshold (step S104-YES), it allocates a communication opportunity to the i-th candidate terminal station (for example, the second candidate terminal station) (step S105). That is, the allocation unit 123 adds the i-th candidate terminal station to the targets for spatial multiplexing. If the allocation unit 123 determines that the overlap rate is equal to or greater than the second threshold (step S104-NO), or after processing step S105, it adds 1 to i (step S106).

[0046] In addition, when i=3 and communication opportunities have been allocated to the first candidate terminal station and the second candidate terminal station, in the processing of step S103, the allocation unit 123 determines whether the position of the third candidate terminal station is away from the positions of the candidate terminal stations to which communication opportunities have been allocated (e.g., the first candidate terminal station and the second candidate terminal station) by a distance equal to or greater than the first threshold.

[0047] Furthermore, if the allocation unit 123 determines in the processing of step S103 that the location of the third candidate terminal station is away from the locations of candidate terminal stations to which communication opportunities have been allocated (for example, the first candidate terminal station and the second candidate terminal station) by a distance equal to or greater than the first threshold, the allocation unit 123 determines in the processing of step S104 whether the overlap rate is less than a second threshold. Specifically, first, the allocation unit 123 refers to the clustering information for each candidate terminal station it holds, and reads out the clustering information of the third candidate terminal station and the clustering information of the candidate terminal stations to which communication opportunities have been allocated (for example, the first candidate terminal station and the second candidate terminal station). Next, the allocation unit 123 compares the read clustering information to calculate the overlap rate. In this way, the more candidate terminal stations to which communication opportunities have been allocated, the more targets there are to compare.

[0048] In the processing of step S107, if the allocation unit 123 determines that the number of candidate terminal stations to which communication opportunities have been allocated is equal to or greater than the maximum allocable number (step S107-NO), the base station 10 performs spatial multiplexing transmission with the candidate terminal stations that have been added as targets for spatial multiplexing (step S109).

[0049] In the process of step S108, if the allocation unit 123 determines that the value of i is greater than the number of candidate terminal stations (step S108-YES), this means that allocation determination has been performed for all candidate terminal stations extracted in step S101. In this case, the base station 10 executes spatial multiplexing transmission with the candidate terminal stations that have been added as targets for spatial multiplexing (step S109). In this way, the base station 10 repeats the process shown in FIG. 4 until the maximum allocatable number of candidate terminal stations is reached or until there are no candidate terminal stations that are candidates for spatial multiplexing. Note that if there are no candidate terminal stations that are candidates for spatial multiplexing and the maximum allocatable number is not met, the base station 10 may add new candidate terminal stations that are candidates for spatial multiplexing.

[0050] According to the distributed antenna system 100 configured as described above, spatial correlation during spatial multiplexing transmission can be reduced without acquiring CSI between all antennas, thereby improving communication efficiency. Specifically, in the distributed antenna system 100, the base station 10 includes a terminal station extraction unit 122 that extracts multiple candidate terminal stations from multiple wireless communication terminals 30, and an allocation unit 123 that allocates communication opportunities to two or more candidate second communication devices from among the extracted multiple candidate terminal stations, where the distance between the candidate terminal stations is equal to or greater than a first threshold and the overlap rate of each antenna allocated to each candidate second communication device is less than a second threshold. Each antenna 20 allocated to the two or more candidate terminal stations to which communication opportunities are allocated performs spatial multiplexing transmission to the two or more candidate terminal stations. In this way, spatial correlation between wireless communication terminals 30 that are targets for simultaneous communication through spatial multiplexing can be reduced, and the probability of overlapping of antennas 20 to which streams are simultaneously allocated can be reduced, thereby increasing the number of streams allocated per device. Therefore, it is possible to reduce spatial correlation when performing spatial multiplexing transmission without acquiring CSI between all antennas, thereby improving communication efficiency.

[0051] Furthermore, the distributed antenna system 100 is expected to reduce processing load by avoiding interference between wireless communication terminals using only analog beamforming, without performing precoding or postcoding processing in high frequency bands.

[0052] Below, modifications of the distributed antenna system 100 will be described. (Variation 1) The functional units of the base station 10 may be divided and arranged into a CU (Centralized Unit), a DU (Distributed Unit), and an RU (Radio Unit) in 5G NR. In such a configuration, for example, a transmission unit 11 is arranged in the CU, a control unit 12, a signal processing unit 13, and a MIMO processing unit 14 are arranged in the DU, and a transceiver unit 15 and an antenna 20 are arranged in the RU.

[0053] (Variation 2) In the above embodiment, a configuration for a downlink from the base station 10 to the wireless communication terminal 30 is shown, but the above processing in the distributed antenna system 100 can also be applied to an uplink from the wireless communication terminal 30 to the base station 10. For example, the distributed antenna system 100 may perform MU-MIMO by simultaneously transmitting multiple streams from multiple wireless communication terminals 30 to multiple antennas 20.

[0054] (Variation 3) In scheduling, the base station 10 may take into consideration not only spatial correlation but also other factors such as fairness of communication opportunities and traffic volume, and may perform scheduling control taking into account location information and / or clustering information of wireless communication terminals.

[0055] (Regarding correspondence with claims) The base station 10 is one aspect of a first communication device, a second communication device, and a wireless communication device. The wireless communication terminal 30 is one aspect of a first communication device, a second communication device, and a wireless communication device. When the base station 10 is the first communication device, the wireless communication terminal 30 is the second communication device, and when the base station 10 is the second communication device, the wireless communication terminal 30 is the first communication device.

[0056] Some or all of the functional units of the base station 10 and the wireless communication terminal 30 in the above-described embodiments are realized as software by one or more processors, such as a CPU (Central Processing Unit), executing a program stored in a storage device having a non-volatile storage medium (non-transitory storage medium) and a memory. The program may be recorded on a computer-readable non-transitory storage medium. Examples of computer-readable non-transitory storage media include portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), CD-ROMs (Compact Discs), and storage devices such as hard disks built into computer systems.

[0057] Some or all of the functional units of the base station 10 and the wireless communication terminal 30 may be realized using hardware including electronic circuits (electronic circuits or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0058] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Industrial Applicability]

[0059] The present invention can be applied to a wireless communication system using MIMO. [Explanation of symbols]

[0060] 10...base station, 20...antenna, 21...subarray, 30...wireless communication terminal, 11...transmission unit, 12...control unit, 13...signal processing unit, 14...MIMO processing unit, 15...transmission / reception unit, 121...location information acquisition unit, 122...terminal station extraction unit, 123...allocation unit

Claims

1. A distributed antenna system including a first communication device and a plurality of antennas that communicate with a plurality of second communication devices by spatial multiplexing under control of the first communication device, The first communication device an extracting unit that extracts a plurality of candidate second communication devices that are candidates for performing spatial multiplexing from the plurality of second communication devices; an allocation unit that allocates communication opportunities to two or more candidate second communication devices from the extracted plurality of candidate second communication devices, the two or more candidate second communication devices satisfying the conditions that the distance between the candidate second communication devices is equal to or greater than a first threshold value and the overlap rate of each antenna allocated to each candidate second communication device is less than a second threshold value, as targets for communication by spatial multiplexing; Equipped with each antenna assigned to the two or more candidate second communication devices to which communication opportunities have been assigned among the plurality of antennas performs spatial multiplexing transmission to the two or more candidate second communication devices; Distributed Antenna System.

2. The first communication device a location information acquisition unit that acquires location information from each of the plurality of second communication devices; the allocation unit determines whether a distance between the candidate second communication devices is equal to or greater than a first threshold based on the location information of each candidate second communication device acquired by the location information acquisition unit; 10. The distributed antenna system of claim 1.

3. the allocation unit calculates, as the overlap rate, a ratio of the number of identical antennas allocated to different candidate second communication devices to a total number of antennas allocated to each candidate second communication device; 3. A distributed antenna system according to claim 1 or 2.

4. A wireless communication method in a distributed antenna system including a first communication device and a plurality of antennas that communicate with a plurality of second communication devices by spatial multiplexing under control of the first communication device, The first communication device, extracting a plurality of candidate second communication devices that are candidates for performing spatial multiplexing from the plurality of second communication devices; assigning communication opportunities to two or more candidate second communication devices from among the extracted plurality of candidate second communication devices, which satisfy the conditions that the distance between the candidate second communication devices is equal to or greater than a first threshold value and the overlap rate of each antenna assigned to each candidate second communication device is less than a second threshold value, as targets for communication by spatial multiplexing; each antenna assigned to the two or more candidate second communication devices to which a communication opportunity has been assigned among the plurality of antennas performs spatial multiplexing transmission to the two or more candidate second communication devices; Wireless communication method.

5. a plurality of antennas that perform spatial multiplexing transmission to a plurality of communication devices; an extracting unit that extracts a plurality of candidate communication devices that are candidates for performing spatial multiplexing from the plurality of communication devices; an allocation unit that allocates communication opportunities to two or more candidate communication devices from the extracted plurality of candidate communication devices, the two or more candidate communication devices satisfying the conditions that the distance between the candidate communication devices is equal to or greater than a first threshold value and the overlap rate of each antenna allocated to each candidate communication device is less than a second threshold value, as targets for communication by spatial multiplexing; Equipped with each of the antennas assigned to the two or more candidate second communication devices to which communication opportunities have been assigned performs spatial multiplexing transmission to the two or more candidate communication devices; Wireless communication device.

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