Wireless communication system, wireless communication method, control device, and program

Abstract

A wireless communication system according to the present disclosure comprises a mobile station, a base station, and a control device. The mobile station is provided with a plurality of antennas and has a MIMO processing function for transmitting / separating a plurality of signals in parallel. The base station is provided with: a plurality of base station antennas arranged in a distributed manner within the same range as or a wider range than the communicable area of the mobile station; and a plurality of signal processing devices having a MIMO processing function and connected to one of the plurality of base station antennas. The control device detects or estimates a request condition for communication performance between the mobile station and the base station. For MIMO processing of a reception signal from the mobile station, the base station is configured to use a signal processing device, among the plurality of signal processing devices, that satisfies the request condition detected or estimated by the control device or that is closest to the request condition.

Description

Wireless communication system, wireless communication method, control device, and program

[0001] The present disclosure relates to a wireless communication system, a wireless communication method, a control device, and a program.

[0002] For example, as disclosed in Non-Patent Document 1, many wireless communication use cases are expected for non-terrestrial networks (NTN), including direct accommodation of terrestrial mobile terminals, mobile backhaul, accommodation of IoT terminals, etc. Since the transmission capacity is expected to increase compared to existing satellite communication services, there is a demand for an increase in the capacity of the feeder link, which is the backbone line connecting the airborne platform and the terrestrial gateway station.

[0003] An example of a technology for increasing the capacity of feeder links is disclosed in Non-Patent Document 2. The technology disclosed in Non-Patent Document 2 is a MIMO technology that performs spatial multiplexing by installing multiple antennas on an airborne platform and also installing multiple terrestrial gateway antennas on the ground. This conventional technology is expected to increase transmission capacity by installing a large number of antennas for transmission and reception and increasing the number of spatial multiplexing.

[0004] Non-Patent Document 3 discloses a method for increasing the capacity of a feeder link by forming a massive MIMO by arranging a large number of small antennas over a wide area. This conventional technology makes it possible to effectively utilize antennas that receive signals, thereby achieving a high transmission capacity.

[0005] However, NTN provides a wide range of applications. For some applications, it is expected that delay requirements will be more important than transmission capacity requirements. Each of the above conventional technologies utilizes signals from antennas deployed over a wide area. This naturally increases the transmission distance, which poses the problem of increased delay.

[0006] 3GPP TR 38.821, "Solutions for NR to Support Non-Terrestrial Networks (NTN) (Release 16)", V16.1.0, May. 2021. A. Knopp, RT Schwarz, D. Ogermann, CA Hofmann and B. Lankl, "Satellite System Design Examples for Maximum MIMO Spectral Efficiency in LOS Channels", IEEE GLOBECOM 2008 - 2008 IEEE Global Telecommunications Conference, 2008, pp. 1-6. Tategami et al., "Proposal of a Hierarchical Base Station Configuration for Ultra-Wideband Massive MIMO Systems", IEICE General Conference, B-3-5, Mar. 2023.

[0007] The present disclosure has been made in view of the above-mentioned problems, and aims to provide a technology that can achieve the transmission capacity and delay required by applications in an NTN where communication areas change due to various altitudes and mobility.

[0008] The present disclosure provides a wireless communication system for achieving the above-mentioned object. The wireless communication system of the present disclosure includes a mobile station, a base station, and a control device. The mobile station includes multiple antennas and has a MIMO processing function for transmitting / separating multiple signals in parallel. The base station includes multiple base station antennas distributed over an area equal to or larger than the communication area of ​​the mobile station, and multiple signal processing devices with MIMO processing function connected to any of the multiple base station antennas. The control device is configured to detect or estimate requirements for communication performance between the mobile station and the base station. The base station is also configured to use, from among the multiple signal processing devices, a signal processing device that satisfies or is closest to the requirements detected or estimated by the control device for MIMO processing of received signals from the mobile station.

[0009] The present disclosure provides a wireless communication method for achieving the above-mentioned object. The wireless communication method of the present disclosure is a method for performing wireless communication between a mobile station and a base station. The mobile station has multiple antennas and has a MIMO processing function for transmitting / separating multiple signals in parallel. The base station has multiple base station antennas distributed over an area equal to or wider than the communication area of ​​the mobile station, and multiple signal processing devices with MIMO processing function connected to any of the multiple base station antennas. The wireless communication method of the present disclosure includes the following steps. The first step is a step of detecting or estimating requirements for communication performance between the mobile station and the base station. The second step is a step of using, from among the multiple signal processing devices, a signal processing device that satisfies or is closest to the required conditions for MIMO processing of a signal received from the mobile station.

[0010] The present disclosure provides a control device to achieve the above-mentioned object. The control device of the present disclosure is a control device for a wireless communication system that performs wireless communication between a mobile station and a base station. The mobile station has multiple antennas and a MIMO processing function for transmitting / separating multiple signals in parallel. The base station has multiple base station antennas distributed over an area equal to or wider than the communication area of ​​the mobile station, and multiple signal processing devices with MIMO processing function that are connected to any of the multiple base station antennas. The control device of the present disclosure is configured to perform the following processes. The first process is a process for detecting or estimating requirements for communication performance between the mobile station and the base station. The second process is a process for causing a signal processing device that satisfies or is closest to the requirements among the multiple signal processing devices to perform MIMO processing on a received signal from the mobile station.

[0011] The present disclosure provides a program for achieving the above-mentioned object. The program of the present disclosure is a program including a plurality of instructions for operating a control device of a wireless communication system that performs wireless communication between a mobile station and a base station. The mobile station has a plurality of antennas and a MIMO processing function for transmitting / separating a plurality of signals in parallel. The base station has a plurality of base station antennas distributed over an area equal to or larger than the communication area of ​​the mobile station, and a plurality of signal processing devices having a MIMO processing function and connected to any of the plurality of base station antennas. The plurality of instructions included in the program of the present disclosure are configured to cause the control device to perform the following processes. The first process is a process for detecting or estimating requirements for communication performance between the mobile station and the base station. The second process is a process for causing a signal processing device among the plurality of signal processing devices that satisfies or is closest to the requirements to perform MIMO processing on a received signal from the mobile station.

[0012] According to the technology of the present disclosure, a signal processing device that meets the requirements for communication performance between a mobile station and a base station is used for MIMO processing of received signals from a mobile station, thereby achieving the transmission capacity and delay required by the application.

[0013] 1 is a diagram showing an example of the configuration of a wireless communication system according to an embodiment; FIG. 2 is a diagram showing functions of a mobile station according to an embodiment; FIG. 3 is a diagram showing an example of the hardware configuration of a mobile station according to an embodiment; FIG. 4 is a diagram showing functions of a sub-base station according to an embodiment; FIG. 5 is a diagram showing an example of the hardware configuration of a sub-base station according to an embodiment; FIG. 6 is a diagram showing functions of a cooperative station according to an embodiment; FIG. 7 is a diagram showing an example of the hardware configuration of a cooperative station according to an embodiment; FIG. 8 is a flow diagram of the operation of a mobile station according to an embodiment; FIG. 9 is a diagram showing an example of a transmission signal; FIG. 10 is a flow diagram of the operation of a base station according to an embodiment; FIG. 11 is a diagram showing a specific example of the operation of a wireless communication system according to an embodiment; FIG. 12 is a diagram showing a specific example of the operation of a wireless communication system according to an embodiment; FIG. 13 is a diagram showing a modified example of the configuration of a wireless communication system according to an embodiment.

[0014] 1. Configuration of a Wireless Communication System Fig. 1 is a diagram showing an example of the configuration of a wireless communication system according to an embodiment. The wireless communication system 11 is an NTN consisting of mobile stations 30 moving in the sky and base stations (also referred to as receiving systems) 20 installed on the ground. The mobile stations 30 are, for example, HAPS or LEO satellites. The base station 20 has a MIMO processing function (at least a MIMO receiving function) and includes multiple sub-base stations (hereinafter simply referred to as sub-base stations) 40 distributed across the ground. Each sub-base station 40 is equipped with multiple antennas 41 (hereinafter referred to as base station antennas).

[0015] The mobile station 30 is equipped with multiple antennas 31 and has a MIMO processing function (at least a MIMO transmission function) for transmitting / separating multiple signals in parallel. The mobile station 30 also includes a control device 100. The shape of the communication area of ​​the mobile station 30, i.e., the area where signals can reach wirelessly, is not limited. It is sufficient that the base station antennas 41 are distributed over the same range as or a wider range than the communication area of ​​the mobile station 30. For example, if the mobile station 30 is a HAPS satellite with a low altitude, the communication area will be shaped to cover only one sub-base station 40. If the mobile station 30 is a LEO satellite with a higher altitude than the HAPS, the communication area will be shaped to span multiple sub-base stations 40. The mobile station 30 performs wireless MIMO communication with the sub-base stations 40 within its communication area.

[0016] The base station 20 has a hierarchical structure. Each layer of the hierarchical structure includes multiple stations serving as signal processing devices. The sub-base station 40 is a station located in the highest layer, i.e., the first layer. Multiple cooperative stations 50 are located in each layer from the second layer onward. Each sub-base station 40 and cooperative station 50 is assigned a unique ID. In the example shown in FIG. 1 , each sub-base station 40 and cooperative station 50 is assigned a unique ID represented by "x, y." The "x" in this unique ID represents the layer, and the "y" represents the order within the layer. For example, sub-base station 1,1 means the first station in the first layer, and sub-base station 1,N means the Nth station in the first layer. Furthermore, cooperative station 2,1 means the first station in the second layer, and cooperative station M,N-M+1 means the N-M+1th station in the Mth layer. In the example shown in FIG. 1 , the number of layers is the same as the number of sub-base stations 40, but this is merely an example, and the number of layers may be fewer than the number of sub-base stations 40.

[0017] The sub-base stations 40 and cooperative stations 50 are interconnected between layers via communication lines 26 such as optical lines or wireless lines. The sub-base stations 40 are connected to multiple cooperative stations 50 belonging to the second layer. In the example shown in FIG. 1 , the sub-base station 40 is connected to two cooperative stations 50 belonging to the second layer. For example, sub-base stations 1 and 2 are connected to cooperative stations 2 and 1 and cooperative stations 2 and 2 in the second layer. Note that some sub-base stations 40, for example, sub-base station 1 and 1, appear to be connected to only one cooperative station 50 belonging to the second layer, but this is because FIG. 1 shows only a portion of the base station 20.

[0018] A cooperative station 50 is connected to multiple sub-base stations 40 or cooperative stations 50 belonging to the next higher layer and multiple cooperative stations 50 belonging to the next lower layer. In the example shown in FIG. 1 , a cooperative station 50 belonging to the second layer is connected to two sub-base stations 40 belonging to the first layer and two cooperative stations 50 belonging to the third layer. Furthermore, a cooperative station 50 in the i-th layer (i is an integer greater than or equal to 3) is connected to two sub-base stations 40 belonging to the i-1-th layer and two cooperative stations 50 belonging to the i+1-th layer. Note that some cooperative stations 50, for example, cooperative stations 2 and 1, appear to be connected to only one cooperative station 50 belonging to the next lower layer, but this is because FIG. 1 shows only a portion of a base station 20.

[0019] The base station 20 performs MIMO communication by coordinating the sub-base stations 40 using multiple cooperative stations 50 that are interconnected with the multiple sub-base stations 40 in a hierarchical structure. As will be described in detail later, each of the sub-base stations 40 and the cooperative stations 50 is provided with a MIMO processing function. When MIMO communication is performed with the mobile station 30, the MIMO processing is performed in any one of the sub-base stations 40 or cooperative stations 50 in the hierarchical structure. Each of the sub-base stations 40 and the cooperative stations 50 is connected to the core network 2 via a communication line 27 such as an optical line or a wireless line. The signal demodulated by the MIMO processing is transmitted to the core network 2.

[0020] The transmission capacity and delay required in an NTN, i.e., communication performance, differs for each application. However, communication performance between sub-base stations 40 and mobile stations 30 is not necessarily the same for all sub-base stations 40. Similarly, communication performance between cooperative stations 50 and mobile stations 30 is not necessarily the same for all cooperative stations 50. Furthermore, the communication line capacity between the sub-base stations 40 and the core network 2 also differs depending on the individual sub-base stations 40 and the individual cooperative stations 50. The base station 20 is required to perform MIMO processing by the sub-base stations 40 or cooperative stations 50 that meets the required communication performance. The function for satisfying this requirement is a control device 100 installed in the mobile station 30. The configuration of the mobile station 30 will be described below. Furthermore, the configurations of the signal processing devices constituting the base station 20, i.e., the sub-base stations 40 and cooperative stations 50, will be described.

[0021] 2 is a functional block diagram showing the configuration of a mobile station 30 according to this embodiment. As shown in FIG. 2, the mobile station 30 includes a transmission data generation unit 301, a transmission signal generation unit 302, and a control device 100.

[0022] The transmission data generator 301 generates transmission data including a payload and control information required for communication.

[0023] The transmission signal generation unit 302 adds the control information generated by the control device 100 to the transmission data generated by the transmission data generation unit 301. The transmission signal generation unit 302 performs processing such as modulation and frequency conversion on the transmission data to which the control information has been added, and radiates the transmission signal generated by this processing from the antenna 31.

[0024] The control device 100 includes a position information calculation unit 101, a communication target detection unit 102, a communication performance calculation unit 103, a communication request detection unit 104, a processing station determination unit 105, and a control information generation unit 106.

[0025] The location information calculation unit 101 uses, for example, GPS to calculate location information of the own station 30. The location information of the own station 30 is information necessary for the base station 20 to determine which stations 40 and 50 will process the signals.

[0026] The communication target detection unit 102 detects the sub-base station 40 and the cooperative station 50 that are targets of MIMO communication from the position of the own station 30 calculated by the position information calculation unit 101 and the communication area of ​​the own station 30. For example, in the example shown in Fig. 1 , if only the sub-base station 40(1,1) is included in the communication area of ​​the own station 30, the sub-base station 40(1,1) is detected as a target of MIMO communication. If the communication area of ​​the own station 30 spans the sub-base station 40(1,1) and the sub-base station 40(1,2), the sub-base station 40(1,1), the sub-base station 40(1,2), and the cooperative station 50(2,1) are detected as targets of MIMO communication.

[0027] The communication performance calculation unit 103 calculates the transmission capacity and delay obtained by the communication targets detected by the communication target detection unit 102 from the configuration of the base station 20, i.e., the position and hierarchical structure of the base station antenna 41. For example, if the sub-base station 40 (1, 1), the sub-base station 40 (1, 2), and the cooperative station 50 (2, 1) are detected as targets of MIMO communication, the transmission capacity and delay obtained by each of the communication target stations are calculated. The communication line capacity with the core network 2 is used as a parameter in calculating the transmission capacity and delay.

[0028] The communication request detection unit 104 detects or estimates requirements regarding the transmission speed and delay of data transmitted from the local station 30 to the base station 20, i.e., requirements regarding communication performance. Since requirements regarding communication performance differ depending on the application, the requirements are detected or estimated according to the application.

[0029] The processing station determination unit 105 compares the communication performance of each communication target station in MIMO communication calculated by the communication performance calculation unit 103 with the required conditions for communication performance detected by the communication request detection unit 104, and determines the communication target station that satisfies the required conditions as the processing station. If none of the communication target stations satisfies the required conditions, the processing station determination unit 105 determines the communication target station that is closest to the required conditions among the communication target stations detected by the communication target detection unit 102 as the processing station.

[0030] The control information generator 106 generates control information based on the determination result of the processing station determiner 105. The control information is information for determining which sub-base station 40 or cooperative station 50 of the base station 20 will perform MIMO processing. The control information includes a unique ID for identifying the sub-base station 40 or cooperative station 50 that will perform the MIMO processing. The control information generator 106 outputs the generated control information to the transmission signal generator 302 of the mobile station 30.

[0031] 3 is a diagram showing an example of the hardware configuration of the mobile station 30. The mobile station 30 is a signal processing device including a processor 32, a program memory 33, an information memory 35, and a wireless communication interface 36 for MIMO communication. There may be a plurality of each of the processors 32, the program memories 33, and the information memories 35.

[0032] The processor 32 may be a CPU, RISC, DSP, FPGA, ASIC, PLD, or another processing unit, or may be a combination of two or more thereof, or may be a dedicated processor for the wireless communication system according to this embodiment. The processor 32 may also be communicatively coupled to the program memory 33 and the information memory 35, or may incorporate the program memory 33 and the information memory 35.

[0033] The program memory 33 stores a plurality of instructions 34 executable by the processor 32. A program made up of the plurality of instructions 34 may be stored in a computer-readable non-transitory storage medium or provided via a network. At least some of the plurality of instructions 34 are configured to cause the processor 32 to operate as the above-mentioned transmission data generation unit 301, transmission signal generation unit 302, and control device 100. The information memory 25 stores various information such as payload, control information for communication, position information of the host station 30, communication area, and a list of unique IDs of each sub-base station 40 and cooperative station 50.

[0034] 4 is a functional block diagram showing the configuration of a sub-base station 40 according to this embodiment. As shown in Fig. 4, the sub-base station 40 includes a signal receiving unit 401, a processing station determining unit 402, a signal transmission method determining unit 403, a signal transmitting unit 404, and a MIMO demodulating unit 405.

[0035] The signal receiving unit 401 receives a transmission signal from the mobile station 30 at the base station antenna 41 and performs processing such as frequency conversion on the received signal. The signal receiving unit 401 outputs the processed signal to the processing station determining unit 402.

[0036] The processing station determination unit 402 extracts control information assigned to the signal. Based on the control information, the processing station determination unit 402 determines whether to perform MIMO processing in the local station or to transmit the signal to the cooperative station 50 in the second layer. If the unique ID included in the control information matches the unique ID of the local station, the processing station determination unit 402 determines to perform MIMO processing in the local station. If the unique ID included in the control information does not match the unique ID of the local station, the processing station determination unit 402 determines to transmit the signal to the cooperative station 50 in the second layer. If it is determined that MIMO processing is to be performed in the local station, the processing station determination unit 402 outputs the signal to the MIMO demodulation unit 405. If it is determined that the signal is to be transmitted to the cooperative station 50, the processing station determination unit 402 outputs the signal to the signal transmission method determination unit 403.

[0037] The MIMO demodulation unit 405 performs signal separation by performing general MIMO processing such as timing synchronization, frequency synchronization, and channel estimation on the signals acquired from the processing station determination unit 402. The MIMO demodulation unit 405 demodulates the separated signals and transmits the demodulated signals to the core network 2.

[0038] The signal transmission method determination unit 403 determines a method for transmitting signals to the cooperative station 50 based on a predetermined algorithm. There are no limitations on the transmission method, but a transmission method that reduces the number of signals output from the local station compared to the number of signals input to the local station is preferable. For example, a method of transmitting only signals with power exceeding a threshold, or transmitting signals with a reduced number of signals by maximum ratio combining may be used.

[0039] The signal transmission unit 404 performs signal processing using the method determined by the signal transmission method determination unit 403, and transmits the processed signal to the cooperative station 50 in the second layer. The cooperative station 50 to which the signal is transmitted is the cooperative station 50 that belongs to the second layer and is directly connected to the cooperative station 50 via the communication line 26.

[0040] 5 is a diagram showing an example of the hardware configuration of the sub-base station 40. The sub-base station 40 is a signal processing device including a processor 42, a program memory 43, an information memory 45, a wireless communication interface 46 for MIMO communication, and a communication interface 47. The communication interface 47 is a communication interface for communicating with the communication line 26 and the communication line 27. There may be a plurality of each of the processors 42, the program memories 43, and the information memories 45.

[0041] The processor 42 may be a CPU, RISC, DSP, FPGA, ASIC, PLD, or another processing unit, or may be a combination of two or more thereof, or may be a dedicated processor for the wireless communication system according to the present embodiment. The processor 42 may also be communicatively coupled to the program memory 43 and the information memory 45, or may incorporate the program memory 43 and the information memory 45.

[0042] The program memory 43 stores a plurality of instructions 44 executable by the processor 42. A program consisting of the plurality of instructions 44 may be stored in a computer-readable non-transitory storage medium or provided via a network. At least some of the plurality of instructions 44 are configured to cause the processor 42 to operate as the above-mentioned signal receiving unit 401, processing station determining unit 402, signal transmission method determining unit 403, signal transmitting unit 404, and MIMO demodulating unit 405. The information memory 45 stores, for example, a unique ID of the own station.

[0043] 6 is a functional block diagram showing the configuration of a cooperative station 50 according to this embodiment. As shown in Fig. 6, the cooperative station 50 includes a signal receiving unit 501, a processing station determining unit 502, a signal transmission method determining unit 503, a signal transmitting unit 504, and a MIMO demodulating unit 505.

[0044] The signal receiving unit 501 receives signals from multiple cooperative stations 50 in the immediately higher layer. The received signals are transmission signals from the mobile station 30 that have been processed at the time of signal transmission by the sub-base station 40 or a cooperative station 50 in the immediately higher layer. The source of the received signal is a cooperative station 50 that belongs to the immediately higher layer and is directly connected to the cooperative station 50 via a communication line 26. The signal receiving unit 501 outputs the received signal to the processing station determining unit 502.

[0045] The processing station determination unit 502 extracts control information assigned to the signal. Based on the control information, the processing station determination unit 502 determines whether to perform MIMO processing in the local station or to transmit the signal to the cooperative station 50 in the immediately lower layer. If the unique ID included in the control information matches the unique ID of the local station, the processing station determination unit 502 determines to perform MIMO processing in the local station. If the unique ID included in the control information does not match the unique ID of the local station, the processing station determination unit 502 determines to transmit the signal to the cooperative station 50 in the immediately lower layer. If it is determined that MIMO processing is to be performed in the local station, the processing station determination unit 502 outputs the signal to the MIMO demodulation unit 505. If it is determined that the signal is to be transmitted to the cooperative station 50 in the immediately lower layer, the processing station determination unit 502 outputs the signal to the signal transmission method determination unit 503.

[0046] The MIMO demodulation unit 505 performs signal separation by performing general MIMO processing such as timing synchronization, frequency synchronization, and channel estimation on the signals acquired from the processing station determination unit 502. The MIMO demodulation unit 505 demodulates the separated signals and transmits the demodulated signals to the core network 2.

[0047] The signal transmission method determination unit 503 determines a method for transmitting signals to the cooperative station 50 in the immediately lower layer based on a predetermined algorithm. There are no limitations on the transmission method, but a transmission method that reduces the number of signals output from the local station compared to the number of signals input to the local station is preferable. For example, a method of transmitting only signals with power exceeding a threshold or a method of transmitting signals with the number of signals reduced by maximum ratio combining may be used.

[0048] The signal transmission unit 504 performs signal processing using the method determined by the signal transmission method determination unit 503, and transmits the processed signal to the cooperative station 50 in the immediately lower layer. The cooperative station 50 to which the signal is transmitted is the cooperative station 50 that belongs to the immediately lower layer and is directly connected to the cooperative station 50 itself via the communication line 26.

[0049] 7 is a diagram showing an example of the hardware configuration of the cooperative station 50. The cooperative station 50 is a signal processing device including a processor 51, a program memory 52, an information memory 54, and a communication interface 55. The communication interface 55 is a communication interface for communicating with the communication line 26 and the communication line 27. There may be a plurality of each of the processors 51, the program memories 52, and the information memories 54.

[0050] The processor 51 may be a CPU, RISC, DSP, FPGA, ASIC, PLD, or another processing unit, or may be a combination of two or more thereof, or may be a dedicated processor for the wireless communication system according to this embodiment. The processor 51 may also be communicatively coupled to the program memory 52 and the information memory 54, or may incorporate the program memory 52 and the information memory 54.

[0051] The program memory 52 stores a plurality of instructions 53 executable by the processor 51. A program consisting of the plurality of instructions 53 may be stored in a computer-readable non-transitory storage medium or provided via a network. At least some of the plurality of instructions 53 are configured to cause the processor 51 to operate as the above-mentioned signal receiving unit 501, processing station determining unit 502, signal transmission method determining unit 503, signal transmitting unit 504, and MIMO demodulating unit 505. The information memory 54 stores, for example, a unique ID of the own station.

[0052] 5. Operation of the Wireless Communication System Next, the operation of the wireless communication system 11 will be described with reference to FIGS.

[0053] First, the operation of the mobile station 30 will be described. The operation of the mobile station 30 is shown in the flow diagram of Fig. 8. In step S101, the mobile station 30 generates transmission data including a payload. In step S102, the mobile station 30 detects the required conditions for transmission capacity and delay of the transmission data generated in step S101 based on the application information.

[0054] In step S103, the mobile station 30 acquires its own location information using, for example, GPS. Next, in step S104, the mobile station 30 detects the sub-base station 40 and cooperative station 50 that are targets of MIMO processing, based on the own location information acquired in step S103 and known information about the size of the communication area formed by the mobile station.

[0055] In step S105, the mobile station 30 determines whether or not the transmission capacity and delay have been calculated for all sub-base stations 40 and cooperative stations 50 detected in step S104. The calculation of the transmission capacity and delay is performed in step S106. In step S106, the mobile station 30 calculates the transmission capacity and delay for each station in order from the highest hierarchical level.

[0056] In step S107, the mobile station 30 determines whether the transmission capacity and delay calculated in step S106 satisfy the requirements detected in step S102. Until the requirements are satisfied for any station, the flow returns to step S105, and the calculation in step S106 and the determination in step S107 are performed again.

[0057] If the requirements are met in step S107, the flow proceeds to step S108. In step S108, the mobile station 30 determines the sub-base station 40 or cooperative station 50 that meets the requirements as the processing station that will perform MIMO processing on the transmission data.

[0058] On the other hand, if the calculation of the transmission capacity and delay for all the sub-base stations 40 and cooperative stations 50 is completed without the required conditions being satisfied, the flow proceeds to step S109. In step S109, the mobile station 30 determines the sub-base station 40 or cooperative station 50 that most closely meets the required conditions as the processing station that will perform MIMO processing on the transmission data.

[0059] If a processing station is determined in step S108 or step S109, the flow proceeds to step S110. In step S110, the mobile station 30 generates control information for processing station determination based on the determination result in step S108 or step S109. The control information includes a unique ID of the sub-base station 40 or cooperative station 50 determined as the processing station in step S108 or step S109.

[0060] In step S111, the mobile station 30 adds the control information generated in step S110 to the transmission data generated in step S101, and performs processing such as modulation and frequency conversion to generate a transmission signal.

[0061] In step S112, the mobile station 30 emits the transmission signal generated in step S111 from the antenna 31. Here, the format of the transmission signal transmitted from the mobile station 30 will be described. The base station 20 needs to extract control information from the transmission signal to determine the processing station. To facilitate extraction of the control information at the sub-base station 40 or the cooperative station 50, the transmission signal has a format as shown in any of the embodiments in FIG. 9. In each embodiment, the payload is the target of MIMO multiplexing transmission, and the control information can be extracted without MIMO processing. In the first embodiment, the control information is an orthogonal sequence such as a Gold sequence, and is inserted before or after the payload frame. In the second embodiment, the control information is separated from the payload on the time axis. In the third embodiment, the control information is separated from the payload on the frequency axis.

[0062] Next, we will continue to explain the operation of the base station 20. The operation of the base station 20 is shown in the flow diagram of Fig. 10. The first execution of step S201 is performed by the sub-base station 40. The sub-base station 40 receives a transmission signal from the mobile station 30 at the base station antenna 41 and performs processing such as frequency conversion on the received signal.

[0063] Next, in step S202, the sub-base station 40 extracts control information added to the signal for determining the processing station. At this time, the control information is extracted using a method corresponding to the form of the transmission signal. For example, a correlator is used when an orthogonal sequence is used, and a filter is used when frequency division is used. The sub-base station 40 determines whether the unique ID included in the control information matches the unique ID of its own station.

[0064] If the unique ID included in the control information matches the unique ID of the sub-base station 40, the flow proceeds to step S203. In step S203, the sub-base station 40 performs MIMO processing such as timing synchronization, frequency synchronization, and channel estimation on the acquired signals to separate the signals and demodulate the separated signals. Then, in step S204, the sub-base station 40 transmits the demodulated signals to the core network 2. This completes the processing in the base station 20.

[0065] On the other hand, if the unique ID included in the control information does not match the unique ID of the sub-base station 40, the flow proceeds to step S205. In step S205, the sub-base station 40 determines whether MIMO processing is performed by a station in the same hierarchical layer, i.e., another sub-base station 40. Whether the other sub-base station 40 is a processing station can be determined from the number representing the hierarchical layer of the unique ID included in the control information.

[0066] If the sub-base station 40 is not a processing station and MIMO processing is not performed by other sub-base stations 40, the flow proceeds to step S206. In step S206, the sub-base station 40 determines to transmit a signal to the cooperative station 50 in the immediately lower layer. Then, in step S207, the sub-base station 40 determines a signal transmission method for the cooperative station 50 in the immediately lower layer based on a set algorithm, and processes the received signal based on the determined signal transmission method. The sub-base station 40 then transmits the processed signal to the cooperative station 50 in the immediately lower layer.

[0067] If the sub-base station 40 is not a processing station but MIMO processing is performed by another sub-base station 40, the flow proceeds to step S208. In this case, MIMO processing on the received signal is performed by the other sub-base station 40, so there is no need to transmit the signal to the lower cooperative station 50. Therefore, in step S208, the sub-base station 40 discards the received signal and does not transmit the signal to the cooperative station 50.

[0068] When the sub-base station 40 transmits a signal to the cooperative station 50 in the next lower hierarchical layer, the flow returns to step S201. Steps S201 to S208 are executed by the cooperative station 50 from the second time onwards. In step S201, the cooperative station 50 receives a signal from a station in the next higher hierarchical layer. Next, in step S202, the cooperative station 50 extracts control information attached to the signal and determines whether the unique ID included in the control information matches its own unique ID.

[0069] If the unique ID of the cooperative station 50 does not match the unique ID included in the control information, the flow proceeds to step S205. In step S202, the cooperative station 50 determines whether another cooperative station 50 in the same hierarchical layer is performing MIMO processing. The operations of steps S202, S205, S206, S207, and S201 are repeated until the condition for determination in step S202 is met, or until the condition for determination in step S205 is met. However, each time the flow returns to step S201, the operating cooperative station 50 is switched to the cooperative station 50 in the immediately lower hierarchical layer.

[0070] If the unique ID of the cooperative station 50 matches the unique ID included in the control information, the flow proceeds to step S203. In step S203, the cooperative station 50 performs MIMO processing on the acquired signal. Then, in step S204, the cooperative station 50 transmits the demodulated signal to the core network 2. This ends the processing in the base station 20.

[0071] By operating the wireless communication system 11 as described above, the sub-base station 40 or cooperative station 50 according to the required conditions is used for MIMO processing of the received signal from the mobile station 30, so that the transmission capacity and delay required by the application can be realized.

[0072] 6. Specific Examples of Operation of the Wireless Communication System Next, a specific example of the operation of the wireless communication system 11 will be described. Figures 11 to 13 are diagrams showing specific examples of the operation of the wireless communication system 11. In the following specific examples, it is assumed that the communication area 300 of the mobile station 30 is small compared to the sub-base stations 40 that are widely deployed, and that signals reach only some of the sub-base stations 40. In the following specific examples, it is assumed that the mobile station 30 is a LEO satellite whose communication area varies over time. In the following specific examples, it is assumed that the mobile station 30 is equipped with two antennas 31, and each sub-base station 40 is equipped with four base station antennas 41.

[0073] 11, the communication area 300 of the mobile station 30 spans the sub-base station 40(1,1) and the sub-base station 40(1,2). In this case, the communication target detection unit 102 of the mobile station 30 detects the sub-base station 40(1,1) and the sub-base station 40(1,2) and the second-layer cooperative station 50(2,1) to which the sub-base station 40(1,1) and the sub-base station 40(1,2) are connected as communication target stations.

[0074] 12 shows the operation of the wireless communication system 11 when the required conditions for communication performance are low transmission capacity and low delay. In this case, the processing station determination unit 105 of the mobile station 30 first determines which stations among the communication target stations satisfy the required conditions of low transmission capacity and low delay. If the determination result indicates that the sub-base station 40 (1, 1) satisfies the required conditions, control information including the unique ID (1, 1) is generated. Then, a signal with the control information attached is transmitted from the mobile station 30 to the base station 20.

[0075] The signal with the control information transmitted from the mobile station 30 to the base station 20 is received by the sub-base station 40(1,1) and the sub-base station 40(1,2). Upon detecting that its own unique ID (1,1) matches the unique ID (1,1) included in the control information, the sub-base station 40(1,2) performs MIMO processing on the signal received from the base station 20 and transmits the demodulated signal to the core network 2.

[0076] Meanwhile, sub-base station 40(1,2) confirms that its own unique ID (1,2) does not match the unique ID (1,1) included in the control information. It also confirms from the hierarchical layer number of the unique ID (1,1) included in the control information that another sub-base station 40 in the same hierarchical layer is performing MIMO processing. Therefore, sub-base station 40(1,2) discards the received signal and terminates processing.

[0077] 13 shows the operation of the wireless communication system 11 when a required condition for communication performance is a large transmission capacity. In this case, the processing station determination unit 105 of the mobile station 30 first determines which stations among the communication target stations satisfy the required condition of a large transmission capacity. The determination is made in the order of the sub-base station 40 (1,1), the sub-base station 40 (1,2), and the cooperative station 50 (2,1) from the highest hierarchy. If the determination result indicates that the cooperative station 50 (2,1) satisfies the required condition, control information including the unique ID (2,1) is generated. Then, a signal with the control information attached is transmitted from the mobile station 30 to the base station 20.

[0078] The signal with the control information transmitted from the mobile station 30 to the base station 20 is received by the sub-base station 40(1,1) and the sub-base station 40(1,2). Because the sub-base station 40(1,1) and the sub-base station 40(1,2) do not match their own unique IDs with the unique IDs included in the control information and because the hierarchical number of the unique ID included in the control information indicates a lower hierarchical layer, the sub-base station 40(1,1) and the sub-base station 40(1,2) transmit the signal received from the base station 20 to the cooperative station 50 in the immediately lower hierarchical layer.

[0079] The signals transmitted from the sub-base station 40(1,1) and the sub-base station 40(1,2) are received by the cooperative station 50(2,1) in the second layer. Upon detecting that its own unique ID (2,1) matches the unique ID (2,1) included in the control information, the cooperative station 50(2,1) performs MIMO processing on the signals received from the base station 20 and transmits the demodulated signals to the core network 2.

[0080] 7. Modifications Fig. 14 is a diagram showing a modification of the configuration of the wireless communication system according to the embodiment. In the modification, a wireless communication system 12 includes a control device 100 in a control station 60. The control station 60 exists independently of the mobile stations 30 and the base stations 20, and controls the mobile stations 30 and the base stations 20. The control station 60 and the mobile stations 30 are connected wirelessly. The control station 60 and the base stations 20 are connected wirelessly or by wire. For example, as illustrated in Fig. 14, the control station 60 and each sub-base station 40 of the base station 20 may be connected by an optical line 28. In this case, control information generated by the control device 100 can be transmitted to each sub-base station 40 via the optical line 28.

[0081] 2 Core network 11, 12 Wireless communication system 20 Base station 30 Mobile station 31 Antenna 40 Sub-base station (signal processing device) 41 Base station antenna 50 Cooperative station (signal processing device) 100 Control device 300 Communication area

Claims

1. A wireless communication system comprising: a mobile station equipped with multiple antennas and having a MIMO processing function for transmitting / separating multiple signals in parallel; a base station equipped with multiple base station antennas distributed over an area equal to or larger than the communication area of ​​the mobile station and multiple signal processing devices having MIMO processing functions and connected to any of the multiple base station antennas; and a control device configured to detect or estimate required conditions for communication performance between the mobile station and the base station, wherein the base station is configured to use, among the multiple signal processing devices, a signal processing device that satisfies or is closest to the required conditions detected or estimated by the control device for MIMO processing of received signals from the mobile station.

2. A wireless communication system according to claim 1, wherein the control device is configured to execute the following operations: select a base station antenna to be used for communication with the mobile station from among the plurality of base station antennas based on the position of the mobile station; select a signal processing device that satisfies the required conditions or is closest to the required conditions from among one or more signal processing devices connected to the selected base station antenna; and generate control information to identify the selected signal processing device; and the base station is configured to select a signal processing device to be used for MIMO processing of the received signal in accordance with the control information.

3. A wireless communication system according to claim 2, wherein the base station has a hierarchical structure consisting of a plurality of signal processing devices, the plurality of signal processing devices including a plurality of sub-base stations belonging to the highest hierarchy and equipped with a plurality of base station antennas, and a plurality of cooperative stations belonging to a hierarchy lower than the second hierarchy, each of the plurality of sub-base stations being connected to a plurality of cooperative stations belonging to the second hierarchy, each of the plurality of cooperative stations being connected to a plurality of sub-base stations or cooperative stations belonging to an immediately higher hierarchy and a plurality of cooperative stations belonging to an immediately lower hierarchy, and each of the plurality of sub-base stations and cooperative stations being configured to determine, based on the control information provided by the control device, whether to perform MIMO processing on the received signal in the own station or to transmit the received signal to a lower station.

4. A wireless communication system according to claim 3, characterized in that the control device is configured to generate the control information based on communication line capacity between each of the plurality of sub-base stations and cooperative stations and a core network.

5. A wireless communication system according to any one of claims 1 to 4, characterized in that the control device is mounted on the mobile station, or on a control station that exists independently of the mobile station and the base station and communicates with the mobile station and the base station.

6. A wireless communication method for wireless communication between a mobile station and a base station, wherein the mobile station is equipped with multiple antennas and has a MIMO processing function for transmitting / separating multiple signals in parallel, and the base station is equipped with multiple base station antennas distributed over an area equal to or larger than the communication area of ​​the mobile station, and multiple signal processing devices having a MIMO processing function and connected to any of the multiple base station antennas, the wireless communication method comprising: detecting or estimating required conditions for communication performance between the mobile station and the base station; and using, among the multiple signal processing devices, a signal processing device that satisfies the required conditions or is closest to the required conditions for MIMO processing of a signal received from the mobile station.

7. A control device for a wireless communication system that performs wireless communication between a mobile station and a base station, wherein the mobile station is equipped with multiple antennas and has a MIMO processing function for transmitting / separating multiple signals in parallel, and the base station is equipped with multiple base station antennas that are distributed over an area equal to or larger than the communication area of ​​the mobile station, and multiple signal processing devices having a MIMO processing function that are connected to any of the multiple base station antennas, and the control device is configured to: detect or estimate required conditions for communication performance between the mobile station and the base station, and cause a signal processing device among the multiple signal processing devices that satisfies the required conditions or is closest to the required conditions to perform MIMO processing on a received signal from the mobile station.

8. A program including a plurality of instructions for operating a control device of a wireless communication system that performs wireless communication between a mobile station and a base station, wherein the mobile station has a plurality of antennas and has a MIMO processing function for transmitting / separating a plurality of signals in parallel, and the base station has a plurality of base station antennas that are distributed over an area equal to or larger than the communication area of ​​the mobile station, and a plurality of signal processing devices having a MIMO processing function that are connected to any of the plurality of base station antennas, and the plurality of instructions are configured to cause the control device to execute the following: detect or estimate required conditions for communication performance between the mobile station and the base station; and cause a signal processing device among the plurality of signal processing devices that satisfies the required conditions or is closest to the required conditions to perform MIMO processing on a received signal from the mobile station.