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

Abstract

The present disclosure relates to a wireless communication system, a wireless communication method, a wireless communication device, and a wireless communication program. This wireless communication system is provided with: a transmission station having at least one transmission antenna; and a reception station that has a plurality of reception antennas and a plurality of signal synthesis units for synthesizing received signals and that performs wireless communication with the transmission station. This reception station is configured to execute: processing of clustering a plurality of reception antennas into at least one cluster such that the plurality of reception antennas are included in each cluster; processing of assigning a signal synthesis unit to the at least one cluster; processing of setting, for the plurality of reception antennas assigned to the same cluster, antenna pairs such that the minimum propagation delay time difference is maximized, and performing mapping for assigning the signal synthesis unit to each antenna pair; and processing of synthesizing signals received from the transmission station on the basis of the mapping.

Description

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

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

[0002] In recent years, in wireless communication using a non-terrestrial network (NTN), many use cases of wireless communication are assumed. For example, Non-Patent Document 1 discloses use cases such as direct accommodation of terrestrial mobile terminals, mobile backhaul, or accommodation of IoT terminals. Non-Patent Document 2 also discloses a technique using an ultra-wideband massive MIMO (Multiple-Input and Multiple-Output) system.

[0003] On the other hand, Non-Patent Document 3 discloses MIMO demodulation that can reduce the amount of computation. In this MIMO demodulation, MIMO equalization is performed by synthesizing the received signals of each antenna before performing synchronization or channel estimation.

[0004] Inter-symbol interference (ISI) occurs in the above synthesis. In Non-Patent Document 3, delay compensation is performed to remove ISI.

[0005] The above delay compensation is performed by adopting an orthogonal frequency division multiplexing (OFDM) system as a communication method and using a guard interval (Cyclic Prefix: CP) inserted at the head of each symbol.

[0006] 3GPP TR 38.821, Solutions for NR to Support Non-Terrestrial Networks (NTN) (Release 16), V16.1.0, May. 2021. Tatekami et al., "Proposal for a Hierarchical Base Station Configuration in a Massive Wide-Area MIMO System," IEICE General Conference, B-3-5, Mar. 2023. Tatekami et al., "Proposal for a Demodulation Method Using OFDM in Satellite MIMO Utilizing Large-Scale GW Antennas," IEICE General Conference, B-3-6, Mar. 2024.

[0007] To eliminate ISI using a CP (Control Panel), the length of the CP (CP length) must be greater than the maximum propagation delay time difference of the combined signals. However, increasing the CP length reduces transmission efficiency, leading to a problem of reduced transmission capacity.

[0008] On the other hand, in order to reduce the CP length, it is preferable to combine received signals with similar propagation delay times. However, combining received signals with similar propagation delay times is likely to increase the correlation of the MIMO spatial channels after combination. High correlation of MIMO spatial channels can lead to problems such as deterioration of MIMO equalization performance, i.e., spatial signal separation performance, or capacity fluctuations during satellite movement.

[0009] The primary objective of this disclosure is to provide a wireless communication system that can improve transmission capacity by reducing the correlation of MIMO spatial channels and simultaneously reducing the CP length, in order to solve the aforementioned problems.

[0010] Furthermore, a second objective of this disclosure is to provide a wireless communication method that can improve transmission capacity by reducing the correlation of MIMO spatial channels and simultaneously reducing the CP length.

[0011] Furthermore, a third objective of this disclosure is to provide a wireless communication device that can improve transmission capacity by reducing the correlation of MIMO spatial channels and simultaneously reducing the CP length.

[0012] Furthermore, a fourth objective of this disclosure is to provide a wireless communication program that can improve transmission capacity by reducing the correlation of MIMO spatial channels and simultaneously reducing the CP length.

[0013] A first aspect of the present disclosure is preferably a wireless communication system comprising: a transmitting station having at least one transmitting antenna; a plurality of receiving antennas; a plurality of signal combining units for combining received signals; and a receiving station performing wireless communication with the transmitting station, wherein the receiving station is configured to perform the following processes: clustering the plurality of receiving antennas into at least one cluster such that each cluster includes a plurality of receiving antennas; assigning a signal combining unit to at least one cluster; setting up antenna pairs for the plurality of receiving antennas assigned to the same cluster such that the smallest propagation delay time difference is maximized, and performing mapping to assign a signal combining unit to each antenna pair; and combining the signals received from the transmitting station based on the mapping.

[0014] Furthermore, a second aspect of the present disclosure is a wireless communication method to be implemented in a wireless communication system comprising: a transmitting station having at least one transmitting antenna; a plurality of receiving antennas; and a plurality of signal combining units for combining received signals, and a receiving station performing wireless communication with the transmitting station, wherein the wireless communication method preferably comprises: clustering the plurality of receiving antennas into at least one cluster such that each cluster includes a plurality of receiving antennas; assigning a signal combining unit to at least one cluster; setting up antenna pairs for the plurality of receiving antennas assigned to the same cluster such that the smallest propagation delay time difference is maximized, and performing mapping for assigning a signal combining unit to each antenna pair; and combining the signals received from the transmitting station based on the mapping.

[0015] Furthermore, a third aspect of the present disclosure is a wireless communication device that performs wireless communication with a transmitting station having a plurality of receiving antennas and a plurality of signal combining units for combining received signals, wherein the wireless communication device comprises: a process of clustering the plurality of receiving antennas into at least one cluster such that each cluster includes a plurality of receiving antennas; a process of assigning a signal combining unit to at least one cluster; a process of setting up antenna pairs for the plurality of receiving antennas assigned to the same cluster such that the smallest propagation delay time difference is maximized, and performing mapping to assign a signal combining unit to each antenna pair; and a process of combining signals received from the transmitting station based on the mapping.

[0016] Furthermore, a fourth aspect of the present disclosure is preferably a wireless communication program to be implemented by a wireless communication device that performs wireless communication with a transmitting station having a processor, memory, a plurality of receiving antennas, a plurality of signal combining units for combining received signals, and at least one transmitting antenna, the program being stored in memory and computer-readable, and which causes the processor to perform the following processes: clustering the plurality of receiving antennas into at least one cluster such that each cluster contains a plurality of receiving antennas; assigning a signal combining unit to at least one cluster; setting up antenna pairs for the plurality of receiving antennas assigned to the same cluster such that the smallest propagation delay time difference is maximized, and performing mapping to assign a signal combining unit to each antenna pair; and combining signals received from the transmitting station based on the mapping.

[0017] According to the first to fourth aspects of this disclosure, transmission capacity can be improved by reducing the correlation of MIMO spatial channels and simultaneously reducing the CP length.

[0018] This figure shows an example configuration of a wireless communication system according to Embodiment 1 of this disclosure. This figure shows an example configuration of a transmitting station according to Embodiment 1 of this disclosure. This figure shows an example configuration of a receiving station according to Embodiment 1 of this disclosure. This figure shows the hardware configuration of a receiving station according to Embodiment 1 of this disclosure. This flowchart shows the processing performed by the wireless communication system according to Embodiment 1 of this disclosure. This figure shows the signal synthesis performed by the signal synthesis unit according to the first comparative example. This figure shows the signal synthesis performed by the signal synthesis unit according to the second comparative example. This figure shows the first clustering result according to Embodiment 1 of this disclosure. This figure shows the second clustering result according to Embodiment 1 of this disclosure. This figure shows the third clustering result according to Embodiment 1 of this disclosure. This figure shows an example configuration of a wireless communication system according to Embodiment 2 of this disclosure. This figure shows an example configuration of a transmitting station according to Embodiment 2 of this disclosure. This figure shows an example configuration of a receiving station according to Embodiment 2 of this disclosure. This flowchart shows the processing performed by the wireless communication system according to Embodiment 2 of this disclosure.

[0019] Each embodiment will be described with reference to the drawings. The same or corresponding components will be denoted by the same reference numerals, and repetition of the description may be omitted.

[0020] Embodiment 1 Figure 1 is a diagram showing an example configuration of a wireless communication system according to Embodiment 1 of the present disclosure. The wireless communication system 100 includes a transmitting station 2. The transmitting station 2 has transmitting antennas 21a to 21m. That is, the transmitting station 2 has m transmitting antennas, where m is any natural number.

[0021] Transmitting station 2 communicates wirelessly with receiving station 4 via transmitting antennas 21a to 21m. Receiving station 4 communicates wirelessly with transmitting station 2 via receiving antennas 41a to 41n. In other words, receiving station 4 has n receiving antennas, where n is any natural number. Hereafter, receiving antennas 41a to 41n will be referred to as the antenna section 41.

[0022] The signal received by the antenna unit 41 is transmitted to the signal assignment unit 42. The signal assignment unit 42 assigns the received signal. This assignment is performed based on the mapping performed by the signal assignment control unit 44, which will be described later. Details of the assignment method will be described later.

[0023] Furthermore, the signal synthesis units 43a to 43l synthesize the received signals according to the assignments made by the signal assignment unit 42.

[0024] As described above, the wireless communication system 100 notifies the receiving station 4 of the CP length arbitrarily set by the transmitting station 2. The receiving station 4 controls the allocation of signals to be combined based on the notified CP length.

[0025] Figure 2 shows an example of the configuration of a transmitting station according to Embodiment 1 of the present disclosure. The transmitting station 2 has a CP length setting unit 24. The CP length setting unit 24 sets an arbitrary CP length.

[0026] The CP length setting unit 24 transmits the set CP length to the CP length notification unit 26. The CP length notification unit 26 notifies the receiving station 4 of the received CP length. The receiving station 4 controls signal synthesis based on the notified CP length.

[0027] The CP length setting unit 24 also transmits the set CP length to the transmission signal generation unit 28. The transmission signal generation unit 28 generates a signal for wireless communication. The transmission signal generation unit 28 generates a signal for wireless communication by, for example, performing S / P conversion, error correction, or modulation. This signal is a signal that can be time / frequency equalized at the receiving station 4.

[0028] The signal generated by the transmission signal generation unit 28 is transmitted to the transmission antennas 21a to 21m. The transmission antennas 21a to 21m transmit the received signal to the receiving antennas 41a to 41n.

[0029] Figure 3 shows an example of the configuration of a receiving station according to Embodiment 1 of the present disclosure. The receiving station 4 has receiving antennas 41a to 41n. The receiving antennas 41a to 41n receive signals from the transmitting station 2.

[0030] The receiving antenna 41a transmits the received signal to the signal transmitting / receiving unit 46a. The signal transmitting / receiving unit 46a transmits the received signal to the receiving unit 47a. This transmission may be performed, for example, by wireless communication or by optical fiber communication. Optical fiber communication is, for example, RoF (Radio over Fiber).

[0031] Similarly, the receiving antenna 41b transmits the received signal to the signal transmitting / receiving unit 46b. Similarly, the signal transmitting / receiving unit 46b transmits the received signal to the receiving unit 47b. The same applies to the receiving antennas 41c to 41n and the signal transmitting / receiving units 46c to 46n.

[0032] The receiving units 47a to 47n transmit the received signals to the signal assignment unit 42. If the transmission of signals from the signal transmitting / receiving units 46a to 46n to the receiving units 47a to 47n is performed using optical fiber communication, this transmission involves conversion from optical signals to electrical signals.

[0033] The signal assignment unit 42 assigns the received signals. Details of the assignment method will be described later.

[0034] The signal combining unit 43a combines the received signals. In doing so, the signal combining unit 43a combines the signals without synchronization. That is, the signal combining unit 43a receives a pseudo-multipath signal. The signal combining unit 43a then transmits the combined signal to the time / frequency equalization unit 48a. The same applies to the signal combining units 43b to 43l.

[0035] The time / frequency equalization unit 48a performs time equalization and frequency equalization of the synthesized signal. That is, the time / frequency equalization unit 48a performs time equalization and frequency equalization on the pseudo-multipath signal. As a result, the pseudo-multipath signal is spatially multiplexed. The time / frequency equalization unit 48a then transmits the time-equalized and frequency-equalized signal to the MIMO demodulation unit 49. The same applies to the time / frequency equalization units 48b to 48l.

[0036] The MIMO demodulation unit 49 separates the signals by performing MIMO equalization on the signals that have undergone time equalization and frequency equalization.

[0037] Meanwhile, the CP length information acquisition unit 45 of the receiving station 4 acquires the CP length reported by the transmitting station 2 and transmits it to the signal allocation control unit 44. Based on the received CP length, the signal allocation control unit 44 performs clustering of receiving antennas 41a to 41n and allocation of signal combining units 43a to 43l.

[0038] Specifically, the signal allocation control unit 44 first clusters the receiving antennas 41a to 41n based on the CP length. This clustering is performed so that the receiving antennas 41a to 41n are clustered into at least one cluster such that each cluster contains multiple receiving antennas.

[0039] Next, the signal assignment control unit 44 assigns signal synthesis units 43a to 43l to each cluster. Furthermore, the signal assignment control unit 44 performs mapping.

[0040] Let's explain the mapping. First, the signal assignment control unit 44 sets up antenna pairs for receiving antennas assigned to the same cluster so that the propagation delay time difference, which is the minimum, is maximized. Next, the signal assignment control unit 44a assigns a signal combining unit, which is assigned to the same cluster, to each antenna pair.

[0041] The signal assignment control unit 44 transmits the mapping result to the signal assignment unit 42. The signal assignment unit 42 assigns the received signals based on the received mapping result. The signal synthesis unit 43a receives the signals assigned based on the mapping and synthesizes them.

[0042] Figure 4 shows the hardware configuration of a receiving station according to Embodiment 1 of this disclosure. Each function of the receiving station 4 may be partially or entirely configured by hardware such as a PLD (Programmable Logic Device) or FPGA (Field Programmable Gate Array), or it may be configured as a program executed by a processor such as a CPU.

[0043] For example, the receiving station 4 can be implemented using a computer and a program, and the program can be recorded on a storage medium or provided via a network.

[0044] As shown in FIG. 4, the receiving station 4 includes an input unit 400, an output unit 401, a communication unit 402, a CPU 403, a memory 404, and an HDD 405 connected via a bus 406, and has functions as a computer. Further, the receiving station 4 is capable of inputting and outputting data to and from a computer-readable storage medium 407.

[0045] The input unit 400 is, for example, a keyboard and a mouse. The output unit 401 is, for example, a display device such as a display.

[0046] The communication unit 402 is, for example, a communication interface that communicates with a wireless device to be controlled.

[0047] The CPU 403 controls each part constituting the receiving station 4 and performs predetermined processing and the like. The memory 404 and the HDD 405 store data and the like.

[0048] The storage medium 407 is capable of storing a program for executing the functions of the receiving station 4. Note that the architecture constituting the receiving station 4 is not limited to the example shown in FIG. 4.

[0049] FIG. 5 is a flowchart showing the processing performed by the wireless communication system according to Embodiment 1 of the present disclosure. Here, the processing performed by the transmitting station 2 and the receiving station 4 is shown in a flowchart.

[0050] First, in step 100, the transmitting station 2 determines the CP length. Next, in step 102, the transmitting station 2 notifies the receiving station 4 of the set CP length. Next, in step 104, the receiving station 4 receives the CP length.

[0051] Next, in step 106, the receiving station 4 performs clustering of the receiving antennas 41a to 41n. This clustering is performed by clustering a plurality of receiving antennas into at least one cluster such that each cluster includes a plurality of receiving antennas. The propagation delay time difference between the signals received by the receiving antennas in the same cluster is made shorter than the CP length.

[0052] Next, in step 108, the receiving station 4 assigns signal combining units 43a to 43l to each cluster.

[0053] Next, in step 110, the receiving station 4 performs mapping. First, the receiving station 4 sets up antenna pairs such that the smallest propagation delay time difference is maximized for receiving antennas assigned to the same cluster. Next, the receiving station 4 assigns a signal combining unit, which is assigned to the same cluster, to each antenna pair.

[0054] Next, in step 112, the transmitting station 2 generates a signal for wireless communication. This signal is generated to reflect the CP length set in step 100.

[0055] Next, in step 114, the transmitting station 2 checks whether the generated signal has been assigned to the receiving station 4. If it has been assigned, the process proceeds to step 116. If it has not been assigned, step 114 is repeated until assignment information is received.

[0056] Next, in step 116, transmitting station 2 transmits a signal via transmitting antennas 21a to 21m. Next, in step 118, receiving station 4 receives the signal with receiving antennas 41a to 41n. Next, in step 120, receiving station 4 acquires the signal from receiving antennas 41a to 41n.

[0057] Next, in step 122, the receiving station 4 combines the received signals. This combination is performed based on the mapping done in step 110. At this time, the receiving station 4 combines the signals without any synchronization or other processes. In other words, the receiving station 4 receives a pseudo-multipath signal.

[0058] Next, in step 124, the receiving station 4 performs time equalization and frequency equalization of the combined signals. As a result, the pseudo-multipath signals are spatially multiplexed.

[0059] Next, in step 126, the receiving station 4 performs MIMO equalization on the spatially multiplexed signal and terminates the processing. As a result, the signal received by the receiving station 4 is separated.

[0060] As a result of the above processing, the receiving station 4 can limit the maximum value of the propagation delay time difference input to each signal combining unit according to the announced CP length. In other words, channel correlation can be reduced.

[0061] The effects obtained by the wireless communication system according to this disclosure will be explained with reference to the figures. Figure 6 is a diagram showing the signal synthesis performed by the signal synthesis unit in the first comparative example. The first comparative example performs MIMO communication using a wireless communication system with the same configuration as the wireless communication system 100. The transmitting station 2 is a single satellite, and the receiving station 4 has distributed receiving antennas 41a to 41n.

[0062] The signal combining units 43a to 43l in the first comparative example acquire a MIMO-utilized signal by combining multiple received signals. This combination allows the receiving station 4 to process the multiple received signals as a multipath signal. Here, for example, we show the case where the signal combining unit 43a combines the received signals received from each of the receiving antennas 41a to 41n.

[0063] The receiving antennas 41a to 41n each receive signals that include a Fast Fourier Transform (FFT) section, which is their symbol. The FFT section includes signals such as s1 and s2, which are the target of wireless communication. A CP is inserted at the beginning of the FFT section. Furthermore, τ1 is defined as the maximum difference in propagation delay time of the signals received by each of the receiving antennas 41a to 41n.

[0064] Figure 7 shows the signal synthesis performed by the signal synthesis unit in the second comparative example. The second comparative example performs MIMO communication using the same wireless communication system as the first comparative example.

[0065] The signal synthesis unit 43a in the second comparative example acquires the MIMO utilization signal by synthesizing the received signals received from each of the receiving antennas 41a to 41n, similar to the case in Figure 6. However, in the second comparative example, the maximum value τ2 of the propagation delay time difference of the signals received by each of the receiving antennas 41a to 41n is larger than in the first comparative example. That is, τ2 is larger than τ1.

[0066] The issues addressed by this disclosure will be explained in detail with reference to Figures 6 and 7. In recent years, many wireless communication use cases are envisioned for wireless communication using NTN. For example, Non-Patent Literature 1 discloses use cases such as direct connection of terrestrial mobile terminals, mobile backhaul, and connection of IoT terminals.

[0067] As a result, wireless communication using NTN tends to have increased transmission capacity compared to existing satellite communication services. Therefore, increasing the capacity of the feeder link is required for wireless communication using NTN.

[0068] The feeder link is a circuit that connects the aerial platform to the ground gateway station. The aerial platform is, for example, a satellite or a High Altitude Platform Station (HAPS).

[0069] As a method for increasing the capacity of the feeder link, for example, Non-Patent Document 2 discloses a technology that uses an ultra-wide-area Massive MIMO system. In this technology, an ultra-wide-area Massive MIMO system is formed by arranging multiple antennas on an aerial platform and numerous small antennas on a ground gateway station. In other words, the number of spatial multiplexing operations is increased by installing numerous antennas on both the transmitting and receiving sides. As a result, an increase in the capacity of the feeder link can be expected.

[0070] The aforementioned technology requires the installation of numerous antennas, resulting in a problem of enormous computational load. To solve this problem, Non-Patent Document 3 discloses MIMO demodulation that can reduce the computational load. In this MIMO demodulation, MIMO equalization is performed by combining the received signals from each antenna before synchronization or channel estimation.

[0071] In the aforementioned synthesis, ISI occurs. Non-patent document 3 describes delay compensation to eliminate ISI.

[0072] The aforementioned delay compensation is achieved by adopting the OFDM method as the communication method and utilizing the CP inserted at the beginning of each symbol.

[0073] To eliminate ISI using a CP, the length of the CP (CP length) must be greater than the maximum value τ1 of the propagation delay time difference of the combined signals, as shown in the first comparative example in Figure 6. However, increasing the CP length reduces transmission efficiency, leading to the problem of reduced transmission capacity.

[0074] On the other hand, in order to reduce the CP length, it is preferable to combine received signals with similar propagation delay times. However, since received signals with similar propagation delay times have similar propagation delay path lengths, their phases tend to be close to the same phase. In other words, there is a high possibility that the correlation of the MIMO spatial channels after combination will be high. When the correlation of MIMO spatial channels is high, problems arise such as deterioration of MIMO equalization performance, i.e., spatial signal separation performance, or capacity fluctuations during satellite movement.

[0075] Furthermore, in order to reduce the correlation of MIMO spatial channels, it is preferable to combine received signals that have different phases. That is, as in the second comparative example shown in Figure 7, it is preferable to combine received signals that have a large maximum propagation delay time difference. However, in this case, because the propagation delay time difference is large, it is necessary to increase the CP length. As a result, the transmission efficiency decreases, leading to the problem of reduced transmission capacity.

[0076] As described above, there is a trade-off relationship between CP length and MIMO spatial channel. Therefore, in order to maintain high transmission capacity, a wireless communication system that can optimize the correlation between CP length and MIMO spatial channel is required. This disclosure aims to achieve this.

[0077] The assignment method according to Embodiment 1 of this disclosure will be explained with specific examples. Figure 8 is a diagram showing the first clustering result according to Embodiment 1 of this disclosure. Figure 9 is a diagram showing the second clustering result according to Embodiment 1 of this disclosure. Figure 10 is a diagram showing the third clustering result according to Embodiment 1 of this disclosure.

[0078] In Figures 8 to 10, the receiving station 4 is assumed to have eight receiving antennas 41a to 41h and four signal combining units 43a to 43d. Each signal combining unit combines two signals received by two receiving antennas, respectively.

[0079] Figure 8 shows the case where the receiving antennas 41a to 41h are clustered into a single cluster 80a as a result of the clustering performed in step 106 described above. In this case, as a result of the assignment performed in step 108 described above, the signal combining units 43a to 43d are assigned to cluster 80a.

[0080] In this case, step 110 described above first sets up antenna pairs for the receiving antennas assigned to the same cluster so that the smallest propagation delay time difference is maximized. For this reason, receiving antennas 41a and 41e, receiving antennas 41b and 41f, receiving antennas 41c and 41g, and receiving antennas 41d and 41h are each set up as antenna pairs.

[0081] Next, in step 110 described above, each pair of antennas is assigned a signal combining unit that is assigned to the same cluster. Therefore, the receiving antennas 41a and 41e are assigned a signal combining unit 43a, the receiving antennas 41b and 41f are assigned a signal combining unit 43b, the receiving antennas 41c and 41g are assigned a signal combining unit 43c, and the receiving antennas 41d and 41h are assigned a signal combining unit 43d.

[0082] Figure 9 shows the result of the clustering performed in step 106 above, where receiving antennas 41a to 41d are clustered into cluster 80a, and receiving antennas 41e to 41h are clustered into cluster 80b. In this case, as a result of the assignment performed in step 108 above, signal combining units 43a and 43b are assigned to cluster 80a, and signal combining units 43c and 43d are assigned to cluster 80b.

[0083] In this case, step 110 described above first sets up antenna pairs for receiving antennas assigned to the same cluster so that the smallest propagation delay time difference is maximized. For this reason, receiving antennas 41a and 41c, receiving antennas 41b and 41d, receiving antennas 41e and 41g, and receiving antennas 41f and 41h are set up as antenna pairs.

[0084] Next, in step 110 described above, each pair of antennas is assigned a signal combining unit that is assigned to the same cluster. Therefore, the receiving antennas 41a and 41c are assigned a signal combining unit 43a, the receiving antennas 41b and 41d are assigned a signal combining unit 43b, the receiving antennas 41e and 41g are assigned a signal combining unit 43c, and the receiving antennas 41f and 41h are assigned a signal combining unit 43d.

[0085] Figure 10 shows the result of the clustering performed in step 106 above, where receiving antennas 41a and 41b are clustered to cluster 80a, receiving antennas 41c and 41d are clustered to cluster 80b, receiving antennas 41e and 41f are clustered to cluster 80c, and receiving antennas 41g and 41h are clustered to cluster 80d. In this case, as a result of the assignment performed in step 108 above, the signal combining unit 43a is assigned to cluster 80a, the signal combining unit 43b is assigned to cluster 80b, the signal combining unit 43c is assigned to cluster 80c, and the signal combining unit 43d is assigned to cluster 80d.

[0086] In this case, step 110 described above first sets up antenna pairs for receiving antennas assigned to the same cluster so that the smallest propagation delay time difference is maximized. For this reason, receiving antennas 41a and 41b, receiving antennas 41c and 41d, receiving antennas 41e and 41f, and receiving antennas 41g and 41h are set up as antenna pairs.

[0087] Next, in step 110 described above, each pair of antennas is assigned a signal combining unit that is assigned to the same cluster. Therefore, the receiving antennas 41a and 41b are assigned a signal combining unit 43a, the receiving antennas 41c and 41d are assigned a signal combining unit 43b, the receiving antennas 41e and 41f are assigned a signal combining unit 43c, and the receiving antennas 41g and 41h are assigned a signal combining unit 43d.

[0088] As described above, in the first clustering result, the eight receiving antennas are clustered into one cluster. As a result, the channel correlation between the combined signals becomes low, but it becomes necessary to increase the CP length.

[0089] On the other hand, in the third clustering result, the eight receiving antennas are clustered into four clusters. As a result, the channel correlation between the combined signals is increased, while the CP length can be shortened.

[0090] Furthermore, in the second clustering result, the eight receiving antennas are clustered into two clusters. As a result, the CP length can be shortened compared to the first clustering result, and the channel correlation can be lowered compared to the third clustering result.

[0091] In this embodiment, when the reported CP length is long, a case with high channel correlation, as in the third clustering result, is not selected. In other words, it is possible to avoid problems such as deterioration of MIMO equalization performance, i.e., spatial signal separation performance, or capacity fluctuations during satellite movement, which can occur due to high channel correlation.

[0092] As described above, in the wireless communication system according to Embodiment 1 of this disclosure, the signals received by each clustered receiving antenna are combined. Therefore, compared to a case where the receiving antennas are not clustered, the propagation delay time difference can be reduced, and thus the CP length can be shortened. In other words, the transmission capacity can be improved.

[0093] Furthermore, in the wireless communication system according to Embodiment 1 of this disclosure, the clustered receiving antennas combine the signals with the largest propagation delay time difference from among the signals they have received. As a result, the correlation of MIMO spatial channels can be reduced compared to the case where propagation delay time difference is not considered. In other words, spatial signal separation performance can be improved, or capacity fluctuations during satellite movement can be reduced.

[0094] Embodiment 2 Figure 11 shows an example of the configuration of a wireless communication system according to Embodiment 2 of the present disclosure. The wireless communication system 100a differs from Embodiment 1 in that the receiving station 4a determines the CP etc. that maximizes the transmission capacity and notifies the transmitting station 2a of the determined CP.

[0095] Figure 12 shows an example configuration of a transmitting station according to Embodiment 2 of the present disclosure. The transmitting station 2a has a CP length setting unit 24a. The CP length setting unit 24a sets the CP length based on the CP length reported from the receiving station 4a.

[0096] Figure 13 shows an example of the configuration of a receiving station according to Embodiment 2 of the present disclosure. The receiving station 4a has a signal allocation control unit 44a. The signal allocation control unit 44a determines the allocation of CP, clustering, and signal combining units to maximize transmission capacity.

[0097] Specifically, the signal allocation control unit 44a first performs clustering of the receiving antennas 41a to 41n. This clustering is performed in all possible patterns, considering the number of clusters and the number of receiving antennas included in each cluster.

[0098] Next, the signal allocation control unit 44a determines the CP length based on the arrangement of receiving antennas included in each cluster. Then, the signal allocation control unit 44a performs mapping.

[0099] Furthermore, the signal allocation control unit 44a calculates the transmission capacity in each cluster. This transmission capacity is calculated taking into account the transmission efficiency based on the CP length.

[0100] Next, the signal allocation control unit 44a optimizes each parameter. These parameters include the number of clusters in the clustering, the number of receiving antennas included in each cluster, the CP length, and the mapping. Specifically, the signal allocation control unit 44a selects the clustering, CP length, and mapping that maximize the transmission capacity.

[0101] The signal assignment control unit 44a transmits the selected CP length to the CP length notification unit 26. The CP length notification unit 26 notifies the transmitting station 2a of the received CP length. The transmitting station 2a sets the CP length based on the notified CP length.

[0102] Figure 14 is a flowchart showing the processes performed by the wireless communication system according to Embodiment 2 of this disclosure. Here, the processes performed by the transmitting station 2a and the receiving station 4a are shown in flowchart form. In addition, the processes performed by the signal allocation control unit 44a are separately extracted and shown from the processes performed by the receiving station 4a.

[0103] First, in step 130, the signal assignment control unit 44a performs clustering of the receiving antennas 41a to 41n. This clustering is performed by grouping multiple receiving antennas into at least one cluster such that each cluster contains multiple receiving antennas. Furthermore, this clustering is performed in all possible patterns regarding the number of clusters and the number of receiving antennas included in each cluster.

[0104] Next, in step 132, the signal allocation control unit 44a checks whether the transmission capacity for all clusters has been calculated. If it has been calculated, the process proceeds to step 140. If it has not been calculated, the process proceeds to step 134.

[0105] In step 134, the signal assignment control unit 44a determines the CP length based on the arrangement of receiving antennas included in each cluster.

[0106] Next, in step 136, the signal assignment control unit 44a performs mapping. First, the signal assignment control unit 44a sets up antenna pairs for receiving antennas assigned to the same cluster so that the propagation delay time difference, which is the minimum, is maximized. Next, the signal assignment control unit 44a assigns a signal combining unit, which is assigned to the same cluster, to each antenna pair.

[0107] Next, in step 138, the signal allocation control unit 44a calculates the transmission capacity in each cluster and returns to step 132. This transmission capacity is calculated taking into account the transmission efficiency due to the CP length.

[0108] In step 140, the signal allocation control unit 44a optimizes each parameter. Specifically, the signal allocation control unit 44a selects the clustering, CP length, and mapping that maximize the transmission capacity. Next, in step 142, the signal allocation control unit 44a notifies the transmitting station 2a of the optimized CP length.

[0109] In step 144, the transmitting station 2a determines the CP length. This determination is made based on the announced CP length.

[0110] Next, in step 146, the transmitting station 2a generates a signal for wireless communication. This signal is generated to reflect the CP length set in step 144. Then, in step 148, the transmitting station 2a transmits the signal via the transmitting antennas 21a to 21m.

[0111] In step 150, the receiving station 4a performs mapping based on the parameters optimized in step 140. Steps 118 to 126 are as described above.

[0112] As a result of the above processing, the receiving station 4a can search for each parameter that maximizes the transmission capacity. Therefore, this embodiment can maximize the transmission capacity by considering the trade-off between the CP length and the MIMO spatial channel correlation. In other words, this embodiment can select the parameter that best maximizes the transmission capacity from among all parameters.

[0113] The possible forms of disclosure are listed as an addendum.

[0114] [Note 1] A wireless communication system in which a receiving station having a receiving antenna performs wireless communication with a transmitting station having a transmitting antenna, wherein the receiving station comprises: a signal combining unit that combines signals received from the transmitting station without synchronization; a signal assignment unit that assigns the receiving antenna to the signal combining unit; a time / frequency equalization unit that performs time equalization and frequency equalization of the combined signals; a MIMO demodulation unit that performs MIMO equalization on the signals that have been time equalized and frequency equalized; and a signal assignment control unit configured to perform a process of clustering the receiving antennas according to the signal reception timing and a process of determining the assignment of the receiving antenna to the signal combining unit so that the channel correlation between the combined signals is low. [Note 2] The wireless communication system according to Note 1, wherein the assignment is realized by performing the clustering so as to compensate for the propagation delay time difference superimposed by the signal combining unit. [Note 3] The wireless communication system according to Note 2, wherein the transmitting station is configured to perform a process of setting a guard section, and the assignment is realized by performing clustering so as to fit within the guard section. [Note 4] The wireless communication system according to Note 1, wherein the assignment is realized by performing clustering to compensate for the propagation delay time difference superimposed by the signal matching unit, the clustering is realized by generating a plurality of clusters, and the signal assignment control unit is configured to further perform the process of calculating the transmission capacity for the plurality of clusters and the process of selecting the cluster with the maximum transmission capacity. [Note 5] The wireless communication system according to Note 4, wherein the transmitting station is configured to perform the process of setting a guard section, and the transmission capacity is calculated taking into account the transmission efficiency due to the guard section.

[0115] 2, 2a Transmitting station 4, 4a Receiving station 21a-21m Transmitting antenna 41a-41n Receiving antenna 43a-43l Signal combining unit 80a-80d Cluster 100 Wireless communication system 100a Wireless communication system 404 Memory

Claims

1. A wireless communication system comprising: a transmitting station having at least one transmitting antenna; a receiving station having a plurality of receiving antennas and a plurality of signal combining units for combining received signals, and performing wireless communication with the transmitting station, wherein the receiving station is configured to perform the following processes: clustering the plurality of receiving antennas into at least one cluster such that each cluster includes a plurality of receiving antennas; assigning the signal combining units to the at least one cluster; setting up antenna pairs for the plurality of receiving antennas assigned to the same cluster such that the smallest propagation delay time difference is maximized, and performing mapping to assign the signal combining units to each antenna pair; and combining the signals received from the transmitting station based on the mapping.

2. A wireless communication method to be implemented in a wireless communication system comprising a transmitting station having at least one transmitting antenna, a plurality of receiving antennas, and a plurality of signal combining units for combining received signals, and a receiving station for wireless communication with the transmitting station, the method comprising: clustering the plurality of receiving antennas into at least one cluster such that each cluster includes a plurality of receiving antennas; assigning the signal combining unit to the at least one cluster; setting up antenna pairs for the plurality of receiving antennas assigned to the same cluster such that the smallest propagation delay time difference is maximized, and performing mapping to assign the signal combining unit to each antenna pair; and combining the signals received from the transmitting station based on the mapping.

3. A wireless communication device that performs wireless communication with a transmitting station having a plurality of receiving antennas and a plurality of signal combining units for combining received signals, and a transmitting station having at least one transmitting antenna, comprising: a process of clustering the plurality of receiving antennas into at least one cluster such that each cluster contains a plurality of receiving antennas; a process of assigning the signal combining unit to the at least one cluster; a process of setting antenna pairs for the plurality of receiving antennas assigned to the same cluster such that the smallest propagation delay time difference is maximized, and performing mapping to assign the signal combining unit to each antenna pair; and a process of combining signals received from the transmitting station based on the mapping.

4. A wireless communication program to be implemented by a wireless communication device that performs wireless communication with a transmitting station having a processor, memory, multiple receiving antennas, and multiple signal combining units for combining received signals, and at least one transmitting antenna, the program being stored in the memory and computer-readable, and including a program to cause the processor to perform: a process of clustering the multiple receiving antennas into at least one cluster such that each cluster contains multiple receiving antennas; a process of assigning the signal combining units to the at least one cluster; a process of mapping the multiple receiving antennas assigned to the same cluster such that the propagation delay time difference is maximized and the minimum is set to maximize the difference, and assigning the signal combining units to each antenna pair; and a process of combining the signals received from the transmitting station based on the mapping.

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