Wireless communication system, receiving station, wireless communication method, and program for wireless communication

Abstract

The purpose of the present disclosure is to, without extracting amplitude and phase information from reception signals for each reception antenna during MIMO signal processing, select the reception signals having mutually low channel correlation. A wireless communication system according to the present disclosure comprises a transmission station and a reception station that carries out MIMO wireless communication with the transmission station. The reception station has a plurality of reception antennas. The reception station measures the strength of reception signals at the plurality of reception antennas. Furthermore, for at least one of the plurality of reception antennas, fluctuation in the reception signal strength is compared with a threshold value. When the fluctuation in the reception signal strength is equal to or less than the threshold value, the reception station selects reception antennas having a mutually large difference in reception strength from among the plurality of reception antennas, and synthesizes the reception signals of the selected reception antenna group. Meanwhile, when the fluctuation in the reception signal strength exceeds the threshold value, the reception station selects reception antennas in descending order of the strength of the reception signal until a signal-to-noise ratio of the reception signals after synthesis can be regarded as satisfying a desired value, and synthesizes the reception signals of the selected reception antenna group.

Description

Wireless communication system, receiving station, wireless communication method, and wireless communication program

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

[0002] Non-terrestrial networks (NTNs) are expected to have many use cases, such as direct accommodation of terrestrial terminals, mobile backhaul, and accommodation of IoT terminals, and are expected to generate more traffic than existing satellite communications (e.g., Non-Patent Document 1). To increase the capacity of the line, a technique has been disclosed for performing MIMO (Multiple-Input and Multiple-Output) wireless communications using multiple antennas installed at an overhead radio station and multiple antennas installed at a terrestrial base station (e.g., Non-Patent Document 2). Alternatively, a method has been proposed for configuring massive MIMO by distributing a large number of small antennas over a wide area at terrestrial base stations (e.g., Non-Patent Document 3).

[0003] 3GPP TR 38.821, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; 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, Proceedings of Communications Lectures 1, B-3-5, Mar 2023. L. Zhu, J. Zhu, S. Wang and J. Zhang, "Adaptive Transmit Antenna Selection Based on PCA for Millimeter Wave LOS MIMO Channel," in IEEE Access, vol. 7, pp. 12087-12096, 2019.

[0004] In order to simultaneously reduce the signal processing load and maintain the quality of received signals in MIMO signal processing, it is necessary to select received signals with low channel correlation from among the received signals received at a large number of antennas. In Non-Patent Document 4, channel correlation is grasped by extracting amplitude and phase information from the received signals at each receiving antenna and performing channel estimation based on this information. However, in MIMO wireless communication with a large number of antennas, obtaining amplitude and phase information for the received signals at each receiving antenna means an increase in overhead.

[0005] In order to solve the above-mentioned problems, a first object of the present disclosure is to provide a wireless communication system that can select received signals with low channel correlation with each other in MIMO signal processing without extracting amplitude and phase information from the received signals at each receiving antenna.

[0006] A second object of the present disclosure is to provide a receiving station that can select received signals with low channel correlation without extracting amplitude and phase information from the received signals at each receiving antenna in MIMO signal processing.

[0007] A third object of the present disclosure is to provide a wireless communication method capable of selecting received signals with low channel correlation without extracting amplitude and phase information from the received signals at each receiving antenna in MIMO signal processing.

[0008] A fourth object of the present disclosure is to provide a wireless communication program that can select received signals with low channel correlation without extracting amplitude and phase information from the received signals at each receiving antenna in MIMO signal processing.

[0009] A first aspect of the present disclosure is preferably a wireless communication system comprising: a transmitting station; and a receiving station that performs MIMO wireless communication between the transmitting station and the receiving station, wherein the receiving station has a plurality of receiving antennas and is configured to perform the following processes: measuring the strength of received signals at the plurality of receiving antennas; comparing fluctuations in the strength for at least one of the plurality of receiving antennas with a threshold; selecting, if the fluctuations in strength are equal to or less than the threshold, receiving antennas having a large difference in receiving strength from among the plurality of receiving antennas, and combining the received signals of the selected group of receiving antennas; and, if the fluctuations in strength exceed the threshold, selecting the receiving antennas in descending order of received signal strength until the signal-to-noise ratio of the combined received signal can be considered to satisfy a desired value, and combining the received signals of the selected group of receiving antennas.

[0010] A second aspect is a receiving station that performs MIMO wireless communication with a transmitting station, and is equipped with a plurality of receiving antennas, and is configured to perform the following processes: measuring the strength of received signals at the plurality of receiving antennas; comparing fluctuations in the strength for at least one of the plurality of receiving antennas with a threshold; selecting, when the fluctuations in the strength are equal to or less than the threshold, receiving antennas that have a large difference in receiving strength from among the plurality of receiving antennas, and combining the received signals of the selected group of receiving antennas; and when the fluctuations in the strength exceed the threshold, selecting the receiving antennas in descending order of received signal strength until the signal-to-noise ratio of the combined received signal can be considered to satisfy a desired value, and combining the received signals of the selected group of receiving antennas.

[0011] A third aspect is preferably a wireless communication method including: a receiving station that performs MIMO wireless communication with a transmitting station; measuring the strength of received signals at multiple receiving antennas that the receiving station has; comparing the fluctuation in the strength for at least one of the multiple receiving antennas with a threshold; if the fluctuation in the strength is equal to or less than the threshold, selecting receiving antennas from the multiple receiving antennas that have a large difference in receiving strength with each other, and combining the received signals of the selected group of receiving antennas; if the fluctuation in the strength exceeds the threshold, selecting the receiving antennas in descending order of received signal strength until the signal-to-noise ratio of the combined received signal can be considered to satisfy a desired value, and combining the received signals of the selected group of receiving antennas.

[0012] A fourth aspect is preferably a wireless communication program to be executed by a receiving station that performs MIMO wireless communication with a transmitting station, the program including a program that causes the receiving station to execute the following processes: a process of measuring the strength of received signals at multiple receiving antennas possessed by the receiving station; a process of comparing fluctuations in the strength for at least one of the multiple receiving antennas with a threshold; a process of selecting, when the fluctuations in strength are equal to or less than the threshold, receiving antennas having a large difference in receiving strength from among the multiple receiving antennas, and combining the received signals of the selected group of receiving antennas; and a process of selecting, when the fluctuations in strength exceed the threshold, receiving antennas in descending order of received signal strength until the signal-to-noise ratio of the combined received signal can be considered to satisfy a desired value, and combining the received signals of the selected group of receiving antennas.

[0013] The present disclosure provides a wireless communication system, a receiving station, a wireless communication method, and a wireless communication program that can identify received signals with low channel correlation based on the strength of the received signals at each receiving antenna, thereby enabling selection of received signals with low channel correlation without extracting amplitude and phase information from the received signals at each receiving antenna in MIMO signal processing.

[0014] 1 is a diagram illustrating an example configuration of a wireless communication system according to a first embodiment of the present disclosure. FIG. 2 is a block diagram of a transmitting station according to the first embodiment of the present disclosure. FIG. 3 is a block diagram of a receiving station according to the first embodiment of the present disclosure. FIG. 4 is a block diagram of a selection circuit of a receiving station according to the first embodiment of the present disclosure. FIG. 5 is a diagram illustrating the strength of a received signal at each receiving antenna according to the first embodiment of the present disclosure. FIG. 6 is a diagram illustrating fluctuations in a received signal at a single receiving antenna. FIG. 7 is a diagram illustrating a method for selecting a receiving antenna in a line-of-sight environment according to the first embodiment of the present disclosure. FIG. 8 is a diagram illustrating a method for selecting a receiving antenna in a fading environment according to the first embodiment of the present disclosure. FIG. 9 is a flowchart of processing performed by a transmitting station and a receiving station according to the first embodiment of the present disclosure. FIG. 10 is a flowchart of processing performed by a transmitting station and a receiving station according to the first embodiment of the present disclosure.

[0015] Embodiments of the present disclosure will be described with reference to the drawings. The same or corresponding components will be designated by the same reference numerals, and repeated description may be omitted.

[0016] 1 is a diagram illustrating a configuration example of a wireless communication system 100 according to a first embodiment of the present disclosure. The wireless communication system 100 includes a transmitting station 110 and a receiving station 120. The transmitting station 110 has two transmitting antennas (hereinafter referred to as antennas) 111-1 and 111-2. The receiving station 120 has multiple receiving antennas (hereinafter referred to as antennas) 121-1, 121-2, and so on.

[0017] In the following description, the description can be applied to each of the antennas 111-1, 111-2, etc., and when there is no need to distinguish between them, they will simply be referred to as antenna 111. The same applies to antennas 121-1, 121-2, etc., and lines 10-1, 10-2, etc., lines 20-1, 20-2, etc., which will be described later.

[0018] The multiple antennas 111 of the transmitting station 110 are connected to each of the multiple antennas 121 of the receiving station 120 via line 10 or line 20, and perform MIMO wireless communication using spatial multiplexing. Specifically, the antenna 111-1 connects the antennas 121-1, 121-2, etc. to line 10-1, line 10-2, etc., respectively. Similarly, the antenna 111-2 connects the antennas 121-1, 121-2, etc. to line 20-1, line 20-2, etc., respectively.

[0019] The transmitting station 110 generates information signals intended for each of the antennas 111-1, 111-2, ... and distributes them to the corresponding antennas 111. The antenna 111 transmits the received information signals to the receiving station 120 via the multiple lines 10 or 20 connected to it. The receiving station 120 receives the information signals originating from each of the antennas 111-1, 111-2, ... at each antenna 121.

[0020] Although the case where the transmitting station 110 has two antennas 111 has been described here, the number of antennas 111 is not limited, and may be one.

[0021] 2 is a block diagram of the transmitting station 110 according to the first embodiment of the present disclosure. The transmission signal generating circuit 112 generates and distributes information signals to the target antennas 111. The demodulation and combining circuit 113 performs MIMO signal processing (described later) on the received signals received by each antenna 111.

[0022] 3 is a block diagram of a receiving station 120 according to the first embodiment of the present disclosure. During reception, a selection circuit 122 selects an antenna 121 to be used for combining received signals from among the multiple antennas 121 based on measurement results of the strength of the received signals at each antenna 121. Based on instructions from the selection circuit 122, a switching circuit 123 extracts the received signals at the antennas 121 to be used for combining and outputs them to a demodulation and combining circuit 124. The demodulation and combining circuit 124 performs MIMO signal processing on each of the received signals at the antennas 121 to be used for combining.

[0023] The MIMO signal processing includes timing synchronization processing for the received signals at each antenna 111. It also includes MIMO equalization processing for the received signals at each antenna 111 based on the results of channel estimation and the like performed on the received signals. The MIMO equalization processing separates the information signals originating from antenna 111-1, antenna 111-2, .... The MIMO signal processing also includes demodulation and combining processing for demodulating and combining the received signals at each antenna 111.

[0024] The function of the transmission signal generating circuit 125 is the same as that of the transmission signal generating circuit 112 in the transmitting station 110, and therefore a description thereof will be omitted.

[0025] 4 is a block diagram of the selection circuit 122 of the receiving station 120 according to the first embodiment of the present disclosure. The measurement circuit 131 measures the strength of the received signal at each antenna 121. The determination circuit 132 determines, based on fluctuations in the strength of the received signal, whether the MIMO wireless communication environment is a line-of-sight environment where direct waves are dominant, or a fading environment where indirect waves are dominant. The decision circuit 133 determines the group of antennas 121 to be used for signal combining using a method that differs depending on whether the environment is a line-of-sight environment or a fading environment. The determined group of antennas 121 is stored in the memory 134.

[0026] 5 is a diagram illustrating the strength of a received signal at each antenna 121 according to the first embodiment of the present disclosure. The horizontal axis indicates the number assigned to each antenna 121. Measurement circuit 131 measures the strength of the received signal at each of antennas 121-1, 121-2, and so on.

[0027] FIG. 6 is a diagram illustrating fluctuations in the received signal at a single antenna 121. When the fluctuations are small, as shown by the solid line, it can be said that direct waves are dominant in the received waves that reach the antenna 121. On the other hand, when the fluctuations are large, as shown by the dashed line, it can be said that indirect waves are dominant in the received waves that reach the antenna 121. The determination circuit 132 calculates the magnitude of fluctuations for the received signal at each antenna 121 and compares it with a threshold. If it is determined that there are not a predetermined number or more of antennas 121 with fluctuations that exceed the threshold, it is determined that the MIMO wireless communication environment is a line-of-sight environment. On the other hand, if it is determined that there are a predetermined number or more of antennas 121 with fluctuations that exceed the threshold, it is determined that the MIMO wireless communication environment is a fading environment.

[0028] The method of comparing the magnitude of fluctuations in each antenna 121 with the threshold value is not limited to the above, and for example, the sum of the magnitudes of fluctuations in each antenna 121 may be calculated and compared with the threshold value. Furthermore, it is not necessary to compare the fluctuations of all antennas 121 with the threshold value in order to determine whether the environment is a line-of-sight environment or a fading environment, and only one antenna 121 may be used for the determination.

[0029] 7 is a diagram illustrating a method for selecting an antenna 121 in a line-of-sight environment according to the first embodiment of the present disclosure. When the MIMO wireless communication environment is a line-of-sight environment, the decision circuit 133 selects multiple antennas 121 with large differences in reception strength. This is based on the knowledge that antennas 121 with large differences in reception strength are spatially separated from each other, and the received signals at such antennas 121 have low correlation with each other. By combining a group of antennas 121 with large differences in reception strength, it is possible to selectively combine received signals with low channel correlation with each other. This also facilitates separation processing of the combined signal.

[0030] The decision circuit 133 first groups the multiple antennas 121 based on their reception strength. In the example of FIG. 1 , antenna 121-1 with the highest reception strength and antenna 121-2, whose reception strength differs from antenna 121-1 by less than Δ, are placed in the same group A. Furthermore, antenna 121-5, which has the highest reception strength excluding antenna 121 in group A, and antenna 121-6, whose reception strength differs from antenna 121-5 by less than Δ, are placed in group B. Similarly, a group consisting of the antenna 121 with the highest reception strength excluding antennas 121 belonging to existing groups is created, and antennas 121 whose reception strength differs from that antenna 121 by less than Δ are included in the same group. In this way, antennas 121-3 and 121-8 are placed in group C. Antennas 121-4 and 121-7 are placed in groups D and E, respectively.

[0031] The decision circuit 133 selects one antenna 121 from each group to be used for combining. That is, antenna 121-1 is selected from group A, antenna 121-5 from group B, antenna 121-3 from group C, antenna 121-4 from group D, and antenna 121-7 from group E. In this way, in a group that includes multiple antennas 121, it is desirable to select the antenna 121 with the strongest reception strength, but the selection method is not limited thereto.

[0032] The method of grouping the antennas 121 based on the reception strength is not limited to this.

[0033] 8 is a diagram illustrating a method for selecting an antenna 121 in a fading environment according to the first embodiment of the present disclosure. When the MIMO wireless communication environment is a fading environment, the decision circuit 133 selects the antenna 121 in descending order of reception strength until the SNR (Signal-to-Noise Ratio) of the combined received signal is deemed to satisfy a desired value. This is based on the knowledge that in a fading environment, not only direct waves but also indirect waves arrive at the antenna 121, and therefore the received signals become low-correlated even if the antennas 121 are not spatially separated from each other. By selecting the antenna 121 in descending order of reception strength, it is possible to generate a combined signal that satisfies the desired SNR while suppressing the number of received signals used for combination.

[0034] 8, the decision circuit 133 selects antenna 121-1, antenna 121-2, antenna 121-5, antenna 121-6, and antenna 121-3 in that order, estimating the SNR of the combined received signal each time. When antenna 121-3 is added, the estimated SNR exceeds the desired value, so the decision circuit 133 discontinues the selection.

[0035] 9 is a flowchart of processing executed by the transmitting station 110 and the receiving station 120 according to the first embodiment of the present disclosure. First, the transmission signal generating circuit 112 of the transmitting station 110 generates and distributes an information signal intended for the target antenna 111 (step S01). Next, the antenna 111 transmits the received information signal to the receiving station 120 via the line 10 or line 20 connected to the transmitting station 110 (step S02).

[0036] Furthermore, each antenna 121 of the receiving station 120 receives the information signal (step S03), and the measuring circuit 131 measures the strength of the received signal at each antenna 121 (step S04).

[0037] Furthermore, the determination circuit 132 determines the magnitude of fluctuation for the received signal at each antenna 121 (step S05). Furthermore, the determined fluctuation for the received signal strength at each antenna 121 is compared with a threshold value to determine whether or not a predetermined number of antennas 121 have fluctuations exceeding the threshold value (step S06). If it is determined that a predetermined number of antennas 121 have fluctuations exceeding the threshold value, this indicates that the MIMO wireless communication environment is a line-of-sight environment. Therefore, the determination circuit 133 selects multiple antennas 121 with large differences in received signal strength as the antennas 121 to be used for signal combining (step S07). Furthermore, the memory 134 stores information on the group of antennas 121 to be used for signal combining (step S08).

[0038] Furthermore, the switching circuit 123 extracts received signals from the group of antennas 121 to be used for combining from the plurality of antennas 121, and outputs the extracted signals to the demodulation and combining circuit 124 (step S09). The demodulation and combining circuit 124 then performs the above-described MIMO signal processing on each of the received signals received from the switching circuit 123 (step S10). Finally, the processing ends.

[0039] On the other hand, if it is determined in step S06 that there are a predetermined number or more antennas 121 with fluctuations exceeding the threshold, this means that the MIMO wireless communication environment is a fading environment. In this case, the decision circuit 133 selects antennas 121 in descending order of reception strength until the SNR of the combined received signal is deemed to satisfy the desired value (step S11). Then, the process proceeds to step S08.

[0040] 10 is a flowchart of a process executed by the transmitting station 110 and the receiving station 120 according to the first embodiment of the present disclosure. Here, a method of using information about the group of antennas 121 stored in the memory 134 when transmitting an information signal from the receiving station 120 to the transmitting station 110 will be described.

[0041] First, the transmission signal generation circuit 125 of the receiving station 120 generates an information signal for each antenna 121 (step S21). Then, the transmission signal generation circuit 125 references the memory 134 to read information about the group of antennas 121 selected for combining the received signals, and selects the antenna 121 to be used for transmission (step S22). Then, the switching circuit 123 distributes the information signal to the antenna 121 to be used for transmission (step S23). Then, the antenna 121 that receives the information signal from the switching circuit 123 transmits the information signal to the transmitting station 110 via the line 10 or line 20 to which it is connected (step S24).

[0042] The transmitting station 110 then receives information signals at each antenna 111 (step S25). The demodulation and combining circuit 113 then performs the above-described MIMO signal processing on each of the received signals received by the antennas 111 (step S26). Finally, the processing ends. By using the group of antennas 121 selected for combining the received signals for transmission in this manner, it is possible to use only the lines 10 and 20, which are known to have low channel correlation. This reduces the overhead of MIMO signal processing at the transmitting station 110.

[0043] As described above, in the present disclosure, received signals with low channel correlation are identified based on the strength of the received signals at each antenna 121. This makes it possible to provide a wireless communication system, a receiving station, a wireless communication method, and a wireless communication program that are capable of selecting received signals with low channel correlation without extracting amplitude and phase information from the received signals at each receiving antenna in MIMO signal processing.

[0044] The processes performed by the judgment circuit 132 and the decision circuit 133 of the receiving station 120 may be executed by a program using a computer equipped with a CPU and memory and storing a program in the memory. Alternatively, the processes may be executed by a program using an integrated circuit such as an FPGA (Field Programmable Gate Array). The program may be provided by being recorded on a storage medium or via a network. This point is common to all of the following embodiments.

[0045] The wireless communication system 100 of the present disclosure exhibits particularly excellent effects when applied to an NTN system. The transmitting station 110 therein is an airborne radio station, such as a satellite moving in the sky, including outer space. The receiving station 120 is a terrestrial base station. In this case, the lines 10 and 20 are feeder link lines. Feeder link lines in an NTN system are typically assumed to be line-of-sight environments. On the other hand, in MIMO wireless communication, a small, wide-directivity antenna 121 is installed in the terrestrial base station, so it is assumed that indirect waves will be received, and a fading environment may also be present. The present disclosure determines whether the feeder link line is in a line-of-sight environment or a fading environment based on the strength of the received signal at each antenna 121, and can select received signals with low channel correlation using different methods depending on the environment. Therefore, the present disclosure exhibits particularly excellent effects in an NTN system.

[0046] The present disclosure is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the spirit of the present disclosure. Furthermore, the embodiments may be implemented in appropriate combinations, and in such cases, the combined effects can be obtained.

[0047] Aspects of the present disclosure are summarized below as appendices. (Appendix 1) A wireless communication system comprising: a transmitting station; and a receiving station that performs MIMO wireless communication with the transmitting station, wherein the receiving station has multiple receiving antennas and is configured to perform the following processes: measuring the strength of received signals at the multiple receiving antennas; comparing a fluctuation in the strength for at least one of the multiple receiving antennas with a threshold; selecting, if the fluctuation in strength is equal to or less than the threshold, receiving antennas from the multiple receiving antennas that have a large difference in received strength, and combining the received signals of the selected receiving antennas; and, if the fluctuation in strength exceeds the threshold, selecting the receiving antennas in descending order of received signal strength until the signal-to-noise ratio of the combined received signal can be considered to satisfy a desired value, and combining the received signals of the selected receiving antennas. (Appendix 2) The wireless communication system according to Appendix 1, wherein the receiving station is configured to perform the following processes: distributing an information signal to be transmitted to the selected receiving antennas; and transmitting the information signal via a line connecting each of the selected receiving antennas to a transmitting antenna of the transmitting station. (Supplementary Note 3) A receiving station that performs MIMO wireless communication with a transmitting station, comprising a plurality of receiving antennas, and configured to perform the following processes: measuring the strength of received signals at the plurality of receiving antennas; comparing fluctuations in the strength for at least one of the plurality of receiving antennas with a threshold; selecting, when the fluctuations in the strength are equal to or less than the threshold, receiving antennas that have a large difference in received strength from among the plurality of receiving antennas, and combining the received signals of the selected group of receiving antennas; and when the fluctuations in the strength exceed the threshold, selecting the receiving antennas in descending order of received signal strength until the signal-to-noise ratio of the combined received signal can be considered to satisfy a desired value, and combining the received signals of the selected group of receiving antennas.(Supplementary Note 4) A wireless communication method comprising: a receiving station that performs MIMO wireless communication with a transmitting station; measuring the strength of received signals at multiple receiving antennas that the receiving station has; comparing the fluctuation in the strength for at least one of the multiple receiving antennas with a threshold; if the fluctuation in the strength is equal to or less than the threshold, selecting receiving antennas from the multiple receiving antennas that have a large difference in received strength with each other, and combining the received signals of the selected group of receiving antennas; if the fluctuation in the strength exceeds the threshold, selecting the receiving antennas in descending order of received signal strength until the signal-to-noise ratio of the combined received signal can be considered to satisfy a desired value, and combining the received signals of the selected group of receiving antennas. (Supplementary Note 5) A wireless communication program to be executed by a receiving station that performs MIMO wireless communication with a transmitting station, the program causing the receiving station to execute the following processes: measuring the strength of received signals at multiple receiving antennas possessed by the receiving station; comparing fluctuations in the strength for at least one of the multiple receiving antennas with a threshold; selecting, when the fluctuations in strength are equal to or less than the threshold, receiving antennas having a large difference in reception strength from among the multiple receiving antennas, and combining the received signals of the selected group of receiving antennas; and when the fluctuations in strength exceed the threshold, selecting the receiving antennas in descending order of received signal strength until the signal-to-noise ratio of the combined received signal can be considered to satisfy a desired value, and combining the received signals of the selected group of receiving antennas.

[0048] 10, 20 Line, 100 Wireless communication system, 110 Transmitting station, 111 Transmitting antenna, 112 Transmitting signal generating circuit, 113 Demodulation and combining circuit, 120 Receiving station, 121 Receiving antenna, 122 Selection circuit, 123 Switching circuit, 124 Demodulation and combining circuit, 125 Transmitting signal generating circuit, 131 Measurement circuit, 132 Judgment circuit, 133 Decision circuit, 134 Memory

Claims

1. A wireless communication system comprising a transmitting station and a receiving station that performs MIMO wireless communication with the transmitting station. The receiving station has a plurality of receiving antennas, and performs processing for measuring the intensity of received signals in the plurality of receiving antennas, processing for comparing the variation in the intensity with a threshold for at least one of the plurality of receiving antennas, when the variation in the intensity is less than or equal to the threshold, selecting receiving antennas having a large difference in received intensity from among the plurality of receiving antennas and performing processing for synthesizing the received signals of the selected receiving antenna group, and when the variation in the intensity exceeds the threshold, selecting the receiving antennas in descending order of received signal intensity until the signal-to-noise ratio of the synthesized received signal can be considered to satisfy a desired value, and performing processing for synthesizing the received signals of the selected receiving antenna group.

2. A receiving station that performs MIMO wireless communication with a transmitting station, comprising a plurality of receiving antennas, and performing processing for measuring the intensity of received signals in the plurality of receiving antennas, processing for comparing the variation in the intensity with a threshold for at least one of the plurality of receiving antennas, when the variation in the intensity is less than or equal to the threshold, selecting receiving antennas having a large difference in received intensity from among the plurality of receiving antennas and performing processing for synthesizing the received signals of the selected receiving antenna group, and when the variation in the intensity exceeds the threshold, selecting the receiving antennas in descending order of received signal intensity until the signal-to-noise ratio of the synthesized received signal can be considered to satisfy a desired value, and performing processing for synthesizing the received signals of the selected receiving antenna group.

3. A receiving station that performs MIMO wireless communication with a transmitting station measures the strength of received signals at a plurality of receiving antennas possessed by the station itself, compares the variation in the strength with a threshold for at least one of the plurality of receiving antennas, selects receiving antennas with a large difference in received strength from among the plurality of receiving antennas when the variation in the strength is less than or equal to the threshold, and synthesizes the received signals of the selected receiving antenna group; and when the variation in the strength exceeds the threshold, selects the receiving antennas in descending order of the strength of the received signals until the signal-to-noise ratio of the synthesized received signal can be regarded as satisfying a desired value, and synthesizes the received signals of the selected receiving antenna group. A wireless communication method comprising the above steps.

4. A wireless communication program for causing a receiving station that performs MIMO wireless communication with a transmitting station to execute a process of measuring the strength of received signals at a plurality of receiving antennas possessed by the receiving station, a process of comparing the variation in the strength with a threshold for at least one of the plurality of receiving antennas, a process of selecting receiving antennas with a large difference in received strength from among the plurality of receiving antennas when the variation in the strength is less than or equal to the threshold, and synthesizing the received signals of the selected receiving antenna group, and a process of selecting the receiving antennas in descending order of the strength of the received signals until the signal-to-noise ratio of the synthesized received signal can be regarded as satisfying a desired value when the variation in the strength exceeds the threshold, and synthesizing the received signals of the selected receiving antenna group. A wireless communication program comprising the above program.

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