Wireless communication system and wireless communication method

Abstract

The present disclosure relates to a wireless communication system and a wireless communication method. This wireless communication system comprises: a zero-order communication station having a single or a plurality of antennas for first communication and a single or a plurality of antennas for second communication; a primary communication station having a single or a plurality of antennas for first communication and a single or a plurality of antennas for second communication; and a secondary communication station having a single or a plurality of antennas for second communication. The zero-order communication station is configured to carry out processing for performing wireless communication using the first communication for communication with the primary communication station when the first communication is available, and to carry out processing for performing wireless communication using the second communication by MIMO for communication with the primary communication station when the first communication is not available. The secondary communication station occupies and uses the second communication of the zero-order communication station when the primary communication station uses the first communication, and uses the second communication of the zero-order communication station in common with the primary communication station when the primary communication station uses the second communication by MIMO.

Description

Wireless Communication System and Wireless Communication Method

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

[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.

[0003] As a result, wireless communication using NTN tends to have an increased transmission capacity compared to existing satellite communication services. Therefore, in wireless communication using NTN, an increase in the capacity of the feeder link is required.

[0004] To increase the capacity of the feeder link, there is a technology that uses free space optical (FSO) communication that can secure a wide bandwidth. However, FSO communication has a problem that the communication performance deteriorates due to fluctuations in the communication environment accompanying atmospheric disturbances or weather changes.

[0005] To solve this problem, Non-Patent Document 2 discloses a wireless communication technology using hybrid FSO / RF communication that combines FSO communication and RF communication. In this technology, the communication performance is maintained by switching the communication method so that FSO communication is used in sunny weather and RF communication is used in rainy weather.

[0006] 3GPP TR 38.821, Solutions for NR to Support Non-Terrestrial Networks (NTN) (Release 16), V16.1.0, May. 2021.OB Yahia, E. Erdogan, GK Kurt, I. Altunbas and H. Yanikomeroglu, “A Weather-Dependent Hybrid RF / FSO Satellite Communication for Improved Power Efficiency”, in IEEE Wireless Communications Letters, vol. 11, no. 3, pp. 573-577, March 2022.

[0007] However, the aforementioned technology had a problem: because RF communication was not used during clear weather, the utilization efficiency of the communication links that should have been used for RF communication decreased. Furthermore, the aforementioned technology had a problem where the data rate decreased because the communication method was switched from FSO communication to RF communication during rainfall.

[0008] The primary objective of this disclosure is to provide a wireless communication system that can improve the utilization efficiency of communication links to be used for RF communication while maintaining the data rate, by efficiently using FSO communication and RF communication in combination to solve the aforementioned problems.

[0009] Furthermore, a second objective of this disclosure is to provide a wireless communication method that can improve the utilization efficiency of communication links to be used for RF communication while maintaining the data rate, by efficiently using FSO communication and RF communication in combination.

[0010] A first aspect of the present disclosure is preferably a wireless communication system comprising: a zero-order communication station having one or more antennas for first communications and one or more antennas for second communications; a primary communication station having one or more antennas for first communications and one or more antennas for second communications; and a secondary communication station having one or more antennas for second communications, wherein the zero-order communication station is configured to perform the following: when first communications are available, to perform wireless communication using first communications for communication with the primary communication station; and when first communications are not available, to perform wireless communication using second communications via MIMO for communication with the primary communication station; and the secondary communication station preferably monopolizes and uses the second communications of the zero-order communication station when the primary communication station uses first communications, and shares the second communications of the zero-order communication station with the primary communication station when the primary communication station uses second communications via MIMO.

[0011] Furthermore, a second aspect of the present disclosure is a wireless communication method implemented by a wireless communication system comprising: a zero-order communication station having one or more antennas for first communications and one or more antennas for second communications; a primary communication station having one or more antennas for first communications and one or more antennas for second communications; and a secondary communication station having one or more antennas for second communications, wherein, when the zero-order communication station is able to use first communications, wireless communication is performed using first communications for communication with the primary communication station; and when the zero-order communication station is unable to use first communications, wireless communication is performed using second communications by MIMO for communication with the primary communication station, wherein the secondary communication station exclusively uses the second communications of the zero-order communication station when the primary communication station uses first communications, and shares the second communications of the zero-order communication station with the primary communication station when the primary communication station uses second communications by MIMO.

[0012] According to the first and second aspects of this disclosure, by efficiently using FSO communication and RF communication in combination, the utilization efficiency of communication links to be used for RF communication can be improved.

[0013] This figure shows an example configuration of a wireless communication system according to Embodiment 1 of this disclosure. This figure shows the hardware configuration of a zero-order communication 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 an example configuration of a wireless communication system according to a comparative example. This figure shows the communication method and data rate of the wireless communication performed by the wireless communication system according to a comparative example. This figure shows the configuration of a wireless communication system according to an embodiment of Embodiment 1 of this disclosure. This figure shows the communication method according to Embodiment 1 of this disclosure in weather conditions in which FSO communication is available. This figure shows the communication method according to Embodiment 1 of this disclosure in weather conditions in which FSO communication is not available. This figure shows the communication method according to Embodiment 2 of this disclosure in weather conditions in which FSO communication is not available. This figure shows the communication method according to Embodiment 3 of this disclosure in weather conditions in which FSO communication is not available. This figure shows a first example of repurposing a secondary communication station according to Embodiment 1 of this disclosure for positioning. This figure shows a second example of repurposing a secondary communication station according to Embodiment 1 of this disclosure for positioning.

[0014] 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.

[0015] 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 zero-order communication station 2. The zero-order communication station 2 is a communication station that can utilize FSO communication and RF communication, and is, for example, a satellite station.

[0016] Furthermore, the 0th-order communication station 2 conducts wireless communication using different methods for multiple types of wireless communication targets. When there are two types of wireless communication targets, these wireless communications are referred to as primary communication and secondary communication, respectively.

[0017] Primary communication is, for example, communication between a zero-order communication station 2, which is a GEO satellite, and a first-order communication station 4, which is a ground base station and will be described later. Secondary communication is, for example, communication between a zero-order communication station 2, which is a GEO satellite, and a second-order communication station 6a, which is a LEO satellite and will be described later.

[0018] Primary communication may be, for example, wireless communication requiring high-capacity communication or high-priority wireless communication. On the other hand, secondary communication may be, for example, wireless communication that does not require high-capacity communication or low-priority wireless communication. However, the relationship between primary and secondary communication is not limited to these. Primary and secondary communication may be wireless communications targeting different types of communication stations.

[0019] The zero-order communication station 2 has a first transmitting / receiving unit 21. The first transmitting / receiving unit 21 generates a signal to be transmitted in primary communication and transmits it to the selection unit 23. The first transmitting / receiving unit 21 generates a signal for wireless communication by, for example, performing S / P conversion, error correction, or modulation.

[0020] The zero-order communication station 2 also has a second transmitting / receiving unit 22. The second transmitting / receiving unit 22 generates a signal to be transmitted in secondary communication and transmits it to the selection unit 23. The second transmitting / receiving unit 22 generates a signal for wireless communication by, for example, performing S / P conversion, error correction, or modulation.

[0021] The selection unit 23 selects the destination for the received signal. Specifically, the selection unit 23 selects the destination for the received signal so that it can be transmitted using the communication method determined by the communication control unit 24. The communication control unit 24 determines the communication method for transmitting the signal based on the weather. The destination is either the FSO transceiver 25 or the RF transceiver 26.

[0022] If the communication method determined by the communication control unit 24 is FSO communication, the selection unit 23 transmits the received signal to the FSO transmitting / receiving unit 25. The FSO transmitting / receiving unit 25 transmits the received signal to the primary communication station 4 via the FSO antenna 27. The primary communication station 4 receives the signal via the FSO antenna 41. The FSO antenna 41 transmits the received signal to the FSO transmitting / receiving unit 43. The FSO transmitting / receiving unit 43 transmits the received signal to the selection unit 45.

[0023] The selection unit 45 transmits the received signal to the first transmitting / receiving unit 46. The first transmitting / receiving unit 46 performs demodulation processing on the received signal.

[0024] If the communication method determined by the communication control unit 24 is RF communication, the selection unit 23 transmits the received signal to the RF transceiver unit 26. The RF transceiver unit 26 transmits the received signal to the communication station to which it is to be transmitted. The communication station to which it is to be transmitted is the primary communication station 4 or the secondary communication station 6a or 6b.

[0025] If the transmission target is primary communication station 4, the RF transceiver 26 transmits the received signal to primary communication station 4 via RF antennas 28a to 28n. Primary communication station 4 receives the signal via RF antennas 42a to 42m. RF antennas 42a to 42m transmit the received signal to RF transceiver 44. RF transceiver 44 transmits the received signal to selection unit 45.

[0026] The selection unit 45 transmits the received signal to the first transmitting / receiving unit 46. The first transmitting / receiving unit 46 performs demodulation processing on the received signal.

[0027] If the transmission target is secondary communication station 6a, the RF transceiver 26 transmits the received signal to secondary communication station 6a via RF antennas 28a to 28n. Secondary communication station 6a receives the signal via RF antennas 42a to 42l. RF antennas 42a to 42l transmit the received signal to RF transceiver 44. RF transceiver 44 transmits the received signal to a second transceiver 47. The second transceiver 47 performs demodulation processing on the received signal.

[0028] If the transmission target is secondary communication station 6b, the RF transceiver 26 transmits the received signal to secondary communication station 6b via RF antennas 28a to 28m. Secondary communication station 6b receives the signal via RF antennas 42a to 42k. RF antennas 42a to 42k transmit the received signal to RF transceiver 44. RF transceiver 44 transmits the received signal to a second transceiver 47. The second transceiver 47 performs demodulation processing on the received signal.

[0029] The above describes the case in the wireless communication system 100 where the zero-order communication station 2 transmits signals and the primary communication station 4, secondary communication stations 6a and 6b receive signals. Alternatively, in the wireless communication system 100, the primary communication station 4, secondary communication stations 6a and 6b may transmit signals and the zero-order communication station 2 may receive signals. In this case, the selection of the destination for the received signal by the selection unit 45 is made based on the judgment of the communication control unit 24. Otherwise, the functional units with the same names perform their respective processes.

[0030] Figure 2 shows the hardware configuration of a zero-order communication station according to Embodiment 1 of the present disclosure. Each function of the zero-order communication station 2 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.

[0031] For example, the zero-order communication station 2 can be implemented using a computer and a program, and the program can be recorded on a storage medium or provided via a network.

[0032] As shown in Figure 2, the zero-order communication station 2 has an input unit 208, an output unit 201, a communication unit 202, a CPU 203, a memory 204, and an HDD 205 connected via a bus 206, and functions as a computer. The zero-order communication station 2 is also configured to be able to input and output data to and from a computer-readable storage medium 207.

[0033] The input unit 208 is, for example, a keyboard and mouse. The output unit 201 is, for example, a display device such as a display.

[0034] The communication unit 202 is, for example, a communication interface that communicates with a wireless device to be controlled.

[0035] The CPU 203 controls each component of the zero-order communication station 2 and performs predetermined processing. The memory 204 and HDD 205 store data, etc.

[0036] The storage medium 207 is capable of storing programs and the like that execute the functions of the zero-order communication station 2. Note that the architecture constituting the zero-order communication station 2 is not limited to the example shown in Figure 2.

[0037] Figure 3 is a flowchart showing the processes performed by the wireless communication system according to Embodiment 1 of this disclosure. Here, the flowchart shows the processes performed by the communication control unit 24 of the zero-order communication station 2 in order to determine the communication method of the signal to be transmitted.

[0038] First, in step 100, the communication control unit 24 determines whether FSO communication is available for primary communication. This determination is made, for example, based on whether the weather at the time of the determination is suitable for FSO communication. If it is available, the process proceeds to step 102. If it is not available, the process proceeds to step 108.

[0039] The weather conditions under which FSO communication is available include, for example, clear skies. Alternatively, the weather conditions under which FSO communication is available include, for example, weather conditions where atmospheric disturbances or weather changes are below a certain threshold. The specific threshold may be defined, for example, by precipitation, wind speed, etc.

[0040] Step 102 determines whether the signal to be transmitted is subject to primary communication. If it is subject to primary communication, proceed to step 104. If it is not subject to primary communication, proceed to step 106.

[0041] In step 104, the system determines that the communication method of the signal to be transmitted is FSO communication and terminates processing. The signal determined in step 104 enables high-capacity communication using FSO communication as the primary communication method.

[0042] In step 106, the system determines that the communication method of the signal to be transmitted is RF communication and terminates processing. The signal determined in step 106 will implement secondary communication using RF communication. That is, if the primary communication uses FSO communication, the secondary communication will exclusively use the RF communication of the 0th-order communication station 2. Note that this RF communication may also be MIMO RF communication.

[0043] In step 108, it is determined whether the signal to be transmitted is the target of primary communication. If it is the target of primary communication, the process proceeds to step 110. If it is not the target of primary communication, the process proceeds to step 112.

[0044] In step 110, it is determined that the communication method of the signal to be transmitted is RF communication by MIMO, and the process ends. The signal determined in step 110 realizes medium-capacity communication using RF communication by MIMO as primary communication.

[0045] In step 112, it is determined that the communication method of the signal to be transmitted is RF communication, and the process ends. The signal determined in step 112 realizes communication using RF communication as secondary communication.

[0046] Note that the RF communication by MIMO determined in step 112 uses a part of the RF communication by MIMO determined in step 110. That is, when primary communication uses RF communication by MIMO, secondary communication shares and uses the RF communication of the zero-order communication station 2 with the primary communication station 4. Details of the mode of using a part of the RF communication by MIMO by division will be specifically described in the embodiments described later.

[0047] The advantages brought about by this embodiment will be described. FIG. 4 is a diagram showing a configuration example of a wireless communication system according to a comparative example. The wireless communication system 500 according to the comparative example includes a satellite 200. The satellite 200 performs wireless communication with the base station 400. This wireless communication is switched between FSO communication or RF communication. That is, the wireless communication system 500 is a wireless communication system using hybrid FSO / RF communication.

[0048] FIG. 5 is a diagram showing the communication method and data rate of the wireless communication performed by the wireless communication system according to the comparative example. The wireless communication system 500 switches the communication method so as to use FSO communication in sunny weather and RF communication in rainy weather.

[0049] There are two challenges in switching to the communication method in the comparative example. The first is that, because RF communication is not used in clear weather, the utilization efficiency of the communication link that should be used for RF communication decreases. This problem arises because FSO communication can secure a wider bandwidth compared to RF communication, eliminating the need to use RF communication in conjunction with it.

[0050] The second issue is that the data rate decreases during rainfall. This problem arises because RF communication cannot secure as much bandwidth as FSO communication.

[0051] As described above, the wireless communication system 500 in the comparative example has two problems and therefore fails to sufficiently improve transmission efficiency. On the other hand, the wireless communication system 100 according to this embodiment uses FSO communication and RF communication in combination when the weather conditions allow for FSO communication, and uses RF communication via MIMO when the weather conditions do not allow for FSO communication. As a result, since FSO communication and RF communication can be used in combination efficiently, the utilization efficiency of the communication link that should be used for RF communication can be improved while maintaining the data rate.

[0052] Hereafter, examples of this embodiment will be shown. Figure 6 is a diagram showing the configuration of a wireless communication system according to an embodiment of Embodiment 1 of this disclosure. The wireless communication system 1000 according to Embodiments 1 to 3 is a data relay relay system for multiple observation satellites via geostationary (GEO) satellites.

[0053] The wireless communication system 1000 includes a zero-order communication station 20. The zero-order communication station 20 is a GEO satellite that aggregates data from multiple observation satellites and transmits it to a ground base station. The zero-order communication station 20 has an FSO antenna 27 and RF antennas 28a to 28c.

[0054] The wireless communication system 1000 also includes a primary communication station 40. The primary communication station 40 is a ground base station. The primary communication station 40 has an FSO antenna 41 and RF antennas 42a and 42b.

[0055] The wireless communication system 1000 also includes secondary communication stations 60a, 60b, and 60c. The secondary communication stations 60a, 60b, and 60c are LEO satellites, which are observation satellites (EO). Secondary communication station 60a has an RF antenna 42a. Secondary communication station 60b has an RF antenna 42b. Secondary communication station 60c has an RF antenna 42c.

[0056] In the wireless communication system 1000, the feeder link communication between the zero-order communication station 20 and the primary communication station 40 is defined as the primary communication described above. This primary communication is performed using hybrid FSO / RF communication, which allows for the selection or combination of FSO communication and RF communication.

[0057] Furthermore, the zero-order communication station 20 and the primary communication station 40 have multiple RF antennas. Therefore, RF communication in primary communication can be performed using MIMO RF communication.

[0058] On the other hand, in the wireless communication system 1000, the data relay communication between the primary communication station 20 and the secondary communication stations 60a, 60b, and 60c is referred to as the secondary communication described above. This secondary communication is RF communication.

[0059] Furthermore, the primary communication station 20 has multiple RF antennas. In addition, the secondary communication stations 60a, 60b, and 60c each have RF antennas. Therefore, RF communication in secondary communication can be performed using MIMO RF communication.

[0060] Figure 7 shows a communication method according to Embodiment 1 of the present disclosure, in weather conditions in which FSO communication is available. For example, when the weather is clear, FSO communication becomes available. Therefore, the zero-order communication station 20 in this embodiment decides to use FSO communication for primary communication and RF communication for secondary communication.

[0061] As a result, the primary communication in this embodiment is FSO communication performed by FSO antenna 27 and FSO antenna 41. The secondary communication in this embodiment is RF communication using MIMO performed by RF antenna 28a and RF antenna 42a, RF antenna 28b and RF antenna 42b, and RF antenna 28c and RF antenna 42c.

[0062] Specifically, first, secondary communication stations 60a, 60b, and 60c transmit signals to primary communication station 20 on the same frequency. Primary communication station 20 separates the signals by performing MIMO interference compensation on all received signals. As a result, primary communication station 20 can demodulate the signals transmitted from each of the secondary communication stations 60a, 60b, and 60c. Primary communication station 20 aggregates the data contained in all the demodulated signals and transmits it to primary communication station 40.

[0063] As described above, when FSO communication is available, the wireless communication system 1000 uses FSO communication for primary communication and RF communication for secondary communication. As a result, RF communication is always in use, which improves the utilization efficiency of the communication link that should be used for RF communication.

[0064] Figure 8 shows a communication method for weather conditions where FSO communication is unavailable, according to Embodiment 1 of Embodiment 1 of the present disclosure. For example, when it is raining, FSO communication becomes unavailable. Therefore, the zero-order communication station 20 according to this embodiment decides to use RF communication by MIMO for primary communication and RF communication by MIMO for secondary communication.

[0065] The wireless communication system 1000 uses MIMO RF communication shared for primary and secondary communication. Specifically, the wireless communication system 1000 uses frequency f1 for primary communication and frequency f2 for secondary communication, thereby dividing and utilizing MIMO RF communication. In other words, the wireless communication system 1000 divides the MIMO RF communication shared during rainfall using frequency division.

[0066] As a result, the primary communication in this embodiment is RF communication using MIMO performed by RF antennas 28a to 28c and RF antennas 42a and 42b. The secondary communication in this embodiment is also RF communication using MIMO performed by RF antennas 28a and 42a, RF antenna 28b and 42b, and RF antenna 28c and 42c.

[0067] Specifically, first, secondary communication stations 60a, 60b, and 60c transmit signals to primary communication station 20 at frequency f2. Primary communication station 20 separates the signals by performing MIMO interference compensation on all received signals. As a result, primary communication station 20 can demodulate the signals transmitted from each of the secondary communication stations 60a, 60b, and 60c. Primary communication station 20 aggregates the data contained in all the demodulated signals and transmits it to primary communication station 40 at frequency f1.

[0068] As described above, when FSO communication is unavailable, the wireless communication system 1000 uses RF communication via MIMO, dividing it into primary and secondary communication. As a result, transmission efficiency can be increased compared to when using RF communication without MIMO. In other words, the data rate can be maintained even in weather conditions where FSO communication is unavailable.

[0069] Figure 9 shows a communication method for weather conditions where FSO communication is unavailable, according to Embodiment 2 of Embodiment 1 of the present disclosure. The wireless communication system 1000a according to this embodiment differs from Embodiment 1 in that it divides the RF communication using MIMO, which is shared during rainfall, using spatial partitioning with MIMO technology.

[0070] For example, if the weather is rainy, FSO communication becomes unavailable. Therefore, the primary communication station 20 in this embodiment decides to use RF communication by MIMO for primary communication and RF communication by MIMO for secondary communication.

[0071] The wireless communication system 1000a utilizes RF communication by dividing it into primary and secondary communications using MIMO. Specifically, the wireless communication system 1000a uses the same frequency for both primary and secondary communications. The primary communication station 40 and the secondary communication station 60a utilize RF communication by dividing it through MIMO by performing signal separation using MIMO technology.

[0072] As a result, the primary communication in this embodiment is RF communication using MIMO performed by RF antennas 28a to 28c and RF antennas 42a and 42b. The secondary communication in this embodiment is also RF communication using MIMO performed by, for example, RF antenna 28a and RF antenna 42a.

[0073] As described above, when FSO communication is unavailable, the wireless communication system 1000a uses RF communication via MIMO, dividing it into primary and secondary communications. As a result, transmission efficiency can be improved compared to using RF communication without MIMO. In other words, the data rate can be maintained even in weather conditions where FSO communication is unavailable.

[0074] Figure 10 shows a communication method for weather conditions where FSO communication is unavailable, according to Embodiment 3 of Embodiment 1 of the present disclosure. The wireless communication system 1000b according to this embodiment differs from Embodiment 1 in that it divides the RF communication using MIMO, which is shared during rainfall, using time division.

[0075] For example, if the weather is rainy, FSO communication becomes unavailable. Therefore, the primary communication station 20 in this embodiment decides to use RF communication by MIMO for primary communication and RF communication by MIMO for secondary communication.

[0076] The wireless communication system 1000b divides and utilizes RF communication using MIMO into primary and secondary communication. Specifically, the wireless communication system 1000 divides and utilizes RF communication using MIMO by using time zone t2 for primary communication and time zone t1 for secondary communication.

[0077] As a result, the primary communication in this embodiment is RF communication using MIMO performed by RF antennas 28a to 28c and RF antennas 42a and 42b. The secondary communication in this embodiment is also RF communication using MIMO performed by RF antennas 28a and 42a, RF antenna 28b and 42b, and RF antenna 28c and 42c.

[0078] Specifically, first, secondary communication stations 60a, 60b, and 60c transmit signals to primary communication station 20 during time t1. Primary communication station 20 separates the signals by performing MIMO interference compensation on all received signals. As a result, primary communication station 20 can demodulate the signals transmitted from each of the secondary communication stations 60a, 60b, and 60c. Primary communication station 20 aggregates the data contained in all the demodulated signals and transmits it to primary communication station 40 during time t2.

[0079] As described above, when FSO communication is unavailable, the wireless communication system 1000b uses RF communication via MIMO, dividing it into primary and secondary communications. As a result, transmission efficiency can be improved compared to using RF communication without MIMO. In other words, the data rate can be maintained even in weather conditions where FSO communication is unavailable.

[0080] Figure 11 shows a first example of repurposing a secondary communication station for positioning according to Embodiment 1 of the present disclosure. When the secondary communication stations 6a and 6b are ground stations, the functions used by the secondary communication stations 6a and 6b when communicating with the primary communication station 2 can be repurposed for radar functions used to position the positioning target 8.

[0081] For example, secondary communication station 6a transmits a chirp signal. The chirp signal is reflected by the positioning target 8. In this case, secondary communication station 6b can receive the chirp signal reflected by the positioning target 8 and perform positioning of the positioning target 8.

[0082] Figure 12 shows a second example of using a secondary communication station according to Embodiment 1 of this disclosure for positioning. In the first example, the positioning of the positioning target 8 was performed by receiving a chirp signal reflected from the positioning target 8. In the second example, when the positioning target is an illegal satellite 9, the positioning of the illegal satellite 9 is performed by receiving illegal radio waves transmitted by the illegal satellite 9.

[0083] For example, illegal satellite 9 transmits illegal radio waves. Subsequently, secondary communication stations 6a and 6b receive the illegal radio waves. By sharing information such as the arrival timing and Doppler shift of the radio waves they each received, secondary communication stations 6a and 6b can calculate the position of illegal satellite 9.

[0084] Furthermore, the zero-order communication station 2 and the primary communication station 4 in Embodiment 1 of this disclosure have multiple RF antennas. Therefore, the conversion to positioning shown in Figures 11 and 12 can also be performed on the zero-order communication station 2 and the primary communication station 4. In addition, if the zero-order communication station 2 is a satellite station, the conversion to positioning shown in Figures 11 and 12 can also be performed even if the positioning target 8 or illegal satellite 9 is located on the ground.

[0085] Furthermore, while this disclosure describes a configuration in which the communication method to be used is selected from FSO communication or RF communication depending on whether FSO communication is available, the configuration of this disclosure is not limited to this. That is, this disclosure may be configured in which the communication method to be used is selected from a first communication or a second communication different from the first communication depending on whether a particular first communication is available. In this case, it is preferable that the first communication is a communication method that can secure a wide bandwidth, and the second communication is a communication method in which the transmission efficiency is less likely to fluctuate when affected by changes in the communication environment.

[0086] The possible forms of disclosure are listed as an addendum.

[0087] [Note 1] A wireless communication system that performs primary communication using one of several different bands and secondary communication using a specific band included in the band selected by the primary communication, wherein the secondary communication occupies and uses the specific band if the primary communication does not select the specific band, and shares and uses the specific band if the primary communication selects the specific band. [Note 2] The wireless communication system according to Note 1, wherein the several different bands are the FSO band and the RF band, and the specific band is the RF band. [Note 3] The wireless communication system according to Note 1 or 2, comprising one or more transmitting and receiving antennas and an interference compensation function for transmitting and receiving signals. [Note 4] The wireless communication system according to any one of Notes 1 to 3, wherein the primary communication selects the FSO band if the FSO band is available, and selects the RF band if the FSO band is not available, thereby realizing MIMO wireless communication.

[0088] 2, 20 Primary communication station 4, 40 Primary communication station 6a, 6b, 60a, 60b, 60c Secondary communication station 27 FSO antenna 28a-28n RF antenna 41 FSO antenna 42a-42m RF antenna 100, 500, 1000, 1000a, 1000b Wireless communication system

Claims

1. A wireless communication system comprising: a zero-order communication station having one or more antennas for first communications and one or more antennas for second communications; a primary communication station having one or more antennas for the first communications and one or more antennas for the second communications; and a secondary communication station having one or more antennas for the second communications, wherein the zero-order communication station is configured to perform the following: when the first communications are available, the first communications are used to perform wireless communication with the primary communication station using the first communications; and when the first communications are not available, the second communications are used to perform wireless communication with the primary communication station using MIMO; and the secondary communication station is configured to exclusively use the second communications of the zero-order communication station when the primary communication station uses the first communications; and to share the second communications of the zero-order communication station with the primary communication station when the primary communication station uses the second communications using MIMO.

2. The wireless communication system according to claim 1, wherein the first communication is FSO communication and the second communication is RF communication.

3. The wireless communication system according to claim 1, wherein the primary communication station and the secondary communication station share and utilize the RF communication of the zeroth-order communication station by applying frequency division, spatial division, or time division.

4. A wireless communication method implemented by a wireless communication system comprising: a zero-order communication station having one or more antennas for first communications and one or more antennas for second communications; a primary communication station having one or more antennas for the first communications and one or more antennas for the second communications; and a secondary communication station having one or more antennas for the second communications, wherein, when the zero-order communication station is able to use the first communications, the first communications are used for wireless communication with the primary communication station; and when the zero-order communication station is unable to use the first communications, the second communications by MIMO are used for wireless communication with the primary communication station, wherein the secondary communication station, when the primary communication station uses the first communications, exclusively uses the second communications of the zero-order communication station; and when the primary communication station uses the second communications by MIMO, the second communications of the zero-order communication station are shared with the primary communication station.

Images