COMMUNICATION SYSTEM AND COMMUNICATION METHOD

Abstract

In the present invention, a capacity estimation unit estimates a channel capacity associated with wireless communication between a communication device and a relay device. A scheme determination unit determines a transmission scheme for data from the communication device to the relay device such that at a larger channel capacity, the scheme has lower transmission efficiency and higher transmission quality and such that at a lower channel capacity, the scheme has lower transmission quality and higher transmission efficiency.

Description

[Technical field]

[0001] The present invention relates to a communication system and a communication method. [Background technology]

[0002] With the development of IoT (Internet of Things) technology, it is being considered to install IoT terminals equipped with various sensors in various locations. For example, it is expected that IoT will be used to collect data from locations where it is difficult to install base stations, such as marine buoys, ships, and mountainous areas. Meanwhile, there is technology that uses UAVs (Unmanned Aerial Vehicles) and geostationary satellites to wirelessly communicate with ground-based communication devices (for example, see Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Wei Feng, et al. "UAV-aided MIMO communications for 5G Internet of Things", IEEE Internet of Things Journal,Volume6, Issue2,2019,p.1731-1740 Summary of the Invention [Problem to be solved by the invention]

[0004] When a relay device is mounted on a UAV or a geostationary satellite, the channel capacity for wireless communication between the ground communication device and the relay device changes as the relay device moves. Therefore, depending on the timing of data transmission, the amount of information may be too small for the channel capacity, and communication resources may not be used effectively. On the other hand, depending on the timing of transmission, the amount of information may be too large for the channel capacity, and data received by the relay device may be missing.

[0005] In view of the above circumstances, an object of the present invention is to provide a communication system and a communication method that can effectively utilize communication resources in communication between a relay device that communicates while moving and a ground-based transmitting device. [Means for solving the problem]

[0006] A first aspect of the present invention is a communication system comprising a relay device which communicates while moving and a communication device which transmits data to the relay device, the communication system further comprising: a capacity estimation unit which estimates a channel capacity for wireless communication between the communication device and the relay device; and a method determination unit which determines a transmission method for the data from the communication device to the relay device to be a method with lower transmission efficiency and higher transmission quality when the channel capacity is larger, and determines a method with lower transmission quality and higher transmission efficiency when the channel capacity is smaller.

[0007] A second aspect of the present invention is a communication method between a relay device that communicates while moving and a communication device that transmits data to the relay device, comprising the steps of: estimating a channel capacity for wireless communication between the communication device and the relay device; determining a transmission method for the data from the communication device to the relay device to a method having lower transmission efficiency and higher transmission quality when the channel capacity is larger, and determining a method having lower transmission quality and higher transmission efficiency when the channel capacity is smaller; and transmitting the data from the communication device to the relay device in accordance with the determined transmission method. Effect of the Invention

[0008] According to at least one of the above aspects, communication resources can be effectively utilized in communication between a relay device that communicates while moving and a ground transmitting device. [Brief description of the drawings]

[0009] [Figure 1] 1 is a configuration diagram of a wireless communication system according to an embodiment. [Diagram 2] FIG. 11 is a flow chart showing a process of a mobile relay station according to the embodiment. [Diagram 3] FIG. 11 is a flow chart showing a process of a terminal station according to the embodiment. [Figure 4] FIG. 11 is a flow chart showing processing of a base station according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0011] 1 is a configuration diagram of a wireless communication system 1 according to an embodiment. The wireless communication system 1 includes a mobile relay station 2, a terminal station 3, and a base station 4. The wireless communication system 1 includes any number of mobile relay stations 2, terminal stations 3, and base stations 4, but it is assumed that the wireless communication system 1 includes a large number of terminal stations 3.

[0012] The mobile relay station 2 is an example of a relay device that communicates while moving. The mobile relay station 2 is provided, for example, on a LEO (Low Earth Orbit) satellite. The altitude of the LEO satellite is 2000 km or less, and it orbits the Earth in about 1.5 hours. The terminal station 3 and the base station 4 are installed on the Earth, such as on the ground or on the sea. The terminal station 3 is, for example, an IoT terminal. The terminal station 3 collects data such as environmental data detected by a sensor, and transmits the data to the mobile relay station 2 by wireless. In the figure, only two terminal stations 3 are shown. The mobile relay station 2 receives data transmitted from each of the multiple terminal stations 3 by wireless signals while moving in the Earth's sky, and transmits the received data by wireless to the base station 4. The base station 4 receives the data collected by the terminal station 3 from the mobile relay station 2.

[0013] As the mobile relay station 2, a relay station mounted on a geostationary satellite, a drone, or an unmanned aerial vehicle such as a HAPS (High Altitude Platform Station) may be used. However, in the case of a relay station mounted on a geostationary satellite, the ground coverage area (footprint) is wide, but the link budget for an IoT terminal installed on the ground is very small due to the high altitude. On the other hand, in the case of a relay station mounted on a drone or HAPS, the link budget is high but the coverage area is narrow. Furthermore, a battery is required for the drone, and a solar panel is required for the HAPS. In this embodiment, the mobile relay station 2 is mounted on a LEO satellite. Therefore, in addition to the link budget being within the limit, the LEO satellite has no air resistance because it orbits outside the atmosphere, and consumes little fuel. In addition, the footprint is larger than when a relay station is mounted on a drone or HAPS.

[0014] However, since the mobile relay station 2 mounted on the LEO performs communication while moving at high speed, Doppler shift occurs in the radio signal. In addition, the relay station mounted on the LEO has a smaller link budget than the relay station mounted on a drone or HAPS. Therefore, the mobile relay station 2 receives radio signals from the terminal station 3 by multiple antennas and transmits radio signals to the base station 4 by multiple antennas. The communication quality can be improved by the diversity effect and beamforming effect of communication using multiple antennas. In this embodiment, the mobile relay station 2 will be described by way of example, where the mobile relay station 2 relays the radio signals received from the terminal station 3 by multiple antennas to the base station 4 by MIMO (Multiple Input Multiple Output). Note that the method of relaying to the base station 4 may be other than MIMO.

[0015] The configuration of each device will be described. The mobile relay station 2 includes a plurality of first antennas 21, a terminal communication unit 22, a base station communication unit 24, and a plurality of second antennas 25. The terminal communication unit 22 includes a storage unit 221, a reception schedule determination unit 222, a capacity specification unit 223, a method determination unit 224, a transmission unit 225, a reception unit 226, a synthesis unit 227, and a spectrum conversion unit 228.

[0016] The storage unit 221 stores position data of the terminal station 3 and orbit data of the LEO satellites. The position data of the terminal station 3 is represented by, for example, latitude and longitude. The LEO orbit data is data that makes it possible to obtain the position, speed, moving direction, etc. of the LEO satellite at any time. The storage unit 221 has a storage area for storing spectrum data of the terminal uplink signal received from the terminal station 3.

[0017] The reception schedule determination unit 222 specifies the timing for receiving a signal from each terminal station 3 based on the position data and orbit data of the terminal station 3 stored in the storage unit 221 .

[0018] The capacity specifying unit 223 specifies a channel capacity for communication with the terminal station 3 at the reception timing determined by the reception schedule determination unit 222. For example, the capacity specifying unit 223 can obtain the channel capacity from an error rate in a signal received from the terminal station 3. Furthermore, for example, the capacity specifying unit 223 may receive a control signal including a value of the channel capacity from the terminal station 3.

[0019] The method determination unit 224 determines the transmission method for data transmission by the terminal station 3 based on the channel capacity specified by the capacity specification unit 223. The method determination unit 224 determines a method with lower transmission efficiency and higher transmission quality as the channel capacity increases, and determines a method with lower transmission quality and higher transmission efficiency as the channel capacity decreases. Specifically, the method determination unit 224 adopts a transmission method with a larger number of multi-levels as the channel capacity decreases. The larger the number of multi-levels, the larger the amount of information per symbol can be, and the higher the transmission efficiency. On the other hand, the smaller the number of multi-levels, the lower the symbol error rate and the higher the transmission quality. Also, the method determination unit 224 determines the number of bits of the error correction code as the channel capacity decreases. Small The shorter the error correction code, the larger the amount of information in the payload for the data frame, and the higher the transmission efficiency. On the other hand, the longer the error correction code, the larger the number of bits that can correct errors, and the higher the transmission quality. In other embodiments, an error detection code may be added instead of an error correction code. Even when an error detection code is used, the method determination unit 224 determines whether the channel capacity is large enough to accommodate the error correction code. small The shorter the error detection code, the greater the amount of information in the payload for the data frame, and the higher the transmission efficiency. Furthermore, the method determination unit 224 increases the transmission power of the signal as the channel capacity decreases. The higher the transmission power, the higher the transmission quality. Since the terminal station 3 with a small channel capacity transmits using a transmission method with high transmission efficiency and low transmission quality, the probability of error occurrence can be reduced by increasing the transmission power and lowering the S / N ratio. Furthermore, when the channel capacity specified by the capacity specification unit 223 is smaller than a predetermined threshold, the method determination unit 224 may determine not to communicate with the terminal station 3 at the reception timing determined by the reception schedule determination unit 222. In other words, the method determination unit 224 may determine to transmit data at the next or subsequent opportunity when the channel capacity is large. In another embodiment, the method determination unit 224 may determine the transmission method not for each terminal station 3, but for each area obtained by dividing the ground into a plurality of meshes.

[0020] The transmitter 225 transmits, as a terminal downlink signal, report information indicating the transmission method determined by the method determination unit 224 for each terminal station 3 via the multiple first antennas 21. That is, the report information includes data associating the ID of the terminal station 3 with the determined transmission method. The report information does not necessarily include the transmission methods of all terminal stations 3, and may include, for example, the transmission method related to the terminal station 3 that includes the reception timing determined by the reception schedule determination unit 222 within a certain period starting from the time point at which the report information is transmitted. The report information may include orbit data of the LEO satellite.

[0021] The receiving unit 226 receives signals via the multiple first antennas 21. The combining unit 227 combines the multiple signals received by the receiving unit 226 via the multiple first antennas 21 in accordance with a predetermined combining parameter. The combining parameter is represented by, for example, the phase and amplitude offset of each first antenna 21. Note that the combining parameter may be found based on the signal reception timing and the positional relationship between the mobile relay station 2 and the communication partner terminal station 3 at the signal reception timing, or may always be a constant value. The combiner 227 regenerates the terminal uplink signal by combining the signals.

[0022] The spectrum conversion unit 228 converts the signal synthesized by the synthesis unit 227 into a frequency spectrum. The spectrum conversion unit 228 obtains the frequency spectrum of the received signal by, for example, FFT (Fast Fourier Transform). The spectrum conversion unit 228 records spectrum data representing the generated frequency spectrum in the storage unit 221. The spectrum data is represented by a combination of frequency and power of the frequency.

[0023] The base station communication unit 24 transmits spectrum data representing a waveform of the terminal uplink signal received by the terminal communication unit 22 to the base station 4 by MIMO. The base station communication unit 24 includes a storage unit 241, a transmission schedule determination unit 242, a control unit 243, a MIMO communication unit 244, a data generation unit 245, and a transmission data modulation unit 246.

[0024] The storage unit 241 stores a communication time period with the base station 4 that is determined in advance from the position of the base station 4 and the orbit of the LEO satellite. The storage unit 241 also stores in advance a weight of the base station downlink signal transmitted from each second antenna 25 for each transmission time period in the communication time period. The transmission time may be expressed, for example, as the elapsed time from the transmission start timing. The weight for each transmission time period is calculated based on the orbit data of the LEO satellite and the position of each antenna station 41.

[0025] The transmission schedule determination unit 242 determines a transmission time zone for each piece of spectrum data based on the communication time zone and the number of spectrum data stored in the storage unit 221. For example, the transmission schedule determination unit 242 determines the transmission time zone for each piece of spectrum data by dividing the length of the communication time zone by the number of spectrum data, and determines the transmission time zone for each piece of spectrum data by dividing the communication time zone by the transmission time.

[0026] The control unit 243 instructs the MIMO communication unit 244 on the weight for each transmission time read from the storage unit 241. The MIMO communication unit 244 establishes MIMO communication with the base station 4 using a predetermined protocol.

[0027] The data generator 245 converts the spectrum data stored in the memory 221 into parallel signals and modulates the parallel signals. The modulated parallel signals are weighted by weights specified by the controller 243 and transmitted from each second antenna 25 as a base station downlink signal.

[0028] The terminal station 3 includes a data storage unit 31, a receiver unit 32, a condition determination unit 33, a transmitter unit 34, and one or more antennas 35. The terminal station 3 is an example of a communication device that transmits data to a relay device. The data storage unit 31 stores sensor data and orbit data of LEO satellites. The receiver unit 32 receives a terminal downlink signal from the mobile relay station 2 via the multiple antennas 35 and reads out the broadcast information.

[0029] The condition determination unit 33 reads out the transmission method associated with the ID of the own station from the broadcast information read by the receiving unit 32, and determines the transmission method of the transmitting unit 34. The condition determination unit 33 also determines the transmission time zone of the terminal uplink signal based on the orbit data of the LEO satellite. That is, the condition determination unit 33 determines the time zone in which the terminal station 3 exists within the coverage of the first antenna 21 of the mobile relay station 2 as the transmission time zone of the terminal uplink signal. Note that, when the broadcast information read by the receiving unit 32 stores information indicating that communication is not to be performed instead of the transmission method, the condition determination unit 33 determines not to transmit the terminal uplink signal.

[0030] The transmitter 34 wirelessly transmits a terminal uplink signal, in which the sensor data stored in the data storage unit 31 is set as terminal transmission data, from the antenna 35 according to the transmission time zone and transmission method determined by the condition determination unit 33. That is, the transmitter 34 transmits a signal with the multi-value number, error correction code, and transmission power stored in the broadcast information from the mobile relay station 2. The transmitter 34 transmits a signal, for example, by LPWA (Low Power Wide Area). LPWA includes LoRaWAN (registered trademark), Sigfox (registered trademark), LTE-M (Long Term Evolution for Machines), NB (Narrow Band)-IoT, etc., but any wireless communication method can be used. In addition, the transmitter 34 may transmit with other terminal stations 3 by time division multiplexing, OFDM (Orthogonal Frequency Division Multiplexing), MIMO, etc. The transmitter 34 determines a channel and transmission timing to be used by the own station for transmitting the terminal uplink signal by a method predetermined in the wireless communication method to be used. Furthermore, the transmitting unit 34 may perform beamforming of signals to be transmitted from the multiple antennas 35 using a method that is determined in advance in the wireless communication system being used.

[0031] The base station 4 includes a plurality of antenna stations 41, a MIMO receiving unit 42, a base station signal receiving and processing unit 43, and a terminal signal receiving and processing unit 44.

[0032] The antenna station 41 is disposed at a position away from the other antenna stations 41 so as to increase the difference in the arrival angles of signals from each of the multiple second antennas 25 of the mobile relay station 2. Each antenna station 41 converts a base station downlink signal received from the mobile relay station 2 into an electrical signal and outputs it to the MIMO receiving unit 42.

[0033] The MIMO receiver 42 aggregates base station downlink signals received from a plurality of antenna stations 41. The MIMO receiver 42 stores a weight for each reception time for the base station downlink signal received by each antenna station 41 based on the orbit data of the LEO satellite and the position of each antenna station 41. For example, the reception time may be expressed as an elapsed time from the timing of starting reception. The MIMO receiver 42 multiplies the base station downlink signal input from each antenna station 41 by a weight corresponding to the reception time of the base station downlink signal, and combines the weight-multiplied reception signals. Note that the same weight may be used regardless of the reception time. The base station signal reception processor 43 demodulates and decodes the combined reception signal to obtain demodulated information. The base station signal reception processor 43 outputs the demodulated information to the terminal signal reception processor 44.

[0034] The terminal signal reception processing unit 44 performs reception processing of the terminal uplink signal. The terminal signal reception processing unit 44 decodes the symbols of the terminal uplink signal from the spectrum data indicated by the demodulation information, and obtains the terminal transmission data transmitted from the terminal station 3. That is, the terminal signal reception processing unit 44 decodes the symbols of the terminal uplink signal by converting the frequency domain waveform indicated by the spectrum data into a time domain waveform.

[0035] The operation of the wireless communication system 1 will be described. FIG. 2 is a flow diagram showing the processing of the mobile relay station 2 according to the embodiment. FIG. 3 is a flow diagram showing the processing of the terminal station 3 according to the embodiment. FIG. 4 is a flow diagram showing the processing of the base station 4 according to the embodiment. As shown in FIG. 2, the reception schedule determination unit 222 of the mobile relay station 2 determines the terminal station 3 that is a target for receiving the terminal uplink signal for each time based on the position data and orbit data of the terminal station 3 stored in the storage unit 221 (step S121). The capacity determination unit 223 determines the channel capacity in communication at the reception timing determined in step S121 for each terminal station 3 (step S122).

[0036] The method determination unit 224 determines the transmission method of data transmission for each terminal station 3 based on the channel capacity specified in step S122 (step S123). That is, the method determination unit 224 determines the number of multi-levels and the number of bits of the error correction code so that the transmission efficiency is lower and the transmission quality is higher as the channel capacity is larger. In addition, the method determination unit 224 determines the transmission power so that the transmission power is higher for a terminal station that adopts a transmission method with lower transmission quality (step S124). The transmitter 225 transmits report information indicating the transmission method determined by the method determination unit 224 for each terminal station 3 as a terminal downlink signal via the multiple first antennas 21 (step S125).

[0037] On the other hand, the terminal station 3 acquires data detected by a sensor (not shown) provided externally or internally as shown in Fig. 1, and writes the acquired data to the data storage unit 31 (step S101). The receiver 32 of the terminal station 3 receives the terminal downlink signal transmitted from the mobile relay station 2 in step S125 (step S102). The condition determination unit 33 reads out the transmission method associated with the ID of the own station from the broadcast information included in the terminal downlink signal received in step S101, and determines the transmission method of the transmitter 34 (step S103). The condition determination unit 33 also determines the transmission time zone of the terminal uplink signal based on the orbit data of the LEO satellite (step S104).

[0038] The transmitting unit 34 of the terminal station 3 determines whether or not the current time is included in the transmission time period of the uplink signal determined by the condition determining unit 33 (step S105). If the transmitting unit 34 determines that the current time is not included in the transmission time period of the uplink signal (step S105: NO), the terminal station 3 returns the process to step S101.

[0039] On the other hand, if the transmitting unit 34 determines that the current time is included in the transmission time zone of the uplink signal (step S105: YES), it reads out the sensor data from the data storage unit 31, sets the read sensor data as terminal transmission data, and sets it in the terminal uplink signal of the transmission method determined in step S103. The transmitting unit 34 wirelessly transmits the terminal uplink signal in which the terminal transmission data is set from the antenna 35 (step S106). The terminal station 3 returns the process to step S105. As a result, the terminal station 3 continues transmitting the uplink signal during the transmission time zone.

[0040] As shown in Fig. 2, the multiple receivers 226 of the mobile relay station 2 receive the terminal uplink signal transmitted from the terminal station 3 (step S126). Depending on the wireless communication method of the source terminal station 3, the terminal uplink signal may be received from only one terminal station 3 in a time-division manner for the same frequency, or may be received from multiple terminal stations 3 simultaneously at the same frequency. The combiner 227 combines the terminal uplink signals received by the multiple receivers 226 in accordance with the combination parameters set in step S122 (step S127). The spectrum converter 228 converts the signal combined by the combiner 227 into spectrum data, and records it in the storage unit 221 (step 128).

[0041] The transmission schedule determination unit 242 refers to the storage unit 241 and determines whether the current time is included in the communication time zone with the base station 4 (step S129). If the current time is not included in the communication time zone with the base station 4 (step S129: NO), the process returns to step S121. On the other hand, if the current time is included in the communication time zone with the base station 4 (step S129: YES), the transmission schedule determination unit 242 determines the transmission time for each spectrum data based on the number of spectrum data stored in the storage unit 221 and the length of the communication time zone with the base station 4 (step S130).

[0042] The data generation unit 245 performs parallel conversion on the spectrum data stored in the storage unit 221, and the transmission data modulation unit 246 modulates the parallel converted spectrum data. The MIMO communication unit 244 weights the transmission data modulated by the transmission data modulation unit 246 with the weight instructed by the control unit 243, and generates a base station downlink signal to be transmitted from each second antenna 25. The MIMO communication unit 244 transmits each generated base station downlink signal from the second antenna 25 by MIMO (step S131). When the mobile relay station 2 has transmitted all the spectrum data stored in the storage unit 221, the process returns to step S121.

[0043] As shown in FIG. 4, each antenna station 41 of the base station 4 receives a base station downlink signal from the mobile relay station 2 (step S141). Each antenna station 41 converts the received base station downlink signal into an electrical signal and outputs the electrical signal to the MIMO receiving unit 42. The MIMO receiving unit 42 synchronizes the timing of the received signals received from each antenna station 41. The MIMO receiving unit 42 combines the received signals received by each antenna station 41 based on the weight. The base station signal receiving processing unit 43 demodulates the combined received signal (step S142). The base station signal receiving processing unit 43 outputs waveform data obtained by decoding the demodulated received signal to the terminal signal receiving processing unit 44.

[0044] The terminal signal decoder 441 of the terminal signal reception processor 44 decodes the symbols of the terminal uplink signal indicated by the waveform data, and obtains the terminal transmission data transmitted from the terminal station 3 (step S143). The terminal signal decoder 441 can also use a decoding method with a large calculation load, such as SIC (Successive Interference Cancellation). The base station 4 repeats the process from step S141.

[0045] According to this embodiment, the mobile relay station 2 varies the target band for sampling the waveform data based on the channel capacity related to communication with the terminal station 3. Specifically, the mobile relay station 2 generates waveform data such that the target band becomes wider as the channel capacity increases. This allows the mobile relay station 2 to effectively utilize communication resources while preventing loss of received data. In other words, the wireless communication system 1 can transmit information in a wide band when the channel capacity is large.

[0046] As described above, according to the above embodiment, the mobile relay station 2 determines the data transmission method from the terminal station 3 to the mobile relay station 2 to be a method with lower transmission efficiency and higher transmission quality as the channel capacity increases. This allows the mobile relay station 2 to effectively use communication resources in communication between the terminal station 3 and the mobile relay station 2.

[0047] The mobile relay station 2 includes a processor, a memory, an auxiliary storage device, and the like, which are connected by a bus, and functions as a device including a terminal communication unit 22 and a base station communication unit 24 by executing a relay program. Examples of the processor include a CPU (Central Processing Unit), a GPU (Graphic Processing Unit), and a microprocessor. The relay program may be recorded in a computer-readable recording medium. The computer-readable recording medium is, for example, a storage device such as a magnetic disk, a magneto-optical disk, an optical disk, a semiconductor memory, etc. The relay program may be transmitted via a telecommunication line. All or part of the functions of the mobile relay station 2 may be realized using a custom LSI (Large Scale Integrated Circuit) such as an ASIC (Application Specific Integrated Circuit) or a PLD (Programmable Logic Device). Examples of PLDs include PAL (Programmable Array Logic), GAL (Generic Array Logic), CPLD (Complex Programmable Logic Device), and FPGA (Field Programmable Gate Array). Such integrated circuits are also included in the example of a processor.

[0048] (Other embodiments) Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to the above, and various design changes are possible. That is, in other embodiments, the order of the above-mentioned processes may be changed as appropriate. Also, some of the processes may be executed in parallel.

[0049] The mobile relay station 2 according to the above-described embodiment may be configured by a single computer, or the configuration of the mobile relay station 2 may be distributed across multiple computers, and the multiple computers may work together to function as the mobile relay station 2.

[0050] According to the above-mentioned embodiment, the method determining unit 224 determines the multi-level number and the error correction code, but is not limited to this. For example, in another embodiment, the multi-level number may be a fixed value, and the method determining unit 224 may determine only the error correction code or the error detection code. In another embodiment, the number of bits of the error correction code or the error detection code may be a fixed value, and the method determining unit 224 may determine only the multi-level number. According to the above-mentioned embodiment, the method determining unit 224 determines the transmission power, but is not limited to this. For example, the transmission power in another embodiment may be a fixed value.

[0051] According to the above-mentioned embodiment, the scheme determination unit 224 of the mobile relay station 2 determines the transmission scheme of the terminal station 3, but this is not limited thereto. For example, in another embodiment, the mobile relay station 2 may include the channel capacity of each terminal station 3 in the downlink signal, and each terminal station 3 may determine the transmission scheme based on the channel capacity. That is, in another embodiment, the terminal station 3 may be provided with the scheme determination unit 224. In still another embodiment, each terminal station 3 may specify the channel capacity based on the orbit of the LEO satellite. That is, in the wireless communication system 1, the capacity determination unit 223 and the scheme determination unit 224 may be provided in the mobile relay station 2 or in the terminal station 3.

[0052] In the above-described embodiment, the mobile relay station 2 is mounted on a LEO satellite, but is not limited thereto. For example, the mobile relay station 2 according to other embodiments may be mounted on other flying objects such as a geostationary satellite, a drone, or a HAPS. Also, in the above-described embodiment, the mobile relay station 2 moves above the Earth, and the terminal station 3 and the base station 4 are provided on the Earth, but the wireless communication system 1 according to other embodiments may target a celestial body other than the Earth, such as the Moon.

[0053] In the above-described embodiment, the capacity specifying unit 223 of the mobile relay station 2 specifies the channel capacity related to the communication with the base station 4 by MIMO communication with the base station 4, but is not limited to this. For example, the capacity specifying unit 223 according to another embodiment may store the channel capacity related to the communication with the base station 4 in advance in the storage unit 241 for each time, and read the channel capacity from the storage unit 241. Furthermore, the capacity specifying unit 223 according to another embodiment may obtain the elevation angle of the mobile relay station 2 with respect to the base station 4 based on the orbit data and the position of the base station 4, and estimate the channel capacity from the elevation angle.

[0054] In the mobile relay station 2 according to the embodiment described above, when the channel capacity specified by the capacity specifying unit 223 is smaller than a predetermined threshold, the mobile relay station 2 determines to transmit data at the next or subsequent opportunity when the channel capacity is large. In another embodiment, when a plurality of LEO satellites form a constellation, data may be transmitted to the mobile relay station 2 mounted on the other LEO satellites forming the constellation. The plurality of mobile relay stations 2 forming the constellation recognize the reception status of the other mobile relay stations 2 by transmitting and receiving reception status information regarding the reception status of the terminal uplink signal to each other. Here, when the channel capacity specified by the capacity specifying unit 223 is smaller than a predetermined threshold, the transmission unit 225 of the mobile relay station 2 stores in the reception status information that communication with the terminal station 3 was not possible. As a result, the reception schedule determination unit 222 of the other mobile relay station 2 determines a reception schedule from the terminal station 3 with which communication was not possible based on the reception status information, and the method determination unit 224 can determine the transmission method of the data transmission by the terminal station 3. [Explanation of symbols]

[0055] 1...wireless communication system 2...mobile relay station 21...first antenna 22...terminal communication unit 221...storage unit 222...reception schedule determination unit 223...capacity specification unit 224...system determination unit 225...transmission unit 226...reception unit 227...synthesis unit 228...spectrum conversion unit 24...base station communication unit 241...storage unit 242...transmission schedule determination unit 243...control unit 244...MIMO communication unit 245...data generation unit 246...transmission data modulation unit 25...second antenna 3...terminal station 31...data storage unit 32...reception unit 33...condition determination unit 34...transmission unit 35...antenna 4...base station 41...antenna station 42...MIMO reception unit 43...base station signal reception processing unit 44...terminal signal reception processing unit

Claims

1. A communication system including a relay device that communicates while moving and a communication device that transmits data to the relay device, a capacity specification unit that specifies a channel capacity related to wireless communication between the communication device and the relay device; a method determining unit that determines a method for transmitting the data from the communication device to the relay device to be a method with lower transmission efficiency and higher transmission quality as the channel capacity increases, and determines a method with lower transmission quality and higher transmission efficiency as the channel capacity decreases; A communication system comprising:

2. The method determining unit increases the number of multi-levels of the transmission method as the channel capacity decreases. The communication system according to claim 1 .

3. The method determination unit reduces the amount of data of the error correction code or the error detection code of the transmission method as the channel capacity decreases. The communication system according to claim 1 or 2.

4. The method determination unit increases a transmission power for transmitting the data as the channel capacity decreases. A communication system according to any one of claims 1 to 3.

5. the capacity specifying unit and the method determining unit are provided in the relay device, the relay device includes a notification unit that notifies the communication device of the determined transmission method; The communication device includes a transmission unit that transmits the data to the relay device in accordance with the transmission method notified by the relay device. A communication system according to any one of claims 1 to 4.

6. The method determination unit determines not to transmit the data when the channel capacity is smaller than a predetermined threshold. A communication system according to any one of claims 1 to 5.

7. A communication method between a relay device which performs communication while moving and a communication device which transmits data to the relay device, comprising the steps of: estimating a channel capacity related to wireless communication between the communication device and the relay device; determining a transmission method of the data from the communication device to the relay device to be a method with lower transmission efficiency and higher transmission quality as the channel capacity increases, and a method with lower transmission quality and higher transmission efficiency as the channel capacity decreases; transmitting the data from the communication device to the relay device in accordance with the determined transmission method; A communication method comprising:

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