Wireless communication system, relay device, and wireless communication method

Abstract

A mobile relay device includes a first signal receiving section, a storage section, and a second signal transmitting section. The first signal receiving section receives a first signal wirelessly transmitted by a first communication device. The storage section stores waveform data showing a waveform of the first signal. The second signal transmitting section wirelessly transmits a second signal showing the waveform data stored in the storage section at a timing at which communication with a second communication device is possible. The second communication device includes a second signal receiving section, a second signal receiving processing section, and a first signal receiving processing section. The second signal receiving section receives the second signal. The second signal receiving processing section performs reception processing of the second signal to acquire the waveform data. The first signal receiving processing section performs reception processing of the first signal shown by the waveform data to acquire data set as the first signal by the first communication device.

Description

Technical Field

[0001] This invention relates to wireless communication systems, relay devices, and wireless communication methods. Background Technology

[0002] With the development of IoT (Internet of Things) technology, research is underway on deploying IoT terminals equipped with various sensors in a wide variety of locations. For example, it is envisioned to effectively utilize IoT to collect data from locations where it is difficult to set up base stations, such as buoys or ships at sea and mountainous areas. On the other hand, there are technologies that use UAVs (Unmanned Aerial Vehicles) or geostationary satellites to conduct wireless communication with ground-based communication devices (for example, see Non-Patent Document 1).

[0003] Prior art literature

[0004] Non-patent literature

[0005] Non-patent document 1: Naoto Kadowaki et al., "Latest Trends in New Satellite Communication Technology", Journal of the Society of Electronic Information and Communications Technology B, Volume J97-B, Issue 11, pp. 979-991, 2014. Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] Non-Patent Document 1 describes a non-reproducible relay technology related to geostationary satellites. However, when a relay device is mounted on a low-Earth orbit satellite, the area where the relay device can communicate moves along with the movement of the low-Earth orbit satellite. Therefore, the time that communication devices such as IoT terminals or base stations located on Earth can communicate with the relay device is limited.

[0008] In view of the above, the object of the present invention is to provide a wireless communication system, a relay device, and a wireless communication method that can wirelessly relay data received from a communication device to other communication devices even when the communication area moves along with the movement of the relay device.

[0009] Solution for solving the problem

[0010] One aspect of the present invention is a wireless communication system as follows: the aforementioned relay device includes: a first signal receiving unit that receives a first signal wirelessly transmitted by the aforementioned first communication device; a storage unit that stores waveform data showing the waveform of the aforementioned first signal received by the aforementioned first signal receiving unit; and a second signal transmitting unit that, at a timing when communication with the aforementioned second communication device is possible, wirelessly transmits a second signal showing the aforementioned waveform data stored in the aforementioned storage unit to the aforementioned second communication device, the aforementioned second communication device including: a second signal receiving unit that receives the aforementioned second signal wirelessly transmitted by the aforementioned relay device; a second signal receiving processing unit that performs receiving processing of the aforementioned second signal received by the aforementioned second signal receiving unit to obtain the aforementioned waveform data; and a first signal receiving processing unit that performs receiving processing of the aforementioned first signal shown by the aforementioned waveform data obtained by the aforementioned second signal receiving processing unit to obtain data set as the aforementioned first signal by the aforementioned first communication device.

[0011] One aspect of the present invention is a relay device, which is the aforementioned relay device in a wireless communication system having a first communication device, a second communication device, and a mobile relay device. The aforementioned relay device includes: a first signal receiving unit that receives a first signal wirelessly transmitted by the aforementioned first communication device; a storage unit that stores waveform data showing the waveform of the aforementioned first signal received by the aforementioned first signal receiving unit; and a second signal transmitting unit that, at a timing when communication with the aforementioned second communication device is possible, wirelessly transmits a second signal showing the aforementioned waveform data stored in the aforementioned storage unit to the aforementioned second communication device.

[0012] One aspect of the present invention is a wireless communication method performed by a wireless communication system having a first communication device, a second communication device, and a mobile relay device. The wireless communication method includes: a first signal receiving step, in which the relay device receives a first signal wirelessly transmitted by the first communication device; a recording step, in which the relay device writes waveform data showing the waveform of the first signal received in the first signal receiving step into a storage unit; a second signal transmitting step, in which the relay device wirelessly transmits a second signal showing the waveform data stored in the storage unit to the second communication device at a timing when communication with the second communication device is possible; a second signal receiving step, in which the second communication device receives the second signal wirelessly transmitted in the second signal transmitting step; a second signal receiving processing step, in which the second communication device performs receiving processing on the second signal received in the second signal receiving step to obtain the waveform data; and a first signal receiving processing step, in which the second communication device performs receiving processing on the first signal shown by the waveform data obtained in the second signal receiving processing step to obtain data set as the first signal by the first communication device.

[0013] One aspect of the present invention is a wireless communication method performed by the relay device in a wireless communication system having a first communication device, a second communication device, and a mobile relay device. The wireless communication method includes: a first signal receiving step, which receives a first signal wirelessly transmitted by the first communication device; a recording step, which writes waveform data showing the waveform of the first signal received in the first signal receiving step to a storage unit; and a second signal transmitting step, which wirelessly transmits a second signal showing the waveform data stored in the storage unit to the second communication device at a timing when communication with the second communication device is possible.

[0014] Invention Effects

[0015] With this invention, even when the area where communication is possible moves along with the movement of the relay device, data received wirelessly from the communication device can be wirelessly relayed to other communication devices. Attached Figure Description

[0016] Figure 1 This is a configuration diagram of a wireless communication system according to the first embodiment of the present invention.

[0017] Figure 2 This is a flowchart illustrating the processing of a wireless communication system according to this embodiment.

[0018] Figure 3This is a flowchart illustrating the processing of a wireless communication system according to this embodiment.

[0019] Figure 4 This is a configuration diagram of a wireless communication system according to the second embodiment.

[0020] Figure 5 This is a flowchart illustrating the processing of a wireless communication system according to this embodiment.

[0021] Figure 6 This is a configuration diagram of a wireless communication system according to the third embodiment.

[0022] Figure 7 This is a flowchart illustrating the processing of a wireless communication system according to this embodiment. Detailed Implementation

[0023] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0024] (First Embodiment)

[0025] Figure 1 This is a configuration diagram of the wireless communication system 1 according to the first embodiment. The wireless communication system 1 includes a mobile relay station 2, a terminal station 3, and a base station 4. The number of each of the mobile relay station 2, terminal station 3, and base station 4 in the wireless communication system 1 is arbitrary, but it is assumed that the number of terminal stations 3 is many.

[0026] Mobile relay station 2 is an example of a relay device mounted on a mobile vehicle, and its communication range shifts over time. For example, a LEO (Low Earth Orbit) satellite might have a mobile relay station 2. LEO satellites orbit the Earth at altitudes below 2000 km, completing one orbit approximately every 1.5 hours. Terminal station 3 and base station 4 are located on Earth, either on land or at sea. Terminal station 3 is, for example, an IoT terminal. Terminal station 3 collects environmental data detected by sensors and transmits this data wirelessly to mobile relay station 2. Only two terminal stations 3 are shown in this diagram. Mobile relay station 2 moves in the Earth's atmosphere and simultaneously receives data transmitted from multiple terminal stations 3 via wireless signals. Mobile relay station 2 accumulates the received data and, at a time when communication with base station 4 is possible, transmits the pre-accumulated data wirelessly to base station 4. Base station 4 receives the data collected by terminal stations 3 from mobile relay station 2.

[0027] As a mobile relay station, relay stations mounted on geostationary satellites or unmanned aerial vehicles (UAVs) such as drones or HAPS (High Altitude Platform Stations) are considered. However, in the case of a relay station mounted on a geostationary satellite, although the ground coverage area is wide, the link budget for IoT terminals located 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, although the link budget is high, the coverage area is narrow. Moreover, drones require batteries, and HAPS require solar panels. In this embodiment, mobile relay station 2 is mounted on a LEO satellite. Therefore, in addition to the link budget being within the limits, LEO satellites have no air resistance due to orbiting outside the atmosphere and consume less fuel. Furthermore, the coverage area is larger compared to the case of mounting the relay station on a drone or HAPS.

[0028] Mobile relay station 2, mounted on a LEO satellite, moves at high speed and communicates simultaneously, thus limiting the time each terminal station 3 or base station 4 can communicate with it. Specifically, from a ground perspective, mobile relay station 2 takes approximately 10 minutes to pass overhead. Furthermore, various wireless communication methods can be used for terminal stations 3. Therefore, mobile relay station 2 pre-receives uplink signals from terminal stations 3 within its coverage area at its current location and saves the waveform data of the received uplink signals. When base station 4 is within its coverage area, mobile relay station 2 wirelessly transmits a downlink signal obtained by setting the waveform data of the uplink signals to base station 4. Base station 4 demodulates the downlink signals received from mobile relay station 2 to obtain the waveform data of the uplink signals. Base station 4 demodulates and decodes the uplink signals represented by the waveform data to obtain the terminal transmission data, which is the data transmitted by terminal station 3.

[0029] Explain the composition of each device.

[0030] The mobile relay station 2 includes an antenna 21, a terminal communication unit 22, a data storage unit 23, a base station communication unit 24, and an antenna 25.

[0031] The terminal communication unit 22 includes a receiving unit 221 and a receiving waveform recording unit 222. The receiving unit 221 receives the terminal uplink signal via the antenna 21. The receiving waveform recording unit 222 samples the received waveform of the terminal uplink signal received by the receiving unit 221 and generates waveform data that displays the sampled values. The receiving waveform recording unit 222 writes the received waveform information to the data storage unit 23, wherein the received waveform information includes the timing of the reception of the terminal uplink signal from the antenna 21 and the generated waveform data. The data storage unit 23 stores the received waveform information written by the receiving waveform recording unit 222.

[0032] The base station communication unit 24 transmits received waveform information to the base station 4 via a base station downlink signal using any wireless communication method. The base station communication unit 24 includes a storage unit 241, a control unit 242, a transmission data modulation unit 243, and a transmission unit 244. The storage unit 241 stores a transmission start timing calculated in advance based on the orbit information of the LEO satellite carrying the mobile relay station 2 and the position of the base station 4. The LEO orbit information includes information such as the LEO satellite's position, speed, and direction of movement at any given time. The transmission timing can also be represented, for example, by the time elapsed since the transmission start timing.

[0033] The control unit 242 controls the transmission data modulation unit 243 and the transmission unit 244 to transmit received waveform information to the base station 4 at the transmission start timing stored in the storage unit 241. The transmission data modulation unit 243 reads the received waveform information from the data storage unit 23 as transmission data, modulates the read transmission data to generate a base station downlink signal. The transmission unit 244 converts the base station downlink signal from an electrical signal into a wireless signal and transmits it from the antenna 25.

[0034] Terminal station 3 includes a data storage unit 31, a transmission unit 32, and one or more antennas 33. The data storage unit 31 stores sensor data, etc. The transmission unit 32 reads the sensor data from the data storage unit 31 as terminal transmission data, and wirelessly transmits the terminal uplink signal obtained by setting the read terminal transmission data from the antennas 33. The transmission unit 32 transmits signals, for example, via 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. Alternatively, the transmission unit 32 can also transmit by performing time division multiplexing (TDM) or OFDM (Orthogonal Frequency Division Multiplexing) with another terminal station 3. The transmission unit 32 determines the channel and transmission timing used for transmitting the terminal uplink signal by a predetermined method in the wireless communication method used. Alternatively, the transmitting unit can perform beamforming of signals transmitted by multiple antennas 33 using a method predetermined in the wireless communication method used.

[0035] Base station 4 includes antenna 41, receiver 42, base station signal receiving and processing unit 43, and terminal signal receiving and processing unit 44. Receiver 42 converts the terminal downlink signal received through antenna 41 into an electrical signal. Base station signal receiving and processing unit 43 demodulates and decodes the received signal obtained from the electrical signal converted by receiver 42 to obtain received waveform information. Base station signal receiving and processing unit 43 outputs the received waveform information to terminal signal receiving and processing unit 44.

[0036] The terminal signal receiving and processing unit 44 performs receiving and processing of the terminal uplink signal shown in the received waveform information. At this time, the terminal signal receiving and processing unit 44 obtains the terminal transmitted data by performing receiving and processing through the wireless communication method used by the terminal station 3 in transmission. The terminal signal receiving and processing unit 44 includes a terminal signal demodulation unit 441 and a terminal signal decoding unit 442.

[0037] The terminal signal demodulation unit 441 demodulates the waveform data and outputs the demodulated symbols to the terminal signal decoding unit 442. Alternatively, the terminal signal demodulation unit 441 can perform demodulation after processing the signal shown in the waveform data; this processing compensates for the Doppler shift of the terminal uplink signal received by the antenna 21 of the mobile relay station 2. Based on the location of the terminal station 3 and the track information of the LEO carrying the mobile relay station 2, the Doppler shift experienced by the terminal uplink signal received by the antenna 21 is pre-calculated. The terminal signal decoding unit 442 decodes the demodulated symbols from the terminal signal demodulation unit 441 to obtain the terminal transmission data sent from the terminal station 3.

[0038] Explain the operation of wireless communication system 1.

[0039] Figure 2 This is a flowchart illustrating the processing of the wireless communication system 1 when transmitting uplink signals from the terminal station 3. The terminal station 3 continuously acquires data detected by sensors (not shown) located externally or internally within the terminal station 3, and writes the acquired data to the data storage unit 31 (step S111). The transmitting unit 32 reads the sensor data from the data storage unit 31 as terminal transmission data. At a transmission start timing predetermined based on the orbital information of the LEO satellite carrying the mobile relay station 2, the transmitting unit 32 wirelessly transmits the terminal uplink signal obtained after setting the terminal transmission data from the antenna 33 (step S112). The terminal station 3 repeats the processing from step S111 onwards.

[0040] The receiving unit 221 of the mobile relay station 2 receives the terminal uplink signal transmitted from the terminal station 3 (step S121). Depending on the wireless communication method of the transmitting terminal station 3, there are cases where the terminal uplink signal is received from only one terminal station 3 using time-division multiplexing at the same frequency, and cases where the terminal uplink signal is received from multiple terminal stations 3 simultaneously at the same frequency. The received waveform recording unit 222 writes the received waveform information, which associates the waveform data representing the waveform of the terminal uplink signal received by the receiving unit 221 with the received time, to the data storage unit 23 (step S122). The mobile relay station 2 repeats the processing from step S121 onwards.

[0041] Figure 3This is a flowchart illustrating the processing of the wireless communication system 1 when transmitting a base station downlink signal from the mobile relay station 2. If the control unit 242 of the base station communication unit 24 of the mobile relay station 2 detects a transmission start timing stored in the storage unit 241, it instructs the transmission data modulation unit 243 and the transmission unit 244 to transmit received waveform information (step S211). The transmission data modulation unit 243 reads the received waveform information stored in the data storage unit 23 as transmission data, modulates the read transmission data, and generates a base station downlink signal. The transmission unit 244 transmits the base station downlink signal generated by the transmission data modulation unit 243 via the wireless antenna 25 (step S212). The mobile relay station 2 repeats the processing from step S211 onwards.

[0042] Antenna 41 of base station 4 receives downlink signals from mobile relay station 2 (step S221). Receiving unit 42 converts the downlink signals received by antenna 41 into electrical signals and outputs these signals to base station signal receiving and processing unit 43. Base station signal receiving and processing unit 43 demodulates the received signals and decodes the demodulated signals (step S222). Base station signal receiving and processing unit 43 outputs the decoded received waveform information to terminal signal receiving and processing unit 44.

[0043] The terminal signal receiving processing unit 44 performs receiving processing of the terminal uplink signal represented by the waveform data included in the received waveform information (step S223). Specifically, the terminal signal demodulation unit 441 determines the wireless communication mode used by the terminal station 3 in transmitting the terminal uplink signal based on information inherent in the wireless communication mode included in the received signal represented by the waveform data. The terminal signal demodulation unit 441 demodulates the received signal represented by the waveform data according to the determined wireless communication mode and outputs the demodulated symbols to the terminal signal decoding unit 442. The terminal signal decoding unit 442 decodes the symbols input from the terminal signal demodulation unit 441 using the determined wireless communication mode to obtain the terminal transmission data transmitted from the terminal station 3. In addition, the terminal signal decoding unit 442 can also use a decoding mode with a large computational load, such as SIC (Successive Interference Cancellation). The base station 4 repeats the processing from step S221.

[0044] (Second Implementation)

[0045] In this embodiment, the mobile relay station transmits the base station downlink signal using multiple antennas. The following description focuses on the differences from the first embodiment, using MIMO (Multiple Input Multiple Output) in the transmission of the base station downlink signal as an example.

[0046] Figure 4 This is a configuration diagram of the wireless communication system 1a according to the second embodiment. In this diagram, [the diagram shows the configuration of the wireless communication system 1a according to the second embodiment]. Figure 1 The same components as those in the first embodiment of the wireless communication system 1 are indicated by the same symbols and their descriptions are omitted. The wireless communication system 1a includes a mobile relay station 2a, a terminal station 3, and a base station 4a.

[0047] Mobile relay station 2a includes antenna 21, terminal communication unit 22, data storage unit 23, base station communication unit 26, and multiple antennas 25. Base station communication unit 26 transmits received waveform information to base station 4a via MIMO. Base station communication unit 26 includes storage unit 261, control unit 262, transmission data modulation unit 263, and MIMO transmission unit 264. Storage unit 261 stores a transmission start timing pre-calculated based on the orbit information of the LEO satellite carrying mobile relay station 2a and the position of base station 4a. Furthermore, storage unit 261 pre-stores the weight of each transmission moment of the base station downlink signal transmitted from each antenna 25. The weight of each transmission moment is calculated based on the orbit information of the LEO satellite and the positions of each antenna station 410 of base station 4a. Alternatively, fixed weights can be used regardless of the transmission moment.

[0048] Control unit 262 controls transmission data modulation unit 263 and MIMO transmission unit 264 to transmit received waveform information to base station 4a at the transmission start timing stored in storage unit 261. Furthermore, control unit 262 instructs MIMO transmission unit 264 on the weight of each transmission moment read from storage unit 261. Transmission data modulation unit 263 reads received waveform information from data storage unit 23 as transmission data, converts the read transmission data into a parallel signal, and then modulates it. MIMO transmission unit 264 uses the weights instructing by control unit 262 to weight the modulated parallel signal, generating a base station downlink signal transmitted from each antenna 25. MIMO transmission unit 264 transmits the generated base station downlink signal from antenna 25 via MIMO.

[0049] Base station 4a includes multiple antenna stations 410, a MIMO receiver 420, a base station signal receiving and processing unit 430, and a terminal signal receiving and processing unit 44. The antenna stations 410 are positioned separately from other antenna stations 410, increasing the difference in the angle of arrival of the signals from the multiple antennas 25 of mobile relay station 2a. Each antenna station 410 converts the base station downlink signal received from mobile relay station 2a into an electrical signal and outputs it to the MIMO receiver 420.

[0050] The MIMO receiver 420 aggregates base station downlink signals received from multiple antenna stations 410. Based on the orbital information of the LEO satellites and the positions of each antenna station 410, the MIMO receiver 420 stores weights for each reception time of the base station downlink signal received by each antenna station 410. The MIMO receiver 420 multiplies the base station downlink signal input from each antenna station 410 by the weight corresponding to the reception time of that base station downlink signal, synthesizing a weighted received signal. Alternatively, the same weights can be used regardless of the reception time. The base station signal receiving processing unit 430 demodulates and decodes the synthesized received signal to obtain received waveform information. The base station signal receiving processing unit 430 outputs the received waveform information to the terminal signal receiving processing unit 44.

[0051] Explain the operation of wireless communication system 1a.

[0052] The processing of wireless communication system 1a when uplink signals are transmitted from terminal station 3, and Figure 2 The processing of the wireless communication system 1 in the first embodiment shown is the same.

[0053] Figure 5 This is a flowchart illustrating the processing of a wireless communication system 1a when transmitting a base station downlink signal from a mobile relay station 2a. If the control unit 262 of the base station communication unit 26 of the mobile relay station 2a detects a transmission start timing stored in the storage unit 261, it instructs the transmission data modulation unit 263 and the MIMO transmission unit 264 to transmit received waveform information (step S311). The transmission data modulation unit 263 reads the received waveform information stored in the data storage unit 23 as transmission data, performs parallel conversion on the read transmission data, and then modulates it. The MIMO transmission unit 264 uses the weights instructed by the control unit 262 to weight the transmission data modulated by the transmission data modulation unit 263, generating a base station downlink signal as a transmission signal transmitted from each antenna 25. The MIMO transmission unit 264 transmits the generated base station downlink signals from the antennas 25 via MIMO (step S312). The mobile relay station 2a repeats the processing from step S311.

[0054] Each antenna station 410 of base station 4a receives downlink signals from mobile relay station 2a (step S321). Each antenna station 410 converts the received downlink signals into electrical signals and outputs the resulting received signal to MIMO receiver 420. MIMO receiver 420 synchronizes the timing of the received signals received from each antenna station 410. MIMO receiver 420 multiplies the received signals received by each antenna station 410 by weights and adds them together. Base station signal receiving processing unit 430 demodulates the added received signal and decodes the demodulated received signal (step S322). Base station signal receiving processing unit 430 outputs the decoded received waveform information to terminal signal receiving processing unit 44.

[0055] Terminal signal receiving and processing unit 44 communicates with Figure 3 The same process as step S223 in the processing flow of the first embodiment shown is performed to receive the terminal uplink signal represented by the waveform data included in the received waveform information (step S323). That is, the terminal signal demodulation unit 441 determines the wireless communication mode used by the terminal station 3 in transmitting the terminal uplink signal based on the information inherent in the wireless communication mode included in the received signal represented by the waveform data. The terminal signal demodulation unit 441 demodulates the received signal represented by the waveform data according to the determined wireless communication mode and outputs the demodulated symbols to the terminal signal decoding unit 442. The terminal signal decoding unit 442 decodes the symbols input from the terminal signal demodulation unit 441 using the determined wireless communication mode to obtain the terminal transmission data transmitted from the terminal station 3. In addition, the terminal signal decoding unit 442 can also use a decoding mode with a large computational load, such as SIC. The base station 4a repeats the process from step S321.

[0056] According to this embodiment, a mobile relay station can transmit data pre-received and accumulated from multiple terminal stations in a short period of time when it is able to communicate with a base station, with good quality.

[0057] (Third implementation)

[0058] In this embodiment, the mobile relay station receives uplink signals from the terminal via multiple antennas. The following description focuses on the differences from the second embodiment.

[0059] Figure 6 This is a configuration diagram of the wireless communication system 1b according to the third embodiment. In this diagram, [the diagram shows the configuration of the wireless communication system 1b according to the third embodiment]. Figure 4 The same components as those in the wireless communication system 1a shown in the second embodiment are indicated by the same symbols and their descriptions are omitted. The wireless communication system 1b includes a mobile relay station 2b, a terminal station 3, and a base station 4b.

[0060] The mobile relay station 2b includes N antennas 21 (N is an integer greater than or equal to 2), a terminal communication unit 22b, a data storage unit 23, a base station communication unit 26, and multiple antennas 25. The N antennas 21 are referred to as antennas 21-1 to 21-N.

[0061] The terminal communication unit 22b has N receiving units 221b and N received waveform recording units 222b. The N receiving units 221b are designated as receiving units 221b-1 to 221b-N, and the N received waveform recording units 222b are designated as received waveform recording units 222b-1 to 222b-N. Receiving units 221b-n (where n is an integer between 1 and N) receive uplink signals from the terminal via antenna 21-n. The received waveform recording units 222b-n sample the received waveform of the terminal uplink signals received by the receiving units 221b-n, generating waveform data that displays the sampled values. The received waveform recording units 222b-n write the received waveform information to the data storage unit 23. This received waveform information includes the antenna identifier of antenna 21-n, the reception time of the terminal uplink signal in antenna 21-n, and the generated waveform data. The antenna identifier is information that identifies antenna 21-n. The data storage unit 23 stores received waveform information, including waveform data of the terminal uplink signal received by each of the antennas 21-1 to 21-N.

[0062] Base station 4b includes multiple antenna stations 410, MIMO receiver 420, base station signal receiving and processing unit 430, and terminal signal receiving and processing unit 450.

[0063] The terminal signal receiving and processing unit 450 performs reception processing on the terminal uplink signal shown by the received waveform information. At this time, the terminal signal receiving and processing unit 450 obtains the terminal transmitted data by performing reception processing through the wireless communication method used by the terminal station 3 in transmission. The terminal signal receiving and processing unit 450 includes a distribution unit 451, N terminal signal demodulation units 452, a synthesis unit 453, and a terminal signal decoding unit 454. The N terminal signal demodulation units 452 are respectively labeled as terminal signal demodulation units 452-1 to 452-N.

[0064] The distribution unit 451 reads waveform data at the same reception time from the received waveform information and outputs the waveform data to the terminal signal demodulation units 452-1 to 452-N according to the antenna identifier associated with the read waveform data. That is, the distribution unit 451 outputs the waveform data associated with the antenna identifier of antenna 21-n to the terminal signal demodulation unit 452-n. The terminal signal demodulation units 452-1 to 452-N demodulate the signal represented by the waveform data respectively and output the symbol obtained by demodulation to the synthesis unit 453. The terminal signal demodulation unit 452-n may also perform demodulation after processing the signal represented by the waveform data. The processing is a Doppler frequency shift compensation process for the terminal uplink signal received by antenna 21-n of mobile relay station 2. Based on the location of terminal station 3 and the track information of LEO carrying mobile relay station 2b, the Doppler frequency shift of the terminal uplink signal received by each antenna 21-n is pre-calculated. The combining unit 453 adds and combines the symbols input from the terminal signal demodulation units 452-1 to 452-N and outputs them to the terminal signal decoding unit 454. The terminal signal decoding unit 454 decodes the added and combined symbols to obtain the terminal transmission data sent from the terminal station 3.

[0065] Explain the operation of wireless communication system 1b.

[0066] Figure 7 This is a flowchart illustrating the processing of wireless communication system 1b when transmitting uplink signals from terminal station 3. In this diagram, the process is described with... Figure 2 The processing flow shown in the first embodiment is the same as the processing label. Terminal station 3 performs the same... Figure 2 The processing steps S111 to S112 in the processing flow of the first embodiment shown are the same. Furthermore, terminal station 3 can also transmit by performing time-division multiplexing, OFDM, MIMO, etc., with another terminal station 3.

[0067] The receiving units 221b-1 to 221b-N of the mobile relay station 2b receive the terminal uplink signal transmitted from the terminal station 3 (step S421). Depending on the wireless communication method of the transmitting terminal station 3, there are cases where the terminal uplink signal is received from only one terminal station 3 using time-division multiplexing at the same frequency, and cases where the terminal uplink signal is received from multiple terminal stations 3 simultaneously at the same frequency. The received waveform recording unit 222b-n writes the received waveform information associated with the waveform data representing the terminal uplink signal received by the receiving unit 221b-n, the reception time, and the antenna identifier of the antenna 21-n to the data storage unit 23 (step S422). The mobile relay station 2b repeats the processing from step S421.

[0068] The processing of wireless communication system 1b in the case of transmitting base station downlink signals from mobile relay station 2b, except for the following processing, is the same as... Figure 5 The processing flow of the second embodiment shown is the same. That is, in step S323, the terminal signal receiving processing unit 450 performs receiving processing of the terminal uplink signal shown by the received waveform information. Specifically, the allocation unit 451 reads waveform data with the same receiving time from the received waveform information, and outputs the waveform data to the terminal signal demodulation units 452-1 to 452-N according to the antenna identifier associated with the read waveform data. The terminal signal demodulation units 452-1 to 452-N determine the wireless communication mode used by the terminal station 3 in transmitting the terminal uplink signal based on the information inherent in the wireless communication mode included in the received signal represented by the waveform data. The terminal signal demodulation units 452-1 to 452-N demodulate the received signal represented by the waveform data according to the determined wireless communication mode, and output the demodulated symbol to the synthesis unit 453.

[0069] The combining unit 453 performs additive combining on the symbols input from the terminal signal demodulation units 452-1 to 452-N. Through additive combining, the signal transmitted by terminal station 3 is emphasized due to its correlation, while the influence of randomly added noise is reduced. Therefore, diversity effect is achieved when mobile relay station 2b receives the terminal uplink signal from only one terminal station 3 simultaneously. Furthermore, when mobile relay station 2b receives the terminal uplink signal from multiple terminal stations 3 simultaneously, it is equivalent to performing MIMO communication. The combining unit 453 outputs the additively combined symbols to the terminal signal decoding unit 454. The terminal signal decoding unit 454 decodes the additively combined symbols by the combining unit 453 using a determined wireless communication method to obtain the terminal transmission data transmitted from terminal station 3. Furthermore, the terminal signal decoding unit 454 can also use a computationally intensive decoding method such as SIC.

[0070] According to the above implementation method, the mobile relay station receives the terminal uplink signal received from the terminal station through diversity reception or MIMO reception, etc. Therefore, the link budget between the mobile relay station and the terminal station can be improved.

[0071] According to the implementation method described above, the mobile relay station does not demodulate the wireless terminal uplink signal received from the terminal station, but instead stores and accumulates information about the received signal waveform, and transmits it wirelessly at a time when communication with the base station is possible. The base station performs demodulation / decoding and other reception processing on the terminal uplink signal represented by the received signal waveform in the mobile relay station. Therefore, a non-reproducible relay method that does not depend on the communication method can be applied to wireless communication systems using low-Earth orbit satellites. In addition, since non-reproducible relay is performed, it is not necessary to install the wireless communication method used by the terminal station in the mobile relay station. For example, even if a terminal station communicating with a new wireless communication method is added, it is not necessary to change the mobile relay station; only the wireless communication method needs to be added to the base station set on the ground. Therefore, it is possible to accommodate various IoT systems simultaneously and to easily adapt to IoT system updates. Furthermore, since the large Doppler frequency shift experienced by each terminal station can be handled at the base station instead of at the mobile relay station, it is unnecessary to install complex nonlinear calculations for compensating for the Doppler frequency shift at the mobile relay station.

[0072] Furthermore, in the above embodiments, the mobile body carrying the mobile relay station is described as a LEO satellite, but it can also be a geostationary satellite, a drone, or other flying body flying in the air, such as HAPS.

[0073] According to the above embodiments, the wireless communication system includes a first communication device, a second communication device, and a mobile relay device. For example, the first communication device is terminal station 3 in the embodiments, the second communication device is base station 4, 4a, 4b in the embodiments, and the relay device is mobile relay station 2, 2a, 2b in the embodiments.

[0074] The relay device includes a first signal receiving unit, a storage unit, and a second signal transmitting unit. For example, the first signal receiving unit is receiving units 221 and 221b in this embodiment, the storage unit is data storage unit 23 in this embodiment, and the second signal transmitting unit is base station communication unit 24 and 26 in this embodiment. The first signal receiving unit receives a first signal transmitted wirelessly by a first communication device. For example, the first signal is a terminal uplink signal in this embodiment. The storage unit stores waveform data showing the waveform of the first signal received by the first signal receiving unit. When communication with the second communication device is possible, the second signal transmitting unit wirelessly transmits a second signal showing the waveform data stored in the storage unit to the second communication device. For example, the second signal is a base station downlink signal in this embodiment.

[0075] The second communication device includes a second signal receiving unit, a second signal receiving processing unit, and a first signal receiving processing unit. The second signal receiving unit receives a second signal wirelessly transmitted by a relay device. For example, the second signal receiving unit is antenna 41 and receiving unit 42 in the embodiment; and antenna station 410 and MIMO receiving unit 420. The second signal receiving processing unit performs reception processing on the second signal received by the second signal receiving unit to obtain waveform data. For example, the second signal receiving processing unit is base station signal receiving processing unit 43 and base station signal receiving processing unit 430 in the embodiment. The first signal receiving processing unit performs reception processing on the first signal shown by the waveform data obtained by the second signal receiving processing unit, and obtains data set as the first signal by the first communication device. The first signal receiving processing unit is, for example, terminal signal receiving processing units 44 and 450 in the embodiment.

[0076] Furthermore, the first signal receiving processing unit is capable of receiving and processing via various wireless methods. Additionally, the receiving processing performed by the first signal receiving processing unit includes compensation for the Doppler shift experienced by the first signal received in the first signal receiving unit.

[0077] The first signal receiving unit can also receive the first signal via multiple antennas. The storage unit stores waveform data showing the waveforms of the first signals received by each of the multiple antennas. The receiving processing performed by the first signal receiving processing unit includes demodulating the first signals represented by the waveform data corresponding to each of the multiple antennas and decoding the signal after synthesizing and demodulating the result.

[0078] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the specific configuration is not limited to these embodiments, and also includes designs that do not depart from the spirit of the present invention.

[0079] Symbol Explanation

[0080] 1, 1a, 1b... wireless communication systems

[0081] 2, 2a, 2b... mobile relay stations,

[0082] 3...Terminal station,

[0083] 4, 4a, 4b... base stations,

[0084] Antennas 21, 21-1 to 21-N...

[0085] 22, 22b... Terminal Communication Department,

[0086] 23...Data Storage Department

[0087] 24, 26... Base station communication department,

[0088] 25... antenna,

[0089] 31...Data Storage Department

[0090] 32……Sending Department,

[0091] 33... antenna,

[0092] 41...antenna,

[0093] 42……Receiving Department,

[0094] 43, 430... Base station signal receiving and processing unit,

[0095] 44……Terminal signal receiving and processing unit,

[0096] 221, 221b-1 to 221b-N... Receiving section,

[0097] 222, 222b-1 to 222b-N... Receive waveform recording section,

[0098] Storage departments 241, 261...

[0099] 242, 262... Control Department,

[0100] 243, 263... Transmit data modulation unit,

[0101] 244……Sending Department,

[0102] 264...MIMO Transmitter Section

[0103] 410... Antenna Station

[0104] 420...MIMO receiver section,

[0105] 441...Terminal signal demodulation unit,

[0106] 442……Terminal signal decoding unit,

[0107] 450……Terminal signal receiving and processing unit,

[0108] 451... Distribution Department

[0109] 452-1 to 452-N... Terminal signal demodulation unit,

[0110] 453...Synthesis Department,

[0111] 454……Terminal signal decoding unit.

Claims

1. A wireless communication system having a first communication device, a second communication device, and a mobile relay device, the relay device comprising: a first signal receiving section that receives a first signal transmitted by the first communication device through a channel and a transmission timing inherent to a predetermined wireless communication mode by wireless; a storage section that stores reception waveform information associating waveform data showing a waveform of the first signal with a reception time of the first signal without demodulating the first signal received by the first signal receiving section; and a second signal transmitting section that transmits a second signal showing the reception waveform information stored in the storage section to the second communication device by wireless at a timing at which communication with the second communication device is possible, the second communication device comprising: a second signal receiving section that receives the second signal transmitted by the relay device by wireless; a second signal receiving processing section that performs reception processing of the second signal received by the second signal receiving section to acquire the reception waveform information; and a first signal receiving processing section that has a terminal signal demodulating section and a terminal signal decoding section, the terminal signal demodulating section determining the predetermined wireless communication mode inherent to the channel and the transmission timing used for transmission of the first signal based on the channel and the reception timing included in the reception waveform information represented by the waveform data included in the reception waveform information acquired by the second signal receiving processing section, demodulating the first signal shown by the waveform data using the determined predetermined wireless communication mode, and the terminal signal decoding section decoding a symbol input from the terminal signal demodulating section by the predetermined wireless communication mode to acquire data set by the first communication device as the first signal.

2. The wireless communication system according to claim 1, wherein the first signal receiving processing section is capable of performing reception processing of the first signal by a plurality of wireless modes.

3. The wireless communication system according to claim 1, wherein the reception processing performed by the first signal receiving processing section includes processing that compensates for a Doppler shift suffered by the first signal received in the first signal receiving section.

4. The wireless communication system according to claim 1, wherein the first signal receiving section receives the first signal by a plurality of antennas, the storage section stores waveform data showing waveforms of the first signal received by each of the plurality of antennas, the reception processing performed by the first signal receiving processing section includes processing that demodulates the first signal shown by the waveform data corresponding to each of the plurality of antennas and decodes a signal after combining demodulated results.

5. The wireless communication system according to any one of claims 1 to 4, wherein the relay device is provided in a low orbit satellite, the first communication device and the second communication device are provided on the earth.

6. A wireless communication method performed by a wireless communication system having a first communication device, a second communication device, and a mobile relay device, the wireless communication method comprising: a first signal receiving step in which the relay device receives a first signal transmitted by the first communication device through a channel and a transmission timing inherent to a predetermined wireless communication mode by wireless. a recording step of writing, into a storage section, reception waveform information that associates waveform data showing a waveform of the first signal with a reception time of the first signal, without demodulating the first signal received in the first signal receiving step, by the relay device; a second signal transmitting step of transmitting, by the relay device, a second signal showing the reception waveform information stored in the storage section to the second communication device by wireless at a timing at which communication with the second communication device is possible; a second signal receiving step of receiving, by the second communication device, the second signal transmitted by wireless in the second signal transmitting step; a second signal receiving processing step of performing reception processing of the second signal received in the second signal receiving step by the second communication device to acquire the reception waveform information; a first signal receiving processing step of determining, by the second communication device, the predetermined wireless communication mode inherent to the channel and the transmission timing, using the channel used for transmission of the first signal represented by the waveform data included in the reception waveform information acquired in the second signal receiving processing step and the reception time included in the reception waveform information, demodulating the first signal shown by the waveform data using the determined predetermined wireless communication mode, decoding symbols input from the terminal signal demodulation section by the predetermined wireless communication mode using a terminal signal decoding section, and acquiring data set by the first communication device as the first signal. ​

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