Wireless communication system, communication device, and wireless communication method

Abstract

A wireless communication system according to the present invention comprises a mobile first communication device, a mobile second communication device, and a reception device. In a case in which a host device can communicate with any reception device, a first control unit of the first communication device transmits transmission data acquired by the host device to the reception device from a first communication unit, and in a case in which the host device cannot communicate with any reception device, the first control unit of the first communication device transmits the transmission data from a second communication unit to the second communication device, which can communicate with the host device. A second control unit of the second communication device transmits, from a fourth communication unit to a reception device that can communication with the host device, transmission data received by a third communication unit from the first communication device.

Description

[Technical Field]

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

[0002] With the development of IoT (Internet of Things) technology, the installation of IoT terminals equipped with various sensors in various locations is being considered. IoT terminals may be installed in places where it is difficult to install base stations, such as on buoys at sea, on ships, or in mountainous areas. Therefore, it is being considered to relay data collected by IoT terminals installed in various locations to earth stations using low Earth orbit (LEO) satellites equipped with communication devices.

[0003] Conventionally, LEO satellites have received data from IoT devices using an autonomous distributed control LPWA (Low Power Wide Area) system under the condition of a communication environment with high periodicity and reproducibility. LEO satellites store waveform information of LPWA received signals in the memory of their onboard equipment. LEO satellites transmit the stored waveform information via downlink transmission when communication with earth stations is possible (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Ikko Sakamoto and six others, "Evaluation of Terminal Capacity of Each LPWA Method on a 920MHz Band Satellite IoT Platform," IEICE Technical Report, SAT2020-35, February 2021, pp. 35-40 Summary of the Invention [Problem to be solved by the invention]

[0005] Existing technologies take into account the communication environment between LEO satellites and earth station antennas, but do not consider conditions in which a sufficient feeder link network is not available. In other words, when a sufficient feeder link network is not available, the LEO satellite accumulates data to be transmitted to the earth station. As a result, it can take a long time for the LEO satellite to receive data from an IoT device and transmit it to the earth station.

[0006] In view of the above circumstances, the present invention aims to provide a wireless communication system, a communication device, a wireless communication method, and a program that can shorten the time it takes to transmit data to a destination even when there is a period when a mobile communication device cannot communicate directly with the destination of the data. [Means for solving the problem]

[0007] One aspect of the present invention is a wireless communication system comprising one or more mobile first communication devices, one or more mobile second communication devices, and one or more receiving devices, wherein the first communication device comprises a first communication unit that communicates wirelessly with the receiving device, a second communication unit that communicates wirelessly with the second communication device, and a first control unit that, when the first communication device is able to communicate with any of the receiving devices, transmits transmission data acquired in the first communication device from the first communication unit to the receiving device, and when the first communication device is unable to communicate with any of the receiving devices, transmits the transmission data from the second communication unit to the second communication device that is able to communicate with the first communication device; and the second communication device comprises a third communication unit that communicates wirelessly with the first communication device, a fourth communication unit that communicates wirelessly with the receiving device, and a second control unit that transmits the transmission data received by the third communication unit from the first communication device from the fourth communication unit to the receiving device that is able to communicate with the first communication device.

[0008] One aspect of the present invention is a communication device in a wireless communication system having a plurality of mobile communication devices and one or more receiving devices, the communication device comprising: a first communication unit that communicates wirelessly with the receiving device; a second communication unit that communicates wirelessly with other communication devices; and a control unit that, when the communication device is capable of communicating with any of the receiving devices, transmits transmission data acquired in the communication device from the first communication unit to the receiving device, and, when the communication device is unable to communicate with any of the receiving devices, transmits the transmission data from the second communication unit to the communication device and other communication devices that can communicate with any of the receiving devices.

[0009] One aspect of the present invention is a wireless communication method for a wireless communication system comprising one or more mobile first communication devices, one or more mobile second communication devices, and one or more receiving devices, the method comprising: a transmitting step in which, when the first communication device is capable of communicating with any of the receiving devices, the first communication device transmits transmission data acquired in the first communication device to the receiving device from a first communication unit that wirelessly communicates with the receiving device; and, when the first communication device is unable to communicate with any of the receiving devices, the first communication device transmits the transmission data from a second communication unit that wirelessly communicates with the second communication device to the second communication device that is capable of communicating with the first communication device; and a relaying step in which the second communication device transmits the transmission data received from the first communication device by a third communication unit that wirelessly communicates with the first communication device to the receiving device that is capable of communicating with the first communication device from a fourth communication unit that wirelessly communicates with the receiving device.

[0010] One aspect of the present invention is a wireless communication method for a communication device in a wireless communication system comprising a plurality of mobile communication devices and one or more receiving devices, the method comprising: when the device is capable of communicating with any of the receiving devices, transmitting transmission data acquired by the device from a first communication unit that wirelessly communicates with the receiving device to the receiving device; and when the device is unable to communicate with any of the receiving devices, transmitting the transmission data from a second communication unit that wirelessly communicates with other communication devices to the device itself and other communication devices that are capable of communicating with any of the receiving devices. [Effects of the Invention]

[0011] According to the present invention, even when there is a period of time when a mobile communication device cannot directly communicate with a data destination, it is possible to shorten the time it takes to transmit data to the destination. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating a wireless communication system according to a first embodiment. [Figure 2] 10A and 10B are diagrams for explaining a method for selecting a LEO satellite that is permitted to communicate with a GEO satellite according to the embodiment. [Figure 3] FIG. 2 is a block diagram showing the configuration of the LEO satellite communication device according to the embodiment. [Figure 4] FIG. 2 is a block diagram showing the configuration of a GEO satellite communication device according to the embodiment. [Figure 5] FIG. 2 is a block diagram showing the configuration of a gateway for a LEO satellite according to the embodiment. [Figure 6] FIG. 2 is a block diagram showing the configuration of a GEO satellite gateway according to the embodiment. [Figure 7] FIG. 10 is a diagram showing earth station communication information according to the embodiment. [Figure 8] FIG. 10 is a diagram showing satellite communication information according to the same embodiment. [Figure 9] FIG. 10 is a flowchart showing processing of the wireless communication system according to the embodiment. [Figure 10] FIG. 10 is a diagram illustrating a wireless communication system according to a second embodiment. [Figure 11] FIG. 2 is a diagram showing communication destinations of LEO satellites according to the embodiment. [Figure 12] FIG. 2 is a block diagram showing the configuration of the LEO satellite communication device according to the embodiment. [Figure 13] FIG. 10 is a diagram showing an example of routing information according to the embodiment. [Figure 14] FIG. 10 is a flowchart showing processing of the wireless communication system according to the embodiment. [Figure 15] FIG. 10 is a diagram illustrating a wireless communication system according to a third embodiment. [Figure 16] FIG. 2 is a diagram showing communication destinations of LEO satellites according to the embodiment. [Figure 17] FIG. 2 is a block diagram showing the configuration of the LEO satellite communication device according to the embodiment. [Figure 18] FIG. 10 is a flowchart showing processing of the wireless communication system according to the embodiment. [Figure 19] FIG. 1 is a hardware configuration diagram of a LEO satellite communication device according to first to third embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0014] (First embodiment) FIG. 1 is a diagram illustrating an overview of a wireless communication system 1 according to a first embodiment of the present invention. The wireless communication system 1 includes a LEO (Low Earth Orbit) satellite 2, a GEO (Geostationary Orbit) satellite 3, a terminal station 4, a LEO satellite gateway (GWL) 5, a GEO satellite gateway (GWG) 6, and a base station 7. The wireless communication system 1 includes one or more LEO satellites 2, GEO satellites 3, terminal stations 4, GWLs 5, GWGs 6, and base stations 7. However, it is assumed that the number of terminal stations 4 is large. N (N is an integer equal to or greater than 1) LEO satellites 2 will be referred to as LEO satellites 2-1 to 2-N, and M (M is an integer equal to or greater than 1) GWLs 5 will be referred to as GWLs 5-1 to 5-M. In this embodiment, an example will be described in which the number N of LEO satellites 2 is two or more and the number of GEO satellites 3 is less than N. Figure 1 shows an example where N=3 and M=2.

[0015] LEO satellite 2 is constantly moving. The altitude of LEO satellite 2 is 2000 km or less, and it orbits the Earth once in approximately 1.5 hours. The altitude of GEO satellite 3 is approximately 36000 km, and it orbits the Earth once in one day. GEO satellite 3 is always located in the same place in the sky when viewed from Earth. Each of LEO satellite 2 and GEO satellite 3 is equipped with communication equipment. The communication equipment equipped in LEO satellite 2 is referred to as a LEO satellite communication equipment, and the communication equipment equipped in GEO satellite 3 is referred to as a GEO satellite communication equipment. The terminal station 4, GWL 5, GWG 6, and base station 7 are installed on Earth, such as on land or sea. The terminal station 4 is, for example, an IoT terminal. The GWL 5 and GWG 6 are earth stations.

[0016] Hereinafter, the LEO satellite 2 and the GEO satellite 3 will also be collectively referred to as satellites, and the GWL 5 and the GWG 6 will also be collectively referred to as earth stations. Furthermore, a radio signal from the terminal station 4 to the satellite will be referred to as a terminal uplink signal, and a radio signal from the satellite to the terminal station 4 will be referred to as a terminal downlink signal. A radio signal from the earth station to the satellite will be referred to as an earth station uplink signal, and a radio signal from the satellite to the earth station will be referred to as an earth station downlink signal.

[0017] LEO satellite 2 communicates with other LEO satellites 2, GEO satellites 3, terminal station 4, and GWL 5. GEO satellite 3 communicates with LEO satellite 2, other GEO satellites 3, and GWG 6. GEO satellite 3 may also communicate with terminal station 4. GWL 5 communicates with LEO satellite 2 wirelessly, and with base station 7 wired or wirelessly. GWG 6 communicates with GEO satellite 3 wirelessly, and with base station 7 wired or wirelessly.

[0018] As the LEO satellite 2 moves above the Earth, it acquires observation data observed by sensors and the like equipped on the satellite. Meanwhile, each terminal station 4 collects observation data such as environmental data observed by sensors and the like equipped inside or outside the terminal station. Each terminal station 4 transmits a terminal uplink signal containing the collected observation data to the LEO satellite 2. As the LEO satellite 2 moves above the Earth, it receives the terminal uplink signals transmitted from each of the multiple terminal stations 4.

[0019] Data from the terminal station 4 can be received by a communication device mounted on a GEO satellite 3 or an unmanned aerial vehicle such as a drone or a High Altitude Platform Station (HAPS). However, while the GEO satellite 3 has a wide terrestrial coverage area (footprint), its high altitude means that the link budget for the ground-based terminal station 4 is very small. On the other hand, the communication device mounted on a drone or HAPS has a high link budget but a narrow coverage area. Furthermore, a drone requires a battery, and a HAPS requires a solar panel. Therefore, the LEO satellite 2 receives the observation data collected at the terminal station 4. In addition to the link budget being within the limits, the LEO satellite 2 orbits outside the atmosphere, eliminating air resistance and consuming less fuel. Furthermore, its footprint is larger than when a communication device for relaying data is mounted on a drone or HAPS. The LEO satellite 2 may acquire either the observation data observed by itself or the observation data received from the terminal station 4.

[0020] Multiple GWLs 5 are distributed around the earth. Each LEO satellite 2, which is constantly moving, wirelessly transmits acquired observation data to the GWL 5 via an earth station downlink signal. The GWL 5 acquires the observation data from the received earth station downlink signal and transmits the acquired observation data to the base station 7. In this way, the wireless communication system 1 transmits, for example, data observed by the LEO satellite 2 and sensing information collected by a terminal station 4 installed on the earth, from the LEO satellite 2 to the GWL 5, and the base station 7 provides a service providing this information.

[0021] However, there are cases where the number of LEO satellites 2 is less than the number necessary to form a satellite constellation. Even when a global service is provided using a limited number of LEO satellites 2, the wireless communication system 1 of the present embodiment quickly transmits observation data from the LEO satellites 2 to the base station 7.

[0022] As the LEO satellite 2 moves, it transmits the observation data it receives from the terminal station 4 via a feeder link. A feeder link is a radio line between the satellite and an earth station. The orbit of this LEO satellite 2 may pass through an area where it cannot communicate with the GWL 5. In this case, as described above, the LEO satellite 2 accumulates the observation data and waits for the next opportunity to communicate with the GWL 5. In this way, the LEO satellite 2 can save the observation data in storage while it cannot communicate with the GWL 5. However, considering capacity limitations, it is desirable for the LEO satellite 2 to be able to communicate with the GWL 5 at all times as much as possible.

[0023] Furthermore, if the wireless communication system 1 is deployed globally, rather than just in a specific area, observation data will be transmitted one after another from the terrestrial terminal station 4 even while waiting for a feeder link. The LEO satellite 2 accumulates the received observation data, which leads to memory congestion. To deploy a global service, it is necessary to minimize the time spent saving observation data in the storage of the LEO satellite 2, thereby securing time for transmission of the feeder link.

[0024] Therefore, the wireless communication system 1 of this embodiment uses the GEO satellite 3, which can communicate with the LEO satellite 2, as an alternative to the feeder link. That is, the GEO satellite 3 receives observation data from the LEO satellite 2, which cannot communicate with the GWL 5, instead of the GWL 5. The GEO satellite 3, which is always in the same position as seen from the Earth, can always communicate with the GWG 6. The GEO satellite 3 transmits the received observation data to the base station 7 via the GWG 6.

[0025] For example, in FIG. 1 , at a certain time, LEO satellite 2-1 can communicate with GWL 5-1, and LEO satellite 2-3 can communicate with GWL 5-2. LEO satellite 2-1 transmits observation data to GWL 5-1, and LEO satellite 2-3 transmits observation data to GWL 5-2. GWL 5-1 and GWL 5-2 each transmit the received observation data to base station 7. Meanwhile, LEO satellite 2-2 transmits observation data to GEO satellite 3, and GEO satellite 3 transmits the observation data received from LEO satellite 2-2 to GWG 6. GWG 6 transmits the received observation data to base station 7.

[0026] However, there are even more restrictions on the number of GEO satellites 3 than there are on LEO satellites 2. For example, there are limits to the number of GEO satellites 3 that can be connected. If many LEO satellites 2 are connected to a GEO satellite 3 at the same time, there is a risk that the feeder link line will become congested. For this reason, the number of LEO satellites 2 that are connected to a GEO satellite 3 is kept to a minimum.

[0027] Typically, the orbit of a LEO satellite 2 is determined in advance. In other words, the GWLs 5 with which the LEO satellite 2 can communicate at each time can be predicted. Therefore, based on the orbit of the LEO satellite 2 and the position of the GWLs 5, the time periods in which earth station communication is possible and the time periods in which earth station communication is not possible on the orbit of the LEO satellite 2 are calculated. The time periods in which earth station communication is possible are the times when the LEO satellite 2 is located within an area in which it can communicate with any of the GWLs 5. The time periods in which earth station communication is not possible are the time periods other than the time periods in which earth station communication is possible. In other words, the time periods in which earth station communication is not possible are the times when the LEO satellite 2 is located within an area in which it cannot communicate with any of the GWLs 5.

[0028] In this embodiment, during a certain time period, a LEO satellite 2 having a long time period during which earth station communication is unavailable is preferentially permitted to use a detour feeder link using a GEO satellite 3. As a result, from the viewpoint of satellite operation of the entire wireless communication system 1, a feeder link schedule is created using the GEO satellite 3 and GWG 6, and taking into consideration the number of simultaneous satellite connections possible with the GEO satellite 3. This makes it possible to provide a feeder link network with little waste.

[0029] FIG. 2 is a diagram illustrating a method for selecting a LEO satellite 2 that is permitted to communicate with a GEO satellite 3. In the jth (j is an integer equal to or greater than 1) time interval Tj, the length of the earth station communication unavailable time interval during which LEO satellite 2-n cannot communicate with any GWL 5 is defined as time Tj(n). Furthermore, the number of LEO satellites 2 that can simultaneously communicate with a GEO satellite 3 is defined as K (K is an integer equal to or greater than 1). In this case, among the LEO satellites 2 that overlap with earth station communication unavailable time intervals in the time interval Tj(n), K LEO satellites 2 are selected in descending order of the earth station communication unavailable time interval. The selected devices are permitted to connect to the GEO satellite 3 during the earth station communication unavailable time interval. In FIG. 2, time Tj(1)<time Tj(3)<time Tj(2). When K=1, the LEO satellite 2-2 is permitted to connect to the GEO satellite 3 during the earth station communication unavailable time interval.

[0030] Next, the configuration of each device will be explained. Figure 3 is a block diagram showing the configuration of LEO satellite communication device 200 provided in LEO satellite 2. In Figure 3, only functional blocks related to this embodiment are extracted and shown. LEO satellite communication device 200 includes antenna 211, terminal communication unit 212, antenna 221, earth station communication unit 222, antenna 231, LEO satellite communication unit 232, antenna 241, GEO satellite communication unit 242, control unit 260, and data storage unit 270. The number of each of antennas 211, 221, 231, and 241 is arbitrary.

[0031] The antenna 211 receives a terminal uplink signal from the terminal station 4. The antenna 211 also transmits a terminal downlink signal addressed to the terminal station 4. The terminal communication unit 212 performs reception processing of the terminal uplink signal received by the antenna 211. The terminal communication unit 212 outputs observation data acquired from the terminal uplink signal by the reception processing to the control unit 260. The terminal communication unit 212 generates a terminal downlink signal in which transmission data is set, and transmits the signal from the antenna 211.

[0032] The antenna 221 receives an earth station uplink signal from the GWL 5. The antenna 221 also transmits an earth station downlink signal addressed to the GWL 5. The earth station communication unit 222 performs reception processing for the earth station uplink signal received by the antenna 221. The earth station communication unit 222 also generates an earth station downlink signal in which transmission data is set, and transmits it from the antenna 221.

[0033] The antenna 231 transmits and receives radio signals to and from other LEO satellites 2. The LEO satellite communication unit 232 performs reception processing of the radio signals received by the antenna 231. The LEO satellite communication unit 232 also generates radio signals addressed to other LEO satellites 2 and transmits them from the antenna 231.

[0034] The antenna 241 transmits and receives radio signals to and from the GEO satellite 3. The GEO satellite communication unit 242 performs reception processing of the radio signals received by the antenna 241. The GEO satellite communication unit 242 also generates radio signals addressed to the GEO satellite 3 and transmits them from the antenna 241.

[0035] The control unit 260 includes a memory unit 261, a determination unit 262, an instruction unit 263, and a writing unit 264. The memory unit 261 stores communication information. The communication information indicates the GWL 5 or GEO satellite 3 of the communication destination in each time interval of the LEO satellite 2. For example, the communication information includes earth station communication information and satellite communication information. The earth station communication information is information that indicates the GWL 5 of the communication destination in each time interval of the LEO satellite 2. The satellite communication information is information that indicates the GEO satellite 3 with which the LEO satellite 2 is permitted to communicate, and the time interval during which communication with that GEO satellite 3 is permitted. The time interval is represented by a start time and an end time.

[0036] The determination unit 262 references the communication information to determine whether the device itself is currently capable of transmitting observation data to the GWL 5 or the GEO satellite 3, and if communication is possible, further determines the transmission destination of the observation data. Specifically, the determination unit 262 determines that transmission of observation data to the GWL 5 is possible when the earth station communication information includes a communication destination GWL 5 associated with a time interval including the current time. The determination unit 262 determines the GWL 5 associated with that time interval as the transmission destination of the observation data. Furthermore, the determination unit 262 determines that transmission of observation data to the GEO satellite 3 is possible when the satellite communication information includes a communication-permitted GEO satellite 3 associated with a time interval including the current time. The determination unit 262 determines that transmission of observation data to the GEO satellite 3 is possible when the satellite communication information includes a communication-permitted GEO satellite 3 associated with the time interval including the current time. The determination unit 262 determines that transmission of observation data is not possible when the earth station communication information does not include a GWL 5 corresponding to the time interval including the current time and the satellite communication information does not include a communication destination GEO satellite 3. If the determination unit 262 determines that the observation data can be transmitted to the GWL 5 or the GEO satellite 3, it notifies the instruction unit 263 of the transmission destination. If the determination unit 262 determines that the observation data cannot be transmitted, it instructs the write unit 264 to store the observation data.

[0037] When the destination received from the determination unit 262 is GWL 5, the instruction unit 263 outputs the observation data and the address of the destination GWL 5 to the earth station communication unit 222. The earth station communication unit 222 generates a data transmission signal for an earth station downlink signal, with the address of the destination GWL 5 as its destination and with the observation data set, and wirelessly transmits the signal from the antenna 221. When the destination is GEO satellite 3, the instruction unit 263 outputs the observation data and the address of the destination GEO satellite 3 to the GEO satellite communication unit 242. The GEO satellite communication unit 242 generates a data transmission signal with the address of the destination GEO satellite 3 as its destination and with the observation data set, and wirelessly transmits the generated data transmission signal from the antenna 241. The writing unit 264 writes the observation data to the data storage unit 270.

[0038] The data storage unit 270 is a storage that stores data. The data storage unit 270 stores untransmitted observation data. The observation data is one or both of observation data detected by a sensor (not shown) provided on the LEO satellite 2 and observation data received by the terminal communication unit 212 via a terminal uplink signal.

[0039] Figure 4 is a block diagram showing the configuration of a GEO satellite communication device 300 provided on a GEO satellite 3. In Figure 4, only functional blocks related to this embodiment are extracted and shown. The GEO satellite communication device 300 includes an antenna 311, an earth station communication unit 312, an antenna 321, a LEO satellite communication unit 322, an antenna 331, a GEO satellite communication unit 332, and a control unit 340. The number of each of the antennas 311, 321, and 331 is arbitrary.

[0040] The antenna 311 receives earth station uplink signals from the GWG 6. The antenna 311 also transmits earth station downlink signals addressed to the GWG 6. The earth station communication unit 312 performs reception processing for the earth station uplink signals received by the antenna 311. The earth station communication unit 312 also generates earth station downlink signals and transmits them from the antenna 311.

[0041] The antenna 321 transmits and receives radio signals to and from the LEO satellite 2. The LEO satellite communication unit 322 performs reception processing of the radio signals received by the antenna 321. The LEO satellite communication unit 322 also generates a radio signal addressed to the LEO satellite 2 and transmits the generated radio signal from the antenna 321.

[0042] The antenna 331 transmits and receives radio signals to and from other GEO satellites 3. The GEO satellite communication unit 332 performs reception processing of the radio signals received by the antenna 331. The GEO satellite communication unit 332 also generates radio signals addressed to other GEO satellites 3 and transmits the generated radio signals from the antenna 331. The control unit 340 controls each unit.

[0043] Fig. 5 is a block diagram showing the configuration of the GWL 5. Fig. 5 shows only functional blocks related to this embodiment. The GWL 5 includes an antenna station 510, an information generation unit 520, a satellite transmission unit 530, a satellite reception unit 540, a data transmission unit 550, and a communication unit 560.

[0044] Antenna station 510 receives earth station downlink signals from LEO satellite 2. Antenna station 510 also transmits earth station uplink signals destined for LEO satellite 2.

[0045] The information generation unit 520 obtains the earth station communication available time interval for each LEO satellite 2 and the GWL 5 with which communication is possible during that earth station communication available time interval, based on LEO satellite orbit information indicating the orbit of the LEO satellite 2 and earth station position information indicating the position of the GWL 5. The information generation unit 520 generates earth station communication information for each LEO satellite 2 based on the obtained information.

[0046] Furthermore, based on the LEO satellite orbit information and the GEO satellite orbit information indicating the orbit of the GEO satellite 3, the information generation unit 520 identifies GEO satellites 3 at positions where each LEO satellite 2 can communicate during earth station communication unavailable time periods in which it cannot communicate with any GWL 5. The GEO satellite orbit information is information from which the time series positions of the GEO satellites 3 can be obtained. For each combination of each GEO satellite 3 and each time period, the information generation unit 520 selects LEO satellites 2 that are permitted to communicate with the GEO satellite 3 during the earth station communication unavailable time period. At this time, the information generation unit 520 selects a predetermined number of LEO satellites 2 in descending order of the length of the earth station communication unavailable time period. The information generation unit 520 generates satellite communication information that associates the earth station communication unavailable time periods in which each LEO satellite 2 is permitted to communicate with the GEO satellite 3 with the GEO satellite 3 that is the communication destination during that earth station communication unavailable time period.

[0047] The satellite transmitting unit 530 generates an earth station uplink signal addressed to the LEO satellite 2 in which the transmission data is set, and transmits it from the antenna station 510. The transmission data is, for example, earth station communication information and satellite communication information generated by the information generating unit 520.

[0048] The satellite receiving unit 540 performs reception processing of the earth station downlink signal received by the antenna station 510. The data transmitting unit 550 transmits observation data obtained by the satellite receiving unit 540 performing reception processing of the earth station downlink signal to the base station 7. The communication unit 560 transmits and receives data to and from the base station 7 via wired or wireless communication. The communication unit 560 may also transmit and receive data to and from the GWG 6 via wired or wireless communication.

[0049] Fig. 6 is a block diagram showing the configuration of the GWG 6. Fig. 6 shows only the functional blocks related to this embodiment. The GWG 6 includes an antenna station 610, a satellite receiving unit 620, a data transmitting unit 630, a communication unit 640, and a satellite transmitting unit 650.

[0050] The antenna station 610 receives earth station downlink signals from the GEO satellite 3. The antenna station 610 also transmits earth station uplink signals addressed to the GEO satellite 3. The satellite receiving unit 620 performs reception processing for the earth station downlink signals received by the antenna station 610. The data transmitting unit 630 transmits observation data obtained by the satellite receiving unit 620 performing reception processing for the earth station downlink signals to the base station 7. The communication unit 640 transmits and receives data to and from the base station 7 via wired or wireless communication. The communication unit 640 may also transmit and receive data to and from the GWL 5 via wired or wireless communication. The satellite transmitting unit 650 generates earth station uplink signals addressed to the GEO satellite 3, in which transmission data has been set, and transmits the signals from the antenna station 610.

[0051] 7 is a diagram showing an example of earth station communication information. The earth station communication information is information that associates satellite identification information that identifies a LEO satellite 2, a time interval specified by a start time and an end time, and earth station identification information that identifies a GWL 5 that is the communication destination during that time interval. The earth station communication information may also include information on time intervals during which communication with any GWL 5 is not possible. In this case, the earth station communication information is set with a communication destination indicating NULL or communication not possible in association with the GWL 5 and the time interval during which communication is not possible.

[0052] 8 is a diagram showing an example of satellite communication information. The satellite communication information is information that associates satellite identification information that identifies a LEO satellite 2, a time interval specified by a start time and an end time, and satellite identification information that identifies a GEO satellite 3 that is the communication destination during that time interval. The time interval is a time interval during which earth station communication is not possible, but during which communication with the GEO satellite 3 is permitted for the LEO satellite 2 specified by the satellite identification information. The satellite communication information may also include information on time intervals during which communication with any GEO satellite 3 is not possible. In this case, the satellite communication information is set with a communication destination indicating NULL or communication not possible, in association with the time interval during which communication with the GEO satellite 3 is not possible. The earth station communication information and the satellite communication information may be integrated into one piece of information.

[0053] FIG. 9 is a process flow showing the operation of the wireless communication system 1. First, the information generation unit 520 of the GWL 5 acquires LEO satellite orbit information indicating the orbit of each LEO satellite 2, GEO satellite orbit information indicating the orbit of each GEO satellite 3, and earth station position information indicating the position of each GWL 5 (step S101). The information generation unit 520 may acquire this information periodically or at predetermined times, or may acquire this information when an information acquisition instruction is input from an external device or an input unit (not shown). The information generation unit 520 may also receive this information from an external device or read it from a recording medium. This information may also be input to the GWL 5 by an input unit (not shown).

[0054] Based on the position of each LEO satellite 2 at each time indicated by the LEO satellite orbit information and the position of each GWL 5 indicated by the earth station position information, the information generation unit 520 calculates an earth station communication available time interval, which is a time interval during which each LEO satellite 2 can communicate with each GWL 5. The information generation unit 520 generates earth station communication information for each LEO satellite 2 by associating the earth station communication available time interval with the GWL 5 that is the communication destination during that earth station communication available time interval (step S102).

[0055] Next, the information generation unit 520 calculates the GEO satellites 3 at positions where each LEO satellite 2 can communicate during the earth station communication unavailable time interval, based on the time position of each LEO satellite 2 indicated by the LEO satellite orbit information and the time position of each GEO satellite 3 indicated by the GEO satellite orbit information. The information generation unit 520 identifies, for each time interval, LEO satellites 2 at positions where they can communicate with the same GEO satellite 3 during the communication unavailable time interval. For each group of LEO satellites 2 identified for each time interval, the information generation unit 520 selects a predetermined number of LEO satellites 2 in descending order of the length of the earth station communication unavailable time interval. The information generation unit 520 allows the selected LEO satellites 2 to communicate with the GEO satellite 3 during the earth station communication unavailable time. The length of each time interval may be the same, or some or all of them may be different. Furthermore, the number of LEO satellites 2 selected may be different for each GEO satellite 3. The information generation unit 520 generates satellite communication information for each LEO satellite 2 by associating the earth station communication unavailable time during which communication with a GEO satellite 3 is permitted with the GEO satellite 3 with which communication is permitted during that earth station communication unavailable time (step S103).

[0056] The information generation unit 520 outputs the earth station communication information and satellite communication information generated for each LEO satellite 2 to the satellite transmission unit 530. The satellite transmission unit 530 generates an earth station uplink signal in which the earth station communication information and satellite communication information generated for each LEO satellite 2 are set. The satellite transmission unit 530 transmits the earth station uplink signal in which the earth station communication information and satellite communication information of that LEO satellite 2 are set from the antenna station 510 at a timing when communication with the LEO satellite 2 is possible (step S104). Note that the satellite transmission unit 530 may transmit the earth station communication information and satellite communication information generated for all LEO satellites 2 to each LEO satellite 2.

[0057] The LEO satellite communication device 200 of the LEO satellite 2 acquires observation data (step S201). For example, the terminal communication unit 212 receives a terminal uplink signal from the terminal station 4 and outputs the observation data acquired from the received terminal uplink signal to the control unit 260. The observation data may be data obtained by demodulating and decoding the terminal uplink signal, or may be the received waveform of the terminal uplink signal. Alternatively, the control unit 260 acquires the observation data from a sensor provided on the LEO satellite 2.

[0058] When the earth station communication unit 222 receives an earth station uplink signal in which earth station communication information and satellite communication information are set from the GWL 5 (step S202: YES), the LEO satellite communication device 200 performs the process of step S203. That is, the storage unit 261 stores the earth station communication information and satellite communication information acquired by the earth station communication unit 222 from the earth station uplink signal (step S203). After the process of step S203, or when the LEO satellite communication device 200 has not received an earth station uplink signal in which earth station communication information and satellite communication information are set (step S202: NO), the LEO satellite communication device 200 performs the process of step S204.

[0059] The determination unit 262 of the LEO satellite communication device 200 refers to the earth station communication information stored in the storage unit 261 and determines whether or not it is possible to transmit observation data to the GWL 5 at the current time (step S204).

[0060] The determination unit 262 may transmit a transmission permission inquiry to the GWL 5 by an earth station downlink signal to determine whether or not it is possible to transmit observation data to the GWL 5. When the GWL 5 receives the transmission permission inquiry, it determines whether or not it is possible to transmit data from the LEO satellite communications device 200 to the GWL 5 itself. The GWL 5 transmits a transmission permission inquiry response that sets the determination result by an earth station uplink signal. The determination unit 262 of the LEO satellite communications device 200 determines whether or not it is possible to transmit observation data to the GWL 5 based on the transmission permission inquiry response received from the GWL 5.

[0061] The determination unit 262 may also determine whether or not it is possible to transmit observation data to the GWL 5 based on whether or not congestion has occurred between the satellite and the GWL 5. That is, the determination unit 262 determines that it is possible to transmit observation data when there is no congestion in communication between the earth station communication unit 222 and the GWL 5. On the other hand, when there is congestion in communication between the earth station communication unit 222 and the GWL 5 due to overtraffic, the determination unit 262 determines that it is not possible to transmit observation data because no more data can be transmitted from the satellite itself.

[0062] Alternatively, the determination unit 262 may determine that transmission of observation data to GWL 5 is possible when the reception quality of the earth station uplink signal from GWL 5 at the earth station communication unit 222 is better than a predetermined value, and may determine that transmission of observation data to GWL 5 is impossible when the reception quality is below the predetermined value. The determination unit 262 may also determine whether or not transmission of observation data to GWL 5 is possible by combining the above. When the determination unit 262 determines that transmission of observation data to GWL 5 is possible (step S204: YES), it performs the process of step S205.

[0063] That is, the determination unit 262 reads the time interval including the current time and the earth station identification information associated with that time interval from the earth station communication information. The determination unit 262 outputs the read time interval and earth station identification information to the instruction unit 263. Note that if the determination unit 262 determines that data transmission is permitted based on the transmission permission inquiry response, it outputs the earth station identification information of the GWL 5 that transmitted the transmission permission inquiry response. If the determination unit 262 determines that data transmission is permitted based on the reception quality of the earth station uplink signal, it outputs the earth station identification information of the GWL 5 that transmitted the earth station uplink signal. The instruction unit 263 outputs the observation data acquired in step S201 and the address of the GWL 5 indicated by the earth station identification information to the earth station communication unit 222 and instructs transmission. Furthermore, if untransmitted observation data is stored in the data storage unit 270, the instruction unit 263 reads out the observation data and outputs it to the earth station communication unit 222. The earth station communication unit 222 wirelessly transmits, from the antenna 221, a data transmission signal of an earth station downlink signal in which the observation data is set and addressed to the address of the destination GWL 5 (step S205). After processing step S205, the LEO satellite communication device 200 repeats the processing from step S201.

[0064] In step S205, the antenna station 510 of the GWL 5 receives the data transmission signal of the earth station downlink signal transmitted from the LEO satellite communication device 200. The satellite receiving unit 540 performs reception processing on the data transmission signal received by the antenna station 510 to obtain observation data. The data transmitting unit 550 transmits the observation data obtained by the satellite receiving unit 540 from the communication unit 560 to the base station 7.

[0065] If the transmission of the observation data from the earth station communication unit 222 has not finished by the end time indicated by the time interval notified by the determination unit 262, the instruction unit 263 instructs the writing unit 264 to write the observation data. The writing unit 264 stores the untransmitted observation data in the data storage unit 270.

[0066] On the other hand, if the determination unit 262 of the LEO satellite communications device 200 determines that transmission of observation data to the GWL 5 is not permitted (step S204: NO), it performs the process of step S206. That is, the determination unit 262 references the satellite communications information stored in the memory unit 261 and determines whether transmission of observation data to the GEO satellite 3 is permitted at the current time (step S206). The determination unit 262 may also transmit a transmission permission inquiry to the GEO satellite 3. Upon receiving the transmission permission inquiry, the GEO satellite 3 determines whether data transmission from the LEO satellite communications device 200 to the satellite itself is permitted, and returns a transmission permission inquiry response that sets the determination result. The determination unit 262 of the LEO satellite communications device 200 determines whether transmission of observation data to the GEO satellite 3 is permitted based on the transmission permission inquiry response received from the GEO satellite 3. If the determination unit 262 determines that transmission of observation data to the GEO satellite 3 is permitted (step S206: YES), it performs the process of step S207.

[0067] The determination unit 262 reads out the time interval including the current time and the satellite identification information associated with that time interval from the satellite communication information. The determination unit 262 outputs the read-out time interval and satellite identification information to the instruction unit 263. If the determination unit 262 determines that transmission of the observation data is permitted based on the transmission permission inquiry response, it outputs the satellite identification information of the GEO satellite 3 that transmitted the transmission permission inquiry response. The instruction unit 263 outputs the observation data acquired in step S201 and the address of the GEO satellite 3 indicated by the satellite identification information to the GEO satellite communication unit 242 and instructs it to transmit. Furthermore, if untransmitted observation data is stored in the data storage unit 270, the instruction unit 263 reads out the observation data and outputs it to the GEO satellite communication unit 242. The GEO satellite communication unit 242 wirelessly transmits a data transmission signal, addressed to the address of the GEO satellite 3 and containing the observation data, from the antenna 241 (step S207).

[0068] The antenna 321 of the GEO satellite communication device 300 receives the data transmission signal transmitted from the LEO satellite communication device 200 in step S207 (step S301). The LEO satellite communication unit 322 obtains observation data from the data transmission signal received by the antenna 321. The control unit 340 instructs the earth station communication unit 312 to transmit the observation data acquired by the LEO satellite communication unit 322. The earth station communication unit 312 generates a data transmission signal for an earth station downlink signal that sets the observation data acquired by the LEO satellite communication unit 322, and transmits the generated data transmission signal from the antenna 311 (step S302). The antenna station 610 of the GWG 6 receives the data transmission signal transmitted from the GEO satellite communication device 300. The satellite receiving unit 620 performs reception processing on the data transmission signal received by the antenna station 610 to obtain observation data. The data transmitting unit 630 transmits the observation data acquired by the satellite receiving unit 620 to the base station 7 from the communication unit 640.

[0069] If the transmission of the observation data from the GEO satellite communication unit 242 has not finished by the end time indicated by the time interval notified by the determination unit 262, the instruction unit 263 of the LEO satellite communication device 200 instructs the writing unit 264 to write the observation data. The writing unit 264 stores the untransmitted observation data in the data storage unit 270. After the processing of step S207, the LEO satellite communication device 200 repeats the processing from step S201.

[0070] In step S206, if determination unit 262 of LEO satellite communications device 200 determines that transmission of observation data to GEO satellite 3 is not permitted (step S206: NO), it instructs writing unit 264 to store the observation data. Writing unit 264 writes the observation data acquired in step S201 to data storage unit 270 (step S208). LEO satellite communications device 200 performs the processing from step S201.

[0071] In step S207, the instruction unit 263 of the LEO satellite communications device 200 may notify the GEO satellite 3 of the end of data transmission if there is no observation data to transmit, or if it detects that the transmission of the observation data has ended before the end time indicated by the time interval received from the determination unit 262. When the control unit 340 of the GEO satellite communications device 300 mounted on the GEO satellite 3 receives the data transmission end notification, it transmits a transmission inquiry from the LEO satellite communications unit 322 to each LEO satellite 2. When the control unit 260 of the LEO satellite communications device 200 mounted on each LEO satellite 2 receives the transmission inquiry, if it is currently unable to transmit observation data to the GWL 5 or the GEO satellite 3, it returns a transmission inquiry response to the GEO satellite 3 that sets the amount of data stored in the data storage unit 270. A LEO satellite communications device 200 that can transmit observation data to the GWL 5 or the GEO satellite 3 returns a transmission inquiry response to the GEO satellite 3 that sets there is no data or that relaying is not required. The control unit 340 of the GEO satellite communication device 300 mounted on the GEO satellite 3 selects the LEO satellite 2 with the largest amount of data set in the transmission inquiry response from each LEO satellite 2, and permits the selected LEO satellite 2 to transmit observation data. The control unit 340 returns a transmission permission to the LEO satellite 2 that is permitted to transmit the observation data. When the LEO satellite communication device 200 of the LEO satellite 2 receives a transmission permission from the GEO satellite 3, it performs processing from step S207, with the GEO satellite 3 that sent the transmission permission as the transmission destination of the observation data.

[0072] Furthermore, the LEO satellite communication unit 232 of the LEO satellite communication device 200 may transmit communication information such as earth station communication information and satellite communication information acquired by the earth station communication unit 222 from the earth station uplink signal to another LEO satellite communication device 200. The LEO satellite communication unit 232 of the LEO satellite communication device 200 may further transmit the earth station communication information and satellite communication information received from another LEO satellite communication device 200 to the other LEO satellite communication device 200.

[0073] In the above, the GWL 5 includes an information generation unit 520 that generates communication information, but the control unit 260 of the LEO satellite communication device 200 may also include the information generation unit 520. In this case, the LEO satellite communication device 200 receives information for generating communication information from the earth station. The control unit 260 of each LEO satellite communication device 200 may generate communication information for the LEO satellite 2 on which the device is mounted. Alternatively, some of the LEO satellite communication devices 200 may generate communication information for the LEO satellite 2 on which the device is mounted and for each of the other LEO satellites 2. The LEO satellite communication device 200 transmits the communication information of the other LEO satellites 2 to the other LEO satellites 2 from the LEO satellite communication unit 232.

[0074] Alternatively, the base station 7 may have the function of the information generation unit 520. The satellite transmission unit 530 of the GWG 5 receives communication information generated by the base station 7 and transmits the received communication information to the LEO satellite 2 by an earth station uplink signal. Alternatively, the base station 7 transmits the communication information generated by the base station 7 to the LEO satellite 2 via the GWG 6 and the GEO satellite 3.

[0075] Alternatively, the control unit 340 of the GEO satellite communications device 300 may include the information generation unit 520, or the GWG 6 may have the functions of the information generation unit 520. When the GWG 6 includes the information generation unit 520, the satellite transmission unit 650 transmits the generated communication information to the GEO satellite 3 via an earth station uplink signal. The LEO satellite communications unit 322 of the GEO satellite communications device 300 mounted on the GEO satellite 3 transmits the communication information generated by the control unit 340 or the communication information received by the earth station communications unit 312 from the GWG 6 to the LEO satellite 2. The GEO satellite communications unit 332 of the GEO satellite communications device 300 may transmit the communication information to another GEO satellite 3. The GEO satellite communications device 300 may transmit the communication information received by the GEO satellite communications unit 332 from another GEO satellite 3 from the LEO satellite communications unit 322 to the LEO satellite 2, or may further transmit the communication information from the GEO satellite communications unit 332 to another GEO satellite 3.

[0076] According to this embodiment, even if there are insufficient antennas at earth stations, LEO satellites can increase the capacity of the feeder link network and efficiently deploy feeder links by utilizing links to GEO satellites.

[0077] (Second embodiment) In the second embodiment, a LEO satellite located in an area where communication with an earth station is not possible communicates with the earth station via a detour route via another LEO satellite. The second embodiment will be described, focusing on the differences from the first embodiment.

[0078] FIG. 10 is a diagram illustrating an overview of a wireless communication system 11 according to the second embodiment. The wireless communication system 11 includes a LEO satellite 21, a GEO satellite 3, a terminal station 4, a GWL 51, a GWG 6, and a base station 7. The wireless communication system 11 illustrated in FIG. 10 differs from the wireless communication system 1 illustrated in FIG. 1 in that the wireless communication system 11 includes a LEO satellite 21 instead of the LEO satellite 2, and a GWL 51 instead of the GWL 5. Note that the wireless communication system 11 does not necessarily include the GEO satellite 3 and the GWG 6. The wireless communication system 11 includes a plurality of LEO satellites 21. N (N is an integer of 2 or more) LEO satellites 21 are respectively referred to as LEO satellites 21-1 to 21-N, and M (M is an integer of 1 or more) GWLs 51 are respectively referred to as GWLs 51-1 to 51-M. FIG. 10 illustrates an example where N=3 and M=3.

[0079] A LEO satellite 21 that cannot communicate with GWL 51 forms an inter-satellite link with another LEO satellite 21 that can communicate with GWL 51, that is as close as possible to itself, and that can relay data. The LEO satellite 21 performs alternative transmission by transmitting observation data that would otherwise be transmitted via the feeder link to another LEO satellite 21. Each LEO satellite 21 notifies the earth station via GEO satellite 3 whether or not it is possible to relay data received from another LEO satellite 21.

[0080] Fig. 11 is a diagram showing the communication destinations of LEO satellite 21. Fig. 11 shows the communication destinations of LEO satellites 21-1 to 21-3. LEO satellite 21-1 transmits observation data to LEO satellite 21-2 during times when it is unable to communicate with any of the GWLs 51. LEO satellite 21-2 transmits the observation data it has acquired and the observation data it has received from LEO satellite 21-1 to GWL 51-2.

[0081] However, there are time periods when LEO satellite 21-2 cannot communicate with GWL 51. During those time periods, LEO satellite 21-2 forms an inter-satellite link with adjacent LEO satellite 21-3 and transmits observation data acquired by itself and observation data received from LEO satellite 21-1 to LEO satellite 21-3. LEO satellite 21-3 transmits the observation data acquired by itself and the observation data received from LEO satellite 21-2 to GWL 51.

[0082] In this way, the observation data transmitted by the LEO satellite 21-1 is relayed from the LEO satellite 21-2 to the LEO satellite 21-3, and then transmitted to the GWL 51-2 or the GWL 51-3. This allows the LEO satellite 21-1 to continue feeder link transmission.

[0083] Figure 12 is a block diagram showing the configuration of LEO satellite communication device 201 provided in LEO satellite 21 of the second embodiment. Only functional blocks related to this embodiment are extracted and shown in Figure 12. LEO satellite communication device 201 shown in Figure 12 differs from LEO satellite communication device 200 of the first embodiment shown in Figure 3 in that it includes control unit 280 instead of control unit 260.

[0084] The control unit 280 includes a storage unit 281, a determination unit 282, an instruction unit 283, a writing unit 264, and a notification unit 285. The storage unit 281 stores routing information as communication information. The routing information indicates a data transmission path for each time interval of the LEO satellite 21. The paths include a path for transmitting data directly from the LEO satellite 21 to the GWL 51 and a path for transmitting data from the LEO satellite 21 to the GWL 51 via one or more other satellites. The satellites to be transmitted via are other LEO satellites 21, but may also include the GEO satellite 3. When transmitting data from the LEO satellite 21 to the GWL 51 via other satellites, only the next satellite that is the data destination for each LEO satellite 21 on the path may be set as the path in the routing information. Furthermore, area information may be used instead of time interval information.

[0085] The determination unit 282 reads route information associated with the time interval including the current time from the routing information. From the read route information, the determination unit 282 reads the next GWL 51 or satellite on the route after its own satellite as the destination. The determination unit 282 notifies the instruction unit 283 of the read destination. If the determination unit 282 cannot obtain a destination, it instructs the writing unit 264 to store observation data.

[0086] When the destination received from the determination unit 282 is GWL 51, the instruction unit 283 outputs the observation data and the address of the destination GWL 51 to the earth station communication unit 222. The earth station communication unit 222 generates an earth station downlink signal that has the address of the destination GWL 51 as its destination and that includes the observation data, and transmits the generated earth station downlink signal by radio from the antenna 221.

[0087] If the destination is another LEO satellite 21, instruction unit 283 outputs the observation data and the address of the other destination LEO satellite 21 to LEO satellite communication unit 232. LEO satellite communication unit 232 generates a data transmission signal that is addressed to the address of the other destination LEO satellite 21 and that contains the observation data, and wirelessly transmits the generated data transmission signal from antenna 231.

[0088] If the destination is a GEO satellite 3, the instruction unit 283 outputs the observation data and the address of the destination GEO satellite 3 to the GEO satellite communication unit 242. The GEO satellite communication unit 242 generates a data transmission signal that is addressed to the address of the destination GEO satellite 3 and that contains the observation data, and wirelessly transmits the generated data transmission signal from the antenna 241.

[0089] The notification unit 285 generates relay possibility / prohibition information that notifies whether or not relaying of data received from other LEO satellites 21 is possible. The notification unit 285 wirelessly transmits the generated relay possibility / prohibition information from the earth station communication unit 222 to the GWL 51. Alternatively, the notification unit 285 transmits the generated relay possibility / prohibition information from the GEO satellite communication unit 242 to the GEO satellite 3. The GEO satellite 3 transmits the received relay possibility / prohibition information to the GWG 6.

[0090] The configuration of the GWL 51 is the same as that of the GWL 5 of the first embodiment shown in Fig. 5. However, the information generator 520 of the GWL 51 generates the routing information shown in Fig. 13.

[0091] 13 is a diagram showing an example of routing information. The routing information is information that associates satellite identification information that identifies a LEO satellite 21, a time interval specified by a start time and an end time, and a route for data transmission during that time interval. The routing information may include information about time intervals during which communication with any of the GWLs 51 and other satellites is not possible. In that case, the routing information is set with a route indicating NULL or transmission not possible, associated with the time interval.

[0092] FIG. 14 is a process flow showing the operation of the wireless communication system 11. First, the information generation unit 520 of the GWL 51 acquires LEO satellite orbit information indicating the orbit of each LEO satellite 21 and earth station position information indicating the position of each GWL 51 (step S401). The information generation unit 520 may further acquire GEO satellite orbit information indicating the orbit of each GEO satellite 3. The information generation unit 520 may acquire this information at predetermined times, such as periodically, or may acquire this information when an information acquisition instruction is input from an external device or an input unit (not shown). Furthermore, the information generation unit 520 may receive this information from an external device or read it from a recording medium. This information may also be input to the GWL 51 by an input unit (not shown).

[0093] The information generation unit 520 of the GWL 51 acquires relay possibility / prohibition information of each LEO satellite 21 (step S402). Specifically, the information generation unit 520 of the GWL 51 transmits a relay possibility / prohibition inquiry by an earth station uplink signal. Alternatively, the information generation unit 520 of the GWL 51 may request the GWG 6 to transmit the relay possibility / prohibition inquiry, and the GWG 6 may transmit the relay possibility / prohibition inquiry to the GEO satellite 3. The GEO satellite communication device 300 of the GEO satellite 3 transmits the relay possibility / prohibition inquiry received from the GWG 6 to the LEO satellite 21.

[0094] When the notification unit 285 of the LEO satellite communication device 201 mounted on each LEO satellite 21 receives a relay possibility inquiry from the GWL 51 or the GEO satellite 3, it generates relay possibility / prohibition information indicating whether the device itself can relay data received from another LEO satellite 21. The LEO satellite communication device 201 may generate the relay possibility / prohibition information at predetermined timing, such as periodically. For example, the notification unit 285 determines that relay is possible when the amount of data stored in the data storage unit 270 is equal to or less than a threshold, and determines that relay is not possible when the amount of data exceeds the threshold. The relay possibility / prohibition information may be information indicating the amount of data stored in the data storage unit 270. The notification unit 285 adds the satellite identification information of the satellite itself to the relay possibility / prohibition information. The notification unit 285 transmits the relay possibility / prohibition information to the GWL 51 from the earth station communication unit 222 via an earth station downlink signal.

[0095] Alternatively, the notification unit 285 transmits the relay possible / unavailable information from the GEO satellite communication unit 242 to the GEO satellite 3. The GEO satellite communication device 300 of the GEO satellite 3 transmits the relay possible / unavailable information received from the LEO satellite communication device 201 by an earth station downlink signal. The GWG 6 transmits the relay possible / unavailable information obtained from the received earth station downlink signal to the GWL 51 via the base station 7 or directly.

[0096] The information generation unit 520 of the GWL 51 determines a data transmission route for each LEO satellite 21 in each time interval based on the time-series position of each LEO satellite 21 indicated by the LEO satellite orbit information, the position of each GWL 51 indicated by the earth station position information, the time-series position of each GEO satellite 3 indicated by the GEO satellite orbit information, and the relay availability information of each LEO satellite 21. If the LEO satellite 21 can communicate directly with the GWL 51, the information generation unit 520 determines a route for direct transmission from the LEO satellite 21 to the GWL 51. If the LEO satellite 21 cannot communicate directly with the GWL 51, the information generation unit 520 determines a route for transmitting data to the GWL 51 via one or more other LEO satellites 21 that can relay. The information generation unit 520 obtains information on LEO satellites 21 that can relay based on satellite identification information added to the relay availability information indicating that relay is possible. Furthermore, if the GEO satellite 3 is available, a route that includes the GEO satellite 3 may be used. The information generating unit 520 generates routing information indicating the route of each LEO satellite 21 for each time interval (step S403).

[0097] The information generation unit 520 outputs the generated routing information to the satellite transmission unit 530. The satellite transmission unit 530 generates an earth station uplink signal in which the routing information is set. The satellite transmission unit 530 transmits the earth station uplink signal from the antenna station 510 at a timing when communication with the LEO satellite 21 is possible (step S404). The information generation unit 520 may transmit the routing information via the GEO satellite 3. That is, the information generation unit 520 transmits the routing information to the GWG 6. The GWG 6 transmits the received routing information to the GEO satellite 3 by an earth station uplink signal. The GEO satellite communication device 300 of the GEO satellite 3 stores the routing information received from the GWG 6 and transmits it to the LEO satellite 21.

[0098] 9, the LEO satellite communications device 201 acquires observation data (step S501). If the LEO satellite communications device 201 receives the routing information transmitted by the GWL 51 in step S404 from the GWL 51 or via a GEO satellite 3 (step S502: YES), the LEO satellite communications device 201 stores the received routing information in the storage unit 281 (step S503). After the processing of step S503, or if the LEO satellite communications device 201 has not received the routing information (step S502: NO), the LEO satellite communications device 201 performs the processing of step S504.

[0099] The determination unit 282 reads out the time interval including the current time and the route information associated with that time interval from the routing information stored in the storage unit 281. The determination unit 282 reads out the data transmission destination information of the satellite itself from the read route information. Based on the read data transmission destination information, the determination unit 282 determines whether or not it is possible to transmit observation data to the GWL 51 (step S504).

[0100] That is, when the data transmission destination is the GWL 51, the determination unit 282 determines that transmission of observation data to the GWL 51 is possible. Alternatively, the determination unit 282 may determine whether transmission of observation data to the GWL 51 is possible, similar to the processing of step S204 in the first embodiment. Specifically, the determination unit 282 may transmit a transmission permission inquiry to the GWL 51. The determination unit 282 of the LEO satellite communication device 201 determines whether transmission of observation data to the GWL 51 is possible based on the transmission permission inquiry response returned from the GWL 51. The determination unit 282 may also determine whether transmission of observation data to the GWL 51 is possible based on whether congestion occurs between the satellite itself and the data transmission destination GWL 51. That is, the determination unit 282 determines that transmission of observation data is possible when no congestion occurs in communication between the earth station communication unit 222 and the GWL 51, and determines that transmission of observation data is impossible when congestion occurs. Alternatively, the judgment unit 282 may determine that it is possible to transmit observation data to GWL51 if the reception quality of the earth station uplink signal from GWL51 at the earth station communication unit 222 is better than a predetermined level, and may determine that it is not possible to transmit observation data to GWL51 if the reception quality is lower than the predetermined level.

[0101] If the determination unit 282 determines that the observation data can be transmitted to the GWL 51 (step S504: YES), it outputs the data transmission destination to the instruction unit 283. The instruction unit 283 performs the same process as step S205 in Fig. 9 to wirelessly transmit a data transmission signal of an earth station downlink signal in which the observation data is set to the GWL 51 indicated by the data transmission destination (step S505). After the process of step S505, the LEO satellite communication device 201 repeats the process from step S501.

[0102] If the determination unit 282 determines that the observation data cannot be transmitted to the GWL 51 (step S504: NO), it determines whether the communication is via another satellite (step S506). If the data transmission destination is another satellite, the determination unit 282 determines that the communication is via another satellite (step S506: YES), and inquires of the data transmission destination satellite whether the data can be relayed (step S507).

[0103] That is, when the data transmission destination is another LEO satellite 21, determination unit 282 transmits a data relay inquiry from LEO satellite communication unit 232 to the other LEO satellite 21 (hereinafter referred to as relay LEO satellite 21) that is the data transmission destination. When notifying unit 285 of LEO satellite communication device 201 mounted on relay LEO satellite 21 receives the data relay inquiry, it determines whether or not the satellite itself can relay the data. For example, notifying unit 285 determines that relaying is possible if the amount of data stored in data storage unit 270 is equal to or less than a threshold, and determines that relaying is not possible if the amount of data exceeds the threshold. Notifying unit 285 returns a data relay inquiry response setting the determination result of whether relaying is possible to the LEO satellite 21 that sent the data relay inquiry.

[0104] Alternatively, if the data transmission destination is a GEO satellite 3, the determination unit 282 causes the GEO satellite communication unit 242 to transmit a data relay inquiry to the GEO satellite 3. When the control unit 340 of the GEO satellite communication device 300 mounted on the GEO satellite 3 receives the data relay inquiry, it determines whether the device itself is capable of relaying the data received from the LEO satellite 21, and returns a data relay inquiry response containing the determination result to the LEO satellite 21.

[0105] The determination unit 282 of the LEO satellite communication device 201 receives the data relay inquiry response transmitted from the relay LEO satellite 21 or the GEO satellite 3. If the determination unit 282 determines that relay possible is set in the data relay inquiry response (step S508: YES), it outputs the data transmission destination to the instruction unit 283. The instruction unit 283 transmits a data transmission signal in which the observation data is set to the data transmission destination satellite (step S509).

[0106] Specifically, when the data transmission destination is relay LEO satellite 21, instruction unit 283 outputs the observation data acquired in step S201 and the address of relay LEO satellite 21 indicated by the data transmission destination to LEO satellite communication unit 232, and instructs transmission. Furthermore, when untransmitted observation data is stored in data storage unit 270, instruction unit 283 reads out the observation data and outputs it to LEO satellite communication unit 232. LEO satellite communication unit 232 wirelessly transmits, from antenna 231, a data transmission signal in which the observation data is set, with the address of relay LEO satellite 21 as its destination. Furthermore, when the data transmission destination is GEO satellite 3, instruction unit 283 wirelessly transmits, to GEO satellite 3, a data transmission signal in which the observation data is set, by processing similar to that of step S207 in FIG. 9 .

[0107] If route information cannot be read from the routing information (step S506: NO), or if relaying is not possible is set in the data relay inquiry response (step S508: NO), the determination unit 282 of the LEO satellite communications device 201 determines that data transmission via another satellite is not possible. The determination unit 282 instructs the writing unit 264 to store the observation data. The writing unit 264 writes the observation data acquired in step S501 to the data storage unit 270 (step S510). The LEO satellite communications device 201 performs the processing from step S501.

[0108] It should be noted that LEO satellite communications device 201 may omit the processes of steps S507 and S508.

[0109] When the LEO satellite communication device 201 of the relay LEO satellite 21 receives the data transmission signal transmitted by the LEO satellite communication unit 232 from another LEO satellite communication device 201 in step S509, it operates as follows. That is, in step S501, the LEO satellite communication device 201 regards the received data transmission signal as acquired observation data in addition to the observation data acquired from the terminal uplink signal and the observation data acquired from the sensors provided in the relay LEO satellite 21, and performs the processing of Fig. 14. Then, in step S505, the instruction unit 283 further instructs the LEO satellite communication unit 232 to output the data transmission signal received from the other LEO satellite communication device 201 to the earth station communication unit 222. The earth station communication unit 222 transmits the data transmission signal input from the LEO satellite communication unit 232 as an earth station downlink signal.

[0110] Also, in step S509, if the data transmission destination is a LEO satellite 21, the instructing unit 283 further instructs the LEO satellite communication unit 232 to relay the received data transmission signal to the data transmission destination. The LEO satellite communication unit 232 relays the data transmission signal received from another LEO satellite 21 to yet another LEO satellite 21 that is the data transmission destination. Also, in step S509, if the data transmission destination is a GEO satellite 3, the instructing unit 283 further instructs the LEO satellite communication unit 232 to output the received data transmission signal to the GEO satellite communication unit 242. The GEO satellite communication unit 242 transmits the data transmission signal input from the LEO satellite communication unit 232 to the GEO satellite 3 by wireless signal.

[0111] When a GEO satellite 3 receives a data transmission signal from a LEO satellite 21 or another GEO satellite 3, it transmits the received data transmission signal to a relay LEO satellite 21 or another GEO satellite 3 as the data transmission destination based on the routing information.

[0112] (Third embodiment) In the third embodiment, when a LEO satellite located in an area where communication with a GWL is not possible acquires high-priority observation data, it transmits the observation data to an earth station via a detour route via another LEO satellite or a GEO satellite. The high-priority observation data is, for example, observation data transmitted from a high-priority terminal station (Premium User Terminal: PUT) among terminal stations using a wireless communication system. The third embodiment will be described focusing on the differences from the second embodiment.

[0113] FIG. 15 is a diagram illustrating an overview of a wireless communication system 12 according to the third embodiment. The wireless communication system 12 includes a LEO satellite 22, a GEO satellite 3, a terminal station 4, a GWL 51, a GWG 6, and a base station 7. The wireless communication system 12 illustrated in FIG. 15 differs from the wireless communication system 11 of the second embodiment illustrated in FIG. 10 in that the latter includes a LEO satellite 22 instead of the LEO satellite 21. Note that the wireless communication system 12 does not necessarily include the GEO satellite 3 and the GWG 6. The wireless communication system 12 includes a plurality of LEO satellites 22. N (N is an integer equal to or greater than 2) LEO satellites 22 are respectively referred to as LEO satellites 22-1 to 22-N. FIG. 15 illustrates an example where N=3. Some of the terminal stations 4 are PUTs. A PUT terminal station 4 is referred to as PUT4a. In FIG. 15, two PUTs 4a are referred to as PUT4a-1 and PUT4a-2.

[0114] If the LEO satellite 22 receives observation data from a normal priority terminal station 4 during a time period when it cannot communicate with the GWL 51, it stores the observation data and transmits it at a time when it can communicate with the GWL 51. However, if the LEO satellite 22 receives observation data from the PUT 4a during a time period when it cannot communicate with the GWL 51, it immediately notifies the earth station via a detour route via another adjacent LEO satellite 22 or a GEO satellite 3, taking immediacy into consideration.

[0115] 16 is a diagram showing the communication destinations of LEO satellite 22. FIG. 16 shows the communication destinations of LEO satellites 22-1 to 22-3. There are times when LEO satellite 22-1 and LEO satellite 22 are unable to communicate with any of the GWLs 51. If LEO satellite 22-1 receives observation data from PUT 4a-1 during times when it is unable to communicate with GWL 51, it transmits the observation data received from PUT 4a-1 to GEO satellite 3. GEO satellite 3 transmits the observation data received from LEO satellite 22-1 to GWG 6.

[0116] On the other hand, if the LEO satellite 22-2 receives observation data from PUT4a-2 during a time when it cannot communicate with any of the GWLs 51, it transmits the observation data to the adjacent LEO satellite 22-3. The LEO satellite 22-3 transmits the observation data it has acquired and the observation data it has received from the LEO satellite 22-2 to the GWL 51-3.

[0117] Figure 17 is a block diagram showing the configuration of LEO satellite communication device 202 provided in LEO satellite 22 of the third embodiment. Only functional blocks related to this embodiment are extracted and shown in Figure 17. LEO satellite communication device 202 shown in Figure 17 differs from LEO satellite communication device 201 of the second embodiment shown in Figure 12 in that it includes control unit 290 instead of control unit 280.

[0118] The control unit 290 differs from the control unit 280 of the second embodiment in that it includes a determination unit 292 instead of the determination unit 282 and an instruction unit 293 instead of the instruction unit 283.

[0119] The determination unit 292 reads out information about a route associated with a time interval that includes the current time from the routing information stored in the storage unit 281. If the next destination of the satellite on the read out route is GWL 51, the determination unit 292 notifies the instruction unit 293 of GWL 51 as the destination.

[0120] If the next transmission destination of the satellite on the read route is a satellite, i.e., another LEO satellite 22 or a GEO satellite 3, the determination unit 292 determines whether high-priority observation data has been acquired. High-priority observation data is observation data received from PUT 4a. Note that observation data acquired by a predetermined sensor provided on the LEO satellite 22 may also be considered high-priority observation data. If the determination unit 291 determines that high-priority observation data has been acquired, it notifies the instruction unit 293 of the satellite that is the next transmission destination. If the determination unit 292 determines that the acquired observation data is not high-priority, it instructs the write unit 264 to store the observation data.

[0121] When the destination received from the determination unit 292 is GWL 51, the instruction unit 293 performs the same process as the instruction unit 283 of the second embodiment, outputting the observation data and the address of the destination GWL 51 to the earth station communication unit 222. The earth station communication unit 222 generates an earth station downlink signal whose destination is the address of the destination GWL 51 and in which the observation data is set, and wirelessly transmits the generated earth station downlink signal from the antenna 221.

[0122] If the destination is another LEO satellite 22, the instruction unit 293 outputs the high-priority observation data and the address of the other destination LEO satellite 22 to the LEO satellite communication unit 232. The LEO satellite communication unit 232 generates a data transmission signal that is addressed to the address of the other destination LEO satellite 22 and that contains the high-priority observation data, and wirelessly transmits the generated data transmission signal from the antenna 231.

[0123] If the destination is a GEO satellite 3, the instruction unit 293 outputs the high-priority observation data and the address of the destination GEO satellite 3 to the GEO satellite communication unit 242. The GEO satellite communication unit 242 generates a data transmission signal addressed to the address of the destination GEO satellite 3 and containing the high-priority observation data, and wirelessly transmits the generated data transmission signal from the antenna 241.

[0124] Fig. 18 is a processing flow showing the operation of the wireless communication system 12. In Fig. 18, the same processes as those in the processing flow of the second embodiment shown in Fig. 14 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0125] 14, generates routing information and transmits it to the LEO satellites 22. Note that the GWL 51 does not need to execute the process of step S402. In this case, the GWL 51 performs the process of step S403, assuming that all LEO satellites 22 are capable of relaying, and generates routing information.

[0126] The LEO satellite communications device 202 mounted on the LEO satellite 22 performs the same processes as steps S501 to S506 shown in Fig. 14. That is, the LEO satellite communications device 202 acquires observation data (step S501). When the LEO satellite communications device 202 receives routing information, it stores the received routing information in the storage unit 281 (steps S502 and S503). The determination unit 292 reads out from the routing information the time interval including the current time and information on the route associated with that time interval, and further reads out information on the data transmission destination of the satellite itself from the read route information. If the determination unit 292 determines that the data transmission destination is GWL 51 and that transmission of observation data to GWL 51 is possible (step S504: YES), the LEO satellite communications device 202 wirelessly transmits a data transmission signal of an earth station downlink signal in which the observation data is set to GWL 51 (step S505). On the other hand, if the determination unit 292 determines that transmission of observation data to the GWL 51 is not possible (step S504: NO), it determines whether the communication is via another satellite (step S506).

[0127] If the data transmission destination is another satellite, the determination unit 292 determines that the communication is via another satellite (step S506: YES), and executes the process of step S601. That is, the determination unit 292 determines whether the observation data acquired in step S501 has high priority (step S601).

[0128] For example, if the observation data is received from PUT 4a, the determination unit 292 determines that the observation data is high-priority observation data. Specifically, PUT 4a sets PUT information indicating that the data is a PUT in a terminal uplink signal and transmits the signal. If PUT information is set in the received terminal uplink signal, the terminal communication unit 212 of the LEO satellite communication device 202 adds the PUT information to the observation data obtained from the terminal uplink signal and outputs the data to the control unit 290. The determination unit 292 determines whether the observation data is received from PUT 4a based on whether PUT information is added.

[0129] Alternatively, the storage unit 281 may store the terminal ID of the PUT 4a in advance. The terminal ID is information that identifies the terminal station 4. The terminal communication unit 212 adds the terminal ID set in the terminal uplink signal to the observation data acquired from the terminal uplink signal and outputs the data to the control unit 290. The determination unit 292 determines whether the observation data is received from the PUT 4a based on whether the terminal ID added to the observation data matches any of the terminal IDs of the PUT 4a stored in the storage unit 281.

[0130] If the observation data is a received waveform of a terminal uplink signal, PUT information and a terminal ID are set in the terminal uplink signal using a spreading code or the like. This makes it possible to read the PUT information and the terminal ID without demodulation. The determination unit 292 may determine that observation data obtained by a predetermined sensor provided on the LEO satellite 22 is of high priority. The determination unit 292 may also determine that a predetermined type of observation data is of high priority. In this case, information on the type of data is added to the observation data.

[0131] If determination unit 292 determines that the observation data acquired in step S501 is high priority (step S601: YES), LEO satellite communications device 202 performs the same processes as steps S507 to S508 in Fig. 14. That is, LEO satellite communications device 202 inquires of the satellite to which data is to be transmitted whether data relay is possible (step S507). If determination unit 292 determines that relay possible is set in the data relay inquiry response received in response to the inquiry (step S508: YES), it performs the process of step S602.

[0132] Determination unit 292 outputs the data transmission destination to instruction unit 293. Instruction unit 293 transmits a data transmission signal, in which high-priority observation data is set, to the data transmission destination satellite (step S602). Specifically, instruction unit 293 reads out observation data with high priority from among the untransmitted observation data stored in data storage unit 270. Note that instruction unit 293 may read out all of the untransmitted observation data stored in data storage unit 270. Instruction unit 293 sets the observation data acquired in step S501 and the read observation data as observation data to be relayed via detouring.

[0133] When the data transmission destination is another LEO satellite 22, instruction unit 293 outputs the observation data to be detouring relayed and the address of the other LEO satellite 22 indicated by the data transmission destination to LEO satellite communication unit 232 and instructs transmission. LEO satellite communication unit 232 wirelessly transmits from antenna 231 a data transmission signal that has the address of the other LEO satellite 22 as the transmission destination received from instruction unit 293 as its destination and in which the observation data to be detouring relayed is set.

[0134] On the other hand, when the data transmission destination is GEO satellite 3, instruction unit 293 outputs the observation data to be detouring relayed and the address of GEO satellite 3 indicated by the data transmission destination to GEO satellite communication unit 242 and instructs transmission. GEO satellite communication unit 242 wirelessly transmits from antenna 241 a data transmission signal having the address of GEO satellite 3 as its destination and including the observation data to be detouring relayed.

[0135] If the determination unit 292 of the LEO satellite communication device 202 cannot read route information from the routing information (step S506: NO), if it determines that the acquired observation data is not high priority (step S601), or if relaying is not permitted in the data relay inquiry response (step S508: NO), it determines that data transmission via other satellites is not permitted. The determination unit 292 instructs the writing unit 264 to store the observation data. The writing unit 264 writes the observation data acquired in step S501 to the data storage unit 270 (step S603). At this time, if the observation data is high priority, the writing unit 264 adds high priority information to the observation data and writes it to the data storage unit 270. If the observation data includes information indicating high priority, the writing unit 264 does not need to add high priority information.

[0136] The LEO satellite communications device 202 mounted on the data transmission destination LEO satellite 22 that received the data transmission signal transmitted in step S602 operates as follows. That is, in step S501, the LEO satellite communications device 202 regards the received data transmission signal as acquired observation data in addition to the observation data acquired from the terminal uplink signal and the observation data acquired from the sensors equipped on the LEO satellite 22, and performs the processing of Fig. 18. Then, in step S505, the instructing unit 293 further instructs the LEO satellite communications unit 232 to output the data transmission signal received from the other LEO satellite communications device 202 to the earth station communications unit 222.

[0137] Also, in step S601, the instruction unit 293 determines that the data transmission signal received from another LEO satellite communication device 202 is high-priority observation data.

[0138] In step S602, if the data transmission destination is a LEO satellite 22, the instruction unit 293 instructs the LEO satellite communication unit 232 to relay the received data transmission signal to the data transmission destination. The LEO satellite communication unit 232 relays the data transmission signal received from another LEO satellite 22 to yet another LEO satellite 22 that is the data transmission destination.

[0139] Also, in step S602, if the data transmission destination is a GEO satellite 3, the instruction unit 293 instructs the LEO satellite communication unit 232 to output the received data transmission signal to the GEO satellite communication unit 242. The GEO satellite communication unit 242 transmits the data transmission signal input from the LEO satellite communication unit 232 to the GEO satellite 3 by wireless signal.

[0140] When a GEO satellite 3 receives a data transmission signal from a LEO satellite 22 or another GEO satellite 3, it transmits the received data transmission signal to the GWG 6, the LEO satellite 22 to which the data is to be transmitted, or another GEO satellite 3, based on the routing information.

[0141] If no detouring relay via LEO satellite 22 is performed, the communication system of the third embodiment can be configured in the same manner as the wireless communication system 1 of the first embodiment. In this case, the wireless communication system 1 performs the same processing as the processing of the first embodiment shown in Fig. 9, except for the following. That is, in step S103 of Fig. 9, the information generation unit 520 of the GWL 5 selects all LEO 2 that are in positions where they can communicate with the same GEO satellite 3 during the communication unavailable time period as LEO 2 that are permitted to communicate with the GEO satellite 3, and generates satellite communication information.

[0142] Furthermore, before the processing of step S206, the determination unit 262 of the LEO satellite communication device 200 performs the same processing as in step S601 above to determine whether the observation data received in step S201 is high-priority observation data. If the determination unit 262 determines that the observation data is high-priority observation data, it performs the processing of step S206. If the determination unit 262 determines that the observation data is not high-priority observation data, or if the determination in step S206 is NO, it performs the processing of step S603 instead of the processing of step S208.

[0143] Furthermore, in step S207, the instruction unit 263 outputs the observation data acquired in step S201, the untransmitted high-priority observation data stored in the data storage unit 270, and the address of the GEO satellite 3 to the GEO satellite communication unit 242, and instructs transmission. Note that the instruction unit 263 may also output all of the untransmitted observation data stored in the data storage unit 270 to the GEO satellite communication unit 242.

[0144] Next, an example of the hardware configuration of the LEO satellite communication devices 200, 201, and 202 will be described. Fig. 19 is a device configuration diagram showing an example of the hardware configuration of the LEO satellite communication devices 200, 201, and 202. The LEO satellite communication devices 200, 201, and 202 each include a processor 801, a storage unit 802, a communication interface 803, and a user interface 804.

[0145] The processor 801 is a central processing unit that performs calculations and control. The processor 801 is, for example, a CPU (central processing unit). The storage unit 802 is a storage device such as various memories or a hard disk. The processor 801 reads and executes programs from the storage unit 802, thereby realizing the control units 260, 280, and 290. Some of the functions of the control units 260, 280, and 290 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The storage unit 802 further has a work area and the like used when the processor 801 executes various programs. The communication interface 803 is connected to other devices so that communication is possible. The communication interface 803 corresponds to the terminal communication unit 212, the earth station communication unit 222, the LEO satellite communication unit 232, and the GEO satellite communication unit 242. The user interface 804 is an input device such as a keyboard, a pointing device (a mouse, a tablet, etc.), a button, a touch panel, etc., and a display device such as a display, etc. Human operations are input through the user interface 804.

[0146] The hardware configuration of the GWLs 5 and 51 is also the same as that shown in Fig. 19. A processor 801 reads out and executes a program from a storage unit 802, thereby realizing an information generation unit 520 and a data transmission unit 550. A communication interface 803 corresponds to a satellite transmission unit 530, a satellite reception unit 540, and a communication unit 560.

[0147] Instead of LEO satellites, other flying objects such as drones and HAPS may be used as mobile objects equipped with communication devices.

[0148] According to the above-described embodiment, the wireless communication system includes one or more mobile first communication devices, one or more mobile second communication devices, and one or more receiving devices. For example, the first communication devices are the LEO satellite communication devices 200, 201, and 202 of the embodiment, the second communication devices are the LEO satellite communication devices 200, 201, and 202 and the GEO satellite communication device 300 of the embodiment, and the receiving devices are GWL5 and GWG6.

[0149] The first communication device has a first communication unit, a second communication unit, and a first control unit. For example, the first communication unit is the earth station communication unit 222 of the embodiment, the second communication unit is the LEO satellite communication unit 232 or the GEO satellite communication unit 242 of the embodiment, and the first control unit is the control units 260, 280, and 290 of the embodiment. The first communication unit wirelessly communicates with the receiving device. The second communication unit wirelessly communicates with the second communication device. If the first communication device can communicate with any of the receiving devices, the first control unit transmits transmission data acquired by the first communication device to the receiving device from the first communication unit, and if the first communication device cannot communicate with any of the receiving devices, transmits the transmission data from the second communication unit to the second communication device that can communicate with the first communication device.

[0150] The second communication device includes a third communication unit, a fourth communication unit, and a second control unit. For example, the third communication unit is the LEO satellite communication unit 232 or 322 of the embodiment, the fourth communication unit is the earth station communication unit 222 or 312 of the embodiment, and the second control unit is the control unit 260, 280, 290 or 340 of the embodiment. The third communication unit wirelessly communicates with the first communication device. The fourth communication unit wirelessly communicates with the receiving device. The second control unit transmits transmission data received by the third communication unit from the first communication device from the fourth communication unit to a receiving device that can communicate with the second communication device.

[0151] The first control unit may transmit transmission data from the second communication unit to the second communication device when the first communication device cannot communicate with any receiving device and is permitted to transmit data to the second communication device. Of the multiple first communication devices, a first communication device permitted to transmit data to the second communication device may be selected based on the length of a time period during which the first communication device cannot communicate with any receiving device.

[0152] The time period during which the first communication device is unable to communicate with any receiving device may be calculated based on time-series location information of the first communication device and the locations of the receiving devices.

[0153] The first communication device may be provided on a low-earth orbit satellite, the second communication device may be provided on a geostationary satellite, and the receiving device may be installed on Earth. The transmission data is data that the first communication device receives wirelessly from a transmitting device installed on Earth. For example, the transmitting device is a terminal station 4 of the embodiment.

[0154] The third communication unit may wirelessly communicate with the first communication device and another second communication device. The second control unit of the second communication device may, when the second communication device can communicate with the receiving device, transmit the transmission data received by the third communication unit to the receiving device from the fourth communication unit, and, when the second communication device cannot communicate with the receiving device, transmit the transmission data received by the third communication unit from the third communication unit to the other second communication device that can communicate with the second communication device.

[0155] The second control unit of the second communication device may, when the device is able to communicate with the receiving device, transmit the transmission data received by the third communication unit and the transmission data acquired in the device from the fourth communication unit to the receiving device, and, when the device is unable to communicate with the receiving device, transmit the transmission data received by the third communication unit and the transmission data acquired in the device from the third communication unit to another second communication device that is able to communicate with the device.

[0156] The first communication device and the second communication device may be provided on a low-earth orbit satellite, and the receiving device may be installed on Earth. The transmission data acquired by the first communication device may be data that the first communication device has wirelessly received from a transmitting device installed on Earth, and the transmission data acquired by the second communication device may be data that the second communication device has wirelessly received from a transmitting device installed on Earth. For example, the transmitting device may be the terminal station 4 of the embodiment.

[0157] The first control unit of the first communication device may determine whether the device is able to communicate with the receiving device at a specified time based on a time period in which the device is able to communicate with the receiving device, which is calculated in advance based on the chronological position of the first communication device and the position of the receiving device.

[0158] The first control unit of the first communication device may determine a second communication device that can communicate with the first communication device at a specified time based on a time period in which the first communication device can communicate with the second communication device, which is calculated in advance based on the chronological position of the first communication device and the chronological position of the second communication device.

[0159] The first control unit may transmit the transmission data from the second communication unit to the second communication device when the device cannot communicate with any receiving device and the acquired transmission data is high priority, and may transmit the transmission data from the first communication unit to the receiving device when the device cannot communicate with any receiving device and the acquired transmission data is not high priority after the device becomes able to communicate with any receiving device. For example, the high priority transmission data is data received from a transmitting device with a high priority among multiple transmitting devices that transmit data.

[0160] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Explanation of symbols]

[0161] 1, 11, 12...wireless communication systems, 2-1~2-3, 21-1~21-3, 22-1~22-3...LEO satellites, 3…GEO satellite, 4...Terminal station, 5, 5-1, 5-2, 51-1~51-3…GWL, 6…GWG, 7...Base station, 200, 201, 202…LEO satellite communication equipment, 211, 221, 231, 241...antennas, 212...terminal communication unit, 222...Earth Station Communications Department, 232…LEO Satellite Communications Department, 242…GEO Satellite Communications Department, 250...data storage unit, 260, 280, 290...Control section, 261, 281...Storage section, 262, 282, 292...judgment department, 263, 283, 293...instruction section, 264...writing section, 285…Notification Department, 300...GEO satellite communication equipment, 311, 321, 331...antennas, 312...Earth Station Communications Department, 322…LEO Satellite Communications Department, 332…GEO Satellite Communications Department, 340...control unit, 510, 610...antenna stations, 520...Information generation section, 530, 650...Satellite transmitter, 540, 620...Satellite receiver, 550, 630...Data transmission unit, 560, 640…Communications Department, 801...processor, 802...Storage section, 803...Communication Interface, 804...User interface

Claims

1. A wireless communication system including one or more mobile first communication devices, one or more mobile second communication devices, and one or more receiving devices, The first communication device a first communication unit that wirelessly communicates with the receiving device; a second communication unit that wirelessly communicates with the second communication device; a first control unit that, when the device itself is capable of communicating with any of the receiving devices, transmits transmission data acquired in the device itself from the first communication unit to the receiving device, and, when the device itself is unable to communicate with any of the receiving devices but is capable of communicating with any of the second communication devices and data transmission from the device itself to the second communication device is permitted based on the amount of transmission data stored in the device itself or the amount of transmission data stored in the second communication device that is capable of communicating with the device itself, The second communication device a third communication unit that wirelessly communicates with the first communication device; a fourth communication unit that wirelessly communicates with the receiving device; a second control unit that transmits the transmission data received by the third communication unit from the first communication device from the fourth communication unit to the receiving device that can communicate with the third communication unit, Wireless communication system.

2. A wireless communication system including one or more mobile first communication devices, one or more mobile second communication devices, and one or more receiving devices, The first communication device a first communication unit that wirelessly communicates with the receiving device; a second communication unit that wirelessly communicates with the second communication device; a first control unit that transmits transmission data acquired by the device itself from the first communication unit to the receiving device when the device itself can communicate with any of the receiving devices, and transmits the transmission data from the second communication unit to the second communication device that can communicate with the device itself when the device itself cannot communicate with any of the receiving devices; The second communication device a third communication unit that wirelessly communicates with the first communication device; a fourth communication unit that wirelessly communicates with the receiving device; a second control unit that transmits the transmission data received by the third communication unit from the first communication device from the fourth communication unit to the receiving device that can communicate with the third communication unit; the first control unit, when the device itself cannot communicate with any of the receiving devices and the device itself is permitted to transmit data to the second communication device, transmits the transmission data from the second communication unit to the second communication device; Among the plurality of first communication devices, the first communication device that is permitted to transmit data to the second communication device is selected based on the length of a time period during which the first communication device cannot communicate with any of the receiving devices. Wireless communication system.

3. a time period during which the first communication device cannot communicate with any of the receiving devices is calculated based on time-series position information of the first communication device and positions of the receiving devices; 3. The wireless communication system according to claim 2.

4. the first communication device is provided on a low earth orbit satellite; the second communication device is provided on a geostationary satellite; The receiving device is installed on Earth. The wireless communication system according to any one of claims 1 to 3.

5. the transmission data is data that the first communication device receives wirelessly from a transmitting device installed on Earth; 5. The wireless communication system according to claim 4.

6. the third communication unit wirelessly communicates with the first communication device and another second communication device; the second control unit, when the device itself can communicate with the receiving device, transmits the transmission data received by the third communication unit from the fourth communication unit to the receiving device, and when the device itself cannot communicate with the receiving device, transmits the transmission data received by the third communication unit from the third communication unit to another second communication device that can communicate with the device itself; 10. The wireless communication system of claim 1.

7. the second control unit, when the device itself can communicate with the receiving device, transmits the transmission data received by the third communication unit and the transmission data acquired by the device itself from the fourth communication unit to the receiving device, and when the device itself cannot communicate with the receiving device, transmits the transmission data received by the third communication unit and the transmission data acquired by the device itself from the third communication unit to another second communication device that can communicate with the device itself; 7. The wireless communication system according to claim 6.

8. the first communication device and the second communication device are provided on a low earth orbit satellite, The receiving device is installed on the Earth, the transmission data acquired by the first communication device is data received by the first communication device wirelessly from a transmitting device installed on Earth, the transmission data acquired by the second communication device is data received by the second communication device wirelessly from a transmitting device installed on Earth; 8. The wireless communication system according to claim 7.

9. the first control unit determines whether the device itself is capable of communicating with the receiving device at a predetermined time based on a time period in which the device itself is capable of communicating with the receiving device, the time period being calculated in advance based on a time series position of the first communication device and a position of the receiving device; 10. The wireless communication system of claim 1.

10. the first control unit determines a second communication device that can communicate with the own device at a predetermined time based on a time period in which the own device can communicate with the second communication device, the time period being calculated in advance based on a time series position of the first communication device and a time series position of the second communication device; 10. The wireless communication system of claim 1.

11. A wireless communication system including one or more mobile first communication devices, one or more mobile second communication devices, and one or more receiving devices, The first communication device a first communication unit that wirelessly communicates with the receiving device; a second communication unit that wirelessly communicates with the second communication device; a first control unit that transmits transmission data acquired by the device itself from the first communication unit to the receiving device when the device itself can communicate with any of the receiving devices, and transmits the transmission data from the second communication unit to the second communication device that can communicate with the device itself when the device itself cannot communicate with any of the receiving devices; The second communication device a third communication unit that wirelessly communicates with the first communication device; a fourth communication unit that wirelessly communicates with the receiving device; a second control unit that transmits the transmission data received by the third communication unit from the first communication device from the fourth communication unit to the receiving device that can communicate with the third communication unit; the first control unit, when the device itself cannot communicate with any of the receiving devices and the acquired transmission data has high priority, transmits the transmission data from the second communication unit to the second communication device, and when the device itself cannot communicate with any of the receiving devices and the acquired transmission data does not have high priority, transmits the transmission data from the first communication unit to the receiving device after the device itself becomes able to communicate with any of the receiving devices; Wireless communication system.

12. The high-priority transmission data is data received from a transmitting device with a high priority among a plurality of transmitting devices that transmit data.

12. The wireless communication system of claim 11.

13. A communication device in a wireless communication system including a plurality of mobile communication devices and one or more receiving devices, a first communication unit that wirelessly communicates with the receiving device; a second communication unit that wirelessly communicates with another communication device; a control unit that, when the device itself is capable of communicating with any of the receiving devices, transmits transmission data acquired in the device itself from the first communication unit to the receiving device, and, when the device itself is unable to communicate with any of the receiving devices but is capable of communicating with any of the other communication devices and data transmission from the device itself to the other communication devices is permitted based on the amount of transmission data stored in the device itself or the amount of transmission data stored in the other communication devices capable of communicating with the device itself, transmits the transmission data from the second communication unit to the device itself and to the other communication devices capable of communicating with any of the receiving devices; A communication device comprising:

14. A communication device in a wireless communication system including a plurality of mobile communication devices and one or more receiving devices, a first communication unit that wirelessly communicates with the receiving device; a second communication unit that wirelessly communicates with another communication device; a control unit that transmits transmission data acquired by the device itself from the first communication unit to the receiving device when the device itself can communicate with any of the receiving devices, and transmits the transmission data from the second communication unit to another communication device that can communicate with the device itself and any of the receiving devices when the device itself cannot communicate with any of the receiving devices; Equipped with the control unit, when the device itself cannot communicate with any of the receiving devices and the device itself is permitted to transmit data to the other communication devices, transmits the transmission data from the second communication unit to the other communication devices; Among the plurality of communication devices, the communication device that is permitted to transmit data to the other communication device is selected based on the length of a time period during which the communication device cannot communicate with any of the receiving devices. Communication equipment.

15. A communication device in a wireless communication system including a plurality of mobile communication devices and one or more receiving devices, a first communication unit that wirelessly communicates with the receiving device; a second communication unit that wirelessly communicates with another communication device; a control unit that transmits transmission data acquired by the device itself from the first communication unit to the receiving device when the device itself can communicate with any of the receiving devices, and transmits the transmission data from the second communication unit to another communication device that can communicate with the device itself and any of the receiving devices when the device itself cannot communicate with any of the receiving devices; Equipped with the control unit, when the device itself cannot communicate with any of the receiving devices and the acquired transmission data has high priority, transmits the transmission data from the second communication unit to the other communication device, and when the device itself cannot communicate with any of the receiving devices and the acquired transmission data does not have high priority, transmits the transmission data from the first communication unit to the receiving device after the device itself becomes able to communicate with any of the receiving devices. Communication equipment.

16. A wireless communication method for a wireless communication system including one or more mobile first communication devices, one or more mobile second communication devices, and one or more receiving devices, a transmitting step in which the first communication device transmits the transmission data acquired in the first communication device to the receiving device from a first communication unit that wirelessly communicates with the receiving device when the first communication device is capable of communicating with any of the receiving devices, and when the first communication device is unable to communicate with any of the receiving devices but is capable of communicating with any of the second communication devices and data transmission from the first communication device to the second communication device that is capable of communicating with the first communication device is permitted based on the amount of transmission data stored in the first communication device or the amount of transmission data stored in the second communication device that is capable of communicating with the first communication device; a relay step in which the second communication device transmits the transmission data received from the first communication device by a third communication unit that wirelessly communicates with the first communication device, from a fourth communication unit that wirelessly communicates with the receiving device to the receiving device that can communicate with the second communication device; A wireless communication method comprising:

17. A wireless communication method for a wireless communication system including one or more mobile first communication devices, one or more mobile second communication devices, and one or more receiving devices, a transmitting step in which the first communication device transmits the transmission data acquired by the first communication device to the receiving device from a first communication unit that wirelessly communicates with the receiving device when the first communication device is capable of communicating with any of the receiving devices, and transmits the transmission data to the second communication device that is capable of communicating with the first communication device from a second communication unit that wirelessly communicates with the second communication device when the first communication device is unable to communicate with any of the receiving devices; a relay step in which the second communication device transmits the transmission data received from the first communication device by a third communication unit that wirelessly communicates with the first communication device, from a fourth communication unit that wirelessly communicates with the receiving device to the receiving device that can communicate with the second communication device; and In the transmitting step, when the first communication device cannot communicate with any of the receiving devices and is permitted to transmit data to the second communication device, the first communication device transmits the transmission data from the second communication unit to the second communication device; Among the plurality of first communication devices, the first communication device that is permitted to transmit data to the second communication device is selected based on the length of a time period during which the first communication device cannot communicate with any of the receiving devices. Wireless communication method.

18. A wireless communication method for a wireless communication system including one or more mobile first communication devices, one or more mobile second communication devices, and one or more receiving devices, a transmitting step in which the first communication device transmits the transmission data acquired by the first communication device to the receiving device from a first communication unit that wirelessly communicates with the receiving device when the first communication device is capable of communicating with any of the receiving devices, and transmits the transmission data to the second communication device that is capable of communicating with the first communication device from a second communication unit that wirelessly communicates with the second communication device when the first communication device is unable to communicate with any of the receiving devices; a relay step in which the second communication device transmits the transmission data received from the first communication device by a third communication unit that wirelessly communicates with the first communication device, from a fourth communication unit that wirelessly communicates with the receiving device to the receiving device that can communicate with the second communication device; and In the transmitting step, when the first communication device cannot communicate with any of the receiving devices and the acquired transmission data has high priority, the first communication device transmits the transmission data from the second communication unit to the second communication device, and when the first communication device cannot communicate with any of the receiving devices and the acquired transmission data does not have high priority, after the first communication device becomes able to communicate with any of the receiving devices, the first communication device transmits the transmission data from the first communication unit to the receiving device. Wireless communication method.

19. A wireless communication method for a communication device in a wireless communication system including a plurality of mobile communication devices and one or more receiving devices, the method comprising: a transmitting step of transmitting transmission data acquired in the device itself from a first communication unit that wirelessly communicates with the receiving device to the receiving device when the device itself is capable of communicating with any of the receiving devices, and transmitting the transmission data from a second communication unit that wirelessly communicates with the other communication devices to the device itself and to the other communication devices that can communicate with any of the receiving devices when the device itself is unable to communicate with any of the receiving devices but is capable of communicating with any of the other communication devices and transmission of data from the device itself to the other communication devices is permitted based on the amount of transmission data stored in the device itself or the amount of transmission data stored in the other communication devices that can communicate with the device itself; A wireless communication method comprising:

20. A wireless communication method for a communication device in a wireless communication system including a plurality of mobile communication devices and one or more receiving devices, the method comprising: a transmitting step of transmitting transmission data acquired by the device itself from a first communication unit that wirelessly communicates with the receiving device to the receiving device when the device itself is capable of communicating with any of the receiving devices, and transmitting the transmission data from a second communication unit that wirelessly communicates with other communication devices to the device itself and other communication devices that can communicate with any of the receiving devices when the device itself is unable to communicate with any of the receiving devices; and In the transmitting step, when the own device cannot communicate with any of the receiving devices and the own device is permitted to transmit data to the other communication devices, the transmission data is transmitted from the second communication unit to the other communication devices; Among the plurality of communication devices, the communication device that is permitted to transmit data to the other communication device is selected based on the length of a time period during which the communication device cannot communicate with any of the receiving devices. Wireless communication method.

21. A wireless communication method for a communication device in a wireless communication system including a plurality of mobile communication devices and one or more receiving devices, the method comprising: a transmitting step of transmitting transmission data acquired by the device itself from a first communication unit that wirelessly communicates with the receiving device to the receiving device when the device itself is capable of communicating with any of the receiving devices, and transmitting the transmission data from a second communication unit that wirelessly communicates with other communication devices to the device itself and other communication devices that can communicate with any of the receiving devices when the device itself is unable to communicate with any of the receiving devices; and In the transmitting step, when the device itself cannot communicate with any of the receiving devices and the acquired transmission data has high priority, the transmission data is transmitted from the second communication unit to the other communication device, and when the device itself cannot communicate with any of the receiving devices and the acquired transmission data is not high priority, the transmission data is transmitted from the first communication unit to the receiving device after the device itself becomes able to communicate with any of the receiving devices. Wireless communication method.

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