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

Abstract

The purpose of the present disclosure is to provide a technology with which an aerial wireless station can transmit a signal in a time zone in which a ground terminal station is waiting. A wireless communication system according to the present disclosure comprises: one or more ground terminal stations present in a predetermined area; and an aerial wireless station that moves on a trajectory in the air and can periodically communicate with the predetermined area. The wireless communication system executes: processing for calculating the latest communicable time zone in the predetermined area of the aerial wireless station; processing for acquiring information relating to a communicable time zone stored by the ground terminal station; and processing for calculating a communicable time zone overlapping between the communicable time zone stored by the ground terminal station and the latest communicable time zone. The aerial wireless station transmits a signal including information relating to the latest communicable time zone during the overlapping communicable time zone. The ground terminal station executes processing for waiting for and receiving a signal in a communicable time zone stored in a storage device, and processing for updating the communicable time zone stored in the storage device with the latest communicable time zone.

Description

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

[0001] The present disclosure relates to a wireless communication system including an airborne radio station and a ground terminal station, a control station, a wireless communication method for communication between the airborne radio station and the ground terminal station, and a wireless communication program.

[0002] With the recent spread of 4G / 5G services, the demand for network communication bandwidth is increasing year by year. Furthermore, ultra-wide coverage is required for future B5G / 6G services. To expand the coverage area, B5G / 6G services are expected to use NTNs (Non-Terrestrial Networks). This will enable the expansion of service areas to locations where the construction of terrestrial base stations is expensive or difficult, such as mountainous, marine, or aerial locations. It will also enable the construction of communication systems that are resistant to terrestrial disasters.

[0003] In NTN, data is relayed by radio stations moving in the sky, including outer space. Because radio stations orbit the sky, they are known to be able to periodically communicate with areas on the ground.

[0004] Patent Literature 1 discloses a technology in which an overhead radio station calculates the antenna coverage for each time period based on its own orbital information and identifies the communication available time periods for each ground area. This enables control such as directing the antenna direction of the overhead radio station to the area where communication is available during the communication available time period.

[0005] International Publication No. 2022 / 137493

[0006] Information about the latest available communication time slots in a given area is notified to ground terminal stations within the area by transmitting a notification signal from an airborne radio station. The airborne radio station transmits a notification signal containing information about the latest available communication time slot during the latest available communication time slot. The ground terminal station waits for and receives the notification signal from the airborne radio station when the available communication time slot stored in its storage device begins. The ground terminal station updates the information about the available communication time slots stored in its storage device with the information about the latest available communication time slot contained in the received notification signal. This allows the ground terminal station to grasp the latest available communication time slots calculated based on the latest orbit information.

[0007] It is generally known that the orbits of overhead radio stations deviate over time, which in turn causes deviations in communication time periods. By having the ground terminal station acquire the latest information on communication time periods, it is possible to reduce the loss of data transmitted from the ground terminal station to the overhead radio station.

[0008] However, the information on the available communication time slots stored in the memory device of the ground terminal station stops updating when the ground terminal station last receives a notification signal. Therefore, the available communication time slots stored in the memory device of the ground terminal station may differ from the latest available communication time slots. In this case, the time slots during which the airborne radio station transmits a notification signal differ from the time slots during which the ground terminal station waits for a notification signal, which means that the airborne radio station must transmit a notification signal even during times when the ground terminal station is not waiting for a signal.

[0009] In order to solve the above-mentioned problems, the present disclosure aims to provide a technology that allows an airborne radio station to transmit a signal during a time period when a terrestrial terminal station is waiting.

[0010] A first aspect of the present disclosure is a wireless communication system comprising: one or more terrestrial terminal stations present in a predetermined area; and an overhead radio station that moves on an orbit in the sky and is periodically capable of communicating with the predetermined area, wherein the system is configured to perform the following processes: calculate the latest available communication time period in the predetermined area of ​​the overhead radio station; acquire information on the available communication time period stored in a memory device of the terrestrial terminal station; and calculate an overlapping communication time period between the available communication time period stored in the memory device of the terrestrial terminal station and the latest available communication time period; wherein the overhead radio station is configured to perform the following processes: transmit a signal including information on the latest available communication time period during the overlapping communication time period; and the terrestrial terminal station is preferably configured to perform the following processes: wait for and receive the signal during the available communication time period stored in the memory device; and update the available communication time period stored in the memory device with the latest available communication time period.

[0011] In addition, a second aspect is preferably a control station configured to perform the following processes: calculating the latest communication time slots in a specified area for an overhead radio station that moves on an orbit in the sky and is periodically able to communicate with the specified area; acquiring information on communication time slots stored in a memory device of a ground terminal station present in the specified area; calculating communication time slots that overlap between the communication time slots stored in the memory device of the ground terminal station and the latest communication time slots; and notifying the overhead radio station of the information on the overlapping communication time slots and the information on the latest communication time slots.

[0012] Furthermore, a third aspect is preferably a wireless communication method including: calculating the latest communication time slot in a specified area for an airborne radio station that moves on an orbit in the sky and is periodically able to communicate with the specified area; acquiring information on the communication time slot stored in a memory device of a ground terminal station present in the specified area; calculating an overlapping communication time slot between the communication time slot stored in the memory device of the ground terminal station and the latest communication time slot; the airborne radio station transmitting a signal including information on the latest communication time slot during the overlapping communication time slot; the ground terminal station waiting to receive the signal during the communication time slot stored in the memory device; and the ground terminal station updating the communication time slot stored in the memory device with the latest communication time slot.

[0013] Furthermore, a fourth aspect is a wireless communication program to be executed by a control station, which preferably includes a program that causes the control station to execute the following processes: a process of calculating the latest communication time slots in a specified area for an overhead radio station that moves on an orbit in the sky and is periodically able to communicate with the specified area; a process of acquiring information on communication time slots stored in a memory device of a ground terminal station present in the specified area; a process of calculating communication time slots that overlap between the communication time slots stored in the memory device of the ground terminal station and the latest communication time slots; and a process of notifying the overhead radio station of the information on the overlapping communication time slots and the information on the latest communication time slots.

[0014] In the present disclosure, an overlapping communication time period between a communication time period stored in a storage device of a ground terminal station and the latest communication time period is calculated. The overhead radio station transmits a signal including information about the latest communication time period during the overlapping communication time period. The overlapping communication time period refers to the time period during which the ground terminal station is waiting for a signal. Therefore, the overhead radio station can transmit a signal during the time period during which the ground terminal station is waiting.

[0015] 1 is a diagram showing an example of the configuration of a wireless communication system according to a first embodiment; FIG. 2 is a diagram showing information on communication available time periods stored in a storage device of a control station according to the first embodiment; FIG. 3 is a diagram explaining overlapping communication available time periods according to the first embodiment; FIG. 4 is a flowchart explaining processing executed by a control station, an airborne radio station, and a ground terminal station according to the first embodiment; FIG. 5 is a block diagram showing an example of the configuration of a control station according to the first embodiment; FIG. 6 is a block diagram showing an example of the configuration of an airborne radio station according to the first embodiment; FIG. 7 is a block diagram showing an example of the configuration of a ground terminal station according to the first embodiment; FIG. 8 is a diagram showing the hardware configuration of a control station according to the first embodiment; FIG. 9 is a diagram showing the hardware configuration of an airborne radio station according to the first embodiment; and FIG. 10 is a diagram showing the hardware configuration of a ground terminal station according to the first embodiment.

[0016] Embodiments of the present disclosure will be described with reference to the drawings. The same or corresponding components will be designated by the same reference numerals, and repeated description may be omitted.

[0017] 1 is a diagram showing an example of the configuration of a wireless communication system 100 according to embodiment 1. The wireless communication system 100 includes a plurality of first layer airborne radio stations 110, a plurality of second layer airborne radio stations 120, and a third layer airborne radio station 130. The wireless communication system 100 further includes a control station 170, a terrestrial terminal station 180, and a plurality of terrestrial base stations 140.

[0018] The first-tier airborne radio station 110 is a radio relay station that moves on an orbit in the sky, including outer space, and is capable of periodically communicating with a predetermined ground area. The first-tier airborne radio station 110 is, for example, a High Altitude Platform System (HAPS), a drone, an unmanned aerial vehicle, or an aircraft.

[0019] Neighboring first-layer airborne radio stations 110 are connected to each other by intralayer circuits 2 and perform wireless or optical signal communication. The first-layer airborne radio stations 110 connected by the intralayer circuits 2 form a first airborne network 111.

[0020] The second-layer airborne radio station 120 is also a radio relay station that moves on an orbit in the sky, including outer space, and is capable of periodically communicating with a predetermined ground area. Examples of the second-layer airborne radio station 120 include a low earth orbit (LEO) satellite that moves on a sun-synchronous orbit, a sun-synchronous subrecurrent orbit, a circular orbit, a polar orbit, or the like at an orbital altitude of 2000 km or less.

[0021] Neighboring second-layer airborne radio stations 120 are connected to each other by intralayer circuits 4 and perform radio or optical signal communication. The second-layer airborne radio stations 120 connected by the intralayer circuits 4 form a second airborne network 121.

[0022] The second layer airborne radio station 120 receives data transmitted from the ground terminal station 180 via the inter-ground station line 1 .

[0023] The second layer airborne radio station 120 relays data via the second airborne network 121 to a second layer airborne radio station 120 that can communicate with an airborne radio station at a different layer from itself, or to a second layer airborne radio station 120 that can communicate with a terrestrial base station 140.

[0024] The second-layer air radio station 120 that can communicate with an air radio station in a different hierarchical layer from itself transmits the received data to the air radio station in a different hierarchical layer from itself via the inter-network lines 3 and 8. The second-layer air radio station 120 that can communicate with the terrestrial base station 140 transmits the received data to the terrestrial base station 140 via the inter-base station line 5.

[0025] The same applies to the third-layer radio station 130, so a description thereof will be omitted. The third-layer radio station 130 is, for example, a GEO (Geostationary Orbit) satellite.

[0026] If necessary, the wireless communication system 100 may include a fourth layer airborne radio station, a fifth layer airborne radio station, and so on.

[0027] Hereinafter, when there is no need to distinguish between the first layer radio station 110, the second layer radio station 120, and the third layer radio station 130, they will be simply referred to as radio stations 160. Only when there is a need to distinguish between them will the respective names be written.

[0028] The terrestrial base station 140 receives data transmitted from the airborne radio station 160 via the inter-base station line 5 and transmits the data to the terrestrial network. In other words, the terrestrial base station 140 functions as a gateway station for the terrestrial network. The terrestrial base station 140 may be a portable radio station such as a very small aperture terminal (VSAT).

[0029] The control station 170 acquires orbit information from the overhead radio station 160 via the control line 6. Based on the acquired orbit information, the control station 170 periodically calculates the communication available time period of the overhead radio station 160 in the area where the ground terminal station 180 is located. The control station 170 is a terrestrial base station that covers the area where the ground terminal station 180 is located and controls the ground terminal station 180. Alternatively, the control station 170 may be one of the overhead radio stations 160, and there is no limitation as to whether it is located on the ground or in the sky.

[0030] The ground terminal station 180 is a smartphone, an IoT terminal, a Bluetooth (registered trademark) communication device, or the like that performs wireless communication with the airborne radio station 160 via the inter-ground station line 1. The ground terminal station 180 transmits data such as internet traffic to the airborne radio station 160.

[0031] In this manner, in the wireless communication system 100 of the present disclosure, the terrestrial terminal station 180 transmits data to the overhead radio station 160. The transmitted data is relayed by the overhead radio station 160 and transmitted to the terrestrial base station 140. Although not explained further, it is of course also possible for the data transmitted by the terrestrial base station 140 to be relayed by the overhead radio station 160 and transmitted to the terrestrial terminal station 180.

[0032] 1 illustrates an example in which multiple airborne radio stations 160 configure a three-layer non-terrestrial network, but the airborne radio stations 160 do not necessarily need to be arranged in layers. The wireless communication system 100 of the present disclosure may include one airborne radio station 160, one or more terrestrial terminal stations 180, and a control station 170.

[0033] (A method in which an overhead radio station transmits a signal during a time period when a ground terminal station is waiting.)

[0034] 2 is a diagram showing information on communication available time periods stored in the storage device 173 of the control station 170 according to the first embodiment. Note that the date and time information in the following figures is an example.

[0035] The control station 170 calculates the communication time periods of the overhead radio stations 160 in a specified area based on the orbital information of the overhead radio stations 160. The calculated information on the communication time periods is listed for each generation time (also called epoch) of the orbital information used in the calculation, and stored in the storage device 173 of the control station 170. The information on the communication time periods is given by the start and end times of communication.

[0036] For example, as shown in the first row of the table, the latest communication time slot 10 calculated based on the latest orbit information is from 10:10 to 10:20. Also, as shown in the third row of the table, the communication time slot calculated based on the orbit information from three days ago is from 10:08 to 10:18. Similarly, as shown in the fourth row of the table, the communication time slot calculated based on the orbit information from five days ago is from 10:12 to 10:22. The communication time slots differ depending on the time the orbit information was generated because the orbit of the overhead radio station 160 shifts over time.

[0037] The control station 170 acquires information about available communication time periods stored in the first and second ground terminal stations 180 present within a predetermined area from each of the ground terminal stations 180. This allows the control station 170 to ascertain the time period information about available communication time periods stored in the first and second ground terminal stations 180. As an example, assume that the information about available communication time periods 20-1 stored in the storage device 183 of the first ground terminal station 180 is information about available communication time periods based on orbit information from three days ago. Similarly, assume that the information about available communication time periods 20-2 stored in the storage device 183 of the second ground terminal station 180 is information about available communication time periods based on orbit information from five days ago. The information about available communication time periods stored in the storage devices 183 of the first and second ground terminal stations 180 stopped updating when each of the ground terminal stations 180 last received a notification signal.

[0038] The control station 170 calculates a communication time period 40 that overlaps between the communication time period 20 stored in the storage device 183 of each of the first and second ground terminal stations 180 and the latest communication time period 10. More specifically, the control station 170 calculates a communication time period 40 that overlaps between the communication time period 20-1 based on the orbit information from three days ago stored in the first ground terminal station 180, the communication time period 20-2 based on the orbit information from five days ago stored in the second ground terminal station 180, and the latest communication time period 10. As described above, the first and second ground terminal stations 180 wait for a notification signal from the overhead radio station 160 when the communication time period stored in their own storage device 183 begins. By calculating the overlap, it is possible to extract only the time periods during which the first and second ground terminal stations 180 wait for a notification signal from the latest communication time period 10.

[0039] In the example of FIG. 2, the overlapping communication time slot 40 is from 10:12 to 10:18 as shown in the second row of the table.

[0040] 3 is a diagram illustrating overlapping communication time periods 40 according to the first embodiment. The diagram shows a communication time period 20-1 based on orbit information from three days ago stored in the first ground terminal station 180, a communication time period 20-2 based on orbit information from five days ago stored in the second ground terminal station 180, and the latest communication time period 10. Furthermore, the diagram shows a communication time period 40 that overlaps between these communication time periods.

[0041] The overlapping communication time period 40 is a time period during which the broadcast signal can be received by both the first and second ground terminal stations 180. By transmitting the broadcast signal from the overhead radio station 160 during the overlapping communication time period 40, the broadcast signal is not transmitted during a time period when only one of the first and second ground terminal stations 180 can receive the signal, thereby reducing transmission loss.

[0042] It should be noted that the number of ground terminal stations 180 does not need to be multiple, and may be one. Even in this case, by calculating the overlap between the latest available communication time slot 10 and the available communication time slot 20 stored in the ground terminal station 180, it is possible to extract only the time slot in which the ground terminal station 180 is waiting for a notification signal from the latest available communication time slot 10. By transmitting a notification signal from the overhead radio station 160 during the overlapping available communication time slot 40, the notification signal will not be transmitted during a time slot in which the ground terminal station 180 cannot receive the signal, thereby reducing transmission loss.

[0043] The non-transmission time period 30 is a time period that does not overlap between the overlapping communication available time period 40 and the communication available time period 20 stored in the first or second ground terminal station 180. The non-transmission time period 30 refers to a time period during which the first and second ground terminal stations 180 wait for a notification signal, but no notification signal is transmitted from the overhead radio station 160.

[0044] FIG. 4 is a flowchart illustrating the processing executed by the control station 170, the airborne radio station 160, and the ground terminal station 180 according to the first embodiment.

[0045] First, the control station 170 acquires the latest orbit information of the overhead radio station 160 (step S01). The acquired orbit information is stored in the storage device 173 together with the time when the orbit information was generated.

[0046] Furthermore, the control station 170 calculates the latest communication time slot 10 for the overhead radio station 160 in the predetermined area based on the acquired latest orbit information (step S02).

[0047] Furthermore, the control station 170 acquires information on the available communication time slots 20 stored in the storage device 183 of the ground terminal station 180 from the ground terminal station 180 present within the predetermined area (step S03). The information on the available communication time slots 20 stored in the storage device 183 of the ground terminal station 180 is acquired from the ground terminal station 180 in response to a request signal from the control station 170. Alternatively, the information may be notified to the control station 170 by the ground terminal station 180 on its own initiative, or may be acquired by another method.

[0048] Furthermore, the control station 170 calculates the communication available time period 40 that overlaps between the communication available time period 20 stored in the storage device 183 of the ground terminal station 180 and the latest communication available time period 10 (step S04).

[0049] Furthermore, the control station 170 notifies the overhead radio station 160 of information on the overlapping communication available time slots 40 and information on the latest communication available time slots 10 (step S05).

[0050] The overhead radio station 160 stores information about the overlapping communication time slots 40 and information about the latest communication time slot 10 in its own storage device (step S06). Furthermore, the overhead radio station 160 transmits a notification signal including information about the latest communication time slot 10 during the overlapping communication time slots 40 (step S07). Examples of a transmission method include a beacon at a specific frequency. Generally, a frequency is assigned to a beacon signal that is unique to the transmitting overhead radio station 160 or that rarely overlaps with other overhead radio stations 160. By using a beacon, the ground terminal station 180 that receives the notification signal can identify the transmitting overhead radio station 160 from the frequency information.

[0051] Next, the ground terminal station 180 waits for a notification signal from the overhead radio station 160 as the communication available time period 20 stored in the storage device 183 begins (step S08). Next, the ground terminal station 180 receives the notification signal and updates the information on the communication available time period 20 stored in the storage device 183 with the information on the latest communication available time period 10 contained in the notification signal (step S09). Furthermore, the ground terminal station 180 transmits data to the overhead radio station 160 during the latest communication available time period 10 contained in the notification signal (step S10).

[0052] The airborne radio station 160 receives data transmitted from the ground terminal station 180 (step S11).

[0053] FIG. 5 is a block diagram showing an example of the configuration of the control station 170 according to the first embodiment.

[0054] The first communication circuit 171 establishes a control line 6 with the overhead radio station 160 and communicates with it. The second communication circuit 172 establishes a line with a ground terminal station 180 located within a specified area and communicates with it. The calculation circuit 174 acquires the latest trajectory information from the overhead radio station 160 via the first communication circuit 171 and stores it in the storage device 173. Based on the acquired latest trajectory information, the calculation circuit 174 calculates the latest communication available time slot 10 for the overhead radio station 160 within the specified area.

[0055] The calculation circuit 174 acquires information on the communication time period 20 stored in the storage device 183 of the ground terminal station 180 from the ground terminal station 180 via the second communication circuit 172, and stores the acquired information in the storage device 173. The calculation circuit 174 calculates the communication time period 40 that overlaps between the communication time period 20 stored in the storage device 183 of the ground terminal station 180 and the latest communication time period 10.

[0056] The calculation circuit 174 notifies the overhead radio station 160 of the information on the overlapping communication available time slots 40 and the information on the latest communication available time slot 10 via the first communication circuit 171 .

[0057] FIG. 6 is a block diagram showing an example of the configuration of an overhead radio station 160 according to the first embodiment. Here, the case of a first-layer overhead radio station 110 will be described, but the same applies to overhead radio stations 160 in other layers. The intra-layer communication circuit 161 connects and communicates with a nearby first-layer overhead radio station 110 via intra-layer line 2. The base station communication circuit 162 connects and communicates with a terrestrial base station 140 via inter-base station line 5. The ground station communication circuit 163 connects and communicates with a terrestrial terminal station 180 via inter-ground station line 1. Note that there may be multiple inter-base station lines 5 and multiple inter-ground station lines 1, and MIMO wireless communication (Multiple-Input and Multiple-Output) may be used. The inter-network communication circuit 166 connects and communicates with nearby overhead radio stations 160 in other layers via inter-network line 3. The control station communication circuit 167 connects and communicates with a control station 170 via control line 6.

[0058] The control circuit 165 generates a notification signal including information on the latest communication time period 10 based on the information on the overlapping communication time period 40 received from the control station 170 and the information on the latest communication time period 10. Furthermore, when the overlapping communication time period 40 starts, the control circuit 165 causes the ground station communication circuit 163 to transmit a notification signal. Note that the notification signal may be transmitted via a control line (not shown) different from the inter-ground station line 1, or may be transmitted by another method.

[0059] 7 is a block diagram showing an example of the configuration of the ground terminal station 180 according to embodiment 1. When the communication available time period 20 stored in the storage device 183 starts, the control circuit 182 instructs the communication circuit 181 to wait for a notification signal from the overhead radio station 160. The control circuit 182 also updates the information on the communication available time period 20 stored in the storage device 183 with information on the latest communication available time period 10 included in the notification signal received by the communication circuit 181.

[0060] Furthermore, when the latest communication time slot 10 newly updated in the storage device 183 starts, the control circuit 182 sends an instruction to the communication circuit 181 to transmit data to the overhead radio station 160. The communication circuit 181 receives a notification signal from the overhead radio station 160 via the inter-ground station line 1 or a control line (not shown). The communication circuit 181 also notifies the control station 170 of the information on the communication time slot 20 stored in the storage device 183. The transmission data generation circuit 184 generates data to be transmitted and sends it to the communication circuit 181.

[0061] The processes performed by the control station 170, the airborne radio station 160, and the ground terminal station 180 described above may be executed by a program using a computer equipped with a CPU and memory and storing a wireless communication program in the memory. Alternatively, the processes may be executed by a program using an integrated circuit such as an FPGA (Field Programmable Gate Array). The wireless communication program may be provided by being recorded on a storage medium or via a network.

[0062] FIG. 8 is a diagram showing the hardware configuration of the control station 170 according to the first embodiment.

[0063] The control station 170 has the functions of a computer, with an input unit 70, an output unit 71, a communication unit 72, a CPU (Central Processing Unit, also called a processor) 73, a memory 74, and an HDD (Hard Disk Drive) 75 connected via a bus 76. The control station 170 is also capable of inputting and outputting data to and from a computer-readable storage medium 77.

[0064] The input unit 70 is, for example, a keyboard and a mouse. The output unit 71 is, for example, a display device. The communication unit 72 is, for example, a communication interface for communicating with the airborne radio station 160 and the ground terminal station 180.

[0065] The memory 74 may be, for example, a volatile or non-volatile semiconductor memory such as a RAM, a ROM, or a flash memory, or a magnetic disk, a flexible disk, an optical disk, a DVD, or the like.

[0066] The memory 74 and HDD 75 are the storage device 173 described above that stores data such as a wireless communication program, acquired orbit information, calculated information on the available communication time zone, and information on the available communication time zone 20 acquired from the ground terminal station 180 and stored in the storage device 183 of the ground terminal station 180. The CPU 73 controls each unit constituting the control station 170. The CPU 73 reads the wireless communication program stored in the memory 74 or the HDD 75 and executes predetermined processes including the process described in the flowchart of FIG. 4 .

[0067] The storage medium 77 is capable of storing a wireless communication program and the like that executes the functions of the control station 170. The storage medium 77 is a USB (Universal Serial Bus) memory, a CD-ROM (Compact Disc Read Only Memory), or the like.

[0068] The architecture that configures the control station 170 is not limited to the example shown in the figure.

[0069] 9 is a diagram showing the hardware configuration of an overhead radio station 160 according to embodiment 1. The overhead radio station 160 has an input unit 60, an output unit 61, a communication unit 62, a CPU 63, a memory 64, and an HDD 65 connected via a bus 66, and functions as a computer. The overhead radio station 160 is also capable of inputting and outputting data to and from a computer-readable storage medium 67.

[0070] The input unit 60 and the output unit 61 are similar to those of the control station 170, and therefore will not be described here. The communication unit 62 is a communication interface for communicating with, for example, other airborne radio stations 160, the control station 170, or the ground terminal station 180.

[0071] The memory 64 and HDD 65 are storage devices that store, for example, a wireless communication program, generated orbit information data, information on overlapping communication time periods 40 notified by the control station 170, and information on the latest communication time period 10. The CPU 63 controls each component of the overhead radio station 160. The CPU 63 reads the wireless communication program stored in the memory 64 or HDD 65 and executes predetermined processes including the process described in the flowchart of FIG. 4.

[0072] The description of the storage medium 67 will be omitted as it is the same as that of the control station 170. The architecture of the overhead radio station 160 is not limited to the example shown in the figure.

[0073] 10 is a diagram showing the hardware configuration of a ground terminal station 180 according to embodiment 1. The ground terminal station 180 has an input unit 80, an output unit 81, a communication unit 82, a CPU 83, a memory 84, and an HDD 85 connected via a bus 86, and functions as a computer. The ground terminal station 180 is also capable of inputting and outputting data to and from a computer-readable storage medium 87.

[0074] The input unit 80 and output unit 81 are similar to those of the control station 170, and therefore will not be described here. The communication unit 82 is a communication interface for communicating with the overhead radio station 160 and the control station 170, for example.

[0075] The memory 84 and HDD 85 are the storage device 183 described above that stores, for example, a wireless communication program and information on the latest communication available time period 10 included in the broadcast signal from the overhead radio station 160. The CPU 83 controls each component of the ground terminal station 180. The CPU 83 reads the wireless communication program stored in the memory 84 or the HDD 85 and executes predetermined processes including the process described in the flowchart of FIG.

[0076] The description of the storage medium 87 will be omitted as it is the same as that of the control station 170. The architecture constituting the ground terminal station 180 is not limited to the example shown in the figure.

[0077] As described above, in the wireless communication system 100 of the present disclosure, the communication time period 40 that overlaps the communication time period 20 stored in the storage device 183 of the ground terminal station 180 and the latest communication time period 10 is calculated. The overhead radio station 160 transmits a signal including information about the latest communication time period 10 during the overlapping communication time period 40. The overlapping communication time period 40 refers to the time period during which the ground terminal station 180 is waiting for a signal. Therefore, the overhead radio station can transmit a signal during the time period during which the ground terminal station is waiting.

[0078] <Variation 1> The process described as being performed by the control station 170 in the flowchart of FIG. 4 does not necessarily have to be performed by the control station 170. That is, it may be performed by at least one of the airborne radio station 160 and the terrestrial terminal station 180. Alternatively, the process described as being performed by the control station 170 in the flowchart of FIG. 4 may be performed by the terrestrial base station 140. In this case, the terrestrial base station 140 calculates the latest communication available time slots of the airborne radio station 160 in a specified area. Furthermore, the terrestrial base station 140 communicates with the terrestrial terminal station 180 in the specified area via a non-terrestrial network or the like, and acquires information on the communication available time slots stored in the storage device 183 of the terrestrial terminal station 180. Furthermore, the terrestrial base station 140 calculates information on the overlapping communication available time slots 40 and information on the latest communication available time slots 10, and notifies the airborne radio station 160 of the calculation results via a non-terrestrial network or the like. This achieves the same effect as described above.

[0079] <Variation 2> Note that, in the above description, the communication available time period 40 is calculated which overlaps between the communication available time period 20-1 stored in the first ground terminal station 180, the communication available time period 20-2 stored in the second ground terminal station 180, and the latest communication available time period 10. However, it is also possible to calculate the communication available time period 40 which overlaps between the communication available time period 20-1 stored in the first ground terminal station 180 and the communication available time period 20-2 stored in the second ground terminal station 180. In this case as well, it is possible to extract the time period in which both the first and second ground terminal stations 180 can receive the notification signal, and the same effect as described above can be obtained.

[0080] The present disclosure is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the spirit of the present disclosure. Furthermore, the embodiments and modifications may be implemented in appropriate combinations, in which case the combined effects can be obtained.

[0081] 1: Inter-ground station line, 2: Intra-layer line, 3: Inter-network line, 4: Intra-layer line, 5: Inter-base station line, 6: Control line, 8: Inter-network line, 10: Latest available communication time slot, 20: Available communication time slot stored in storage device of ground terminal station, 30: Non-transmission time slot, 40: Overlapping available communication time slots, 60: Input unit, 61: Output unit, 62: Communication unit, 63: CPU, 64: Memory, 65: HDD, 66: Bus, 67: Storage medium, 70: Input unit, 71: Output unit, 72: Communication unit, 73: CPU, 74: Memory, 75: HDD, 76: Bus, 77: Storage medium, 80: Input unit, 81: Output unit, 82: Communication unit, 83: CPU, 84: Memory, 85: HDD, 86 : bus, 87: storage medium, 100: wireless communication system, 110: first layer airborne radio station, 111: first airborne network, 120: second layer airborne radio station, 121: second airborne network, 130: third layer airborne radio station, 140: terrestrial base station, 160: airborne radio station, 161: intra-layer communication circuit, 162: base station communication circuit, 163: ground station communication circuit, 165: control circuit, 166: inter-network communication circuit, 167: control station communication circuit, 170: control station, 171: first communication circuit, 172: second communication circuit, 173: storage device, 174: calculation circuit, 180: ground terminal station, 181: communication circuit, 182: control circuit, 183: storage device, 184: transmission data generation circuit

Claims

1. A wireless communication system comprising: one or more terrestrial terminal stations located in a specified area; and an airborne radio station that moves on an orbit in the sky and is periodically capable of communicating with the specified area, wherein the system is configured to perform the following processes: calculate the latest available communication time slots in the specified area of ​​the airborne radio station; acquire information on available communication time slots stored in a memory device of the ground terminal station; and calculate overlapping communication time slots between the available communication time slots stored in the memory device of the ground terminal station and the latest available communication time slots; the airborne radio station is configured to perform the following processes: transmit a signal including information on the latest available communication time slots during the overlapping communication time slots; and the ground terminal station is configured to perform the following processes: wait for and receive the signal during the available communication time slots stored in the memory device; and update the available communication time slots stored in the memory device with the latest available communication time slots.

2. A control station configured to perform the following processes: calculating the latest communication time slots in a specified area for an airborne radio station that moves in an orbit above the ground and is periodically able to communicate with the specified area; acquiring information on communication time slots stored in a memory device of a ground terminal station located in the specified area; calculating communication time slots that overlap between the communication time slots stored in the memory device of the ground terminal station and the latest communication time slot; and notifying the airborne radio station of the information on the overlapping communication time slots and the latest communication time slot.

3. A wireless communication method comprising: calculating the latest available communication time slot in a specified area for an airborne radio station that moves on an orbit in the sky and is periodically able to communicate with the specified area; acquiring information on the available communication time slot stored in a memory device of a ground terminal station located in the specified area; calculating an overlapping communication time slot between the available communication time slot stored in the memory device of the ground terminal station and the latest available communication time slot; the airborne radio station transmitting a signal including information on the latest available communication time slot during the overlapping communication time slot; the ground terminal station waiting to receive the signal during the available communication time slot stored in the memory device; and the ground terminal station updating the available communication time slot stored in the memory device with the latest available communication time slot.

4. A wireless communication program to be executed by a control station, the program causing the control station to execute the following processes: calculating the latest communication time slots in a specified area for an airborne radio station that moves in an orbit above the ground and is periodically able to communicate with the specified area; acquiring information on communication time slots stored in a memory device of a ground terminal station present in the specified area; calculating communication time slots that overlap between the communication time slots stored in the memory device of the ground terminal station and the latest communication time slots; and notifying the airborne radio station of the information on the overlapping communication time slots and the latest communication time slots.

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