Satellite system and satellite communication method

Abstract

To provide a satellite system and a satellite communication method capable of suppressing communication congestion even in a state where communication between a satellite and a terminal is disconnected.SOLUTION: In a satellite system 22, each of one or more satellites 16 has: an acquisition unit 42 that acquires terminal position information transmitted from a communication terminal, via a wide area antenna 36; a determination unit 46 that determines timing when no terrestrial obstacle 54 exists between a narrow area antenna 38 and the communication terminal on the basis of behavior information 90, the terminal position information, and geographical information 92; and a communication unit 48 that communicates with the communication terminal via the narrow area antenna 38 at the timing when no obstacle 54 exists between the narrow area antenna 38 and the communication terminal, and that is on standby without communicating with the communication terminal at timing when there is an obstacle 54 between the narrow area antenna 38 and the communication terminal.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a satellite system and a satellite communication method for communicating with a communication terminal on the ground using one or more communication satellites. [Background technology]

[0002] In satellite communications, where a terrestrial terminal communicates directly with a communications satellite (hereinafter simply referred to as a satellite), communication between the terminal and the satellite can be interrupted. For example, when the terminal or the satellite moves, the radio waves transmitted from the terminal and the satellite can be blocked by obstacles such as mountains.

[0003] Patent Document 1 discloses a technology for controlling the antenna of a terminal when communication between a terrestrial terminal and a satellite is interrupted. In this technology, when communication between the terminal and the satellite is interrupted, the controller widens the beam width of the antenna to expand the reception area of ​​radio waves transmitted from the satellite. Furthermore, after receiving the radio waves, the controller narrows the beam width of the antenna and points the transmission and reception direction of the antenna toward the satellite. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3962025 Publication Summary of the Invention [Problem to be solved by the invention]

[0005] As in the technology of Patent Document 1, if communication continues even when communication between the terminal and the satellite is interrupted, congestion will occur in the communication line, which may result in a decrease in the communication speed of satellite communication.

[0006] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0007] A first aspect of the present invention is a satellite system that uses one or more satellites to communicate with a communication terminal for satellite communication on the ground, wherein the one or more satellites include a wide-area antenna with low gain and a wide communication area on the ground, a narrow-area antenna with high gain and a narrow communication area on the ground, a memory unit that stores terrain information that indicates the three-dimensional shape of the ground and behavior information that indicates the behavior of the satellite, an acquisition unit that acquires terminal position information that indicates the position of the communication terminal transmitted from the communication terminal via the wide-area antenna, a determination unit that determines a timing when no obstacle on the ground exists between the narrow-area antenna and the communication terminal based on the behavior information, the terminal position information, and the terrain information, and a communication unit that communicates with the communication terminal via the narrow-area antenna when no obstacle exists between the narrow-area antenna and the communication terminal, and that waits without communicating with the communication terminal when the obstacle exists between the narrow-area antenna and the communication terminal.

[0008] A second aspect of the present invention is a satellite communication method for communicating with a communication terminal for satellite communication on the ground using one or more satellites, wherein the one or more satellites comprise a wide-area antenna with low gain and a wide communication area on the ground, a narrow-area antenna with high gain and a narrow communication area on the ground, a memory unit that stores terrain information indicating the three-dimensional shape of the ground and behavior information indicating the behavior of the satellite, and one or more processors, and the one or more processors perform the following steps: acquiring terminal position information indicating the position of the communication terminal transmitted from the communication terminal via the wide-area antenna; determining, based on the behavior information, the terminal position information and the terrain information, a timing when no obstacle on the ground exists between the narrow-area antenna and the communication terminal; communicating with the communication terminal via the narrow-area antenna when no obstacle exists between the narrow-area antenna and the communication terminal, and waiting without communicating with the communication terminal when the obstacle exists between the narrow-area antenna and the communication terminal. [Effects of the Invention]

[0009] According to the present invention, congestion on communication lines can be prevented. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a configuration diagram of a communication system according to the first embodiment. [Figure 2] FIG. 2 is a configuration diagram of a satellite system according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing the communication areas of the antennas. [Figure 4] FIG. 4 is a sequence diagram showing the processing performed by the satellite and the first terminal. [Figure 5] FIG. 5 is a diagram showing a situation where there is an obstacle between the future position of the satellite and the terminal position of the first terminal, and a situation where there is no obstacle between the future position of the satellite and the terminal position of the first terminal. [Figure 6] FIG. 6 is a diagram showing the change in the transmission and reception direction of the narrow-area antenna as the satellite moves. [Figure 7] FIG. 7 is a diagram showing changes in the transmission and reception directions of the narrow band antenna as the first terminal moves. [Figure 8] FIG. 8 is a flowchart showing the processing that the satellite's computing device performs in parallel with the processing of step S7 in FIG. [Figure 9] FIG. 9 is a configuration diagram of a communication system according to the second embodiment. [Figure 10] FIG. 10 is a configuration diagram of a satellite system according to the second embodiment. [Figure 11] FIG. 11 is a sequence diagram showing the processing performed by the first satellite, the second satellite, and the first terminal. DETAILED DESCRIPTION OF THE INVENTION

[0011] [1 First Embodiment] [1-1 Configuration of communication system 10] 1 is a configuration diagram of a communication system 10 according to the first embodiment. The communication system 10 according to the first embodiment includes a first terminal 12, a second terminal 14, a plurality of satellites 16, an earth station 18, and a communication network 20. In this specification, the one or more satellites 16 are also referred to as a satellite system 22. In the communication system 10 shown in FIG. 1, the satellite system 22, the earth station 18, and the communication network 20 form a communication link between the first terminal 12 and the second terminal 14.

[0012] The first terminal 12 is a communication terminal capable of directly communicating with the satellite 16, such as a satellite phone. For example, the first terminal 12 is a mobile terminal that can be carried by a user. The first terminal 12 has a function of measuring its own position using satellite navigation, inertial navigation, or the like. For example, the first terminal 12 has a GNSS receiver. Alternatively, the first terminal 12 may have a three-axis acceleration sensor or the like. Before communicating with the second terminal 14, the first terminal 12 transmits terminal position information to the satellite 16. The terminal position information is information indicating the position of the first terminal 12. Note that the first terminal 12 need not be a mobile terminal, but may be a fixed terminal fixed in a fixed position.

[0013] The second terminal 14 may be a mobile terminal such as a mobile phone, or may be a fixed terminal such as a landline phone. Note that the second terminal 14 may also be a communication terminal that can directly communicate with the satellite 16, similar to the first terminal 12.

[0014] The satellites 16 are communication satellites that relay information transmitted from the first terminal 12 to the second terminal 14 and information transmitted from the second terminal 14 to the first terminal 12. Two satellites 16 (satellite 16a, satellite 16b) are shown in FIG. 1. However, the number of satellites 16 may be one, or three or more. At least satellite 16a is required. When there are multiple satellites 16, the satellites 16 can communicate with each other. The satellite 16a and the first terminal 12 can communicate with each other. The satellite 16b and the earth station 18 can communicate with each other.

[0015] The earth station 18 is a base station installed on the ground 24. The communication network 20 is a communication infrastructure on the ground 24 connected to the earth station 18. As described above, if the second terminal 14 is a communication terminal that can communicate directly with the satellite 16, the earth station 18 and the communication network 20 may not be necessary. Alternatively, two earth stations 18 may be connected by the communication network 20.

[0016] [1-2 Configuration of Satellite System 22] Figure 2 is a configuration diagram of a satellite system 22 according to the first embodiment. Figure 2 shows one satellite 16a as the satellite system 22. The satellite 16a communicates with the first terminal 12. The satellite 16a has a processing unit 28, a storage device 30, a positioning device 32, a transponder 34, a wide-area antenna 36, ​​a narrow-area antenna 38, and an inter-satellite antenna 40. The satellite 16a also has a clock (not shown).

[0017] The arithmetic device 28 has a processing circuit. The processing circuit may be a processor such as a CPU or a GPU. The processing circuit may be an integrated circuit such as an ASIC or an FPGA. The processor is capable of performing various processes by executing programs stored in the storage device 30. In the first embodiment, the arithmetic device 28 functions as an acquisition unit 42, a setting unit 44, a determination unit 46, a communication unit 48, and a selection unit 50. At least some of the processes may be performed by electronic circuits including discrete devices.

[0018] The acquisition unit 42 acquires various information. For example, the acquisition unit 42 acquires terminal location information transmitted from the first terminal 12 via the wide-area antenna 36 and the transponder 34. The setting unit 44 sets the transmission and reception direction of the narrow-area antenna 38 to the direction in which the first terminal 12 is located. The determination unit 46 determines the timing when the satellite 16a and the first terminal 12 can communicate with each other and the timing when the satellite 16a and the first terminal 12 cannot communicate with each other. The communication unit 48 performs various types of communication. For example, the communication unit 48 communicates with the first terminal 12 via the narrow-area antenna 38. The selection unit 50 selects one other satellite from multiple other satellites.

[0019] The storage device 30 has a volatile memory and a non-volatile memory. Examples of the volatile memory include RAM. The volatile memory is used as a working memory for the processor. The volatile memory temporarily stores data required for processing or calculation. Examples of the non-volatile memory include ROM and flash memory. The non-volatile memory is used as a storage memory. The non-volatile memory stores programs, tables, maps, etc. At least a part of the storage device 30 may be provided in the processor, integrated circuit, etc. as described above.

[0020] The nonvolatile memory stores behavior information 90 for each satellite 16 that constitutes the satellite system 22. The behavior information 90 includes position information indicating the orbital position of the satellite 16 and time information indicating the time at which the satellite 16 passes each point on the orbit. The nonvolatile memory also stores topographical information 92 that indicates the three-dimensional shape of the Earth 24.

[0021] The positioning device 32 measures the position and attitude of the satellite 16a. For example, the positioning device 32 includes a three-axis acceleration sensor. The positioning device 32 may further include a GNSS receiver.

[0022] The transponder 34 includes a transmitter and a receiver. For example, the transponder 34 amplifies the signal of information received by the narrow-area antenna 38 and transmits it from the inter-satellite antenna 40. The transponder 34 amplifies the signal of information received by the inter-satellite antenna 40 and transmits it from the narrow-area antenna 38.

[0023] The wide-area antenna 36 and the narrow-area antenna 38 are antennas for communicating with the ground 24. The gain of the wide-area antenna 36 is lower than the gain of the narrow-area antenna 38. That is, the wide-area antenna 36 has a low gain, and the narrow-area antenna 38 has a high gain. Therefore, the narrow-area antenna 38 can transmit and receive larger amounts of information than the wide-area antenna 36. Also, as shown in FIG. 3 , the communication area WA of the wide-area antenna 36 on the ground 24 is wider than the communication area NA of the narrow-area antenna 38 on the ground 24. That is, the communication area WA of the wide-area antenna 36 is wider, and the communication area NA of the narrow-area antenna 38 is narrower. The narrow-area antenna 38 is an antenna capable of beamforming, such as a phased array antenna. Note that an attitude adjustment mechanism that changes the attitude of the narrow-area antenna 38 may change the transmission and reception direction of the narrow-area antenna 38. On the other hand, the inter-satellite antenna 40 is an antenna for performing inter-satellite communication with other satellites 16.

[0024] [1-3 Communication processing in communication system 10] Fig. 4 is a sequence diagram showing the processing performed by the satellite 16a and the first terminal 12. When the user performs a predetermined operation on the first terminal 12, the series of processing shown in Fig. 4 starts.

[0025] In step S1, the first terminal 12 acquires terminal location information using a GNSS receiver, etc. The first terminal 12 measures its own location periodically or constantly.

[0026] In step S2, the first terminal 12 transmits (uploads) the terminal location information to the satellite 16a. The first terminal 12 may process the terminal location information into low-volume information and transmit it to the satellite 16a. The first terminal 12 transmits the terminal location information using a communication method that is resistant to noise. For example, the first terminal 12 uses BPSK as the modulation method for the carrier wave. A carrier wave modulated by BPSK is resistant to noise, although the amount of information transmitted is limited to a small amount. The first terminal 12 also narrows the bandwidth of the carrier wave. A narrow-band carrier wave is resistant to noise.

[0027] In step S3, the communication unit 48 of the satellite 16a receives the terminal location information via the wide area antenna 36 and the transponder 34. As a result, the acquisition unit 42 of the satellite 16a acquires the terminal location information. The communication area WA covered by the wide area antenna 36 is large. Therefore, the wide area antenna 36 can receive terminal location information transmitted from various locations.

[0028] In step S4, the determination unit 46 of the satellite 16a determines the timing when the satellite 16a and the first terminal 12 can communicate with each other. The determination unit 46 determines whether the satellite 16a and the first terminal 12 can communicate with each other based on whether an obstacle 54 exists between the satellite 16a and the first terminal 12. FIG. 5 is a diagram showing situations where an obstacle 54 exists between the future position Ps of the satellite 16a and the terminal position pt of the first terminal 12 and situations where an obstacle 54 does not exist between the future position Ps of the satellite 16a and the terminal position pt of the first terminal 12. The future position Ps refers to a position on the orbit through which the satellite 16a will pass. In FIG. 5, an obstacle 54 (such as a mountain) exists on the straight-line path 52a connecting the future position Ps1 and the terminal position pt. On the other hand, no obstacle 54 exists on the straight-line path 52b connecting the future position Ps2 and the terminal position pt. The determination unit 46 identifies each future position Ps based on the orbital position information included in the behavior information 90. The determination unit 46 determines, for each future position Ps, whether a straight-line path 52 connecting the future position Ps and the terminal position pt overlaps with the ground 24 (i.e., an obstacle 54). The determination unit 46 may set a predetermined width for the straight-line path 52. The determination unit 46 distinguishes between and extracts a future position Ps (Ps2) where the straight-line path 52 does not overlap with the ground 24 and a future position Ps (Ps1) where the straight-line path 52 overlaps with the ground 24. This allows the determination unit 46 to determine the range on the trajectory where the straight-line path 52 does not overlap with the ground 24 and the range on the trajectory where the straight-line path 52 overlaps with the ground 24. In the behavior information 90, each point on the trajectory is associated with a passage time. Therefore, the determination unit 46 can determine the timing (time period) when an obstacle 54 exists between the narrow-area antenna 38 and the first terminal 12 and the timing (time period) when an obstacle 54 does not exist between the narrow-area antenna 38 and the first terminal 12. In this way, the determination unit 46 determines the timing when the satellite 16a and the first terminal 12 can communicate with each other and the timing when the satellite 16a and the first terminal 12 cannot communicate with each other.

[0029] In step S5, the communication unit 48 of the satellite 16a transmits timing information indicating the timing when communication is possible to the first terminal 12 via the wide-area antenna 36 and the transponder 34.

[0030] In step S6, the first terminal 12 acquires (receives) timing information. In response to acquiring the timing information, the first terminal 12 notifies the user of the timing at which communication is possible. This allows the user to recognize the timing at which communication using the first terminal 12 is possible.

[0031] In step S7, the acquisition unit 42 of the satellite 16a acquires satellite position information and satellite attitude information from the positioning device 32. The satellite attitude information is information that indicates the attitude of the satellite 16a. The setting unit 44 sets the transmission and reception direction of the narrow-area antenna 38 based on the satellite position information, satellite attitude information, and terminal position information. For example, the setting unit 44 calculates the direction in which the first terminal 12 is located in a coordinate system with the narrow-area antenna 38 as the origin. After the calculation, the setting unit 44 sets the transmission and reception direction of the narrow-area antenna 38 to the calculated direction (the direction in which the first terminal 12 is located).

[0032] In step S8, the satellite 16a and the first terminal 12 communicate with each other via the narrow-area antenna 38. The communication unit 48 controls the transponder 34 to perform beamforming in the direction where the first terminal 12 is located. The communication unit 48 receives information transmitted from the first terminal 12 via the narrow-area antenna 38 and the transponder 34. The information transmitted from the first terminal 12 is received by the second terminal 14 via the satellite 16a, satellite 16b, earth station 18, and communication network 20. Meanwhile, the communication unit 48 transmits information transmitted from the second terminal 14 to the first terminal 12 via the narrow-area antenna 38 and the transponder 34. The information transmitted from the second terminal 14 is received by the first terminal 12 via the communication network 20, earth station 18, satellite 16b, and satellite 16a. The communication between the satellite 16a and the first terminal 12 is performed using a modulation method such as QAM. A carrier wave modulated by QAM is vulnerable to noise, but can transmit large amounts of information.

[0033] As described above, the communication unit 48 of the satellite 16 and the first terminal 12 communicate with each other when communication is possible. On the other hand, the communication unit 48 of the satellite 16 and the first terminal 12 wait without communicating until a communication possible time arrives.

[0034] 6 is a diagram showing changes in the transmission and reception direction of the narrow-area antenna 38 as the satellite 16a moves. The satellite 16a moves along a predetermined orbit. As the satellite 16a moves, the relative position between the satellite 16a and the first terminal 12 changes. This may cause a misalignment between the transmission and reception direction of the narrow-area antenna 38 and the direction in which the first terminal 12 is located. To prevent this, the setting unit 44 of the satellite 16a periodically performs the process of step S7 in FIG. 4 to reset the transmission and reception direction of the narrow-area antenna 38.

[0035] FIG. 7 is a diagram showing changes in the transmission and reception direction of the narrow-area antenna 38 as the first terminal 12 moves. The first terminal 12 may move. As the first terminal 12 moves, the relative position of the satellite 16a and the first terminal 12 changes. In this case, there is also a possibility that a misalignment will occur between the transmission and reception direction of the narrow-area antenna 38 and the direction in which the first terminal 12 is located. To prevent this, the acquisition unit 42 of the satellite 16a may periodically or constantly acquire terminal location information from the first terminal 12 during the processing of step S8 in FIG. 4. Furthermore, the setting unit 44 of the satellite 16a may reset the transmission and reception direction of the narrow-area antenna 38 based on the acquired terminal location information.

[0036] However, if the change in the relative position between the satellite 16a and the first terminal 12 is large, there is a possibility that the satellite 16a and the first terminal 12 will not be able to communicate with each other even if the setting unit 44 resets the transmission and reception direction of the narrow area antenna 38. In other words, there is a possibility that the position of the first terminal 12 will be outside the communication area NA of the narrow area antenna 38.

[0037] Fig. 8 is a flowchart showing the processing that the processing device 28 of the satellite 16a performs in parallel with the processing of step S8 in Fig. 4. The series of processing shown in Fig. 8 is performed to maintain communication between the first terminal 12 and the second terminal 14.

[0038] In step S11, the communication unit 48 of the satellite 16a determines whether there is information to be transmitted from the first terminal 12 or the second terminal 14. If there is information to be transmitted (step S11: YES), the process proceeds to step S12. On the other hand, if there is no information to be transmitted (step S11: NO), the process ends. In this case, communication between the first terminal 12 and the second terminal 14 ends.

[0039] When the process proceeds from step S11 to step S12, the selection unit 50 of the satellite 16a determines whether mutual communication between the satellite 16a and the first terminal 12 is possible. The selection unit 50 identifies the position of the satellite 16a after a predetermined time based on the behavior information 90 of the satellite 16a stored in the storage device 30. Furthermore, the selection unit 50 calculates the communication area NA of the narrow area antenna 38 after the predetermined time. The selection unit 50 determines whether the first terminal 12 will be located within the communication area NA of the narrow area antenna 38 after the predetermined time. If the first terminal 12 is located within the communication area NA of the narrow area antenna 38 (step S12: YES), the process returns to step S11. On the other hand, if the first terminal 12 is not located within the communication area NA of the narrow area antenna 38 (step S12: NO), the process proceeds to step S13.

[0040] When the process proceeds from step S12 to step S13, the selection unit 50 of the satellite 16a selects, from among a plurality of other satellites (not shown) having the same configuration as the satellite 16a, a satellite to take over communication with the first terminal 12. For example, the selection unit 50 predicts the future position Ps of each other satellite based on behavior information 90 of each other satellite stored in the storage device 30. Furthermore, the selection unit 50 selects other satellites that will pass above the first terminal 12 within a predetermined time based on each predicted position and the terminal position information.

[0041] In step S14, the communication unit 48 of the satellite 16a transmits the terminal location information to the other satellite selected in step S13 via the inter-satellite antenna 40 and the transponder 34. This allows the other satellite to take over communication with the first terminal 12 from the satellite 16a.

[0042] In the first embodiment, the satellite 16a communicates with the first terminal 12 using a wide-area antenna 36 and a narrow-area antenna 38. Although the gain of the wide-area antenna 36 is low, the communication area WA of the wide-area antenna 36 is wide. Therefore, by using the wide-area antenna 36, ​​the satellite 16a can receive a small amount of information (terminal location information) from a wide area. On the other hand, although the communication area NA of the narrow-area antenna 38 is narrow, the gain of the narrow-area antenna 38 is high. Therefore, by using the narrow-area antenna 38, the satellite 16a can transmit a large amount of information to the first terminal 12 and receive a large amount of information from the first terminal 12.

[0043] In the first embodiment, the satellite 16a acquires terminal location information of the first terminal 12 using the wide-area antenna 36, ​​and sets the transmission and reception direction of the narrow-area antenna 38 based on the terminal location information. Therefore, according to the first embodiment, the satellite 16a can communicate with the first terminal 12 using the narrow-area antenna 38 regardless of the location of the first terminal 12. In other words, according to the first embodiment, the satellite 16a can be used with both fixed and mobile communication terminals, and is highly versatile.

[0044] In the first embodiment, the satellite 16a communicates when communication is possible, and waits without communicating when communication is difficult. Therefore, according to the first embodiment, congestion of the communication line can be prevented.

[0045] In the first embodiment, the satellite 16a notifies the first terminal 12 of the timing when communication is possible. As a result, the first terminal 12 can communicate when communication is possible, and can wait without communicating when communication is difficult. Therefore, according to the first embodiment, it is possible to reduce the power consumption of the first terminal 12.

[0046] In the first embodiment, the satellite 16a can hand over communication to another satellite, so that the first terminal 12 and the second terminal 14 can continue communication for a long period of time.

[0047] [2 Second Embodiment] [2-1 Configuration of communication system 10] 9 is a configuration diagram of a communication system 10 according to the second embodiment. The communication system 10 according to the second embodiment includes a first terminal 12, a second terminal 14, multiple satellites 16, an earth station 18, and a communication network 20. In the communication system 10 according to the second embodiment, the functions of the single satellite 16a in the first embodiment are distributed to two satellites 16 (a first satellite 16a-1 and a second satellite 16a-2). Note that there are multiple second satellites 16a-2, and one second satellite 16a-2 is selected from the multiple second satellites 16a-2.

[0048] FIG. 10 is a configuration diagram of a satellite system 22 according to the second embodiment. FIG. 10 shows a first satellite 16a-1 and a second satellite 16a-2 as the satellite system 22. In this specification, the same reference numerals are used to designate components of the second embodiment that are the same as those of the first embodiment. Note that the first satellite 16a-1 and the second satellite 16a-2 of the second embodiment each have the same configuration as the satellite 16a of the first embodiment. The same components of the first satellite 16a-1 as those of the satellite 16a are assigned the same reference numerals as those of the satellite 16a plus "-1." Similarly, the same components of the second satellite 16a-2 as those of the satellite 16a are assigned the same reference numerals as those of the satellite 16a plus "-2."

[0049] The first satellite 16a-1 has a processing unit 28-1, a storage device 30-1, a transponder 34-1, a wide-area antenna 36-1, and an inter-satellite antenna 40-1. The processing unit 28-1 of the first satellite 16a-1 functions as an acquisition unit 42-1, a determination unit 46-1, a communication unit 48-1, and a selection unit 50-1. The communication unit (transmitter) 48-1 transmits timing information to the first terminal 12 via the inter-satellite antenna 40. The selection unit 50-1 selects one second satellite 16a-2 from among multiple second satellites 16a-2.

[0050] The second satellite 16a-2 includes a calculation unit 28-2, a storage device 30-2, a positioning device 32-2, a transponder 34-2, a narrow-area antenna 38-2, and an inter-satellite antenna 40-2. The calculation unit 28-2 of the second satellite 16a-2 functions as an acquisition unit 42-2, a setting unit 44-2, a communication unit 48-2, and a selection unit 50-2.

[0051] [2-2 Communication Processing in Communication System 10] Fig. 11 is a sequence diagram showing the processing performed by the first satellite 16a-1, the second satellite 16a-2, and the first terminal 12. When the user performs a predetermined operation on the first terminal 12, the series of processing shown in Fig. 11 is started.

[0052] The processing of steps S21 to S23 is the same as the processing of steps S1 to S3 shown in Fig. 4. However, the processing of step S23 is mainly performed by the acquisition unit 42-1 of the first satellite 16a-1.

[0053] In step S24, the selection unit 50-1 of the first satellite 16a-1 selects a second satellite 16a-2 from the multiple second satellites 16a-2 that will communicate with the first terminal 12. For example, the selection unit 50-1 predicts the future position Ps of each second satellite 16a-2 based on the behavior information 90-2 of each second satellite 16a-2 stored in the storage device 30-1. Furthermore, the selection unit 50-1 selects a second satellite 16a-2 that will pass above the first terminal 12 within a predetermined time based on each predicted position and the terminal position information.

[0054] The processing of steps S25 to S27 is the same as the processing of steps S4 to S6 shown in Fig. 4. However, the processing of step S25 is performed mainly by the determination unit 46-1 of the first satellite 16a-1, and the processing of step S26 is performed mainly by the communication unit 48-1 of the first satellite 16a-1.

[0055] In step S28, the communication unit 48-1 of the first satellite 16a-1 transmits the terminal position information and timing information to the second satellite 16a-2 via the inter-satellite antenna 40-1 and the transponder 34-1.

[0056] In step S29, the communication unit 48-2 of the second satellite 16a-2 acquires (receives) the terminal position information and timing information via the inter-satellite antenna 40-2 and the transponder 34-2. As a result, the acquisition unit 42-2 of the second satellite 16a-2 acquires the terminal position information and timing information.

[0057] The processing in steps S30 and S31 is the same as the processing in steps S7 and S8 shown in Fig. 4. However, the processing in step S30 is mainly performed by the setting unit 44-2 of the second satellite 16a-2. In addition, in step S31, the second satellite 16a-2 and the first terminal 12 communicate with each other via the narrowband antenna 38. The communication unit 48-2 of the second satellite 16a-2 controls the transponder 34-2 to perform beamforming in the direction where the first terminal 12 is located.

[0058] The basic functions of the second embodiment are the same as those of the first embodiment, and therefore the second embodiment has the same effects as the first embodiment.

[0059] [3 Inventions Obtained from the Embodiments] The invention that can be understood from the above embodiment will be described below.

[0060] A first aspect of the present invention is a satellite system (22) that uses one or more satellites (16) to communicate with a communication terminal (12) for satellite communication on the ground (24), wherein the one or more satellites include a wide-area antenna (36, 36-1) with low gain and a wide terrestrial communication area (WA), a narrow-area antenna (38, 38-2) with high gain and a narrow terrestrial communication area (NA), a storage unit (30) that stores topographical information (92) indicating the three-dimensional shape of the ground and behavioral information (90) indicating the behavior of the satellite, and a storage unit (30) that stores terminal position information indicating the position of the communication terminal transmitted from the communication terminal in the wide-area antenna (36, 36-1). The communication device includes an acquisition unit (42, 42-1) that acquires information via an antenna, a determination unit (46, 46-1) that determines the timing when no ground obstacle (54) exists between the narrow-area antenna and the communication terminal based on the behavior information, the terminal position information, and the topographical information, and a communication unit (48, 48-2) that communicates with the communication terminal via the narrow-area antenna when no obstacle exists between the narrow-area antenna and the communication terminal, and that waits without communicating with the communication terminal when the obstacle exists between the narrow-area antenna and the communication terminal.

[0061] According to the above configuration, the satellite communicates when communication is possible, and waits without communicating when communication is difficult, thereby preventing congestion on communication lines.

[0062] In the first aspect, one of the satellites may include the wide-area antenna, the narrow-area antenna, the storage unit, the acquisition unit, the determination unit, and the communication unit.

[0063] In the first aspect, the communication unit may transmit timing information indicating a timing when the obstacle does not exist between the narrow-area antenna and the communication terminal to the communication terminal via the wide-area antenna.

[0064] In a first aspect, a first satellite (16a-1) of the plurality of satellites may be equipped with each of the wide-area antenna, the memory unit, the acquisition unit, and the determination unit, and a second satellite (16a-2) of the plurality of satellites may be equipped with each of the narrow-area antenna and the communication unit, and the first satellite and the second satellite may be capable of communicating with each other.

[0065] In a first aspect, the first satellite may include a transmitter (48-1) that transmits timing information indicating a timing when the obstacle does not exist between the narrow-area antenna and the communication terminal to the communication terminal via the wide-area antenna.

[0066] According to the above configuration, the communication terminal can communicate when communication is possible, and can wait without communicating when communication is difficult, thereby making it possible to reduce power consumption of the communication terminal.

[0067] A second aspect of the present invention is a satellite communication method for communicating with a communication terminal for satellite communication on the ground using one or more satellites, wherein the one or more satellites are provided with a wide-area antenna with low gain and a wide communication area on the ground, a narrow-area antenna with high gain and a narrow communication area on the ground, a storage unit that stores topographical information indicating a three-dimensional shape of the ground and behavioral information indicating behavior of the satellite, and one or more processors (28, 28-1, 28-2), and the one or more processors convert terminal position information indicating the position of the communication terminal transmitted from the communication terminal into terminal position information of the wide-area antenna. The method includes steps (S3, S23) of acquiring the behavior information, the terminal position information, and the topographical information via an antenna; steps (S4, S25) of determining the timing when no obstacles on the ground exist between the narrow-area antenna and the communication terminal based on the behavior information, the terminal position information, and the topographical information; and steps (S8, S31) of communicating with the communication terminal via the narrow-area antenna when no obstacles exist between the narrow-area antenna and the communication terminal, and waiting without communicating with the communication terminal when an obstacle exists between the narrow-area antenna and the communication terminal.

[0068] According to the above configuration, the same effects as those of the first aspect can be obtained.

[0069] The present invention is not limited to the above disclosure, and various configurations can be adopted without departing from the gist of the present invention. [Explanation of symbols]

[0070] 12...First terminal (communication terminal) 16, 16a, 16b...Satellite 16a-1...1st satellite 16a-2...2nd satellite 22...Satellite system 24...Terrestrial 28, 28-1, 28-2...Processor 30...Memory device (memory unit) 36...Wide-area antenna 38...narrow-area antenna 42, 42-1...acquisition unit 46, 46-1...Judgment section 48, 48-2...Communication section 48-1...Communication unit (transmitter) 54...Obstacle 90...Behavior information 92...Terrain information NA, WA...Communication area

Claims

1. A satellite system that uses one or more satellites to communicate with a communication terminal for satellite communication on the ground, One or more of the satellites A low-gain wide-area antenna with a wide ground communication area, A high-gain narrow-area antenna with a narrow ground communication area, a storage unit that stores topographical information indicating a three-dimensional shape of the ground and behavioral information indicating behavior of the satellite; an acquisition unit that acquires, via the wide area antenna, terminal location information indicating a location of the communication terminal transmitted from the communication terminal; a determination unit that determines a timing when no obstacle on the ground exists between the narrow-area antenna and the communication terminal based on the behavior information, the terminal position information, and the topographical information; a communication unit that communicates with the communication terminal via the narrow band antenna when the obstacle does not exist between the narrow band antenna and the communication terminal, and that waits without communicating with the communication terminal when the obstacle exists between the narrow band antenna and the communication terminal; A satellite system comprising:

2. 2. The satellite system of claim 1, one of the satellites includes the wide-area antenna, the narrow-area antenna, the storage unit, the acquisition unit, the determination unit, and the communication unit; Satellite system.

3. 3. The satellite system of claim 2, the communication unit transmits timing information indicating a timing when the obstacle does not exist between the narrow-area antenna and the communication terminal to the communication terminal via the wide-area antenna; Satellite system.

4. 2. The satellite system of claim 1, a first satellite among the plurality of satellites includes the wide-area antenna, the storage unit, the acquisition unit, and the determination unit; a second satellite among the plurality of satellites includes the narrow-area antenna and the communication unit, the first satellite and the second satellite are capable of communicating with each other; Satellite system.

5. 5. A satellite system according to claim 4, the first satellite includes a transmitter that transmits timing information indicating a timing when the obstacle does not exist between the narrow-area antenna and the communication terminal to the communication terminal via the wide-area antenna; Satellite system.

6. A satellite communication method for communicating with a communication terminal for satellite communication on the ground using one or more satellites, comprising: One or more of the satellites A low-gain wide-area antenna with a wide ground communication area, A high-gain narrow-area antenna with a narrow ground communication area, a storage unit that stores topographical information indicating a three-dimensional shape of the ground and behavioral information indicating behavior of the satellite; one or more processors; One or more of the processors acquiring, via the wide area antenna, terminal location information indicating the location of the communication terminal transmitted from the communication terminal; determining a timing when no obstacle on the ground exists between the narrow-area antenna and the communication terminal based on the behavior information, the terminal position information, and the topographical information; a step of communicating with the communication terminal via the narrow band antenna when the obstacle is not present between the narrow band antenna and the communication terminal, and waiting without communicating with the communication terminal when the obstacle is present between the narrow band antenna and the communication terminal; A satellite communication method.

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