Communication device, communication method, and communication system

Abstract

Provided is a communication device which operates as a satellite receiver station that orbits the earth and that receives frames from terminals on the ground.　The communication device comprises: a receiving unit which performs a process for receiving a frame from a terminal; and a determination unit which exchanges, with a nearby satellite receiver station, frame reception information at the time when a frame is received from a terminal and determines a satellite receiver station that is suitable for receiving the frame to be transmitted next by the terminal, said communication device operating as one of satellite receiver stations that orbit the earth in a predetermined orbit and that receive frames from terminals on the ground. The communication device provides notification, to another satellite receiver station which is ahead in the same orbit, of information pertaining to frames which have been received from a terminal by each of the satellite receiver stations in the same orbit.

Description

Technical Field

[0001] The technology disclosed in this specification (hereinafter referred to as "the present disclosure") relates to a communication device and a communication method for receiving a frame wirelessly transmitted from a terminal, and a communication system including a terminal and a receiving station.

Background Art

[0002] In a wireless sensor network, by attaching a wireless sensor terminal to a person or an object and periodically transmitting the information acquired from the sensor, it becomes possible to create a new service. For example, by attaching a wireless sensor terminal with GPS (Global Positioning System) to an elderly person or a child and periodically transmitting the position information, a monitoring service becomes possible.

[0003] In such a wireless communication system for IoT (Internet of Things), it is necessary to enable communication with a large number of wireless sensor terminals attached to various people and objects, and long-distance transmission enabling wide-area communication and multi-terminal accommodation enabling communication with many terminals per base station become important. In recent years, LPWA (Low Power Wide Area), regarded as a promising wireless communication method for IoT, enables long-distance transmission and multi-terminal accommodation, and realizes long-distance transmission of several kilometers to several hundred kilometers between a terminal and a receiving station installed on the ground. However, the installation of a receiving station requires securing of land and laying of a network for cloud connection, etc., which is costly and time-consuming, thus hindering cost reduction of communication services and expansion of communication areas.

[0004] On the other hand, in recent years, private companies have been actively engaged in space development. Conventionally, it has been necessary to spend tens of billions of yen for launching a satellite, but development is progressing aiming at cost reduction to one-tenth to one-hundredth. Also, the miniaturization of satellites is progressing, and by launching a plurality of satellites at once and constructing a constellation, realization of a service covering the entire earth is being considered.

[0005] With the realization of satellite services, as a method of expanding the communication area of LPWA, a method of mounting a receiver on a satellite and receiving radio waves transmitted from a ground terminal on the satellite can be considered. LPWA has achieved communication over several hundred kilometers even on the ground, and it is considered that communication is possible with low-earth orbit satellites (see, for example, Patent Document 1). In addition, since low-earth orbit satellites orbit the earth, in use cases such as IoT that transmit data once every few minutes to several days, it is possible to cover the entire earth with a small number of satellites. Therefore, mounting a receiver on a satellite reduces costs compared to installing many receiving stations on the ground, and it is expected to reduce the cost of communication services and quickly expand the communication area. In addition, it becomes possible to acquire information from the ocean where it is difficult to install receiving stations on the ground, and it becomes possible to provide new services.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Non-Patent Documents

[0007]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] An object of the present disclosure is to provide a communication device and a communication method that operate as a satellite receiving station that orbits the earth on a predetermined orbit and receives a frame from a ground terminal, and a communication system including the ground terminal and the satellite receiving station.

Means for Solving the Problems

[0009] A first aspect of the present disclosure operates as one of satellite receiving stations that orbit the earth on a predetermined orbit and receive a frame from a ground terminal. A receiving unit that receives and processes frames from the terminal, A determination unit that exchanges frame reception information at the time of frame reception from the terminal with surrounding satellite receiving stations, and determines a satellite receiving station suitable for receiving a frame to be transmitted next by the terminal, It is a communication device comprising.

[0010] The communication device according to the first aspect notifies information regarding frames received by each satellite receiving station on the same orbit from the terminal to the satellite receiving station in front on the same orbit. Further, the communication device according to the first aspect notifies information regarding received frames for each terminal within a range corresponding to the maximum number of satellite receiving stations on the same orbit that can simultaneously receive frames from the same terminal.

[0011] The communication device according to the first aspect notifies information regarding the terminal from which each satellite receiving station on the adjacent orbit has received a frame to the satellite receiving stations located at approximately the same latitude on the adjacent orbit. Further, the communication device according to the first aspect determines the satellite receiving stations for which the notification is to be made in consideration of whether the traveling directions of the satellite receiving stations on the adjacent orbit are the same or different, and notifies information regarding each terminal within a range corresponding to the maximum number of orbits that can simultaneously receive frames from the same terminal at the position (latitude) at the time of frame reception.

[0012] The communication device according to the first aspect determines a satellite receiving station suitable for receiving a frame to be transmitted next by the corresponding terminal based on the above notification from other satellite receiving stations on the adjacent orbit. Further, the communication device according to the first aspect notifies the satellite receiving stations determined not to be suitable for receiving the frame to be transmitted next by the corresponding terminal to exclude the corresponding terminal from the reception targets.

[0013] The communication device according to the first aspect notifies information regarding terminals that are not suitable for performing the next frame reception to the satellite receiving stations located at approximately the same latitude on the adjacent orbit. Further, the communication device according to the first aspect makes the above notification within a range corresponding to the maximum number of orbits that can simultaneously receive frames from the same terminal at the position (latitude) at the time of frame reception.

[0014] Further, a second aspect of the present disclosure is a communication method that operates as a satellite receiving station that orbits the Earth on a predetermined orbit and receives frames from a ground terminal, a receiving step of receiving and processing a frame from the terminal; a determination step of exchanging frame reception information at the time of frame reception from the terminal with surrounding satellite receiving stations and determining a satellite receiving station suitable for receiving a frame to be transmitted next by the terminal; It is a communication method having.

[0015] Further, a third aspect of the present disclosure includes a terminal installed on the ground and a plurality of satellite receiving stations that orbit the Earth on a predetermined orbit, respectively. Each of the plurality of satellite receiving stations includes a receiving unit that receives and processes a frame from the terminal, and a determination unit that exchanges frame reception information at the time of frame reception from the terminal with surrounding satellite receiving stations and determines a satellite receiving station suitable for receiving a frame to be transmitted next by the terminal. It is a communication system.

[0016] However, the "system" mentioned here refers to a thing in which a plurality of devices (or functional modules that realize specific functions) are logically aggregated, and it does not particularly matter whether each device or functional module is in a single housing.

Advantages of the Invention

[0017] According to the present disclosure, there can be provided a communication device and a communication method that operate as a satellite receiving station, efficiently acquire information on radio resources of a ground terminal, suppress unnecessary reception and demodulation processing, and receive a frame from the terminal, and a communication system including a ground terminal and a satellite receiving station that suppresses unnecessary reception and demodulation processing and receives a frame from the terminal.

[0018] Note that the effects described in this specification are merely examples, and the effects brought about by the present disclosure are not limited thereto. Further, the present disclosure may have additional effects other than the above effects.

[0019] Still other objects, features, and advantages of the present disclosure will become apparent from the more detailed description based on the embodiments described below and the accompanying drawings.

Brief Description of the Drawings

[0020]

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DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, the present disclosure will be described in the following order with reference to the drawings.

[0022] A. Underlying System B. System Configuration Using Satellite Receiving Stations C. System for Avoiding Duplicate Reception of Satellite Receiving Stations C-1. Satellite Orbit and Adjacent Orbit Satellite Receiving Stations C-2. Device Configuration C-3. Frame Configuration C-4. Processing Operations of the Terminal C-5. Time Slots for Frame Exchange between Satellite Receiving Stations C-6. Configuration of Lists C-7. Processing Operations of Satellite Receiving Stations C-8. Operation of Selecting an Optimal Receiving Station D. Effects

[0023] A. Underlying System In a wireless communication system, in order for a receiving station to demodulate data transmitted by a terminal, it is necessary to know information necessary for demodulation such as a modulation method, a modulation rate, a code, and an encryption key, and wireless resources (time and frequency) used for data transmission for each terminal.

[0024] In a wireless communication system capable of two-way communication such as LTE (Long Term Evolution), by performing signaling to exchange necessary information between the terminal and the receiving station before data transmission, the receiving station designates the radio resources (time and frequency) for transmitting data to the terminal, and thereafter can perform demodulation using the modulation method and modulation rate stored in the data transmitted on the designated radio resources (time and frequency).

[0025] On the other hand, in LPWA, which is a wireless communication method for IoT, performing signaling is not desirable from the perspective of the terminal's power consumption. Also, when only one-way communication from the terminal to the receiving station is supported, signaling does not hold. Therefore, in the LPWA wireless communication system, a method for the receiving station to grasp the radio resources used by the terminal for data transmission is considered.

[0026] Fig. 1 schematically shows a configuration example of an LPWA wireless communication system. In the example shown in the figure, the system is composed of a receiving station and a plurality of terminals. The terminal is a transmitter that periodically transmits information sensed by sensors or the like mounted thereon. The receiving station receives the data transmitted by the terminal and performs demodulation processing. Also, the receiving station transmits the demodulation result (user data) to an application server (not shown) on the cloud as necessary. In the wireless communication system shown in Fig. 1, it is assumed that time synchronization is maintained within the system (between the receiving station and each terminal). Using GPS information or the like can be considered as a method for time synchronization.

[0027] Fig. 2 shows an example of a communication sequence between the terminal and the receiving station within the system shown in Fig. 1.

[0028] First, the terminal transmits a notification frame (SEQ201) to notify its own ID. For the transmission of the notification frame, a randomly selected one from the radio resources (time and frequency) previously allocated in the system for notification frame transmission is used.

[0029] The receiving station executes reception and demodulation processing of the notification frame for the radio resources for transmitting the notification frame (SEQ202). Then, when the demodulation processing is successful, the receiving station registers the ID obtained from the notification frame in the reception target terminal list (SEQ203).

[0030] Based on rules (described later) determined in advance in the system, the terminal calculates the radio resources (time and frequency) for transmitting the data frame and the codes necessary for generating the data frame using its own ID, generates the data frame, and transmits it (SEQ204).

[0031] Here, it is assumed that the time from the transmission of the notification frame to the transmission of the data frame is sufficiently short, and the next data frame to be transmitted can be received by the same satellite receiving station.

[0032] The receiving station calculates the radio resources (time and frequency) for the terminal to transmit the data frame and the codes necessary for demodulating the data frame based on the same rules as the terminal using the ID registered in the reception target terminal list, receives and demodulates the data frame (SEQ205). Also, the receiving station transmits the demodulation result (user data) to an application server (not shown) on the cloud as necessary.

[0033] FIG. 3 shows a functional configuration example of a communication device 100 (hereinafter referred to as terminal 100) that operates as a terminal in the system shown in FIG. 1. The illustrated terminal 100 includes a wireless communication unit 101, a wireless control unit 102, a frame generation unit 103, a sensor 104, a radio resource determination unit 105, and a storage unit 106. Note that the functional configuration of the terminal 100 may be the same regardless of whether the receiving station is a ground station or a satellite receiving station.

[0034] The wireless communication unit 101 transmits a wireless signal. The wireless communication unit 101 converts the frame generated by the frame generation unit 103 into a wireless signal and transmits it under the control of the wireless control unit 102.

[0035] The wireless control unit 102 controls the wireless communication unit 101 to transmit a frame at the transmission time and transmission frequency obtained from the wireless resource determination unit 105.

[0036] The frame generation unit 103 generates a frame to be transmitted by the terminal 100. The frame generation unit 103 acquires a preamble, synchronization information, and a scrambling pattern necessary for frame generation from the wireless resource determination unit 105. Further, the frame generation unit 103 describes, for example, sensor information acquired by the sensor 104 in the payload of the frame.

[0037] The sensor 104 is a sensor that acquires external or internal information of the terminal 100, and is, for example, a temperature sensor or an acceleration sensor.

[0038] The wireless resource determination unit 105 uses the ID and initial value of the terminal 100 itself obtained from the storage unit 106 to generate a wireless resource (time · frequency) for transmitting a frame, a preamble, synchronization information, and a scrambling pattern necessary for frame generation.

[0039] The storage unit 106 holds the ID and initial value of the terminal 100 itself, which are information necessary for determining wireless resources. Of course, the storage unit 106 may hold other information.

[0040] FIG. 4 shows a functional configuration example of a communication device 200 (hereinafter referred to as the receiving station 200) that operates as a receiving station in the system shown in FIG. 1. The illustrated receiving station 200 includes a wireless communication unit 201, a wireless control unit 202, a frame detection / demodulation unit 203, a wireless resource determination unit 204, and a storage unit 205. The illustrated receiving station 200 assumes a ground station installed on the ground.

[0041] The wireless communication unit 201 receives a wireless signal. Under the control from the wireless control unit 202, the wireless communication unit 201 receives radio waves, converts them into wireless signals, and passes them to the frame detection / demodulation unit 203.

[0042] The wireless control unit 202 controls the wireless communication unit 201 to receive a frame at the reception time and reception frequency obtained from the wireless resource determination unit 204.

[0043] The frame detection and demodulation unit 203 detects and demodulates a frame from the received signal. Specifically, the frame detection and demodulation unit 203 generates a known pattern from the preamble, synchronization information, and scramble pattern acquired from the wireless resource determination unit 204, calculates the correlation value between the received signal and the known pattern, and determines that a frame has been detected when the correlation value is equal to or greater than a certain value. Then, when the frame detection and demodulation unit 203 succeeds in frame detection, it extracts the signal corresponding to the frame from the received signal, removes the scramble, extracts the payload, and performs error correction code decoding processing and error detection using CRC (Cyclic Redundancy Code). When the frame detection and demodulation unit 203 succeeds in frame demodulation, it notifies the upper layer (not shown) of the demodulated data.

[0044] The wireless resource determination unit 204 generates the wireless resources (time and frequency) for the terminal 100 to transmit a frame, and the preamble, synchronization information, and scramble pattern required for frame demodulation, using the ID and initial value of the terminal 100 obtained from the storage unit 205.

[0045] The storage unit 205 holds the ID and initial value of the terminal 100, which are the information necessary for determining wireless resources. In addition, the storage unit 205 holds a reception target terminal list that holds the IDs of the terminals 100 that the receiving station 200 targets for reception.

[0046] FIG. 5 shows a configuration example of a frame used in the system shown in FIG. 1. The frame includes fields of ID, DATA, and CRC. It is assumed that both the notification frame and the data frame transmitted from the terminal have the frame configuration shown in FIG. 5.

[0047] The ID field stores the ID, which is the unique identifier of the terminal 100 that is the source. The DATA field stores the transmission data. In the case of a data frame, data obtained from the sensor 104 and the like is stored. In the case of a notification frame, the transmission interval from the notification frame transmission to the data frame transmission, the transmission interval of the data frame transmitted periodically, and the like are stored. The CRC field stores the CRC value calculated for the information stored in the ID field and the DATA field. On the receiving side, demodulation success determination is performed using the CRC value.

[0048] For the series obtained by concatenating the above ID, DATA, and CRC, error correction (Forward Error Correction: FEC) coding and rearrangement of the order (interleaving) are performed to generate a payload. Further, after concatenating a preamble, which is a known pattern used for frame detection and synchronization acquisition, and synchronization information at the head of the payload, a frame is generated by taking the exclusive logical sum (XOR) with the scramble pattern for each bit.

[0049] The radio resources (time and frequency) used for frame transmission, the preamble and synchronization information required for frame generation, and the generation method of the scramble pattern will be described with reference to FIG. 6.

[0050] In the system, rules 1 to 4 for determining, respectively, the radio resources (time and frequency) used for frame transmission, the preamble and synchronization information required for frame generation, and the method for generating the scrambling pattern are determined in advance. The time (Time) used for frame transmission is determined by inputting two initial values Seed(T)-1 and Seed(T)-2 for time calculation into rule 1. The frequency (Freq) used for frame transmission is determined by inputting two initial values Seed(F)-1 and Seed(F)-2 for frequency calculation into rule 2. The preamble and synchronization information (Preamble / Sync) are determined by inputting two initial values Seed(P)-1 and Seed(P)-2 for preamble and synchronization information calculation into rule 3. The scrambling pattern is determined by inputting two initial values Seed(S)-1 and Seed(S)-2 for the scrambling pattern into rule 4.

[0051] Each initial value is determined in advance within the system and is held in the storage unit 106 in the terminal 100 and the storage unit 205 in the receiving station 200. At the time of data frame transmission, the ID, which is the unique identifier of the terminal 100 as the transmission source of the data frame, is input into each of the second initial values (Seed(T)-2, Seed(F)-2, Seed(P)-2, Seed(S)-2). On the other hand, at the time of notification frame transmission, several initial values previously assigned for the notification frame are randomly selected and input into each of the second initial values (Seed(T)-2, Seed(F)-2, Seed(P)-2, Seed(S)-2).

[0052] By using this method, it is possible to obtain the radio resources (time and frequency) used for frame transmission and the information required for frame demodulation only by notifying the receiving station 200 of the terminal ID from the terminal 100. It is not necessary to perform signaling between the terminal 100 and the receiving station 200 before data transmission.

[0053] B. System Configuration Using Satellite Receiving Stations Figure 7 schematically shows a configuration example of an LPWA wireless communication system using satellite receiving stations. In the example shown in the figure, it is composed of a plurality of receiving stations installed on the ground (hereinafter referred to as "ground stations"), a plurality of low-earth orbit satellite receiving stations orbiting the earth in a low orbit (hereinafter also simply referred to as "satellite receiving stations"), and innumerable terminals scattered on the ground. It is assumed that all terminals and receiving stations in the system are time-synchronized. As a method of time synchronization, using GPS information etc. can be considered. Each satellite receiving station orbits the earth in a sun-synchronous orbit, for example, close to a polar orbit passing through the upper air in the very vicinity, where the angle of light from the sun incident on the satellite's orbital plane is the same, and it always passes through the equator at the same local time.

[0054] The terminal is a transmitter that periodically transmits information sensed by sensors etc. installed on it. The satellite receiving station receives the data transmitted by the terminal and performs demodulation processing. Also, the satellite receiving station transmits the demodulation result (user data) to an application server (not shown) on the cloud as necessary. Also, the satellite receiving station enables inter-satellite communication. The communication method between satellite receiving stations is not limited, but it is desirable to be always connected and have high-speed communication. The ground station is a transceiver that communicates with the satellite receiving station. The communication method between the satellite receiving station and the ground station is not limited, but it is desirable to have high-speed communication.

[0055] In the example shown in Figure 7, it is a network design where the receivable range 711 of satellite receiving station 701 and the receivable range 712 of satellite receiving station 702 overlap. Figure 8 shows an example of a communication sequence between terminal 801 existing in the area where receivable range 711 and receivable range 712 overlap, satellite receiving station 701, and satellite receiving station 702. Both satellite receiving station 701 and satellite receiving station 702 can receive the notification frame from terminal 801.

[0056] First, in order to notify its own ID, the terminal 801 transmits (broadcasts) a notification frame (SEQ801). For the transmission of the notification frame, wireless resources (time and frequency) pre-allocated in the system for the transmission of the notification frame are used. At this point, the terminal 801 is within the reception ranges 711 and 712 of both the satellite receiving stations 701 and 702. Therefore, each of the satellite receiving stations 701 and 702 executes reception and demodulation processing of the notification frame for the wireless resources for the transmission of the notification frame (SEQ811, SEQ821), and registers the ID obtained from the notification frame in the reception target terminal list (SEQ812, SEQ822).

[0057] Next, based on rules determined in advance in the system, the terminal 801 calculates the wireless resources (time and frequency) for transmitting the data frame from its own ID and the codes necessary for generating the data frame, and generates and transmits (broadcasts) the data frame (SEQ802).

[0058] Each of the satellite receiving stations 701 and 702 uses the ID registered in the reception target terminal list, and based on the same rules as those of the terminal 801, calculates the wireless resources (time and frequency) for the terminal 801 to transmit the data frame from the ID of the terminal and the codes necessary for demodulating the data frame, and receives and demodulates the data frame (SEQ813, SEQ823).

[0059] In this way, when the terminal 801 exists in the area where the reception range 711 and the reception range 712 overlap, both the satellite receiving stations 701 and 702 receive the notification frame from the terminal 801 and register it in the reception target terminal list, and receive and demodulate the data frame from the terminal 801. It is not desirable from the perspective of accommodating multiple terminals for multiple satellite receiving stations to receive and demodulate the data frames of the same terminal.

[0060] Thereafter, satellite receiving station 701 and satellite receiving station 702 move on the satellite orbit respectively, and terminal 801 moves out of the receivable range 711 of satellite receiving station 701 but remains within the receivable range 712 of satellite receiving station 702. When terminal 801 transmits (broadcasts) a notification frame (SEQ803), only satellite receiving station 702 receives it (SEQ824) and registers the ID of terminal 801 in the reception target terminal list (SEQ825). Then, when terminal 801 generates and transmits (broadcasts) a data frame (SEQ804), only satellite receiving station 702 performs reception and demodulation processing of the data frame from terminal 801 (SEQ826).

[0061] In the communication sequence example shown in FIG. 8, when the terminal is simultaneously to present within the receivable ranges of a plurality of satellite receiving stations, a situation may occur where a plurality of satellite receiving stations receive and demodulate the data frame of the same terminal, which is not desirable from the perspective of accommodating multiple terminals.

[0062] Therefore, in the present disclosure, in view of the perspective of accommodating multiple terminals, etc., even when a plurality of satellite receiving stations receive a notification frame from the same terminal, an optimal satellite receiving station is determined, and only the optimal one satellite receiving station performs reception and demodulation processing. In the present disclosure, the satellite receiving station that can receive the corresponding terminal for a long time is regarded as the optimal one. Then, only the optimal satellite receiving station performs reception and demodulation processing of the data frame from the corresponding terminal, while other satellite receiving stations do not perform reception and demodulation processing of the data frame even if the corresponding terminal is within the receivable range.

[0063] C. System for Avoiding Duplicate Reception of Satellite Receiving Stations In this section, a method for avoiding duplicate reception of frames from the same terminal by a plurality of satellite receiving stations in the system configuration as shown in FIG. 7 will be described.

[0064] C-1. Satellite Orbit and Adjacent Orbit Satellite Receiving Stations FIG. 9 shows an example of the arrangement (satellite constellation) of a plurality of satellite receiving stations orbiting the Earth in low orbits. FIG. 9 shows a plurality of satellite receiving stations orbiting on four satellite orbits. Also, in FIG. 9, for the sake of simplicity of the drawing, only six satellite receiving stations are drawn, but it is assumed that several to several tens of satellite receiving stations are orbiting on each satellite orbit.

[0065] The satellite receiving station is assigned a satellite orbit number indicating the orbit on which it is orbiting and a circulation sequence number indicating which satellite it is among the satellite receiving stations orbiting on the same satellite orbit. For example, satellite receiving station 1-2 is a satellite receiving station orbiting on the first satellite orbit in the second position from the beginning. The number obtained by concatenating the satellite orbit number and the circulation sequence number will be called the "satellite receiving station number".

[0066] FIG. 10 shows the arrangement of satellite receiving station numbers when N satellite receiving stations are orbiting on each of the four satellite orbits. Each satellite orbit is arranged at equal intervals in the latitude direction and orbits on the same longitude. Also, it is assumed that the satellite receiving stations are arranged at equal intervals on each satellite orbit, and the numbers are assigned so that the satellite receiving stations with the same circulation sequence number are located at approximately the same latitude at the same time. Adjacent orbit satellite receiving stations located at approximately the same latitude at the same time in this way are called "adjacent orbit satellite receiving stations". However, since the satellite receiving stations on the orbit with the minimum satellite orbit number and the orbit with the maximum satellite orbit number have different traveling directions, the numbers of the adjacent orbit satellite receiving stations are calculated based on the following formula (1).

[0067]

Equation

[0068] In the above formula (1), No CN indicates the circulation sequence number of the adjacent orbit satellite receiving station of satellite receiving station M-CN, M indicates the maximum value of the satellite orbit number, and CN indicates the circulation sequence number of the satellite receiving station orbiting on satellite orbit M. Also, N indicates the number of satellite receiving stations orbiting on each satellite orbit, and CN 1-northIndicates the orbit sequence number of the satellite receiving station that is moving northward among the satellite receiving stations orbiting satellite orbit 1. However, if the calculation result is greater than N, the value obtained by further subtracting N is used.

[0069] In the arrangement example of the satellite receiving station numbers on each satellite orbit shown in FIG. 10, for example, when using the above formula (1) for the satellite receiving station 4-2, as shown in the following formula (2), the satellite receiving station 1-(N-1), that is, the satellite receiving station moving in the (N-1)th orbit sequence on the first satellite orbit, can be calculated as the adjacent satellite receiving station.

[0070]

Number

[0071] In the examples shown in FIGS. 9 and 10, the satellite orbits of each satellite receiving station are close to polar orbits passing through the upper air near the poles, the angles of light from the sun incident on the orbital plane of the satellite are the same, and it is a sun-synchronous orbit that always passes through the equator at the same local time. Between adjacent satellite orbits, the satellite receiving stations move in the same direction. However, the satellite orbit with the largest satellite orbit number is adjacent to the satellite orbit with the smallest satellite orbit number, and the directions in which the satellite receiving stations move are different.

[0072] C-2. Device Configuration In the LPWA wireless communication system using a satellite receiving station, the configuration of the terminal may be the same as that in FIG. 3. FIG. 11 shows a functional configuration example of the satellite receiving station 1000 in the LPWA wireless communication system using a satellite receiving station. The satellite receiving station 1000 is used by being mounted on a low-orbit satellite orbiting the earth in any of the satellite orbits shown in FIG. 10. The satellite receiving station 1000 includes an LPWA unit 1200 and an inter-satellite communication unit 1300.

[0073] The LPWA unit 1200 receives the frames transmitted by the ground terminal. The LPWA unit 1200 may have the same functional configuration as the receiving station 200 shown in FIG. 4, and the same reference numbers as those in FIG. 4 are assigned to the same components. A detailed description of the functional configuration within the LPWA unit 1200 is omitted.

[0074] The inter-satellite communication unit 1300 includes a wireless communication unit 1301, a wireless control unit 1302, a frame generation unit 1303, a frame detection / demodulation unit 1304, and an optimal orbit determination unit 1305.

[0075] The wireless communication unit 1301 transmits and receives wireless signals. Under the control of the wireless control unit 1302, the wireless communication unit 1301 receives radio waves, converts them into wireless signals, and passes them to the frame detection / demodulation unit 1304. Also, under the control of the wireless control unit 1302, the wireless communication unit 1301 converts the frame generated by the frame generation unit 1303 into a wireless signal and transmits it.

[0076] The wireless control unit 1302 controls the wireless communication unit 1301 so that frames can be transmitted and received between satellite receiving stations.

[0077] The frame generation unit 1303 generates a frame according to a predetermined format using the information obtained from the frame detection / demodulation unit 203 on the LPWA unit 1200 side, the frame detection / demodulation unit 1304 on the inter-satellite communication unit 1300 side, and the optimal orbit determination unit 1305.

[0078] The frame detection / demodulation unit 1304 detects and demodulates a frame from the received signal of the wireless communication unit 1301. When the frame demodulation is successful, the frame detection / demodulation unit 1304 passes the received data to the frame generation unit 1303 and the optimal orbit determination unit 1305.

[0079] The optimal orbit determination unit 1305 determines the optimal satellite receiving station for receiving the data frame transmitted by the ground terminal. In this embodiment, the case where the satellite receiving station that can receive the corresponding terminal for a long time is regarded as optimal will be described.

[0080] C-3. Frame Configuration In this section, the frame configuration used in the LPWA wireless communication system according to the present disclosure will be described. However, since the notification frame and the data frame transmitted from the terminal to the satellite receiving station have the same frame configuration as shown in FIG. 5, detailed description will be omitted here.

[0081] Figure 12 shows the frame configuration of the data part of the same-orbit notification frame. The format other than the data part shall be in accordance with the communication method to be used. The same-orbit notification frame is a frame for notifying the information of the terminal that has received the notification frame by each satellite receiving station on the same orbit to the satellite receiving station in front on the same orbit as the own station.

[0082] The nInfo field stores the number of notification frame information stored in the data part. After the nInfo field, notification frame information (Notification Frame Info) fields follow for the number specified in the nInfo field. In the frame configuration example shown in Figure 12, the nInfo field stores information indicating the value n, and n pieces of notification frame information are stored in the data part.

[0083] Each piece of notification frame information includes an STA ID field, an Rx Time field, and an nSAT field respectively. The STA ID field stores the ID of the terminal that is the source of the notification frame. The Rx Time field stores the reception time of the notification frame. The nSAT field stores the number of remaining satellite receiving stations that will transmit the notification frame information (Notification Frame Info) in the same-orbit notification frame.

[0084] The data part of the same-orbit notification frame has a frame configuration that stores a same-orbit notification frame transmission list (see Figure 19). Later, the processing procedure for the satellite receiving station to transmit the same-orbit notification frame (see Figure 23) and the processing procedure for receiving the same-orbit notification frame (see Figures 24A and 24B) will be described in detail.

[0085] Figure 13 shows the frame configuration of the data part of the adjacent orbit notification frame. The format other than the data part shall be according to the communication method used. The adjacent orbit notification frame is a frame that notifies satellite receiving stations located at approximately the same latitude on adjacent orbits of the information of the terminals that have received the notification frame at each satellite receiving station on the adjacent orbit.

[0086] The nInfo field stores the number of terminal information stored in the data part. After the nInfo field, terminal information (STA Info) fields follow for the number described in the nInfo field. In the frame configuration example shown in Figure 13, the nInfo field stores information indicating the value n, and n pieces of terminal information are stored in the data part.

[0087] Each piece of terminal information includes an STA ID field, an RX Time field, an nSAT field, an nRxInfo field, and Frame Rx Info fields for the number described in the nRxInfo field.

[0088] The STA ID field stores the ID of the terminal that is the source of the notification frame. The Rx Time field stores the reception time of the notification frame from that terminal. The nSAT field stores the number of remaining satellite receiving stations that will transmit the corresponding terminal information (STA Info) in the adjacent orbit notification frame. The nRxInfo field stores the number of frame reception information stored. In the frame configuration example shown in Figure 13, the nRxInfo field stores information indicating the value m, and m pieces of frame reception information are stored in the terminal information field.

[0089] Each Frame Rx Info (Frame Reception Information) field includes an SAT ID field, a Freq.Error field, and a Propagation Delay field. The SAT ID field stores the ID of the satellite receiving station (satellite ID) that is the source of the notification frame. The Freq.Error field stores the estimated frequency error result when the notification frame is received. The Propagation Delay field stores the estimated propagation delay result when the notification frame is received.

[0090] The data part of the adjacent orbit notification frame has a frame configuration that stores an adjacent orbit notification frame transmission list (see FIG. 20). Later, the processing procedure for the satellite receiving station to transmit the adjacent orbit notification frame (see FIG. 26) and the processing procedure for receiving the adjacent orbit notification frame (see FIGS. 27A to 27C) will be described in detail.

[0091] FIG. 14 shows the frame configuration of the data part of the non-optimal orbit notification frame. The format other than the data part shall be according to the communication method used. The non-optimal orbit notification frame is a frame that notifies that the satellite receiving station is not the optimal one for the corresponding terminal to receive the next data frame from satellite receiving stations located approximately equally Latitude in degrees on the adjacent orbit.

[0092] The nInfo field stores the number of terminal information stored in the data part. After the nInfo field, terminal information (STA Info) fields equal to the number described in the nInfo field follow. In the frame configuration example shown in FIG. 14, the nInfo field stores information indicating the value n, and n pieces of terminal information are stored in the data part.

[0093] Each terminal information includes an STA ID field, an RX Time field, and an nSAT field respectively. The STA ID field stores the ID of the terminal that is the source of the notification frame. The Rx Time field stores the reception time of the notification frame. The nSAT field stores the remaining number of satellite receiving stations for transmitting terminal information (STA Info) in the non-optimal orbit notification frame.

[0094] Figure 15 shows the frame configuration of the data part of the receiving target terminal deletion notification frame. The format other than the data part shall be according to the communication method used. The receiving target terminal deletion notification frame is a frame in which a satellite receiving station notifies another satellite receiving station to delete the entry of the corresponding terminal from the receiving target terminal list.

[0095] The nSTA field stores the number of terminal IDs stored in the data part. After the nSTA field, there are as many STA ID fields as the number described in the nSTA field. Each STA ID field stores a terminal ID. In the frame configuration example shown in Figure 15, the nSTA field stores information indicating the value n, and n terminal IDs are stored.

[0096] C-4. Processing Operations of Terminals Figure 16 shows the processing operation performed by the terminal in the form of a flowchart.

[0097] The terminal first determines whether it is immediately after power-on or α hours have elapsed since the previous notification frame was transmitted (step S1601). Assume that the transmission interval α between the notification frame and the data frame is set in advance.

[0098] When it is immediately after power-on or α hours have elapsed since the previous notification frame was transmitted (Yes in step S1601), the terminal executes the transmission process of the notification frame.

[0099] When transmitting a notification frame, the terminal first calculates information such as the radio resources (time and frequency) to be used for transmitting the notification frame, the preamble and synchronization information required for frame generation, and the scrambling pattern based on the above-mentioned Rules 1 to 4 (step S1602).

[0100] Next, the terminal generates a notification frame using the calculated preamble, synchronization information, and scrambling pattern (step S1603).

[0101] Next, the terminal determines whether it has reached the transmission time calculated in step S1602 (step S1604). When the transmission time arrives (Yes in step S1604), the terminal transmits the notification frame generated in step S1603 using the transmission frequency calculated in step S1602 (step S1605).

[0102] After transmitting the notification frame, the terminal calculates information such as the radio resources (time and frequency) to be used for transmitting the data frame, the preamble and synchronization information required for frame generation, and the scrambling pattern (step S1606).

[0103] Next, the terminal generates a data frame using the preamble, synchronization information, and scrambling pattern calculated in step S1606 (step S1607).

[0104] Next, the terminal determines whether it has reached the transmission time calculated in step S1606 (step S1608). When the transmission time arrives (Yes in step S1608), the terminal transmits the data frame generated in step S1607 using the transmission frequency calculated in step S1606 (step S1609). After that, it returns to step S1601, and the terminal repeats the transmission of the notification frame.

[0105] C-5. Time Slots during Frame Exchange between Satellite Receiving Stations FIG. 17 shows time slots during frame exchange for determining an optimal satellite receiving station among satellite receiving stations.

[0106] Let the notification frame reception time calculated for notification frame reception be t. Assume that the transmission interval α between the notification frame and the data frame is set in advance (as described above). The period from when a micro time ε has elapsed since the notification frame reception time t until a time β has elapsed (t + ε to t + ε + β) is defined as the slot for transmitting the same-orbit notification frame. Also, the period from immediately after the slot for transmitting the same-orbit notification frame ends until a further time γ has elapsed (t + ε + β to t + ε + β + γ) is defined as the slot for transmitting the adjacent-orbit notification frame. The time t + ε + β + γ is set to be before the data frame reception time (t + α).

[0107] Also, if the number of satellite receiving stations orbiting on the same orbit is N and the maximum number of satellite receiving stations that can simultaneously receive the notification frame from the terminal is K, then the same-orbit notification frame transmission slot is divided into N + K - 1 slots. FIG. 17 shows an example where N = 8 and K = 3, that is, an example where the same-orbit notification frame transmission slot is divided into 10 slots. #1 indicates the slot in which the satellite receiving station with the orbit sequence number 1 can transmit the same-orbit notification frame.

[0108] Furthermore, if the number of satellite orbits is M and the maximum number of satellite orbits that can simultaneously receive the notification frame from the terminal is L, then the adjacent-orbit notification frame transmission slot is divided into M + L - 1 slots. FIG. 17 shows an example where M = 4 and L = 3, that is, an example where the adjacent-orbit notification frame transmission slot is divided into 6 slots. #1 indicates the slot in which the satellite receiving station in satellite orbit 1 can transmit the adjacent-orbit notification frame.

[0109] C-6. List Configuration In this section, the configurations of the received target terminal list, the same-orbit notification frame transmission list, and the adjacent-orbit notification frame transmission list, which are managed at the satellite receiving station, will be described. Each list is stored in the storage unit 205.

[0110] FIG. 18 shows a configuration example of a reception target terminal list. The satellite receiving station registers a terminal that has successfully received and demodulated a notification frame in the reception target terminal list, and executes reception processing of a data frame for the terminals registered in the reception target terminal list. In the reception target terminal list, the reception time, the frequency error estimation result, and the propagation delay estimation result are registered using the terminal ID as an index. The reception time is the reception time of the notification frame from the corresponding terminal. The frequency error estimation result is the frequency error estimation result when the notification frame from the corresponding terminal is received and demodulated. The propagation delay estimation result is the propagation delay estimation result when the notification frame from the corresponding terminal is received and demodulated.

[0111] FIG. 19 shows a configuration example of an in-orbit notification frame transmission list. The satellite receiving station registers a terminal that has successfully received and demodulated a notification frame in the in-orbit notification frame transmission list, stores the information registered in the in-orbit notification frame transmission list in an in-orbit notification frame (see FIG. 12), and transmits it to the satellite receiving station ahead on the same orbit. In the in-orbit notification frame transmission list, the reception time at the time of frame reception from the corresponding terminal and the number of remaining satellite receiving stations to be transmitted are registered using the terminal ID as an index. The reception time is the reception time of the notification frame from the corresponding terminal. The number of remaining satellite receiving stations to be transmitted is the number of remaining satellite receiving stations to transmit the information of the corresponding terminal ID in the in-orbit notification frame. The number of remaining satellite receiving stations here is a value of the maximum number of in-orbit satellite receiving stations that can receive the notification frame simultaneously - 1. The value of the maximum number of in-orbit satellite receiving stations is determined in advance when constructing the satellite constellation.

[0112] Figure 20 shows a configuration example of an adjacent orbit notification frame transmission list. The satellite receiving station registers the terminals that have successfully received and demodulated the notification frame in the adjacent orbit notification frame transmission list, and stores the information registered in the adjacent orbit notification frame transmission list in the adjacent orbit notification frame (see Fig. 13) and transmits it. The adjacent orbit notification frame transmission list is indexed by the terminal ID, and stores the reception time when receiving the frame from the corresponding terminal, the number of frame reception information (the number of satellite receiving stations that have received the frame from the corresponding terminal), the frame reception information for each of the number of frame reception information (for each satellite receiving station that has received the frame from the corresponding terminal), and the remaining number of transmitting satellite receiving stations. The reception time is the reception time of the notification frame from the corresponding terminal. The number of frame reception information is the number of pieces of frame reception information held for the same terminal ID and reception time, that is, the number of satellite receiving stations that have received the frame from the corresponding terminal. The frame reception information includes the ID of each satellite receiving station that has received the frame from the corresponding terminal, the estimated result of the frequency error at the time of receiving the notification frame, and the estimated result of the propagation delay. The remaining number of transmitting satellite receiving stations is the remaining number of transmitting satellite receiving stations that transmit the frame reception information of the corresponding terminal ID in the adjacent orbit notification frame. The remaining number of transmitting satellite receiving stations in the adjacent orbit notification frame transmission list is determined based on the maximum number of simultaneous reception orbits corresponding to the current position (latitude) of the local station. The value of the maximum number of simultaneous reception orbits corresponding to the latitude is determined in advance when constructing the satellite constellation (see the following description and Fig. 22).

[0113] C-7. Processing Operations of Satellite Receiving Stations In the present disclosure, it is assumed that the satellite receiving station can perform the reception process and transmission process of each frame in parallel.

[0114] Figure 21 shows, in the form of a flowchart, the processing procedure for the satellite receiving station to receive the notification frame.

[0115] First, the satellite receiving station refers to the reception target terminal list and calculates the radio resources (time and frequency) for receiving the notification frame from the registered terminals and the information necessary for demodulating the notification frame based on the above-described rules 1 to 4 (step S2101).

[0116] Next, the satellite receiving station determines whether it is the time to receive the notification frame calculated in step S2101 (step S2102). When the time to receive the notification frame arrives (Yes in step S2102), the satellite receiving station receives and demodulates the notification frame from the corresponding terminal (steps S2103 and S2104). Then, the satellite receiving station determines whether the demodulation of the notification frame is successful (step S2105).

[0117] Here, when the demodulation of the notification frame is successful (Yes in step S2105), the satellite receiving station adds the information regarding the received notification frame to the reception target terminal list, the same orbit notification frame transmission list, and the adjacent orbit notification frame transmission list (steps S2106, S2107, and S2108).

[0118] When adding an entry of the corresponding terminal to the same orbit notification frame transmission list in step S2107, the remaining number of satellite receiving stations to transmit is stored with a value of the maximum number of same orbit satellite receiving stations that can receive the notification frame simultaneously - 1. The value of the maximum number of same orbit satellite receiving stations is determined in advance when constructing the satellite constellation.

[0119] Also, when adding an entry of the corresponding terminal to the adjacent orbit notification frame transmission list in step S2108, the remaining number of satellite receiving stations to transmit is stored with a value of the maximum number of receiving orbits that can receive the notification frame simultaneously - 1. As can be seen from FIG. 9, the interval between adjacent orbits becomes narrower as the latitude increases, so more satellite receiving stations on satellite orbits can receive the notification frame simultaneously. Therefore, in the system, a maximum number of simultaneous reception orbits list as shown in FIG. 22 is maintained, the maximum number of reception orbits corresponding to the latitude at the time of receiving the notification frame is obtained, and the value obtained by subtracting 1 is stored in the remaining number of satellite receiving stations to transmit in the adjacent orbit notification frame transmission list. In the maximum number of simultaneous reception orbits list shown in FIG. 22, the latitude is divided into four regions of 0 - 20 degrees, 20 - 70 degrees, 70 - 80 degrees, and 80 - 90 degrees, and the maximum number of reception orbits 1, 2, 3, and 4 for each region is shown.

[0120] Figure 23 shows, in the form of a flowchart, the processing procedure for a satellite receiving station to transmit an identical orbit notification frame.

[0121] First, the satellite receiving station determines whether it is the start time of the identical orbit notification frame transmission slot assigned to itself (step S2301). Then, when the start time of the identical orbit notification frame transmission slot assigned to the satellite receiving station arrives (Yes in step S2301), the satellite receiving station checks whether the identical orbit notification frame transmission list is not empty (step S2302).

[0122] If the identical orbit notification frame transmission list is not empty (Yes in step S2302), the satellite receiving station repeatedly executes the process consisting of steps S2303 to S2305 for the number of terminals registered in the identical orbit notification frame transmission list.

[0123] In step S2303, the satellite receiving station obtains the terminal ID, reception time, and remaining number of transmitting satellite receiving stations of the terminal that received the notification frame from the entry in the identical orbit notification frame transmission list.

[0124] In step S2304, the satellite receiving station generates notification frame information using the information obtained from the identical orbit notification frame transmission list in step S2303 and stores it in the identical orbit notification frame.

[0125] In step S2305, the satellite receiving station deletes the entry of the terminal that stored the notification frame information in step S2304 from the identical orbit notification frame transmission list.

[0126] Then, when the satellite receiving station finishes the process of storing the notification frame information of all terminals registered in the same orbit notification frame transmission list in the same orbit notification frame, the satellite receiving station stores the number of notification frame information stored in the same orbit notification frame in the nInfo field (step S2306), and transmits the same orbit notification frame to the satellite receiving station with its own orbit sequence number - 1 (i.e., one before on the same orbit) (step S2307). For example, when the ID of the satellite receiving station executing this process is (1 - 3), the same orbit notification frame is transmitted to the satellite receiving station (1 - 2) with the orbit sequence number one before on the same orbit.

[0127] Figures 24A and 24B show the processing procedures for the satellite receiving station to receive the same orbit notification frame in the form of a flowchart.

[0128] First, the satellite receiving station determines whether it has received the same orbit notification frame (step S2401). Then, when the satellite receiving station has received the same orbit notification frame (Yes in step S2401), it demodulates the received frame (step S2402) and determines whether the demodulation process has succeeded (step S2403).

[0129] When the satellite receiving station succeeds in demodulating the same orbit notification frame (Yes in step S2403), it obtains the nInfo indicating the number of notification frame information stored in the same orbit notification frame (step S2404). Then, the satellite receiving station repeatedly executes the processing of each notification frame information (Notification Frame Info) shown in Figure 24B for the number of notification frame information, appropriately updates the receiving target terminal list, the same orbit notification frame transmission list, and the adjacent orbit notification frame transmission list, and registers the corresponding terminal in the non - optimal orbit notification frame transmission list.

[0130] First, the satellite receiving station obtains the terminal ID, the reception time, and the remaining number of satellite receiving stations to be transmitted from the notification frame information (step S2405).

[0131] Next, the satellite receiving station determines whether the difference between the current time and the reception time of the frame from the corresponding terminal is less than (β + ε) (step S2406).

[0132] Here, when the difference between the current time and the reception time (i.e., the elapsed time from the reception time) is (β + ε) or more (No in step S2406), it is because for some reason, the same-orbit notification frame was not transmitted in the time slot between the notification frame transmission and the data frame transmission. In this case, the satellite receiving station skips all subsequent processes and ignores this notification frame information.

[0133] On the other hand, when the difference between the current time and the reception time of the satellite receiving station is less than (β + ε), that is, when the elapsed time from the reception time is less than β + ε (Yes in step S2406), the satellite receiving station determines whether an entry for the corresponding terminal (the terminal ID stored in the notification frame information) exists in its own reception target terminal list (step S2407). And when an entry for the corresponding terminal exists in its own reception target terminal list (Yes in step S2407), the entry for the corresponding terminal is deleted from its own reception target terminal list (step S2408).

[0134] The existence of an entry for the corresponding terminal of the notification frame information in its own reception target terminal list means that the same terminal as that of the satellite receiving station behind on the same orbit is the reception target. It is obvious from, for example, FIG. 7 that the time of the corresponding terminal is longer for the satellite receiving station further behind on the same orbit, and it means that the local station is not the optimal receiving station for receiving the frame from the corresponding terminal. Therefore, in step S2408, by deleting the entry for the corresponding terminal from its own reception target terminal list, it is possible to avoid the waste of multiple satellite receiving stations receiving the data frame of the same terminal and performing demodulation processing.

[0135] Next, the satellite receiving station determines whether an entry for the corresponding terminal exists in its own same-orbit notification frame transmission list (step S2409).

[0136] If an entry for the corresponding terminal exists in the same-orbit notification frame transmission list (Yes in step S2409), the satellite receiving station determines whether the number of remaining satellite receiving stations to transmit is greater than 1 (step S2410).

[0137] If the number of remaining satellite receiving stations to transmit is greater than 1 (Yes in step S2410), the satellite receiving station overwrites the number of remaining satellite receiving stations in the same-orbit notification frame transmission list of the corresponding terminal with the value obtained by subtracting 1 from the value stored in the received notification frame information (step S2411). On the other hand, if the number of remaining satellite receiving stations to transmit is 1 or less (No in step S2410), it means that the frame from the corresponding terminal will not reach the further forward satellite receiving stations on the same orbit. Therefore, the satellite receiving station deletes the entry of the corresponding terminal from its own same-orbit notification frame transmission list (step S2415).

[0138] Also, if an entry for the corresponding terminal does not exist in its own same-orbit notification frame transmission list (No in step S2409), the satellite receiving station determines whether the number of remaining satellite receiving stations to transmit is greater than 1 (step S2416). If the number of remaining satellite receiving stations to transmit is greater than 1 (Yes in step S2416), it means that the frame from the corresponding terminal may reach the further forward satellite receiving stations on the same orbit. Therefore, the satellite receiving station adds an entry for the corresponding terminal to its own same-orbit notification frame transmission list (step S2417). At that time, the number of remaining satellite receiving stations to transmit is changed to the value obtained by subtracting 1 from the value stored in the received notification frame information.

[0139] Next, the satellite receiving station determines whether there is an entry for the corresponding terminal in its adjacent orbit notification frame transmission list (step S2412). If there is an entry for the corresponding terminal in the adjacent orbit notification frame transmission list (Yes in step S2412), the satellite receiving station deletes the entry for the corresponding terminal from its adjacent orbit notification frame transmission list (step S2413). The local station is not the optimal receiving station for receiving frames from the corresponding terminal (as described above), and the corresponding terminal is not included in the reception targets of the local station. Therefore, it is not necessary to notify the information at the time of receiving the notification frame from the corresponding terminal in the adjacent orbit notification frame.

[0140] Subsequently, the satellite receiving station adds the corresponding terminal to its non-optimal orbit notification frame transmission list (step S2414). This is because when multiple satellite receiving stations on the same orbit can receive frames from the corresponding terminal, the further back the satellite receiving station is in the circumferential direction, the longer the reception time of the frames from the corresponding terminal (as described above). At that time, the remaining number of satellite receiving stations for transmitting the entry of the corresponding terminal is changed to a value obtained by subtracting 1 from the value stored in the received notification frame information.

[0141] Fig. 25 shows a configuration example of the non-optimal orbit notification frame transmission list. In the non-optimal orbit notification frame transmission list, the reception time and the remaining number of satellite receiving stations for transmission are registered with the terminal ID as the index. The reception time is the reception time of the notification frame from the corresponding terminal. The remaining number of satellite receiving stations for transmission is the remaining number of satellite receiving stations for transmitting the non-optimal orbit notification frame.

[0142] In the process of registering the non-optimal orbit notification frame transmission list, for the remaining number of satellite receiving stations for transmission, the maximum number of receiving orbits corresponding to the latitude at the notification frame reception time is obtained from the maximum simultaneous reception orbit number list shown in Fig. 22, and a value obtained by subtracting 1 from the maximum number of receiving orbits is stored.

[0143] After the satellite receiving station completes the processing for all the notification frame information stored in the same orbit notification frame according to the processing procedure shown in Fig. 24, it returns to step S2401 and waits for the reception of the same orbit notification frame.

[0144] Figure 26 shows, in the form of a flowchart, the processing procedure for a satellite receiving station to transmit an adjacent orbit notification frame.

[0145] First, the satellite receiving station determines whether it is the start time of the adjacent orbit notification frame transmission slot assigned to itself (step S2601). Then, when the start time of the adjacent orbit notification frame transmission slot assigned to the satellite receiving station arrives (Yes in step S2601), the satellite receiving station checks whether the adjacent orbit notification frame transmission list is not empty (step S2602).

[0146] If the adjacent orbit notification frame transmission list is not empty (Yes in step S2602), the satellite receiving station repeatedly executes the process consisting of steps S2603 to S2605 for the number of terminals registered in the adjacent orbit notification frame transmission list.

[0147] In step S2603, the satellite receiving station obtains from the adjacent orbit notification frame transmission list (see Figure 20) the terminal ID, reception time, number of frame reception information, frame reception information, and number of remaining transmitting satellite receiving stations of the terminal that received the notification frame.

[0148] In step S2604, the satellite receiving station generates terminal information (STA Info) using the information obtained from the adjacent orbit notification frame transmission list in step S2603 and stores it in the adjacent orbit notification frame.

[0149] In step S2605, the satellite receiving station deletes the entry of the terminal that stored the terminal information in step S2604 from the adjacent orbit notification frame transmission list.

[0150] Then, when the process of storing the terminal information of all terminals registered in the adjacent orbit notification frame transmission list in the adjacent orbit notification frame is completed, the satellite receiving station stores the number of notification frame information stored in the adjacent orbit notification frame in the nInfo field (step S2606).

[0151] Next, the satellite receiving station determines whether its satellite orbit number is the maximum satellite orbit (step S2607).

[0152] If its satellite orbit number is the maximum satellite orbit (Yes in step S2607), the direction of travel is different from that of the adjacent satellite orbit. In this case, the satellite receiving station calculates the number of the adjacent orbit satellite receiving station using the above formula (1) (step S2608). Then, the satellite receiving station transmits an adjacent orbit notification frame to all adjacent satellite receiving stations whose satellite ID is satellite orbit number 1 and whose revolution sequence number is the revolution sequence number of the adjacent orbit satellite receiving station ± (the maximum number of simultaneous receptions on the same orbit - 1) (step S2609).

[0153] For example, in the arrangement example of the satellite receiving station numbers shown in FIG. 10, when the ID of the satellite receiving station executing the process shown in FIG. 26 is (4 - 1) and the maximum number of simultaneous receptions on the same orbit is 3, in step S2609, an adjacent orbit notification frame is transmitted to five satellite receiving stations: (1 - 2), (1 - 1), (1 - N), (1 - (N - 1)), and (1 - (N - 2)).

[0154] On the other hand, if its satellite orbit number is not the maximum satellite orbit (No in step S2607), the satellite receiving station transmits an adjacent orbit notification frame to the satellite receiving station with a satellite orbit number of +1 and the same revolution sequence number (step S2610).

[0155] For example, in the arrangement example of the satellite receiving station numbers shown in FIG. 10, when the ID of the satellite receiving station executing the process shown in FIG. 26 is (1 - 3), in step S2610, an adjacent orbit notification frame is transmitted to the satellite receiving station (2 - 3).

[0156] FIGS. 27A to 27C show, in the form of a flowchart, the processing procedure for the satellite receiving station to receive an adjacent orbit notification frame.

[0157] First, the satellite receiving station determines whether it has received an adjacent orbit notification frame (step S2701). Then, when the satellite receiving station has received an adjacent orbit notification frame (Yes in step S2701), it demodulates the received frame (step S2702) and determines whether the demodulation process has succeeded (step S2703).

[0158] When the satellite receiving station has succeeded in demodulating the adjacent orbit notification frame (Yes in step S2703), it obtains nInfo indicating the number of terminal information stored in the adjacent orbit notification frame (step S2704), and repeatedly executes the processing of each terminal information shown in FIGS. 27B and 27C for the number of terminal information.

[0159] First, the satellite receiving station obtains the terminal ID, the reception time, and the remaining number of satellite receiving stations at the time of reception from the terminal information (step S2705).

[0160] Next, the satellite receiving station determines whether the difference between the current time and the reception time of the frame from the corresponding terminal is less than (β + γ + ε) (step S2706).

[0161] Here, when the difference between the current time and the reception time (i.e., the elapsed time from the reception time) is (β + γ + ε) or more (No in step S2706), it is because the adjacent orbit notification frame was not transmitted in the time slot between the notification frame transmission and the data frame transmission for some reason. In this case, the satellite receiving station skips all subsequent processing and ignores the terminal information being processed.

[0162] When the difference between the current time and the reception time of the satellite receiving station is less than (β + γ + ε), that is, when the elapsed time from the reception time is less than β + γ + ε (Yes in step S2706), the satellite receiving station determines whether an entry for the corresponding terminal exists in its adjacent orbit notification frame transmission list (step S2707).

[0163] If the entry of the corresponding terminal exists in the adjacent orbit notification frame transmission list of the local station (Yes in step S2707), the satellite receiving station further determines whether the remaining number of satellite receiving stations to be transmitted stored in the terminal information being processed is greater than 1 (step S2708).

[0164] If the remaining number of satellite receiving stations to be transmitted is greater than 1 (Yes in step S2708), the satellite receiving station overwrites the remaining number of satellite receiving stations in the adjacent orbit notification frame transmission list of the local station with the value obtained by subtracting 1 from the value stored in the terminal information of the received adjacent orbit notification frame, and stores the frame information (number of frame reception information, frame reception information) stored in the terminal information in the adjacent orbit notification frame transmission list (step S2709).

[0165] If the remaining number of satellite receiving stations to be transmitted is 1 or less (No in step S2708), it means that the frame from the corresponding terminal will not reach the satellite receiving stations on the further adjacent orbits. In this case, the satellite receiving station deletes the entry of the corresponding terminal from its adjacent orbit notification frame transmission list (step S2710). Then, the satellite receiving station executes the optimal receiving station determination process for the corresponding terminal (step S2711).

[0166] Next, the satellite receiving station determines whether it is necessary to transmit a reception target terminal deletion notification frame as a result of the optimal receiving station determination process (step S2712). In the optimal receiving station determination process, the satellite receiving station that can receive the frame from the corresponding terminal for the longest time is determined as the optimal receiving station for the corresponding terminal, and the other satellite receiving stations should not regard the corresponding terminal as a reception target, and thus it is determined that it is necessary to transmit a reception target terminal deletion notification frame.

[0167] If it is necessary to transmit a reception target terminal deletion notification frame (Yes in step S2712), the satellite receiving station stores the ID of the corresponding terminal in the reception target terminal cancellation notification frame addressed to the satellite receiving stations that are not the optimal receiving station (step S2713).

[0168] Also, when the entry of the corresponding terminal does not exist in the adjacent orbit notification frame transmission list (No in step S2707), the satellite receiving station determines whether the entry of the corresponding terminal exists in its own non-optimal orbit notification frame transmission list (step S2714).

[0169] When the entry of the corresponding terminal exists in its own non-optimal orbit notification frame transmission list (Yes in step S2714), first, the satellite receiving station acquires nRxInfo indicating the number of frame reception information stored in the terminal information of the received adjacent orbit notification frame (step S2715), and repeats the following processing for the frame reception information nRxInfo times.

[0170] The satellite receiving station first acquires the ID (SAT ID) of the satellite receiving station stored in the frame reception information (step S2716). Next, the satellite receiving station determines whether the satellite receiving station with the acquired ID orbits in the same direction as itself (step S2717). If the satellite receiving station with the acquired ID orbits in the same direction (Yes in step S2717), the satellite receiving station stores the corresponding terminal ID in the reception target terminal deletion notification frame addressed to the acquired satellite receiving station ID (step S2718).

[0171] After the satellite receiving station executes the processing consisting of steps S2716 to S2718 for all the frame reception information stored in the terminal information, it determines whether the remaining number of satellite receiving stations of the entry of the corresponding terminal in the non-optimal orbit notification frame transmission list is greater than 1 (step S2719).

[0172] If the number of remaining satellite receiving stations for transmission is greater than 1 (Yes in step S2719), the satellite receiving station overwrites the number of remaining satellite receiving stations for transmission in that entry with the value obtained by subtracting 1 from the value stored in the received terminal information (step S2720). On the other hand, if the number of remaining satellite receiving stations for transmission is 1 or less, it means that the frame from the corresponding terminal will no longer reach the satellite receiving stations on the adjacent orbits. Therefore, the satellite receiving station deletes the entry of the corresponding terminal from the non-optimal orbit notification frame transmission list (step S2721).

[0173] Also, if the corresponding terminal does not exist in the non-optimal orbit notification frame transmission list (No in step S2714), the satellite receiving station determines whether the number of remaining satellite receiving stations for transmission stored in the terminal information being processed is greater than 1 (step S2722).

[0174] If the number of remaining satellite receiving stations for transmission is greater than 1 (Yes in step S2722), the satellite receiving station adds the corresponding terminal to its adjacent orbit notification frame transmission list using the value stored in the terminal information (step S2723). At that time, the number of remaining satellite receiving stations for transmission is changed to the value obtained by subtracting 1 from the value stored in the received terminal information.

[0175] On the other hand, if the number of remaining satellite receiving stations for transmission is 1 or less (No in step S2723), it means that the frame from the corresponding terminal will no longer reach the satellite receiving stations on the adjacent orbits. In this case, the satellite receiving station executes the optimal receiving station determination process for the corresponding terminal (step S2724). As a result of the optimal receiving station determination process, if it is necessary to transmit a received target terminal deletion notification frame (Yes in step S2725), the satellite receiving station stores the ID of the corresponding terminal in the received target terminal deletion notification frame addressed to the satellite receiving station determined not to be the optimal receiving station (step S2726).

[0176] Once the satellite receiving station has completed the above processing for all the terminal information stored in the adjacent orbit notification frame, it needs to determine whether it is necessary to send a receiving target terminal deletion notification frame (step S2727). Specifically, as a result of executing the optimal receiving station determination process in step S2711 or step S2724, all of the satellite IDs of the frame reception information stored in the terminal information being processed that were not determined to be the optimal receiving station will become the targets for sending the receiving target terminal deletion notification frame.

[0177] And, if it is necessary to send a receiving target terminal deletion notification frame (Yes in step S2727), the satellite receiving station stores the number of terminals stored in the receiving target terminal deletion notification frame in nInfo and sends it (step S2728). Since the receiving target terminal deletion notification frame is sent to each satellite receiving station determined not to be the optimal receiving station, multiple receiving target terminal deletion notification frames may be sent.

[0178] Figure 28 shows, in the form of a flowchart, the procedure of the optimal receiving station determination process that the satellite receiving station performs in the reception process of the adjacent orbit notification frame (in steps S2711 and S2724 in the flowchart shown in Figure 27).

[0179] First, the satellite receiving station obtains nRxInfo indicating the number of frame reception information stored in the terminal information of the adjacent orbit notification frame being processed (step S2801), and checks whether nRxInfo is greater than 1 (step S2802).

[0180] If nRxInfo is greater than 1 (Yes in step S2802), the satellite receiving station estimates the receivable time from the frequency error estimation result and the propagation delay estimation result stored in each frame reception information (step S2803).

[0181] Next, the satellite receiving station estimates the reception available time for all frame reception information stored in the terminal information. Then, the satellite receiving station with the longest reception available time for the frames from the corresponding terminal is determined as the optimal receiving station for the corresponding terminal, and the other satellite receiving stations should not target the corresponding terminal for reception. Therefore, it is determined that it is necessary to transmit a reception target terminal deletion notification frame (step S2804).

[0182] Supplement the frequency error estimation and propagation delay estimation in step S2803 in the flowchart shown in FIG. 28. FIG. 29 shows an example of the time variation of the frequency error and propagation delay when the altitude of the satellite is 600 km and the frequency is 2 GHz. FIG. 29 is an example when the satellite passes over the head of the terminal. It is assumed that the satellite receiving station can receive for 6 minutes from 0 to 6 minutes for one terminal. For the calculation of the frequency error, the model described in 3GPP TR 38.811 V15.1.0 (Non-Patent Document 1) was referred to. In the example shown in FIG. 29, at the 3rd minute, the satellite receiving station is exactly over the head of the terminal, the propagation delay is minimized, and the sign of the frequency error is reversed.

[0183] By comparing the frequency error estimation result and propagation delay estimation result of the received frame from the terminal with the chart in FIG. 29, it is possible to determine at which moment during the 6 minutes when the frame from the terminal can be received. Also, when the satellite receiving station moves in one direction at a predetermined speed over the head of the terminal, the relative positional relationship between the terminal and the satellite receiving station corresponding to the determined moment can be estimated.

[0184] For example, when the data transmission interval is 3 minutes, the frequency error estimation result notified in the frame reception information frame is 30 kHz, and the propagation delay estimation result is 2.5 milliseconds, it corresponds to the 2nd minute during the 6 minutes when reception is possible. Therefore, since the next data frame corresponds to the 5th minute during the 6 minutes when reception is possible, it can be received by the same satellite receiving station.

[0185] On one hand, when the data transmission interval is 3 minutes, the frequency error estimation result notified in the frame reception information frame is -30 kHz, and the propagation delay estimation result is 2.5 milliseconds, it corresponds to the 5th minute out of the receivable 6 minutes. Therefore, since the next data frame corresponds to the time after the elapse of the receivable 6 minutes, it cannot be received by the same receiving station. Thus, considering that the satellite receiving station moves in one direction on the satellite orbit, it is possible to estimate the remaining receivable time at the satellite receiving station that has received the frame from the terminal by combining the frequency error and the propagation delay.

[0186] In short, each satellite receiving station shares frame reception information including the frequency error estimation result and the propagation delay estimation result of the frame received from the terminal, and based on the frequency error estimation result, the propagation delay estimation result, the frame transmission interval, and the positional relationship of adjacent satellite receiving stations, determines whether the next data frame to be transmitted from the corresponding terminal can be received by the same satellite receiving station.

[0187] Figure 30 shows, in the form of a flowchart, the processing procedure for a satellite receiving station to transmit a non-optimal orbit notification frame.

[0188] First, the satellite receiving station determines whether it has reached the start time of the adjacent orbit notification frame transmission slot assigned to itself (step S3001). Then, when the start time of the adjacent orbit notification frame transmission slot assigned to the satellite receiving station has arrived (Yes in step S3001), the satellite receiving station checks whether the non-optimal orbit notification frame transmission list (for example, refer to FIG. 25) is not empty (step S3002).

[0189] If the non-optimal orbit notification frame transmission list is not empty (Yes in step S2602), the satellite receiving station checks whether its satellite orbit is the maximum satellite orbit (step S3003).

[0190] Here, when its own satellite orbit is the maximum satellite orbit (Yes in step S3003), the satellite receiving station deletes from the non-optimal orbit notification frame transmission list all the terminals registered therein (step S3009). Therefore, no non-optimal orbit notification frame is transmitted from the satellite receiving station on the maximum satellite orbit.

[0191] On the other hand, when its own satellite orbit is not the maximum satellite orbit (No in step S3003), the satellite receiving station repeatedly executes the processes of the following steps S3004 to S3006 for the number of terminals registered in the non-optimal orbit notification frame transmission list.

[0192] In step S3004, the satellite receiving station obtains the terminal ID, reception time, and remaining number of satellite receiving stations of the terminal that received the notification frame from the non-optimal orbit notification frame transmission list.

[0193] In step S3005, the satellite receiving station generates terminal information using the information obtained from the non-optimal orbit notification frame transmission list in step S3004 and stores it in the non-optimal orbit notification frame.

[0194] In step S3006, the satellite receiving station deletes the entry of the terminal in which the terminal information was stored in step S3005 from the non-optimal orbit notification frame transmission list.

[0195] Then, when the process of storing the terminal information of all the terminals registered in the non-optimal orbit notification frame transmission list in the non-optimal orbit notification frame is completed, the satellite receiving station stores the number of terminal information stored in the non-optimal orbit notification frame in the nInfo field (step S3007).

[0196] Then, the satellite receiving station transmits a non-optimal orbit notification frame to the satellite receiving station whose satellite ID is the orbit number + 1 and has the same revolution sequence number (that is, the satellite receiving stations located at approximately the same latitude on adjacent orbits) (step S3008).

[0197] For example, in the arrangement example of satellite receiving station numbers shown in FIG. 10, when the ID of the satellite receiving station executing the process shown in FIG. 30 is (1 - 3), in step S3008, a non-optimal orbit notification frame is transmitted to the satellite receiving station (2 - 3).

[0198] FIGS. 31A and 31B show, in the form of a flowchart, the processing procedure for a satellite receiving station to receive a non-optimal orbit notification frame.

[0199] First, the satellite receiving station determines whether it has received a non-optimal orbit notification frame (step S3101). Then, when the satellite receiving station has received a non-optimal orbit notification frame (Yes in step S3101), it demodulates the received frame (step S3102) and determines whether the demodulation process has succeeded (step S3103).

[0200] When the satellite receiving station succeeds in demodulating the non-optimal orbit notification frame (Yes in step S3103), it obtains nInfo indicating the number of terminal information stored in the data part of the non-optimal orbit notification frame (step S3104). Then, the satellite receiving station repeatedly executes the processing of the terminal information shown in FIG. 31B nInfo times.

[0201] First, the satellite receiving station obtains the terminal ID, the reception time, and the remaining number of satellite receiving stations to be transmitted from the terminal information (step S3105).

[0202] Next, the satellite receiving station determines whether the difference between the current time and the reception time of the frame from the corresponding terminal is less than (β + γ + ε) (step S3106).

[0203] Here, when the difference between the current time and the reception time (that is, the elapsed time from the reception time) is (β + γ + ε) or more (No in step S3106), it is because the non-optimal orbit notification frame was not transmitted during the time slot between the notification frame transmission and the data frame transmission for some reason. In this case, the satellite receiving station skips all subsequent processing and ignores the terminal information being processed.

[0204] If the difference between the current time and the reception time of the satellite receiving station is less than (β + γ + ε), that is, if the elapsed time from the reception time is less than β + γ + ε (Yes in step S3106), the satellite receiving station determines whether an entry for the corresponding terminal exists in its own reception target terminal list (step S3107). If the corresponding terminal entry exists in the reception target terminal list (Yes in step S3107), the entry for the corresponding terminal is deleted from the reception target terminal list (step S3108). Therefore, since the satellite receiving station excludes terminals on non-optimal orbits from the reception targets, it is possible to avoid the waste of multiple satellite receiving stations receiving the same terminal redundantly.

[0205] Next, the satellite receiving station determines whether an entry for the corresponding terminal exists in its adjacent orbit notification frame transmission list (step S3109). If the entry for the corresponding terminal exists in the adjacent orbit notification frame transmission list (Yes in step S3109), the satellite receiving station deletes the entry for the corresponding terminal from the adjacent orbit notification frame transmission list (step S3110). Therefore, the satellite receiving station can avoid the waste of notifying the information of the terminal that it has found to be on a non-optimal orbit and excluded from the reception targets in the adjacent orbit notification frame.

[0206] Next, the satellite receiving station determines whether the number of remaining transmitting satellite receiving stations is greater than 1 (step S3111). If the number of remaining transmitting satellite receiving stations is greater than 1 (Yes in step S3111), it means that the frame from the corresponding terminal may reach satellite receiving stations on adjacent orbits. Therefore, the satellite receiving station adds an entry for the corresponding terminal to its non-optimal orbit notification frame transmission list (step S3112). At that time, the number of remaining transmitting satellite receiving stations is changed to the value obtained by subtracting 1 from the value stored in the terminal information during the processing of the received non-optimal orbit notification frame.

[0207] Also, if there is no entry for the corresponding terminal in its own adjacent orbit notification frame transmission list (No in step S3109), the satellite receiving station further determines whether there is an entry for the corresponding terminal in its non-optimal orbit notification frame transmission list (step S3113).

[0208] If there is an entry for the corresponding terminal in the non-optimal orbit notification frame transmission list (Yes in step S3113), the satellite receiving station determines whether the remaining number of satellite receiving stations stored in the terminal information is greater than 1 (step S3114).

[0209] If the remaining number of satellite receiving stations is greater than 1 (Yes in step S3114), the satellite receiving station updates the remaining number of satellite receiving stations in the non-optimal orbit notification frame transmission list (changes it to the value obtained by subtracting 1) (step S3115). Also, if the remaining number of satellite receiving stations is 1 or less (No in step S3114), it means that the frame from the corresponding terminal will not reach the satellite receiving stations on the further adjacent orbit. Therefore, the satellite receiving station deletes the entry for the corresponding terminal from the non-optimal orbit notification frame transmission list (step S3116).

[0210] Also, if there is no entry for the corresponding terminal in the non-optimal orbit notification frame transmission list (No in step S3113), the satellite receiving station determines whether the remaining number of satellite receiving stations is greater than 1 (step S3117). And if the remaining number of satellite receiving stations is greater than 1 (Yes in step S3117), it means that the frame from the corresponding terminal will reach the satellite receiving stations on the further adjacent orbit. Therefore, the satellite receiving station adds an entry for the corresponding terminal to its non-optimal orbit notification frame transmission list (step S3118). At that time, the remaining number of satellite receiving stations is changed to the value obtained by subtracting 1 from the value stored in the terminal information being processed.

[0211] FIG. 32 shows, in the form of a flowchart, the processing procedure for the satellite receiving station to receive the reception target terminal deletion notification frame.

[0212] First, the satellite receiving station determines whether it has received a reception target deletion notification frame (step S3201). Then, when the satellite receiving station has received a reception target deletion notification frame (Yes in step S3201), it demodulates the received frame (step S3202) and determines whether the demodulation process has succeeded (step S3203).

[0213] When the satellite receiving station has succeeded in demodulating the reception target terminal deletion notification frame (Yes in step S3203), it obtains nSTA indicating the number of terminal IDs stored in the data part of the reception target deletion notification frame (step S3204). Then, the satellite receiving station repeatedly executes the processes of steps S3205 to S3207 nSTA times.

[0214] In step S3205, the satellite receiving station obtains the terminal ID from the data part of the reception target terminal deletion notification frame. Next, in step S3206, the satellite receiving station checks whether the terminal ID obtained in step S3205 exists in its own reception target terminal list. And when the obtained terminal ID exists in its own reception target terminal list (Yes in step S3206), in step S3207, the satellite receiving station deletes the entry of that terminal ID from its own reception target terminal list. As a result, the satellite receiving station can avoid the waste of receiving frames from terminals for which it is not the optimal receiving station in duplicate with the optimal receiving station.

[0215] Fig. 33 shows, in the form of a flowchart, the processing procedure for the satellite receiving station to receive a data frame from a terminal. The reception process of the data frame is executed for terminals registered in the reception target terminal list for which β + γ + ε or more has elapsed since the reception time. Also, it is assumed that the satellite receiving station can perform the reception process of the data frame in parallel.

[0216] First, the satellite receiving station refers to the list of terminals to be received, and calculates the radio resources (time and frequency) from which the registered terminals transmit data frames and the information necessary for demodulating the data frames based on the above-described Rules 1 to 4 (step S3301).

[0217] Next, the satellite receiving station determines whether the data frame reception time calculated in step S3301 has arrived (step S3302). When the data frame reception time arrives (Yes in step S3302), the satellite receiving station receives and demodulates the data frame from the corresponding terminal (steps S3303, S3304).

[0218] Then, the satellite receiving station deletes the entry of the terminal that is the target for receiving the data frame from the list of terminals to be received (step S3305), and ends this process.

[0219] C-8. Optimal Receiving Station Selection Operations In this section, an operation example for selecting an optimal receiving station from among satellite receiving stations that can simultaneously receive frames from one terminal will be described according to the present disclosure.

[0220] Figures 34 to 37 show specific operation examples for selecting the optimal receiving station. In Figures 34 to 37, the satellite orbits as shown in Figures 8 to 10 are developed on a plane. There are 8 satellite receiving stations orbiting on each of the 4 satellite orbits, and the satellite receiving stations are arranged at equal intervals on each satellite orbit. The satellite receiving stations with the same orbit sequence number are assigned numbers so that they are located at approximately the same latitude at the same time. In each figure, for the sake of convenience, the vertical direction is assigned a satellite orbit number as the satellite orbit, and the satellite receiving stations drawn in circles are arranged on a two-dimensional matrix so that the same orbit sequence numbers are aligned in the row direction. Here, the number of simultaneously receivable satellite receiving stations is set to 3 for the same orbit and 3 for adjacent orbits. In each figure, the range within which frames from the corresponding terminal can be simultaneously received is shown enclosed by a dotted line. Also, the satellite receiving stations in which the corresponding terminal is registered in the reception target terminal list are shown as circles filled with a light gray, and the other satellite receiving stations are shown as circles filled with a dark gray. Also, for the sake of simplicity of explanation, it is assumed that there is one corresponding terminal.

[0221] Figure 34 shows the state immediately after the satellite receiving stations receive the notification frame from the corresponding terminal. In the figure, satellite receiving stations 2-5, 2-6, 3-5, 3-6, 4-4, and 4-5 receive the notification frame from the corresponding terminal and register the corresponding terminal in their respective reception target terminal lists. Therefore, satellite receiving stations 2-5, 2-6, 3-5, 3-6, 4-4, and 4-5 are shown in light gray.

[0222] Figure 35 shows the state in which each satellite receiving station that has received the notification frame from the corresponding terminal transmits the same orbit notification frame. In the figure, the same orbit notification frame is indicated by a black arrow. Each satellite receiving station that has received the notification frame from the corresponding terminal transmits the same orbit notification frame to the satellite receiving station in front in the circumferential direction on the same orbit. And the satellite receiving station that has received the same orbit notification frame deletes the entry of the corresponding terminal if the corresponding terminal is registered in its own reception target terminal list. The satellite receiving stations 2-5, 3-5, and 4-4 that have deleted the entry of the corresponding terminal from the reception target terminal list have switched from light gray to dark gray display.

[0223] When a frame from a corresponding terminal can be received by a plurality of satellite receiving stations on the same orbit, the later satellite receiving station in the orbiting direction has a longer reception available time for the frame from the corresponding terminal (as described above). In other words, the satellite receiving station that is ahead in the orbiting direction has a short reception available time and is not suitable for receiving the frame from the corresponding terminal. Therefore, each satellite receiving station deletes the entry of the corresponding terminal from the reception target list in response to receiving the same orbit notification frame from a later satellite receiving station on the same orbit. As can be seen from FIG. 35, by each satellite receiving station transmitting the same orbit notification frame, the number of satellite receiving stations that receive the frame from the corresponding terminal redundantly can be reduced.

[0224] FIG. 36 shows a state in which a satellite receiving station transmits an adjacent orbit notification frame and a non-optimal orbit notification frame. Each satellite receiving station transmits the adjacent orbit notification frame and the non-optimal orbit notification frame to a satellite receiving station having a satellite orbit number of +1 and the same orbiting sequence number, which is located at approximately the same latitude on the adjacent orbit. In the figure, the adjacent orbit notification frame is indicated by a black arrow, and the non-optimal orbit notification frame is indicated by a gray arrow. The satellite receiving station 4-5 that has received the non-optimal orbit notification frame deletes the entry of the corresponding terminal from its own reception target terminal list and switches from a light gray display to a dark gray display. As can be seen from FIG. 36, by each satellite receiving station transmitting the adjacent orbit notification frame and the non-optimal orbit notification frame, the number of satellite receiving stations that receive the frame from the corresponding terminal redundantly can be further reduced.

[0225] FIG. 37 shows a state in which an optimal receiving station determination is made and a satellite receiving station transmits a reception target terminal deletion notification frame. In the figure, the reception target terminal deletion notification frame is indicated by a black arrow. When the remaining number of transmitting satellite receiving stations for the terminal information notified by the adjacent orbit notification frame becomes 1 or less, the satellite receiving station performs an optimal receiving station determination process for the corresponding terminal and transmits a reception target terminal deletion notification frame to a satellite receiving station that is not optimal for the corresponding terminal (see FIGS. 27A to 27C).

[0226] Satellite receiving stations 4-6 receive the adjacent orbit notification frame at the stage shown in Fig. 36. Since the number of remaining transmitting satellite receiving stations has reached 1, the optimal receiving station determination process is executed, and among satellite receiving stations 2-6 and 3-6, the satellite receiving station with the longer receivable time becomes the optimal receiving station. In the example shown in Fig. 37, since the receivable time of satellite receiving station 3-6 was longer, satellite receiving station 4-6 transmits a received target terminal deletion notification frame to satellite receiving station 2-6. Satellite receiving station 2-6 receives the received target terminal deletion notification frame, deletes the entry of the corresponding terminal from its received target terminal list, and switches from a light gray display to a dark gray display. As can be seen from Fig. 37, when the satellite receiving station transmits the received target terminal deletion notification frame, only the optimal receiving station receives the frame from the corresponding terminal.

[0227] In the examples shown in Figs. 34 to 37, among the six satellite receiving stations that received the notification frame, finally, the corresponding terminal is registered only in the received target terminal list of satellite receiving station 3-6, which is the optimal receiving station.

[0228] Figs. 38 to 41 show the specific operability for selecting the optimal receiving station when there are satellite receiving stations that can receive simultaneously across the maximum and minimum satellite orbits. In Figs. 38 to 41 as well, the satellite orbits are unfolded on a plane as shown in Figs. 8 to 10. There are 8 satellite receiving stations orbiting on each of the 4 satellite orbits, and the satellite receiving stations are arranged at equal intervals on each satellite orbit. The satellite receiving stations with the same orbit number and the same circumferential sequence number are numbered so that they are located at approximately the same latitude at the same time. The satellite orbit numbers and the circumferential sequence numbers on each satellite orbit are the same as those in the examples shown in Figs. 34 to 37. Also, the number of satellite receiving stations that can receive simultaneously is set as 3 in the same orbit and 3 in adjacent orbits. In each figure, the range within which the frames from the corresponding terminal can be received simultaneously is enclosed by a dotted line and shown.

[0229] Figure 38 shows the state immediately after the satellite receiving station has received the notification frame from the corresponding terminal. In this figure, satellite receiving stations 4-5, 4-6, 1-8, 2-1, and 2-8 have received the notification frame from the corresponding terminal and registered the corresponding terminal in their respective received target terminal lists. Therefore, satellite receiving stations 4-5, 4-6, 1-8, 2-1, and 2-8 are shown in light gray.

[0230] Figure 39 shows the state where each satellite receiving station that has received the notification frame transmits the same orbit notification frame. In this figure, the same orbit notification frame is indicated by a black arrow. Each satellite receiving station that has received the notification frame transmits the same orbit notification frame to the satellite receiving station in front in the circumferential direction on the same orbit. And the satellite receiving station that has received the same orbit notification frame deletes the entry of the corresponding terminal if the corresponding terminal is registered in its received target terminal list. Satellite receiving stations 4-5 and 2-8 that have deleted the entry of the corresponding terminal from the received target terminal list have switched from light gray to dark gray display.

[0231] Each satellite receiving station deletes the entry of the corresponding terminal from the received target list in response to receiving the same orbit notification frame from the satellite receiving station behind on the same orbit. As can be seen from Figure 39, by each satellite receiving station transmitting the same orbit notification frame, the number of satellite receiving stations that receive the frame from the corresponding terminal redundantly can be reduced.

[0232] Figure 40 shows the state where the satellite receiving station transmits the adjacent orbit notification frame and the non-optimal orbit notification frame. Each satellite receiving station transmits the adjacent orbit notification frame and the non-optimal orbit notification frame to the satellite receiving stations located at approximately the same latitude on the adjacent orbit. In this figure, the adjacent orbit notification frame is indicated by a black arrow, and the non-optimal orbit notification frame is indicated by a gray arrow.

[0233] Satellite receiving station 4-6 is the maximum satellite orbit and has a different traveling direction from the adjacent satellite orbits. Therefore, satellite receiving station 4-6 transmits an adjacent orbit notification frame to all adjacent satellite receiving stations 1-5, 1-6, 1-7, 1-8, 1-1 with satellite orbit number 1 and the orbit sequence number being the orbit sequence number of the adjacent orbit satellite receiving stations ± (the maximum number of simultaneous receptions on the same orbit - 1).

[0234] In addition, since satellite receiving station 2-8 has received the adjacent orbit notification frame and also received the same orbit frame, it meets the conditions and transmits a reception target terminal deletion frame to satellite receiving station 1-8. As a result, satellite receiving station 1-8 deletes the entry of the corresponding terminal from its reception target terminal list and switches from a light gray display to a dark gray display.

[0235] As can be seen from FIG. 40, by each satellite receiving station transmitting an adjacent orbit notification frame and a non-optimal orbit notification frame, the number of satellite receiving stations that receive frames from the corresponding terminal redundantly can be further reduced.

[0236] FIG. 41 shows the state where the optimal receiving station determination is performed and the satellite receiving station transmits a reception target terminal deletion notification frame. In the figure, the reception target terminal deletion notification frame is indicated by a black arrow. When the remaining number of satellite receiving stations for transmitting the terminal information notified by the adjacent orbit notification frame becomes 1 or less, the satellite receiving station performs the optimal receiving station determination process for the corresponding terminal and transmits a reception target terminal deletion notification frame to the satellite receiving stations that are not optimal for the corresponding terminal (see FIGS. 27A to 27C).

[0237] Satellite receiving stations 2-4 receive the adjacent orbit notification frame at the stage shown in Fig. 40. Since the number of remaining transmitting satellite receiving stations has become 1, the optimal receiving station determination process is executed, and since it has become the optimal receiving station with a long receivable time, a received target terminal deletion notification frame is transmitted to satellite receiving stations 4-6. Satellite receiving stations 4-6 receive the received target terminal deletion notification frame, delete the entry of the corresponding terminal from their received target terminal list, and have switched from a light gray display to a dark gray display. As can be seen from Fig. 41, when the satellite receiving station transmits the received target terminal deletion notification frame, only the optimal receiving station will be in a state of receiving frames from the corresponding terminal.

[0238] In the example shown in Figs. 38 to 41, among the five satellite receiving stations that received the notification frame, finally, the corresponding terminal is registered only in the received target terminal list of satellite receiving station 2-4, which is the optimal receiving station.

[0239] D. Effects Summarize the effects brought about by the present disclosure.

[0240] According to the present disclosure, even when the terminal exists within the receivable range of a plurality of satellite receiving stations, the plurality of satellite receiving stations can select the optimal receiving station based on the notification frame received from the terminal. Therefore, just by transmitting the notification frame, the terminal can avoid a situation where a plurality of satellite receiving stations receive the data frame of the same terminal and perform demodulation processing. As a result, power consumption reduction and cost reduction of the terminal can be achieved. Furthermore, by preventing wasteful reception and demodulation processing in the satellite receiving station, the following effects are achieved. (1) Increase in the number of accommodated stations per receiving station (2) Reduction in the number of receiving stations required in the system (3) Cost reduction of communication services

Industrial Applicability

[0241] The present disclosure has been described in detail with reference to specific embodiments. However, it is obvious that those skilled in the art can make modifications and substitutions to the embodiments without departing from the gist of the present disclosure.

[0242] In this specification, embodiments applying the present disclosure to LPWA communication systems have been mainly described. However, the gist of the present disclosure is not limited thereto. The present disclosure can be similarly applied to various types of communication systems that communicate between terrestrial terminals and satellite receiving stations orbiting the Earth. Further, in this specification, for convenience, embodiments specialized for a specific satellite constellation have been described. However, the present disclosure can be similarly applied to communication systems using other satellite constellations and can also be compatible with any number of satellite receiving stations.

[0243] In short, the present disclosure has been described by way of example, and the contents described in this specification should not be interpreted restrictively. The claims should be referred to in order to determine the gist of the present disclosure.

[0244] Note that the present disclosure can also be configured as follows.

[0245] (1) It operates as one of the satellite receiving stations orbiting the Earth in a predetermined orbit and receiving frames from terrestrial terminals, a receiving unit that receives and processes frames from the terminal, a determination unit that exchanges frame reception information at the time of frame reception from the terminal with surrounding satellite receiving stations and determines a satellite receiving station suitable for receiving the frame to be transmitted next by the terminal, A communication device comprising:

[0246] (2) The surrounding satellite receiving stations include satellite receiving stations moving in the same orbit and satellite receiving stations moving in adjacent orbits, and the satellite receiving stations moving in adjacent orbits include cases where the traveling directions are the same and different, The communication device according to (1) above.

[0247] (3) Notify information regarding the frames received by each satellite receiving station on the same orbit from the terminal to the satellite receiving station ahead on the same orbit. The communication device according to any one of (1) or (2) above.

[0248] (4) Notify information regarding the received frames for each terminal within a range corresponding to the maximum number of satellite receiving stations on the same orbit that can simultaneously receive frames from the same terminal. The communication device according to (3) above.

[0249] (5) Based on the above notification from the satellite receiving station behind on the same orbit, exclude from the reception targets of its own station the terminals from which the satellite receiving station behind on the same orbit can receive the next frame. The communication device according to any one of (3) or (4) above.

[0250] (6) Notify information regarding the terminals from which each satellite receiving station on an adjacent orbit has received a frame to the satellite receiving stations located at approximately the same latitude on the adjacent orbit. The communication device according to any one of (1) to (5) above.

[0251] (7) Determine the satellite receiving station that performs the above notification in consideration of whether the traveling directions of the satellite receiving stations on the adjacent orbit are the same or different. The communication device according to (6) above.

[0252] (8) Notify information regarding each terminal within a range corresponding to the maximum number of orbits that can simultaneously receive frames from the same terminal at the position (latitude) at the time of frame reception. The communication device according to any one of (6) or (7) above.

[0253] (9) Based on the above notification from other satellite receiving stations on the adjacent orbit, determine the satellite receiving station suitable for receiving the frame to be transmitted next by the corresponding terminal. The communication device according to any one of (6) to (8) above.

[0254] (10) Based on the reception possible time estimated from the frequency error estimation result and propagation delay estimation result at the time of frame reception from the corresponding terminal, determine whether the corresponding terminal is suitable for receiving the frame to be transmitted next. The communication device according to the above (9).

[0255] (11) Notify the satellite receiving station determined not to be suitable for receiving the frame to be transmitted next by the corresponding terminal to exclude the corresponding terminal from the reception targets. The communication device according to any one of the above (9) or (10).

[0256] (12) Notify the satellite receiving stations located at approximately the same latitude on adjacent orbits of information regarding the terminals not suitable for performing the next frame reception. The communication device according to any one of the above (1) to (11).

[0257] (13) Perform the above notification within a range corresponding to the maximum number of orbits capable of simultaneously receiving frames from the same terminal at the position (latitude) at the time of frame reception. The communication device according to the above (12).

[0258] (14) Exclude the corresponding terminal from the reception targets of the local station based on the above reception from other satellite receiving stations on adjacent orbits. The communication device according to any one of the above (12) or (13).

[0259] (15) A communication method that operates as a satellite receiving station orbiting the Earth on a predetermined orbit and receiving frames from terminals on the ground, A reception step of receiving and processing a frame from the terminal, A determination step of exchanging frame reception information at the time of frame reception from the terminal with surrounding satellite receiving stations to determine a satellite receiving station suitable for receiving the frame to be transmitted next by the terminal. A communication method having the above steps.

[0260] (16) Comprising a terminal installed on the ground and a plurality of satellite receiving stations respectively orbiting the Earth on predetermined orbits. Each of the plurality of satellite receiving stations includes a receiving unit that receives and processes a frame from the terminal, and a determination unit that exchanges frame reception information at the time of frame reception from the terminal with surrounding satellite receiving stations to determine a satellite receiving station suitable for receiving a frame to be transmitted next by the terminal. Communication system.

Explanation of symbols

[0261] 100…Terminal, 101…Wireless communication unit, 102…Wireless control unit 103…Frame generation unit, 104…Sensor 105…Wireless resource determination unit, 106…Memory unit 200…Receiving station, 201…Wireless communication unit, 202…Wireless control unit 203…Frame detection / demodulation unit, 204…Wireless resource determination unit 205…Memory unit 1000…Satellite receiving station, 1200…LPWA unit, 1300…Inter-satellite communication unit 1301…Wireless communication unit, 1302…Wireless control unit 1303…Frame generation unit, 1304…Frame detection / demodulation unit 1305…Optimal orbit determination unit

Claims

1. It operates as one of the satellite receiving stations that orbit the Earth on a predetermined orbit and receive frames from ground terminals, a receiving unit that receives and processes frames from the terminal, a determination unit that exchanges frame reception information at the time of frame reception from the terminal with surrounding satellite receiving stations and determines a satellite receiving station suitable for receiving the frame to be transmitted next by the terminal, comprising: notifying satellite receiving stations located at approximately the same latitude on adjacent orbits of information regarding the terminals from which each satellite receiving station on the adjacent orbit has received a frame, the determination unit determines a satellite receiving station suitable for receiving the frame to be transmitted next by the corresponding terminal based on the receivable time estimated from the frequency error estimation result and propagation delay estimation result at the time of frame reception from the corresponding terminal included in the notification from other satellite receiving stations on the adjacent orbit, a communication device.

2. The surrounding satellite receiving stations include satellite receiving stations moving on the same orbit and satellite receiving stations moving on adjacent orbits, and the satellite receiving stations moving on the adjacent orbits include cases where the traveling directions are the same and different, The communication device according to Claim 1.

3. Notifying a satellite receiving station ahead on the same orbit of information regarding the frames received by each satellite receiving station on the same orbit from the terminal, The communication device according to Claim 1.

4. Notifying information regarding the received frames for each terminal within a range corresponding to the maximum number of satellite receiving stations on the same orbit that can simultaneously receive frames from the same terminal, The communication device according to Claim 3.

5. Based on the notification from a satellite receiving station behind on the same orbit, excluding terminals that can receive the next frame by the satellite receiving station behind on the same orbit from the reception targets of its own station, The communication device according to Claim 3.

6. Determining the satellite receiving station that performs the notification in consideration of whether the traveling directions of the satellite receiving stations on the adjacent orbits are the same or different, The communication device according to Claim 1.

7. Notifying information regarding each terminal within a range corresponding to the maximum number of orbits that can simultaneously receive frames from the same terminal at the position (latitude) at the time of frame reception, The communication device according to Claim 1.

8. Notifying a satellite receiving station determined to be unsuitable for receiving the frame to be transmitted next by the corresponding terminal to exclude the corresponding terminal from the reception targets, The communication device according to Claim 1.

9. Notifying satellite receiving stations located at approximately the same latitude on adjacent orbits of information regarding terminals not suitable for performing the next frame reception, The communication device according to claim 1.

10. The notification is performed within a range corresponding to the maximum number of satellite receiving stations on the same orbit capable of simultaneously receiving frames from the same terminal. The communication device according to claim 9.

11. Based on the reception from other satellite receiving stations on adjacent orbits, the corresponding terminal is excluded from the reception targets of the own station. The communication device according to claim 9.

12. A communication method that operates as a satellite receiving station that orbits the Earth on a predetermined orbit and receives frames from terminals on the ground, a receiving step of receiving and processing a frame from the terminal; a step of notifying satellite receiving stations located at approximately the same latitude on adjacent orbits of information regarding the terminals from which the respective satellite receiving stations on the adjacent orbits have received frames; a determination step of determining a satellite receiving station suitable for receiving a frame to be transmitted next by the corresponding terminal based on the receivable time estimated from the frequency error estimation result and the propagation delay estimation result at the time of receiving a frame from the corresponding terminal included in the notification from other satellite receiving stations on adjacent orbits; A communication method having the above.

13. Comprising a terminal installed on the ground and a plurality of satellite receiving stations each orbiting the Earth on a predetermined orbit, each of the plurality of satellite receiving stations receives a frame from the terminal, notifies satellite receiving stations located at approximately the same latitude on adjacent orbits of information regarding the terminals from which the respective satellite receiving stations on the adjacent orbits have received frames, and determines a satellite receiving station suitable for receiving a frame to be transmitted next by the corresponding terminal based on the receivable time estimated from the frequency error estimation result and the propagation delay estimation result at the time of receiving a frame from the corresponding terminal included in the notification from other satellite receiving stations on adjacent orbits. A communication system.

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