Communication device, communication method, and communication system

Abstract

Provided is a communication device for receiving a frame from a terrestrial terminal.　The communication device, which orbits the Earth in a predetermined orbit and operates as one of satellite receiving stations to receive a frame from a terrestrial terminal, comprises a receiving unit for performing a receiving process for a frame from the terminal, and a determining unit which, on the basis of frame reception information at the time of reception of the frame from the terminal, a frame transmission interval of the terminal, and the positional relationship of surrounding satellite receiving stations, determines a satellite receiving station suitable for receiving a frame transmitted from the terminal next. The frame reception information includes a frequency error estimation result and a propagation delay estimation result at the time of reception of the frame.

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 frames wirelessly transmitted from a terrestrial terminal, and a communication system including a terminal and a receiving station. [Background technology]

[0002] In wireless sensor networks, attaching wireless sensor terminals to people and objects and periodically transmitting information acquired from the sensors makes it possible to create new services. For example, by attaching wireless sensor terminals with GPS (Global Positioning System) to elderly people or children and periodically transmitting location information, it becomes possible to provide a monitoring service.

[0003] Wireless communication systems for the Internet of Things (IoT) must enable communication with many wireless sensor terminals attached to various people and objects. Therefore, long-distance transmission, which enables wide-area communication, and multi-terminal accommodation, which allows communication with many terminals per base station, are important. In recent years, Low Power Wide Area (LPWA), which has been considered a promising wireless communication method for the IoT, has made it possible to realize long-distance transmission and multi-terminal accommodation, achieving long-distance transmission of several kilometers to several hundred kilometers between terminals and receiving stations installed on the ground (see, for example, Patent Document 1). However, installing receiving stations requires securing land and laying a network for cloud connection, which is costly and time-consuming, hindering the reduction of communication service costs and the expansion of communication areas.

[0004] Meanwhile, in recent years, space development by private companies has become more active, and while launching a satellite previously required tens of billions of yen, development is underway with the aim of reducing costs to one-tenth to one-hundredth of that amount. Satellites are also becoming smaller, and as a result, the realization of services that cover the entire globe by launching multiple satellites at once and building constellations is being considered.

[0005] As satellite services become a reality, one possible way to expand the LPWA communication area is to install receivers on satellites and receive radio waves transmitted from terrestrial terminals on the satellite. LPWA has already achieved communication over distances of several hundred kilometers on the ground, and it is believed that low-earth orbit satellites will be sufficient for communication. Furthermore, since low-earth orbit satellites orbit the Earth, it is possible to cover the entire globe with a small number of satellites in use cases such as IoT, where data is transmitted once every few minutes to several days. Therefore, installing receivers on satellites is more cost-effective than installing many receiving stations on the ground, and this is expected to reduce the cost of communication services and rapidly expand the communication area. Furthermore, it will be possible to obtain information from the ocean, where it is difficult to install receiving stations on the ground, and new services will become possible. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-193306 [Non-patent literature]

[0007] [Non-Patent Document 1] 3GPP TR 38.811 V15.1.0 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present disclosure is to provide a communication device and a communication method that operates as a satellite receiving station that orbits the Earth in a predetermined orbit and receives frames from a terrestrial terminal, as well as a communication system consisting of a terrestrial terminal and a satellite receiving station. [Means for solving the problem]

[0009] A first aspect of the present disclosure provides a system for receiving frames from a ground terminal, the system comprising: a satellite receiving station that orbits the Earth in a predetermined orbit and operates as one of the satellite receiving stations that receives frames from a ground terminal; a receiving unit that receives and processes frames from the terminal; a determination unit that determines a satellite receiving station suitable for receiving the next frame transmitted by the terminal based on frame reception information when a frame is received from the terminal, a frame transmission interval of the terminal, and the positional relationship of surrounding satellite receiving stations; The communication device is provided with:

[0010] The frame reception information includes a frequency error estimation result and a propagation delay estimation result at the time of frame reception, or includes location information of the terminal.

[0011] The communication device according to the first aspect exchanges frame reception information with surrounding satellite receiving stations, and in this case, the determination unit further determines a satellite receiving station suitable for receiving the next frame transmitted by the terminal based on the frame reception information from the surrounding satellite receiving stations.

[0012] A communication device according to a first aspect notifies a nearby satellite receiving station of information about a terminal added to the target terminal list based on frame reception information from the nearby satellite receiving station, and also deletes information about the terminal from its own target terminal list based on the notification from the nearby satellite receiving station.

[0013] A communication device according to a first aspect notifies a nearby satellite receiving station that the determination unit has determined to be suitable for receiving the next frame transmitted from the terminal of target terminal registration, and removes the terminal that has notified the nearby satellite receiving station of target terminal registration from its own reception target. Also, the communication device according to the first aspect sets the terminal that has been notified of target terminal registration by the nearby satellite receiving station as a reception target for its own reception target.

[0014] If the frame reception information includes a frame transmission interval notified by the terminal, the determination unit estimates the expected reception time of the next frame transmitted from the terminal based on the frame transmission interval and the frequency error estimation result at the time of frame reception, and determines a satellite receiving station that is suitable for receiving the next frame transmitted by the terminal based on the expected reception time of the frame and the positional relationship of surrounding satellite receiving stations.

[0015] A second aspect of the present disclosure is a communication method that operates as a satellite receiving station that orbits the Earth in a predetermined orbit and receives frames from a terrestrial terminal, the method comprising: a receiving step of receiving and processing frames from the terminal; a determination step of determining a satellite receiving station suitable for receiving the next frame transmitted by the terminal based on frame reception information at the time of receiving a frame from the terminal, a frame transmission interval of the terminal, and the positional relationship of surrounding satellite receiving stations; It is a communication method having the above.

[0016] A third aspect of the present disclosure provides a system including a terminal installed on the ground and a plurality of satellite receiving stations each orbiting the Earth in a predetermined orbit; Each of the plurality of satellite receiving stations comprises a receiving unit that receives and processes frames from the terminal, and a determining unit that determines a satellite receiving station that is suitable for receiving the next frame transmitted by the terminal based on frame reception information when frames are received from the terminal, a frame transmission interval of the terminal, and a positional relationship between neighboring satellite receiving stations. It is a communication system.

[0017] However, the term "system" used here refers to a logical collection of multiple devices (or functional modules that realize specific functions), and it does not matter whether each device or functional module is contained within a single housing. [Effects of the Invention]

[0018] According to the present disclosure, it is possible to provide a communication device and a communication method that operate as a satellite receiving station, efficiently acquire information on radio resources of a terrestrial terminal, and receive frames from the terminal while suppressing unnecessary reception and demodulation processing, as well as a communication system that includes a terrestrial terminal and a satellite receiving station that receives frames from the terminal while suppressing unnecessary reception and demodulation processing.

[0019] It should be noted that the effects described in this specification are merely examples, and the effects brought about by the present disclosure are not limited to these. Furthermore, the present disclosure may also bring about additional effects in addition to the effects described above.

[0020] Further objects, features, and advantages of the present disclosure will become apparent from the following detailed description based on the embodiments and accompanying drawings. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an LPWA wireless communication system. [Figure 2] FIG. 2 is a diagram showing an example of a communication sequence between a terminal and a receiving station. [Figure 3] FIG. 3 is a diagram showing an example of the functional configuration of the terminal 100. As shown in FIG. [Figure 4] FIG. 4 is a diagram showing an example of the functional configuration of the receiving station 200. As shown in FIG. [Figure 5] FIG. 5 is a diagram showing an example of a frame configuration. [Figure 6] FIG. 6 is a diagram showing a method for generating radio resources, preambles, synchronization information, and scrambling patterns used in frame transmission. [Figure 7] FIG. 7 is a diagram showing an example of the configuration of an LPWA wireless communication system using a satellite receiving station. [Figure 8] FIG. 8 is a diagram showing an example of a communication sequence between a terminal and a satellite receiving station. [Figure 9] FIG. 9 is a diagram showing an example of a communication sequence between a terminal and a satellite receiving station (first embodiment). [Figure 10]FIG. 10 is a diagram showing an example of the functional configuration of the satellite receiving station 1000. As shown in FIG. [Figure 11] FIG. 11 is a diagram showing an example of the frame structure of the data portion of the frame reception information frame (first embodiment). [Figure 12] FIG. 12 is a flowchart showing the processing operations performed by the terminal. [Figure 13] FIG. 13 is a flowchart showing a processing procedure (first embodiment) for a satellite receiving station to receive a notification frame. [Figure 14] FIG. 14 is a flowchart showing a processing procedure (first embodiment) for a satellite receiving station to receive a data frame. [Figure 15] FIG. 15 is a flowchart showing a processing procedure (first embodiment) for a satellite receiving station to receive a frame reception information frame. [Figure 16] FIG. 16 is a diagram showing an example of the time variation of frequency error and propagation delay when the satellite altitude is 600 km and the frequency is 2 GHz. [Figure 17] FIG. 17 is a diagram showing an example of the frame configuration of the data portion of the frame reception information frame (second embodiment). [Figure 18] FIG. 18 is a flowchart showing a processing procedure (second embodiment) for a satellite receiving station to receive a frame reception information frame. [Figure 19] FIG. 19 is a diagram showing an example of a communication sequence between a terminal and a satellite receiving station (third embodiment). [Figure 20] FIG. 20 is a diagram showing an example of the frame configuration of the data portion of the target terminal list registration notification frame. [Figure 21] FIG. 21 is a flowchart showing a processing procedure (third embodiment) for a satellite receiving station to receive a frame reception information frame. [Figure 22] FIG. 22 is a flowchart showing a processing procedure for a satellite receiving station to receive a target terminal list registration notification frame. [Figure 23]FIG. 23 is a diagram showing an example of a communication sequence between a terminal and a satellite receiving station (fourth embodiment). [Figure 24] FIG. 24 is a diagram showing an example of the frame configuration of the data portion of the frame reception information frame (fourth embodiment). [Figure 25A] FIG. 25A is a flowchart showing a processing procedure (fourth embodiment) for a satellite receiving station to receive a frame reception information frame. [Figure 25B] FIG. 25B is a flowchart showing a processing procedure (fourth embodiment) for a satellite receiving station to receive a frame reception information frame. [Figure 26] FIG. 26 is a diagram showing an example of an adjacent satellite receiving station information list held by a satellite receiving station. [Figure 27] FIG. 27 is a diagram showing an example of a communication sequence between a terminal and a satellite receiving station (fifth embodiment). [Figure 28] FIG. 28 is a diagram showing an example of the frame structure of the data portion of the target terminal registration frame. [Figure 29] FIG. 29 is a flowchart showing a processing procedure (fifth embodiment) for a satellite receiving station to receive a notification frame. [Figure 30] FIG. 30 is a flowchart showing a processing procedure (fifth embodiment) for a satellite receiving station to receive a data frame. [Figure 31] FIG. 31 is a flowchart showing the processing procedure for a satellite receiving station to receive a target terminal list registration frame. [Figure 32] FIG. 32 is a diagram showing an example of a communication sequence between a terminal and a receiving station in a system in which the terminal can arbitrarily transmit a data frame. [Figure 33] FIG. 33 is a diagram showing a configuration example (sixth embodiment) of an LPWA wireless communication system using a satellite receiving station. [Figure 34] FIG. 34 is a diagram showing an example of a communication sequence between a terminal and a satellite receiving station (sixth embodiment). [Figure 35] FIG. 35 is a diagram showing an example of the functional configuration of a satellite receiving station 3500. [Figure 36] FIG. 36 is a diagram showing an example of the configuration of a data frame. [Figure 37] FIG. 37 is a diagram illustrating an example of the frame structure of the data portion of the reception target radio resource information notification frame. [Figure 38] FIG. 38 is a flowchart showing the processing operations performed by the terminal. [Figure 39] FIG. 39 is a flowchart showing the processing operation for the satellite receiving station to receive the initial data frame. [Figure 40] FIG. 40 is a flowchart showing the processing procedure for the satellite receiving station to receive a normal data frame. [Figure 41] FIG. 41 is a flowchart showing a processing procedure for a satellite receiving station to receive a reception target radio resource information notification frame. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present disclosure will be described below in the following order with reference to the drawings.

[0023] A. System requirements B. System configuration using a satellite receiving station C. First Example C-1. Communication sequence example C-2. Equipment configuration C-3.Frame structure C-4. Terminal processing operations C-5. Processing operations of satellite receiving station D. Second Example D-1.Frame configuration example D-2. Frame reception Information Frame reception operation E. Third Example E-1. Communication sequence example E-2.Frame configuration example E-3. Processing operations of satellite receiving station F. Fourth Example F-1. Communication sequence example F-2.Frame configuration example F-3. List of adjacent satellite receiving stations G. Fifth Example G-1. Communication sequence example G-2.Frame configuration example G-3. Processing operations of satellite receiving station H.Effect I. Sixth Example I-1. System Configuration I-2. Communication sequence example I-3. Equipment configuration I-4.Frame configuration example I-5. Terminal processing operations I-6. Processing operations of satellite receiving station I-7.Effects

[0024] A. System requirements In a wireless communication system, in order for a receiving station to demodulate data transmitted by a terminal, it must know the information required for demodulation, such as the modulation method, modulation rate, code, and encryption key, as well as the wireless resources (time and frequency) used for data transmission for each terminal.

[0025] In wireless communication systems capable of two-way communication, such as LTE (Long Term Evolution), signaling is performed between the terminal and the receiving station to exchange necessary information before data transmission. This allows the receiving station to specify the wireless resources (time and frequency) for transmitting data to the terminal, and thereafter demodulate the data using the modulation method and modulation rate stored in the data being transmitted using the specified wireless resources (time and frequency).

[0026] On the other hand, in LPWA, a wireless communication method for IoT, signaling is undesirable from the viewpoint of terminal power consumption. Furthermore, if only one-way communication from the terminal to the receiving station is supported, signaling is not possible. Therefore, we consider a method for the receiving station to grasp the wireless resources used by the terminal for data transmission in an LPWA wireless communication system.

[0027] Figure 1 shows a schematic diagram of an example of the configuration of an LPWA wireless communication system. In the example shown in the figure, the system consists of a receiving station and multiple terminals. The terminals are transmitters that periodically transmit information sensed by on-board sensors, etc. The receiving station receives the data transmitted by the terminals and performs demodulation processing. The receiving station also transmits the demodulated results (user data) to an application server (not shown) on the cloud as necessary. The wireless communication system shown in Figure 1 is based on the premise that time is synchronized within the system (between the receiving station and each terminal). One possible method of time synchronization is to use GPS information.

[0028] FIG. 2 shows an example of a communication sequence between a terminal and a receiving station in the system shown in FIG.

[0029] First, the terminal transmits a notification frame to notify its own ID (SEQ201). The notification frame is transmitted using a randomly selected radio resource (time and frequency) from among those allocated in advance within the system for transmission of notification frames.

[0030] The receiving station receives and demodulates the notification frame using the radio resource for transmitting the notification frame (SEQ202). If the demodulation is successful, the receiving station registers the ID acquired from the notification frame in the target terminal list (SEQ203).

[0031] Based on the rules (described later) predetermined within the system, the terminal calculates the radio resources (time and frequency) for transmitting the data frame using its own ID and the code required to generate the data frame, and then generates and transmits the data frame (SEQ204).

[0032] Here, it is assumed that the time between the transmission of the notification frame and the transmission of the data frame is sufficiently short, and that the next transmitted data frame can be received by the same satellite receiving station.

[0033] The receiving station uses the ID registered in its own list of target terminals to receive data, and calculates the radio resource (time and frequency) for the terminal to transmit the data frame and the code required to demodulate the data frame based on the same rules as the terminal, and receives and demodulates the data frame (SEQ205).The receiving station also transmits the demodulation result (user data) to an application server (not shown) on the cloud as needed.

[0034] Fig. 3 shows an example of the functional configuration of a communication device 100 (hereinafter referred to as terminal 100) that operates as a terminal in the system shown in Fig. 1. The terminal 100 shown in the figure includes a wireless communication unit 101, a wireless control unit 102, a frame generation unit 103, a sensor 104, a wireless resource determination unit 105, and a storage unit 106. Note that the functional configuration of the terminal 100 may be the same whether the receiving station is a terrestrial station or a satellite receiving station.

[0035] The wireless communication unit 101 transmits wireless signals. Under the control of the wireless control unit 102, the wireless communication unit 101 converts frames generated by the frame generation unit 103 into wireless signals and transmits them.

[0036] The radio control unit 102 controls the radio communication unit 101 so that the frame is transmitted at the transmission time and at the transmission frequency obtained from the radio resource determination unit 105 .

[0037] 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 scrambling pattern required for frame generation from the radio resource determination unit 105. The frame generation unit 103 also writes, for example, sensor information acquired by the sensor unit 104 in the payload of the frame.

[0038] The sensor 104 is a sensor that acquires external or internal information of the terminal 100, such as a temperature sensor or an acceleration sensor.

[0039] The radio resource determination unit 105 uses the ID and initial values ​​of the terminal 100 itself obtained from the memory unit 106 to generate the radio resources (time and frequency) for transmitting the frame, as well as the preamble, synchronization information, and scrambling pattern required for frame generation.

[0040] The storage unit 106 stores the ID and initial values ​​of the terminal 100 itself, which are information necessary for determining the radio resources. Of course, the storage unit 106 may store other information.

[0041] Fig. 4 shows an example of the functional configuration of a communication device 200 (hereinafter referred to as 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 and demodulation unit 203, a wireless resource determination unit 204, and a storage unit 205. The illustrated receiving station 200 is assumed to be a terrestrial station installed on the ground.

[0042] The wireless communication unit 201 receives a wireless signal. Under the control of the wireless control unit 202, the wireless communication unit 201 receives a radio wave, converts it into a wireless signal, and passes it to the frame detection and demodulation unit 203.

[0043] The radio control unit 202 controls the radio communication unit 201 so that the frame is received at the reception time and at the reception frequency obtained from the radio resource determination unit 204 .

[0044] The frame detection and demodulation unit 203 detects and demodulates frames from the received signal. Specifically, the frame detection and demodulation unit 203 generates a known pattern from the preamble, synchronization information, and scrambling pattern acquired from the radio resource determination unit 204, calculates the correlation value between the received signal and the known pattern, and determines that a frame has been detected if the correlation value is equal to or greater than a certain value. If frame detection is successful, the frame detection and demodulation unit 203 extracts the signal corresponding to the frame from the received signal, descrambles it, extracts the payload, and performs error correction code decoding and error detection using a CRC (Cyclic Redundancy Code). If frame demodulation is successful, the frame detection and demodulation unit 203 notifies the upper layer (not shown) of the demodulated data.

[0045] The radio resource determination unit 204 uses the ID and initial values ​​of the terminal 100 obtained from the memory unit 205 to generate the radio resources (time and frequency) for the terminal 100 to transmit frames, as well as the preamble, synchronization information, and scrambling pattern required for frame demodulation.

[0046] The storage unit 205 stores the IDs and initial values ​​of the terminals 100, which are information necessary for determining radio resources. The storage unit 205 also stores a target terminal list that stores the IDs of the terminals 100 that the receiving station 200 is to receive from.

[0047] Figure 5 shows an example of the structure of a frame used in the system shown in Figure 1. The frame includes ID, DATA, and CRC fields. Both the notification frame and data frame sent from the terminal shall have the frame structure shown in Figure 5.

[0048] The ID field stores an ID that is a unique identifier of the terminal 100 that is the sender. The DATA field stores the transmitted data. In the case of a data frame, data acquired from the sensor 104 and the like are stored. In the case of a notification frame, the transmission interval from the transmission of the notification frame to the transmission of the data frame, the transmission interval of the periodically transmitted data frames and the like are stored. The CRC field stores a CRC value calculated from the information stored in the ID field and the DATA field. The receiving side uses the CRC value to determine whether demodulation was successful.

[0049] The sequence of the ID, DATA, and CRC is then subjected to Forward Error Correction (FEC) coding and interleaving to generate the payload. A preamble, a known pattern used for frame detection and synchronization acquisition, and synchronization information are then added to the beginning of the payload, and the frame is generated by performing an exclusive OR (XOR) with the scrambling pattern on a bit-by-bit basis.

[0050] 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 scramble pattern will be described with reference to FIG.

[0051] Within the system, rules 1 to 4 are predefined to determine the radio resources (time and frequency) used for frame transmission, the preamble and synchronization information required for frame generation, and the scramble pattern generation method. The time (Time) used for frame transmission is determined by entering two initial values ​​for time calculation, Seed(T)-1 and Seed(T)-2, in rule 1. The frequency (Freq) used for frame transmission is determined by entering two initial values ​​for frequency calculation, Seed(F)-1 and Seed(F)-2, in rule 2. The preamble and synchronization information (Preamble / Sync) are determined by entering two initial values ​​for preamble and synchronization information calculation, Seed(P)-1 and Seed(P)-2, in rule 3. The scramble pattern is determined by entering two initial values ​​for the scramble pattern, Seed(S)-1 and Seed(S)-2, in rule 4.

[0052] Each initial value is determined in advance within the system and is stored in the memory unit 106 in the terminal 100 and the memory unit 205 in the receiving station 200. When transmitting a data frame, an ID, which is a unique identifier of the terminal 100 that is the 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). When transmitting a notification frame, on the other hand, an initial value selected at random from several initial values ​​assigned in advance for notification frames is input into each of the second initial values ​​(Seed(T)-2, Seed(F)-2, Seed(P)-2, Seed(S)-2).

[0053] By using this method, the terminal 100 can obtain the radio resources (time and frequency) used for frame transmission and the information required for frame demodulation simply by notifying the receiving station 200 of the terminal ID.

[0054] B. System configuration using a satellite receiving station Figure 7 shows a schematic diagram of an example of the configuration of an LPWA wireless communication system using satellite receiving stations. The example shown in the figure is composed of multiple receiving stations installed on the ground (hereinafter referred to as "ground stations"), multiple satellite receiving stations orbiting the Earth (hereinafter simply referred to as "satellite receiving stations"), and numerous terminals scattered around the Earth. It is assumed that all terminals and receiving stations within the system are time-synchronized. One possible method for time synchronization is to use GPS information. Note that each satellite receiving station orbits the Earth in a sun-synchronous orbit, which is close to a polar orbit passing over the poles, so that the angle of sunlight incident on the satellite's orbital plane is the same and the satellite always passes the equator at the same local time.

[0055] The terminal is a transmitter that periodically transmits information sensed by an onboard sensor, etc. The satellite receiving station receives the data transmitted by the terminal and performs demodulation processing. The satellite receiving station also transmits the demodulation results (user data) to an application server (not shown) on the cloud as necessary. The satellite receiving station also enables inter-satellite communication. There are no restrictions on the communication method between satellite receiving stations, but constant connection and high-speed communication are desirable. The ground station is a transmitter / receiver that communicates with the satellite receiving station. There are no restrictions on the communication method between the satellite receiving station and the ground station, but high-speed communication is desirable.

[0056] In the case of terrestrial receiving stations, if the terminal is stationary or has a limited range of movement, the receiving stations that can receive the data (radio waves) transmitted by the terminal will always be the same. Therefore, there is no problem if the terminal transmits a notification frame when it is turned on and then infrequently, such as once every few days.

[0057] On the other hand, because low-earth orbit satellites continue to move in their orbits at a speed of several kilometers per second, the receiving station that can receive data transmitted by a terminal is not fixed. For example, if satellite receiving station 701 can receive a notification frame when the terminal transmits it, satellite receiving station 701 can receive and demodulate the data frame transmitted by the terminal as long as the terminal is located within the receivable range 711 of satellite receiving station 701. On the other hand, if, over time, the terminal moves out of the receivable range 711 of satellite receiving station 701 and into the receivable range 712 of the subsequent satellite receiving station 702 on the same satellite orbit, satellite receiving station 701 will not be able to receive and demodulate the data frame transmitted by the terminal.

[0058] 7, the network is designed so that the receivable ranges 711 and 712 of adjacent satellite receiving stations 701 and 702 on the satellite orbit do not overlap. Satellite receiving station 701 and satellite receiving station 702 orbit in the same orbit, for example, but they may orbit in adjacent orbits.

[0059] 8 shows an example of a communication sequence between satellite receiving station 701 and satellite receiving station 702, which are adjacent on a satellite orbit, and terminal 801. Satellite receiving station 701 and satellite receiving station 702 are each continuously moving on their satellite orbits at a speed of several kilometers per second, so there are time periods when the location of terminal 801 is within receivable range 711 of satellite receiving station 701, and time periods when the location is outside receivable range 711 of satellite receiving station 701 and within receivable range 712 of satellite receiving station 702.

[0060] First, terminal 801 transmits (broadcasts) a notification frame to notify its own ID (SEQ801). To transmit the notification frame, radio resources (time and frequency) that have been allocated in advance within the system for transmitting notification frames are used. At this point, terminal 801 is within the receivable range 711 of satellite receiving station 701. Therefore, satellite receiving station 701 receives and demodulates the notification frame using the radio resources for transmitting the notification frame (SEQ811), and registers the ID obtained from the notification frame in its list of target terminals (SEQ812). On the other hand, since the notification frame from terminal 801 does not reach satellite receiving station 702, satellite receiving station 702 does not register the ID of terminal 801 in its list of target terminals.

[0061] Next, based on rules 1 to 4 predetermined within the system, terminal 801 calculates the radio resources (time and frequency) for transmitting the data frame from its own ID and the code required to generate the data frame, and generates and transmits (broadcasts) the data frame (SEQ802).

[0062] The satellite receiving station 701 uses the ID registered in the list of target receiving terminals to calculate, based on the same rules 1 to 4 as for the terminal 801, the radio resources (time and frequency) from the terminal ID for transmitting the data frame and the code required to demodulate the data frame, and receives and demodulates the data frame (SEQ813).

[0063] Furthermore, based on rules 1 to 4 predetermined within the system, terminal 801 calculates the radio resources (time and frequency) for transmitting the next data frame from its own ID and the code required to generate the data frame, and generates and transmits (broadcasts) the next data frame (SEQ803).

[0064] Using the ID registered in the target terminal list, satellite receiving station 701 calculates the radio resources (time and frequency) from which terminal 801 will transmit the data frame and the code required to demodulate the data frame, based on the same rules 1 to 4 as terminal 801, and attempts to receive and demodulate the data frame (SEQ 814). However, because terminal 801 is located outside receivable range 711 and within receivable range 712 of satellite receiving station 702, demodulation of the data frame from terminal 801 fails. Furthermore, although the data frame from terminal 801 reaches satellite receiving station 702, satellite receiving station 702 does not register the ID of terminal 801 in its target terminal list, and therefore does not receive or demodulate the data frame from terminal 801.

[0065] In order to avoid the situation shown in Figure 8 where none of the satellite receiving stations can receive the terminal's data frame due to the movement of each satellite receiving station in its satellite orbit, the terminal could transmit notification frames frequently, but this is undesirable from the viewpoint of terminal power consumption and efficient use of radio resources.Furthermore, it is undesirable from the viewpoint of efficient use of resources at the satellite receiving station for the satellite receiving station to perform reception and demodulation processing for a terminal that has moved out of its reception range.

[0066] Therefore, this disclosure proposes a method in which, by taking into account that the satellite receiving station moves in a satellite orbit, a satellite receiving station whose reception range covers the location where the terminal is located when the terminal transmits a data frame can target the terminal as a reception target, even if the terminal does not transmit notification frames frequently. [Example]

[0067] C. First Example As a first embodiment, a method will be described in which, in a system configuration such as that shown in FIG. 7, frame reception information is shared among multiple satellite receiving stations, and a satellite receiving station that has a reception range that covers the location of a terminal targets that terminal for reception.

[0068] C-1. Communication sequence example 9 shows an example of a communication sequence between satellite receiving station 701, satellite receiving station 702, and terminal 801 when the method according to the present disclosure is applied. Satellite receiving station 701 and satellite receiving station 702 are each continuously moving on their satellite orbits at a speed of several kilometers per second, so there are time periods when the location of terminal 801 is within the receivable range 711 of satellite receiving station 701 and time periods when the location is outside the receivable range 711 of satellite receiving station 701 and within the receivable range 712 of satellite receiving station 702.

[0069] First, terminal 801 transmits (broadcasts) a notification frame to notify its own ID (SEQ901). To transmit the notification frame, terminal 801 uses radio resources (time and frequency) that have been allocated in advance within the system for transmitting notification frames.

[0070] At this point, terminal 801 is within the receivable range 711 of satellite receiving station 701. Therefore, satellite receiving station 701 receives and demodulates the notification frame using the radio resource for transmitting the notification frame (SEQ911), and registers the ID acquired from the notification frame in the list of target terminals (SE912).

[0071] Then, satellite receiving station 701 transmits frame reception information regarding the notification frame received from terminal 801 to satellite receiving station 702, which is located behind in the same satellite orbit (SEQ 913). The frame reception information includes the terminal ID of the source of the notification frame, the data transmission interval, and the estimated frequency error and propagation delay measured when the notification frame was received. The processing procedure for the satellite receiving station to receive the notification frame will be described later (see FIG. 13).

[0072] On the other hand, since the notification frame from terminal 801 does not reach satellite receiving station 702, satellite receiving station 702 does not register the ID of terminal 801 in its list of target terminals. Furthermore, satellite receiving station 702 determines whether or not to register terminal 801 in its list of target terminals based on frame reception information received from satellite receiving station 701 located ahead on the same satellite orbit (SEQ 921). The processing procedure by which the satellite receiving station receives a frame reception information frame and the specific conditions for determination will be described later (see FIG. 15). In the example of the communication sequence shown in FIG. 9, the location of terminal 801 is still outside of receivable range 712 at the time when terminal 801 next transmits a data frame, and therefore the conditions for determination are not met, so satellite receiving station 702 does not register terminal 801 in its list of target terminals.

[0073] Next, based on rules 1 to 4 predetermined within the system, terminal 801 calculates the radio resources (time and frequency) for transmitting the data frame from its own ID and the code required to generate the data frame, and generates and transmits (broadcasts) the data frame (SEQ902).

[0074] Using the ID registered in the list of target terminals for reception, satellite receiving station 701 calculates the radio resources (time and frequency) from which terminal 801 will transmit the data frame and the code required to demodulate the data frame based on the terminal ID and rules 1 to 4 identical to those of terminal 801, and receives and demodulates the data frame (SEQ914). Satellite receiving station 701 then transmits frame reception information regarding the data frame received from terminal 801 to satellite receiving station 702, which is located subsequent to it on the same satellite orbit (SEQ915). The processing procedure for a satellite receiving station to receive a data frame will be described later (see FIG. 14).

[0075] Based on the frame reception information received from satellite receiving station 701, which is located ahead on the same satellite orbit, satellite receiving station 702 determines whether or not to register terminal 801 in its list of target terminals (SEQ 922). Here, the location of terminal 801 satisfies the determination conditions, such as being within receivable range 712 at the time the next data frame is transmitted, so satellite receiving station 702 registers terminal 801 in its list of target terminals.

[0076] Furthermore, based on rules 1 to 4 predetermined within the system, terminal 801 calculates the radio resources (time and frequency) for transmitting the next data frame from its own ID and the code required to generate the data frame, and generates and transmits (broadcasts) the next data frame (SEQ903).

[0077] The satellite receiving station 701 uses the ID registered in the list of target receiving terminals to calculate the radio resource (time and frequency) from the terminal ID that the terminal 801 will use to transmit the data frame and the code required to demodulate the data frame, based on the same rules 1 to 4 as the terminal 801, and attempts to receive and demodulate the data frame (SEQ 916 However, since the location of terminal 801 is outside of reception range 711 and is within reception range 712 of satellite receiving station 702, demodulation of the data frame from terminal 801 fails.

[0078] Furthermore, the data frame from terminal 801 reaches satellite receiving station 702. Satellite receiving station 702 has registered the ID of terminal 801 in its own list of target terminals based on the frame reception information received from terminal 801, and so, based on the same rules 1 to 4 as terminal 801, calculates the radio resources (time and frequency) with which terminal 801 will transmit the data frame and the code required to demodulate the data frame from the terminal's ID, and attempts to receive and demodulate the data frame. Then, because terminal 801 is located within receivable range 712, satellite receiving station 702 succeeds in demodulating the data frame from terminal 801 (SEQ924).

[0079] C-2. Equipment configuration Even in a system that shares frame reception information, the terminal configuration can be the same as in Figure 3, so in this section C, we will omit the explanation of the terminal configuration.

[0080] Fig. 10 shows an example of the functional configuration of a satellite receiving station 1000 in a system that shares frame reception information. The satellite receiving station 1000 is used by being mounted on a low-earth orbit satellite that orbits the Earth in one of the satellite orbits shown in Fig. 7. The satellite receiving station 1000 includes an LPWA unit 1200 and an inter-satellite communication unit 1300.

[0081] The LPWA unit 1200 receives frames transmitted from a terrestrial terminal. The same components of the LPWA unit 1200 as those of the receiving station 200 shown in FIG. 4 are designated by the same reference numerals as in FIG. 4. The LPWA unit 1200 further includes a target terminal determination unit 206. Based on frame reception information received from a satellite receiving station ahead on the same satellite orbit, the target terminal determination unit 206 determines whether or not to register the terminal in question in its own list of target terminals. The frame detection and demodulation unit 203 also outputs the terminal ID of the sender of the received notification frame or data frame, the frame transmission interval, the frequency error estimation result measured when the notification frame was received, and the propagation delay estimation result to the frame generation unit 1303 on the inter-satellite communication unit 1300 side.

[0082] The inter-satellite communication unit 1300 includes a wireless communication unit 1301 , a wireless control unit 1302 , a frame generation unit 1303 , and a frame detection and demodulation unit 1304 .

[0083] 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 and demodulation unit 1304. Also, under the control of the wireless control unit 1302, the wireless communication unit 1301 converts frames generated by the frame generation unit 1303 into wireless signals and transmits them.

[0084] The wireless control unit 1302 controls the wireless communication unit 1301 so that frames can be transmitted and received between satellite receiving stations.

[0085] The frame generation unit 1303 stores the frame reception information acquired from the frame detection and demodulation unit 203 on the LPWA unit 1200 side in data, and generates a frame according to a predetermined format.

[0086] The frame detection and demodulation unit 1304 detects and demodulates frames from the signal received by the wireless communication unit 1301. If the frame detection and demodulation unit 1304 succeeds in demodulating the frame, it passes the received data, i.e., frame reception information, to the target terminal determination unit 206.

[0087] C-3.Frame structure This section describes the frame structure used in the LPWA wireless communication system according to the present disclosure. However, since the notification frame and data frame transmitted from the terminal to the satellite receiving station have the same frame structure as shown in Figure 5, detailed description is omitted here.

[0088] Figure 11 shows an example of the frame structure of the data portion of a frame reception information frame. The format of the portion other than the data portion depends on the communication method used. The frame reception information frame is a frame that notifies subsequent satellite receiving stations on the same satellite orbit of frame reception information regarding frames received by a satellite receiving station from a terminal.

[0089] The nSTA field stores the number of frame reception information (Frame Rx Info) stored in the data portion. The nSTA field is followed by the same number of Frame Rx Info fields as listed in the nSTA field. Each Frame Rx Info field stores frame reception information about a frame received from each terminal. In the frame configuration example shown in Figure 11, the nSTA field stores information indicating the value n, and n Frame Rx Info fields are stored.

[0090] Each Frame Rx Info field includes an ID field, an Ftype field, a Freq.Error field, a Propagation Delay field, a Data Tx Interval field, and a Next Data Tx Interval field.

[0091] The ID field stores the ID (terminal ID) of the terminal that sent the received frame. The Ftype field stores a value indicating the type of received frame. Specifically, a value of 0 in the Ftype field indicates a notification frame, and a value of 1 indicates a data frame. The Freq.Error field stores the frequency error estimation result for the received frame. The Propagation Delay field stores the propagation delay estimation result for the received frame. The Data Tx Interval field stores the data frame transmission interval. The Next Data Tx Interval field stores the time until the next data frame is transmitted. The Next Data Tx Interval field is added only when Ftype is 0, that is, when a notification frame is received.

[0092] C-4. Terminal processing operations FIG. 12 shows the processing operations performed by the terminal in the form of a flowchart.

[0093] The terminal first determines whether or not a time has elapsed immediately after power-on or since the previous notification frame was transmitted (step S1201). The notification frame transmission interval a is assumed to be set in advance.

[0094] Immediately after power-on or when α time has elapsed since the previous notification frame was transmitted (Yes in step S1201), the terminal executes the notification frame transmission process.

[0095] When transmitting a notification frame, the terminal first calculates information such as the radio resources (time, 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 S1202).

[0096] Next, the terminal generates a notification frame using the preamble, synchronization information, and scramble pattern calculated in step S1202 (step S1203).

[0097] Next, the terminal determines whether the transmission time calculated in step S1202 has arrived (step S1204). When the transmission time for the notification frame arrives (Yes in step S1204), the terminal transmits the notification frame generated in step S1203 using the transmission frequency calculated in step S1202 (step S1205).

[0098] On the other hand, immediately after power-on or if α time has not passed since the last notification frame was sent (No in step S1201), or after sending the notification frame, the terminal determines whether β time has passed since the last data frame was sent (step S1206).

[0099] If β time has elapsed since the last data frame was transmitted (Yes in step S1206), 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 based on rules 1 to 4 (step S1207).

[0100] Next, the terminal generates a data frame using the preamble, synchronization information, and scrambling pattern calculated in step S1207 (step S1208).

[0101] Next, the terminal determines whether the transmission time calculated in step S1207 has arrived (step S1209). When the transmission time arrives (Yes in step S1209), the terminal transmits the data frame generated in step S1208 using the transmission frequency calculated in step S1207 (step S1210).

[0102] If β time has not elapsed since the previous data frame was transmitted (No in step S1206), or after the data frame has been transmitted, the process returns to step S1201, and the terminal repeatedly transmits the notification frame.

[0103] C-5. Processing operations of satellite receiving station In the present disclosure, it is assumed that the satellite receiving station can perform the reception process of the notification frame, the reception process of the data frame, and the transmission and reception process of the frame reception information frame in parallel.

[0104] FIG. 13 shows in the form of a flowchart the processing procedure for the satellite receiving station to receive the notification frame.

[0105] First, the satellite receiving station refers to the list of target terminals to receive the notification frame and calculates the radio resources (time and frequency) for receiving the notification frame from the registered terminal and the information required for demodulating the notification frame based on the above-mentioned rules 1 to 4 (step S1301).

[0106] Next, the satellite receiving station determines whether the notification frame reception time calculated in step S1301 has arrived (step S1302). When the notification frame reception time arrives (Yes in step S1302), the satellite receiving station detects the notification frame from the terminal using the preamble and synchronization information calculated in step S1301 (step S1303), and demodulates the received notification frame using the scrambling pattern calculated in step S1301 (step S1304). The satellite receiving station then determines whether demodulation of the notification frame was successful (step S1305).

[0107] If the notification frame is successfully demodulated (Yes in step S1305), the satellite receiving station registers information such as the terminal ID and data transmission interval stored in the received notification frame in the target terminal list (step S1306).

[0108] Next, the satellite receiving station generates a frame reception information frame using the terminal ID and data transmission interval stored in the notification frame, the frequency error estimation result and propagation delay estimation result calculated when detecting and demodulating the notification frame in steps S1303 to S1304, and the transmission interval from the notification frame transmission to the data frame transmission (step S1307).

[0109] Thereafter, the satellite receiving station transmits a frame reception information frame to the subsequent satellite receiving station on the same satellite orbit (step S1308).

[0110] On the other hand, if demodulation of the notification frame fails (No in step S1305), the satellite receiving station does not register the notification frame in the target receiving terminal list, and does not transmit a frame reception information frame.

[0111] In the processing procedure shown in Figure 13, the satellite receiving station transmits a frame reception information frame each time it receives a notification frame, but the satellite receiving station may also receive multiple notification frames and then transmit the frame reception information frame all at once.

[0112] 14 is a flowchart showing the processing steps for a satellite receiving station to receive a data frame. However, the satellite receiving station is capable of performing data frame reception processing in parallel for each terminal registered in the target terminal list.

[0113] First, the satellite receiving station acquires information about the target terminal, such as the terminal ID, from the list of target terminals (step S1401), and calculates the radio resources (time and frequency) for receiving the data frame from the target terminal, as well as the preamble, synchronization information, and scrambling pattern required for demodulating the data frame, based on the above-mentioned rules 1 to 4 (step S1402).

[0114] Next, the satellite receiving station determines whether the data frame reception time calculated in step S1402 has arrived (step S1403). When the data frame reception time arrives (Yes in step S1403), the satellite receiving station detects a data frame from the terminal using the preamble and synchronization information calculated in step S1402 (step S1404), and demodulates the received data frame using the scrambling pattern calculated in step S1402 (step S1405). The satellite receiving station then determines whether the demodulation of the data frame was successful (step S1406).

[0115] Here, if the demodulation of the data frame is successful (Yes in step S1406), the satellite receiving station generates a frame reception information frame (step S1407) using the data transmission interval and the frequency error estimation result and propagation delay estimation result calculated when detecting and demodulating the data frame in steps S1404 to S1405.

[0116] Thereafter, the satellite receiving station transmits a frame reception information frame to the subsequent satellite receiving station on the same satellite orbit (step S1408).

[0117] On the other hand, if demodulation of the data frame fails (No in step S1406), the satellite receiving station does not transmit a frame reception information frame.

[0118] In the processing procedure shown in FIG. 14, the satellite receiving station transmits a frame reception information frame each time it receives a data frame, but the satellite receiving station may also receive multiple data frames and then transmit the frame reception information frame all at once.

[0119] FIG. 15 shows in the form of a flowchart the processing procedure for the satellite receiving station to receive the frame reception information frame.

[0120] First, the satellite receiving station determines whether or not it has received a frame reception information frame (step S1501). Then, when it receives a frame reception information frame (Yes in step S1501), it demodulates the received frame (step S1502) and determines whether or not the demodulation was successful (step S1503).

[0121] If the satellite receiving station succeeds in demodulating the frame reception information frame (Yes in step S1503), it acquires nSTA, which indicates the number of frame reception information stored in the frame reception information frame (step S1504), and repeatedly processes each subsequent frame reception information (Frame Rx Info) for the number of frame reception information pieces.

[0122] First, the satellite receiving station estimates the remaining time during which the notification frame or data frame can be received at the same satellite receiving station from the frequency error estimation result (Freq. Error) and the propagation delay estimation result (Propagation Delay) (step S1505).

[0123] Next, based on the remaining receivable time and data transmission interval estimated in step S1505, it is determined whether the next data frame transmitted from the terminal in question can be received by the same satellite receiving station (step S1506). Here, for the data transmission interval, if Ftype is 0, i.e., the received frame is a notification frame, the value stored in the Next Data Tx Interval field is used, and if Ftype is 1, i.e., the received frame is a data frame, the value stored in the Data Tx Interval field is used.

[0124] If the next data frame transmitted from the terminal can be received by the same satellite receiving station (Yes in step S1506), the satellite receiving station returns to step S1505 and repeats the processing of the next frame reception information (Frame Rx Info).

[0125] On the other hand, if the next data frame transmitted from the terminal cannot be received by the same satellite receiving station (No in step S1506), the satellite receiving station registers the terminal ID and data transmission interval stored in the frame reception information (Frame Rx Info) in its own list of target terminals to receive data (step S1507), and then returns to step S1505 to repeatedly process the next frame reception information (Frame Rx Info).

[0126] A supplementary note will be made regarding the frequency error estimation and propagation delay estimation in step S1505 in the flowchart shown in Figure 15. Figure 16 shows an example of the change in frequency error and propagation delay over time when the satellite is at an altitude of 600 km and has a frequency of 2 GHz. Figure 16 shows an example in which a satellite passes overhead, and the satellite receiving station is capable of receiving signals from one terminal for six minutes, from 0 to 6 minutes. The frequency error was calculated using the model described in 3GPP TR 38.811 V15.1.0 (Non-Patent Document 1). In the example shown in Figure 16, the satellite receiving station is exactly overhead at the third minute, and the propagation delay is minimized and the sign of the frequency error is reversed.

[0127] By comparing the frequency error estimation result and propagation delay estimation result of the received frame from the terminal with the chart in Figure 16, it is possible to determine which time within the six minutes during which the frame from the terminal can be received. In addition, when the satellite receiving station moves in one direction at a specified speed above the terminal, it is possible to estimate the relative positional relationship between the terminal and the satellite receiving station that corresponds to the calculated time.

[0128] For example, if the data transmission interval is 3 minutes, the estimated frequency error reported in the frame reception information frame is 30 kHz, and the estimated propagation delay is 2.5 milliseconds, this corresponds to the second minute of the six minutes available for reception. Therefore, the next data frame corresponds to the fifth minute of the six minutes available for reception, and can be received by the same satellite receiving station.

[0129] On the other hand, if the data transmission interval is 3 minutes, the estimated frequency error reported in the frame reception information frame is -30 kHz, and the estimated propagation delay is 2.5 milliseconds, this corresponds to the fifth minute of the six minutes of available reception time. Therefore, the next data frame will be received after the six minutes have elapsed, and will not be receivable by the same receiving station. In this way, considering that the satellite receiving station moves in one direction along the satellite orbit, it is possible to estimate the remaining reception time at the satellite receiving station that received the frame from the terminal by combining the frequency error and propagation delay.

[0130] In short, in the method according to the first embodiment, each satellite receiving station shares frame reception information including the frequency error estimation result and propagation delay estimation result of the frame received from the terminal, and determines whether the next data frame transmitted from the terminal can be received by the same satellite receiving station based on the frequency error estimation result, propagation delay estimation result, frame transmission interval, and the positional relationship of adjacent satellite receiving stations.

[0131] According to the first embodiment, by a satellite receiving station transmitting frame reception information to a subsequent satellite receiving station on the same orbit, even if the terminal does not transmit notification frames frequently, when the terminal next transmits a data frame, a satellite receiving station that has a reception range that includes the location of the terminal can receive and demodulate the data frame from the terminal. [Example]

[0132] D. Second Example In the first embodiment, a method was described in which satellite receiving stations notify each other of the frequency error estimation result and the propagation delay estimation result of a frame received from a terminal, and determine whether or not a data frame transmitted from the terminal can be received by the same satellite receiving station. In contrast, in the second embodiment, a method is described in which, when the terminal is equipped with a GPS receiver, satellite receiving stations notify each other of the terminal's position coordinates (latitude and longitude), and determine whether or not a data frame transmitted from the terminal can be received by the same satellite receiving station.

[0133] D-1.Frame configuration example 17 shows an example of the frame configuration of the data portion of a frame reception information frame when notifying the terminal's position coordinates. The format of the portion other than the data portion depends on the communication method used. As described above, the frame reception information frame is a frame that notifies subsequent satellite receiving stations on the same satellite orbit of frame reception information regarding a frame received by a satellite receiving station from a terminal.

[0134] The nSTA field stores the number of frame reception information (Frame Rx Info) stored in the data portion. The nSTA field is followed by the same number of Frame Rx Info fields as listed in the nSTA field. Each Frame Rx Info field stores frame reception information about a frame received from each terminal. In the frame configuration example shown in Figure 17, the nSTA field stores information indicating the value n, and n Frame Rx Info fields are stored.

[0135] Each Frame Rx Info field includes an ID field, an Ftype field, a Longitude field, a Latitude field, a Frame Rx Time field, a Data Tx Interval field, and a Next Data Tx Interval field.

[0136] The ID field stores the ID (terminal ID) of the terminal that sent the received frame. The Ftype field stores a value indicating the type of frame received. Specifically, a value of 0 stored in the Ftype field indicates a notification frame, and a value of 1 indicates a data frame. The Longitude field stores the latitude where the terminal is located. The Latitude field stores the longitude where the terminal is located. The Frame Rx Time field stores the time the frame was received from the terminal. The Data Tx Interval field stores the data frame transmission interval. The Next Data Tx Interval field stores the time until the next data frame is transmitted. The Next Data Tx Interval field is only added when Ftype is 0, that is, when a notification frame is received.

[0137] D-2. Frame reception Information Frame reception operation FIG. 18 shows in the form of a flowchart the processing procedure for the satellite receiving station to receive the frame reception information frame.

[0138] First, the satellite receiving station determines whether or not it has received a frame reception information frame (step S1801). Then, when it receives a frame reception information frame (Yes in step S1801), it demodulates the received frame (step S1802) and determines whether or not the demodulation was successful (step S1803).

[0139] If the satellite receiving station succeeds in demodulating the frame reception information frame (Yes in step S1803), it acquires nSTA, which indicates the number of frame reception information stored in the frame reception information frame (step S1804), and repeatedly processes each subsequent frame reception information (Frame Rx Info) for the number of frame reception information pieces.

[0140] First, the remaining time during which the notification frame or data frame can be received by the same satellite receiving station is estimated from the position coordinates of the terminal and the time of reception of the frame from that terminal (step S1805).

[0141] Next, based on the remaining receivable time and data transmission interval estimated in step S1805, it is determined whether the next data frame transmitted from the terminal in question can be received by the same satellite receiving station (step S1806). Here, for the data transmission interval, if Ftype is 0, i.e., the received frame is a notification frame, the value stored in the Next Data Tx Interval field is used, and if Ftype is 1, i.e., the received frame is a data frame, the value stored in the Data Tx Interval field is used.

[0142] If the next data frame transmitted from the terminal can be received by the same satellite receiving station (Yes in step S1806), the satellite receiving station returns to step S1805 and repeats the processing of the next frame reception information (Frame Rx Info).

[0143] On the other hand, if the next data frame transmitted from the terminal cannot be received by the same satellite receiving station (No in step S1806), the satellite receiving station registers the terminal ID and data transmission interval stored in the frame reception information (Frame Rx Info) in its own list of target terminals (step S1807), and then returns to step S1805 to repeatedly process the next frame reception information (Frame Rx Info).

[0144] In order to transmit the data received via LPWA to the ground, the satellite receiving station must communicate with the ground station via satellite communication. For this reason, the satellite receiving station generally knows its own location coordinates using GPS or other means.

[0145] In addition, when constructing a satellite constellation, information on satellite receiving stations orbiting the same satellite is stored. For example, assume that the information is such that the satellite in front of it passes the same point on Earth every six minutes.

[0146] Specifically, if the time the frame reception information frame was received is 12:00, the time the location information notified by the terminal in the data frame becomes within reception range is 12:05, and the frame is received at 11:58, the remaining reception time at the satellite receiving station that received the notification frame or data frame is 7 minutes. If the data transmission interval is 3 minutes, the next data frame can be received by the same receiving station.

[0147] On the other hand, if the time the frame reception information frame was received was 12:00, the time the location information notified by the terminal in the data frame became within reception range was 12:01, and the frame was received at 11:59, the remaining reception time at the satellite receiving station that received the notification frame or data frame would be 2 minutes. If the data transmission interval is 3 minutes, the next data frame cannot be received by the same receiving station.

[0148] Considering that low-orbit satellites move in one direction in their satellite orbits and that the relative positions of each satellite receiving station can be determined using the constellation, it is possible to estimate the remaining reception time at the receiving station that received the frame from the location information notified by the terminal and the time the frame was received. [Example]

[0149] E. Third Example In the first embodiment (the example of the communication sequence shown in FIG. 9), satellite receiving station 701 keeps terminal 801 registered in its list of target terminals even after the location where terminal 801 is located has passed its own reception range 711, and performs unnecessary reception and demodulation processing on data frames from terminal 801. In contrast, in the third embodiment, a method will be described in which the satellite receiving station does not perform unnecessary reception and demodulation processing on terminals that have passed out of its reception range.

[0150] E-1. Communication sequence example 19 shows an example of a communication sequence between satellite receiving station 701, satellite receiving station 702, and terminal 801 when the method according to the third embodiment is applied. Satellite receiving station 701 and satellite receiving station 702 continue to move on their respective satellite orbits at a speed of several kilometers per second, so there are time periods when the location of terminal 801 is within receivable range 711 of satellite receiving station 701, and time periods when the location is outside receivable range 711 of satellite receiving station 701 and within receivable range 712 of satellite receiving station 702.

[0151] First, terminal 801 transmits (broadcasts) a notification frame to notify its own ID (SEQ1901). To transmit the notification frame, terminal 801 uses radio resources (time and frequency) that have been allocated in advance within the system for transmitting notification frames.

[0152] At this point, terminal 801 is within the receivable range 711 of satellite receiving station 701. Therefore, satellite receiving station 701 receives and demodulates the notification frame using the radio resources for transmitting the notification frame (SEQ1911), and registers the ID acquired from the notification frame in a list of target terminals (SE1912). Then, satellite receiving station 701 transmits frame reception information regarding the notification frame received from terminal 801 to satellite receiving station 702, which is located subsequent to terminal 801 on the same satellite orbit (SEQ1913). The frame reception information includes the terminal ID of the source of the notification frame, the data transmission interval, the position coordinates of the terminal, and the reception time of the notification frame. Satellite receiving station 701 receives and demodulates the notification frame and transmits the notification frame according to the processing procedure shown in FIG. 13.

[0153] On the other hand, since the notification frame from terminal 801 does not reach satellite receiving station 702, satellite receiving station 702 does not register the ID of terminal 801 in its list of target terminals to receive. Satellite receiving station 702 also receives and processes the frame reception information frame from satellite receiving station 701, which is located ahead on the same satellite orbit, and determines whether or not to register terminal 801 in its own list of target terminals to receive (SEQ1921). The processing procedure by which a satellite receiving station receives a frame reception information frame will be described later (see FIG. 21). Here, satellite receiving station 702 determines that it will be unable to receive the next data frame transmitted from terminal 801 based on the remaining receivable time and data transmission interval estimated based on the frequency error estimation result and propagation delay estimation result, and does not register terminal 801 in its own list of target terminals to receive.

[0154] Next, based on rules 1 to 4 predetermined within the system, terminal 801 calculates the radio resources (time and frequency) for transmitting the data frame from its own ID and the code required to generate the data frame, and generates and transmits (broadcasts) the data frame (SEQ1902).

[0155] Using the ID registered in the target terminal list, satellite receiving station 701 calculates the radio resources (time and frequency) from which terminal 801 will transmit the data frame and the code required to demodulate the data frame based on the same rules 1 to 4 as terminal 801, and receives and demodulates the data frame (SEQ1914). Satellite receiving station 701 then transmits frame reception information regarding the data frame received from terminal 801 to satellite receiving station 702, which is located subsequent on the same satellite orbit (SEQ1915). Satellite receiving station 701 performs the process of receiving and demodulating the data frame and transmitting the notification frame according to the processing procedure shown in FIG.

[0156] Satellite receiving station 702 receives and processes the frame reception information frame from satellite receiving station 701, which is located ahead on the same satellite orbit, and determines whether or not to register terminal 801 in its own list of target terminals for reception (SEQ1922). The processing procedure by which a satellite receiving station receives a frame reception information frame will be described later (see FIG. 21). Here, satellite receiving station 702 determines that the next data frame transmitted from terminal 801 can be received by satellite receiving station 702 based on the remaining receivable time and data transmission interval estimated based on the frequency error estimation result and propagation delay estimation result, and registers terminal 801 in its list of target terminals for reception (SEQ1923).

[0157] Then, satellite receiving station 702 transmits a target terminal list registration notification frame to satellite receiving station 701, which is located ahead on the same satellite orbit, to notify it that terminal 801 has been registered in the target terminal list (SEQ 1924). Upon receiving the target terminal list registration notification frame from satellite receiving station 702, satellite receiving station 701 deletes the entry for terminal 801 from its own target terminal list (SEQ 1916).

[0158] Furthermore, based on rules 1 to 4 predetermined within the system, terminal 801 calculates the radio resources (time and frequency) for transmitting the next data frame from its own ID and the code required to generate the data frame, and generates and transmits (broadcasts) the next data frame (SEQ1903).

[0159] At this point, the location of terminal 801 is outside the coverage area 711 of satellite receiving station 701. Since satellite receiving station 701 has already deleted terminal 801 from its list of target terminals for reception, it does not perform unnecessary reception and demodulation processing on the data frame from terminal 801.

[0160] In addition, the satellite receiving station 702 has registered the ID of the terminal 801 in its list of target terminals based on the frame reception information received from the satellite receiving station 701, and therefore, based on the same rules 1 to 4 as the terminal 801, calculates the radio resources (time and frequency) from which the terminal 801 transmits the data frame and the code required to demodulate the data frame from the terminal's ID, and attempts to receive and demodulate the data frame, which is successful (SEQ1925).

[0161] According to the example communication sequence shown in FIG. 19, the satellite receiving station 701 can avoid performing unnecessary reception and demodulation processing after the terminal 801 has passed its coverage area 711 by receiving notification from the subsequent satellite receiving station 702 on the same satellite orbit.

[0162] E-2.Frame configuration example Figure 20 shows an example of the frame configuration of the data portion of the target terminal list registration notification frame. The format of the portion other than the data portion will depend on the communication method used. As shown in Figure 19, the target terminal list registration notification frame is a frame that notifies a satellite receiving station that it has registered a terminal in its own target terminal list based on frame reception information received from a satellite receiving station ahead in the same satellite orbit.

[0163] The nSTA field stores the number of terminal IDs (STA Rx ID) stored in the data section. The nSTA field is followed by the same number of STA ID fields as the number listed in the nSTA field. Each STA ID field stores information about the terminal ID registered in the receiving terminal list.

[0164] E-3. Processing operations of satellite receiving station FIG. 21 shows in the form of a flowchart the processing procedure for the satellite receiving station to receive the frame reception information frame.

[0165] First, the satellite receiving station determines whether or not it has received a frame reception information frame (step S2101). Then, when it receives a frame reception information frame (Yes in step S2101), it demodulates the received frame (step S2102) and determines whether or not the demodulation was successful (step S2103).

[0166] If the satellite receiving station succeeds in demodulating the frame reception information frame (Yes in step S2103), it acquires nSTA, which indicates the number of frame reception information stored in the frame reception information frame (step S2104), and repeatedly processes each subsequent frame reception information (Frame Rx Info) for the number of frame reception information pieces.

[0167] First, the remaining time during which the notification frame or data frame can be received by the same satellite receiving station is estimated from the frequency error estimation result (Freq. Error) and the propagation delay estimation result (Propagation Delay) (step S2105).

[0168] Next, based on the remaining receivable time and data transmission interval estimated in step S2105, it is determined whether the next data frame transmitted from the terminal in question can be received by the same satellite receiving station (step S2106). Here, for the data transmission interval, if Ftype is 0, i.e., the received frame is a notification frame, the value stored in the Next Data Tx Interval field is used, and if Ftype is 1, i.e., the received frame is a data frame, the value stored in the Data Tx Interval field is used.

[0169] If the next data frame transmitted from the terminal can be received by the same satellite receiving station (Yes in step S2106), the satellite receiving station returns to step S2105 and repeats the processing of the next frame reception information (Frame Rx Info).

[0170] On the other hand, if the next data frame transmitted from the terminal in question cannot be received by the same satellite receiving station (No in step S2106), the satellite receiving station registers the terminal ID and data transmission interval stored in the frame reception information (Frame Rx Info) in its own target terminal list (step S2107), then adds the terminal ID of the terminal in question to the target terminal list registration notification frame (see Figure 20) (step S2108), and then returns to step S2105 to repeatedly process the next frame reception information (Frame Rx Info).

[0171] When processing is completed for all of the frame reception information for nSTAs stored in the frame reception information frame received in step S2101, the satellite receiving station determines whether or not it is necessary to transmit a target terminal list registration notification frame (step S2109). If it is necessary to transmit a target terminal list registration notification frame (Yes in step S2109), the satellite receiving station stores the number of stored target terminal list registration IDs in nSTA, and transmits the target terminal list registration notification frame (step S2110).

[0172] FIG. 22 shows in the form of a flowchart the processing procedure for a satellite receiving station to receive a target terminal list registration notification frame.

[0173] First, the satellite receiving station determines whether or not it has received a target terminal list registration notification frame (step S2201). Then, when it receives a target terminal list registration notification frame (Yes in step S2201), it demodulates the received frame (step S2202) and determines whether or not the demodulation process was successful (step S2203).

[0174] If the satellite receiving station succeeds in demodulating the target terminal list registration notification frame (Yes in step S2203), it acquires nSTAs indicating the number of STA ID fields stored in the target terminal list registration notification frame (step S2204), and repeatedly executes the processing of each subsequent STA ID field the number of times equal to nSTAs. In this repeated processing, it deletes the entry of the terminal ID stored in the target terminal list registration notification frame from its own target terminal list (step S2205).

[0175] By processing the target terminal list registration notification frame according to the processing procedure shown in Figure 22, the satellite receiving station can delete from its own target terminal list a terminal that has become a new target for reception at a subsequent satellite receiving station in the same satellite orbit.

[0176] Therefore, according to the communication sequence of the third embodiment, the satellite receiving station can avoid performing unnecessary reception and demodulation processing for a terminal that has passed through its own coverage area. [Example]

[0177] F. Fourth Example In the first embodiment described above, it is assumed that when a terminal that is the target of reception by a certain satellite receiving station transmits a data frame next, the location of the terminal will be within the reception range of the terminal itself or the satellite receiving station that is the next in the same satellite orbit (see, for example, the example communication sequence shown in FIG. 9).

[0178] However, if the data transmission interval of a terminal is long, such as several hours, it is possible that when the terminal next transmits a data frame, it will have moved into the reception range of a satellite receiving station several (two or more) behind the satellite receiving station that is the target of reception on the same satellite orbit.

[0179] Therefore, in the fourth embodiment, a method is described in which the appropriate satellite receiving station can receive the data frame even if the terminal moves within the reception range of a satellite receiving station several (two or more) away on the same satellite orbit during the data transmission interval.

[0180] F-1. Communication sequence example 23 shows an example of a communication sequence between satellite receiving stations 701 to 703 and terminal 801 when the method according to the fourth embodiment is applied. Satellite receiving stations 701 to 703 each continue to move on a satellite orbit at a speed of several kilometers per second, so there are time periods when the location of terminal 801 is within receivable range 711 of satellite receiving station 701, time periods when the location is outside receivable range 711 of satellite receiving station 701 and within receivable range 712 of satellite receiving station 702, and time periods when the location is outside receivable range 712 of satellite receiving station 702 and within receivable range 713 of satellite receiving station 703.

[0181] Based on rules 1 to 4 predetermined within the system, terminal 801 calculates the radio resources (time and frequency) for transmitting a data frame from its own ID and the code required to generate the data frame, and then generates and transmits (broadcasts) the data frame (SEQ2301).

[0182] It is assumed that terminal 801 is within receivable range 711 of satellite receiving station 701, and that satellite receiving station 701 has registered terminal 801 in its list of target terminals to receive data from. Therefore, using the ID registered in its list of target terminals to receive data from, satellite receiving station 701 calculates the radio resources (time and frequency) with which terminal 801 will transmit a data frame and the code required to demodulate the data frame based on the terminal's ID and the same rules 1 to 4 as for terminal 801, and receives and demodulates the data frame (SEQ2311). Here, it is assumed that satellite receiving station 701 successfully receives and demodulates the data frame.

[0183] Then, satellite receiving station 701 transmits frame reception information regarding the data frame received from terminal 801 to satellite receiving station 702, which is located subsequent to it on the same satellite orbit (SEQ2312). The frame reception information includes information such as the ID of the terminal that received the data frame, the frequency error estimation result, the propagation delay estimation result, and the ID of the receiving satellite receiving station.

[0184] Satellite receiving station 702 receives and processes the frame reception information frame from satellite receiving station 701, which is located ahead on the same satellite orbit, and determines whether or not to register terminal 801 in its own list of target receiving terminals (SEQ2321). Here, satellite receiving station 702 determines that it is unable to receive the next data frame transmitted from terminal 801 based on the remaining receivable time and data transmission interval estimated based on the frequency error estimation result and propagation delay estimation result, and does not register terminal 801 in its own list of target receiving terminals.

[0185] Next, based on the received frame reception information, satellite receiving station 702 determines whether or not to transmit this frame reception information to satellite receiving station 703, which is located subsequent to it on the same satellite orbit (SEQ2322). Then, based on the result of the determination, satellite receiving station 702 transmits the frame reception information to satellite receiving station 703 (SEQ2323).

[0186] Satellite receiving station 703 receives and processes the frame reception information frame from satellite receiving station 702, which is located ahead on the same satellite orbit, and determines whether or not terminal 801 should be registered in its own list of target receiving terminals (SEQ2331). Here, satellite receiving station 703 determines that the next data frame transmitted from terminal 801 can be received by satellite receiving station 703 based on the remaining receivable time and data transmission interval estimated based on the frequency error estimation result and propagation delay estimation result, and registers terminal 801 in its list of target receiving terminals (SEQ2332).

[0187] Then, satellite receiving station 703 transmits a target terminal list registration notification frame to satellite receiving station 701 that has received the data frame from terminal 801, notifying it that terminal 801 has been registered in the target terminal list (SEQ2333). Upon receiving the target terminal list registration notification frame from satellite receiving station 702, satellite receiving station 701 deletes the entry for terminal 801 from its own target terminal list (SEQ2313).

[0188] Furthermore, based on rules 1 to 4 predetermined within the system, terminal 801 calculates the radio resources (time and frequency) for transmitting the next data frame from its own ID and the code required to generate the data frame, and generates and transmits (broadcasts) the next data frame (SEQ2302).

[0189] At this point, the location of terminal 801 is outside the receivable range 711 of satellite receiving station 701 and the receivable range 712 of satellite receiving station 702. Satellite receiving station 701 has already deleted terminal 801 from its list of target terminals to receive, so it does not perform unnecessary reception and demodulation processing on data frames from terminal 801. Furthermore, satellite receiving station 702 has not registered terminal 801 in its list of target terminals to receive, so it does not perform reception and demodulation processing on data frames from terminal 801.

[0190] In addition, the satellite receiving station 703 has registered the ID of the terminal 801 in its list of target terminals based on the frame reception information received from the satellite receiving station 702, and therefore, based on the same rules 1 to 4 as those of the terminal 801, calculates the radio resources (time and frequency) from which the terminal 801 transmits the data frame and the code required to demodulate the data frame from the terminal's ID, and attempts to receive and demodulate the data frame, which is successful (SEQ2334).

[0191] 23, when terminal 801 next transmits a data frame, it will have moved into the coverage area 713 of satellite receiving station 703, which is two stations behind satellite receiving station 701 that is the target receiving station for terminal 801, but satellite receiving station 703 will be able to receive the next data frame from terminal 801. Furthermore, by receiving a notification from the subsequent satellite receiving station 703 on the same satellite orbit, satellite receiving station 701 can avoid performing unnecessary reception and demodulation processing after terminal 801 has passed out of coverage area 711 of its own.

[0192] F-2.Frame structure Figure 24 shows an example of the frame structure of the data portion of a frame reception information frame. The format of the portion other than the data portion depends on the communication method used. The frame reception information frame is a frame that notifies subsequent satellite receiving stations on the same satellite orbit of frame reception information regarding a frame received by a satellite receiving station from a terminal.

[0193] The nSTA field stores the number of frame reception information (Frame Rx Info) stored in the data portion. The nSTA field is followed by the same number of Frame Rx Info fields as listed in the nSTA field. Each Frame Rx Info field stores frame reception information about a frame received from each terminal. In the frame configuration example shown in Figure 24, the nSTA field stores information indicating the value n, and n Frame Rx Info fields are stored.

[0194] Each Frame Rx Info field includes an ID field, an Ftype field, a Freq.Error field, a Propagation Delay field, a Data Tx Interval field, a Next Data Tx Interval field, and a Data Rx SAT ID.

[0195] The ID field stores the ID (terminal ID) of the terminal that sent the received frame. The Ftype field stores a value indicating the type of frame received. Specifically, a value of 0 in the Ftype field indicates a notification frame, and a value of 1 indicates a data frame. The Freq.Error field stores the frequency error estimation result of the received frame. The Propagation Delay field stores the propagation delay estimation result of the received frame. The Data Tx Interval field stores the data frame transmission interval. The Next Data Tx Interval field stores the time until the next data frame is transmitted. The Next Data Tx Interval field is only added when Ftype is 0, that is, when a notification frame is received. The Data Rx SAT ID field stores the ID (SAT ID) of the satellite receiving station that received the frame in question.

[0196] F-3. Frame reception Information Frame reception operation 25A and 25B show, in the form of a flowchart, the processing procedure for the satellite receiving station to receive the frame reception information frame.

[0197] First, the satellite receiving station determines whether or not it has received a frame reception information frame (step S2501). Then, when it receives a frame reception information frame (Yes in step S2501), it demodulates the received frame (step S2502) and determines whether or not the demodulation was successful (step S2503).

[0198] If the satellite receiving station succeeds in demodulating the frame reception information frame (Yes in step S2503), it acquires nSTA, which indicates the number of frame reception information stored in the frame reception information frame (step S2504), and repeatedly processes each subsequent frame reception information (Frame Rx Info) for the number of frame reception information pieces.

[0199] In processing the frame reception information, the satellite receiving station first estimates the remaining time during which the notification frame or data frame can be received at the same satellite receiving station from the frequency error estimation result (Freq. Error) and propagation delay estimation result (Propagation Delay) (step S2505).

[0200] Next, based on the remaining receivable time and data transmission interval estimated in step S2505, it is determined whether the next data frame transmitted from the terminal in question can be received by the same satellite receiving station (step S2506). Here, for the data transmission interval, if Ftype is 0, i.e., the received frame is a notification frame, the value stored in the Next Data Tx Interval field is used, and if Ftype is 1, i.e., the received frame is a data frame, the value stored in the Data Tx Interval field is used.

[0201] If the next data frame transmitted from the terminal can be received by the same satellite receiving station (Yes in step S2506), the satellite receiving station returns to step S2505 and repeats the processing of the next frame reception information (Frame Rx Info).

[0202] On the other hand, if the next data frame transmitted from the terminal cannot be received by the same satellite receiving station (No in step S2506), the satellite receiving station further determines whether it can receive the next data frame transmitted from the terminal based on the remaining receivable time and the data transmission interval estimated in step S2505 (step S2507).

[0203] If the satellite receiving station is capable of receiving the next data frame transmitted from the terminal in question (Yes in step S2507), the satellite receiving station registers the terminal ID and data transmission interval stored in the frame reception information (Frame Rx Info) in its own list of target terminals to receive (step S2508), then adds the terminal ID of the terminal in question to the target terminal list registration notification frame (step S2509), and then returns to step S2505 to repeatedly process the next frame reception information (Frame Rx Info).

[0204] On the other hand, if the satellite receiving station is unable to receive the next data frame transmitted from the terminal (No in step S2507), the satellite receiving station adds the frame reception information to a frame reception information frame to be transmitted to the subsequent satellite receiving station on the same satellite orbit (step S2510), and then returns to step S2505 to repeatedly process the next frame reception information (Frame Rx Info).

[0205] When processing is completed for all of the frame reception information for nSTAs stored in the frame reception information frame received in step S2501, the satellite receiving station determines whether or not it is necessary to transmit a target terminal list registration notification frame (step S2511). If it is necessary to transmit a target terminal list registration notification frame (Yes in step S2511), the satellite receiving station stores the number of stored target terminal list registration IDs in nSTA and transmits the target terminal list registration notification frame (step S2512).

[0206] Next, the satellite receiving station determines whether it is necessary to transmit a frame reception information frame to a subsequent satellite receiving station on the same satellite orbit (step S2513). If it is necessary to transmit a target terminal list registration notification frame (Yes in step S2513), the satellite receiving station stores the number of target terminal list registration IDs stored in nSTA and transmits the frame reception information frame (step S2514).

[0207] F-3. List of adjacent satellite receiving stations FIG. 26 shows an example of an adjacent satellite receiving station information list held by a satellite receiving station. The adjacent satellite receiving station information list shown in the figure registers information about each adjacent satellite receiving station that orbits on the same satellite orbit as the satellite receiving station. The entry for each adjacent satellite receiving station stores the relative position from the own station, a satellite ID that identifies the satellite receiving station, and the distance from the own station. Here, the relative position is information that indicates the position of the satellite on the same satellite orbit relative to the own station. A negative number indicates a position ahead on the satellite orbit, and a positive number indicates a position behind on the satellite orbit. A relative position of 0 indicates the own station. Furthermore, the distance is information that indicates the positional distance from the own station. A negative number indicates a position ahead on the satellite orbit, and a positive number indicates a position behind on the satellite orbit. A distance of 0 indicates the own station.

[0208] For example, in the examples shown in Figures 16 and 26, if the data transmission interval is 10 minutes, the frequency error estimation result notified in the frame reception information frame is -30 kHz, the propagation delay estimation result is 2.5 milliseconds, and the satellite ID of the satellite receiving station that received the frame is 502, then the next data frame can be received by the local station.

[0209] On the other hand, for example, if the data transmission interval is 10 min, the estimated frequency error reported in the frame reception information frame is -30 kHz, the estimated propagation delay is 2.5 ms, and the satellite ID of the satellite receiving station that received the frame is 503, the next data frame cannot be received by the same satellite receiving station or by the station itself, and frame reception information must be sent to the subsequent satellite receiving station.

[0210] According to the fourth embodiment, the terminal does not need to transmit notification frames frequently, and even if the terminal moves into the reception range of a satellite receiving station several stations away during a long data transmission interval, the satellite receiving station that has the terminal in its reception range can receive and demodulate the data frame from the terminal. [Example]

[0211] G. Fifth Example In the first, third, and fourth embodiments described above, each satellite receiving station must process the received frame reception information, which may increase the processing load of the satellite receiving station. Therefore, in the fifth embodiment, a method will be described in which a satellite receiving station that has received a notification frame or a data frame determines which satellite receiving station will receive the next data frame.

[0212] G-1. Communication sequence example 27 shows an example of a communication sequence between satellite receiving stations 701 to 703 and terminal 801 when the method according to the fifth embodiment is applied. Satellite receiving stations 701 to 703 each continue to move on a satellite orbit at a speed of several kilometers per second, so there are time periods when the location of terminal 801 is within receivable range 711 of satellite receiving station 701, time periods when the location is outside receivable range 711 of satellite receiving station 701 and within receivable range 712 of satellite receiving station 702, and time periods when the location is outside receivable range 712 of satellite receiving station 702 and within receivable range 713 of satellite receiving station 703.

[0213] Based on rules 1 to 4 predetermined within the system, terminal 801 calculates the radio resources (time and frequency) for transmitting a data frame from its own ID and the code required to generate the data frame, and then generates and transmits (broadcasts) the data frame (SEQ2701).

[0214] It is assumed that terminal 801 is within receivable range 711 of satellite receiving station 701, and that satellite receiving station 701 has registered terminal 801 in its list of target terminals to receive data from. Therefore, using the ID registered in its list of target terminals to receive data from, satellite receiving station 701 calculates the radio resources (time and frequency) with which terminal 801 will transmit a data frame and the code required to demodulate the data frame based on the terminal's ID and the same rules 1 to 4 as for terminal 801, and receives and demodulates the data frame (SEQ2711). Here, it is assumed that satellite receiving station 701 successfully receives and demodulates the data frame.

[0215] Then, based on the terminal ID at the time of receiving the data frame, the frequency error estimation result, the propagation delay estimation result, and information on adjacent satellite receiving stations, the satellite receiving station 701 determines that the satellite receiving station 703 can receive the next data frame transmitted from the terminal 801 (SEQ2712), and transmits a reception target terminal registration frame to the satellite receiving station 703 (SEQ2713).

[0216] The satellite receiving station 703 registers the terminal ID and data transmission interval stored in the target receiving terminal registration frame received from the satellite receiving station 701 in its own target receiving terminal list (SEQ2731).

[0217] Furthermore, since satellite receiving station 701 determines that it cannot receive the next data frame transmitted from terminal 801 (SEQ2712), it deletes the entry for terminal 801 from its own list of target terminals for reception (SEQ2714).

[0218] After that, some time passes and the terminal 801 generates and transmits (broadcasts) the next data frame (SEQ2702).

[0219] At this point, the location of terminal 801 is outside the receivable range 711 of satellite receiving station 701 and the receivable range 712 of satellite receiving station 702. Satellite receiving station 701 has already deleted terminal 801 from its list of target terminals to receive, so it does not perform unnecessary reception and demodulation processing on data frames from terminal 801. Furthermore, satellite receiving station 702 has not registered terminal 801 in its list of target terminals to receive, so it does not perform reception and demodulation processing on data frames from terminal 801.

[0220] In addition, the satellite receiving station 703 has registered the ID of terminal 801 in its own list of target terminals based on the target terminal registration frame received from the satellite receiving station 701, and therefore, based on the same rules 1 to 4 as those used by terminal 801, calculates the radio resources (time and frequency) from which terminal 801 will transmit the data frame and the code required to demodulate the data frame from the terminal's ID, and attempts to receive and demodulate the data frame, succeeding in the demodulation (SEQ2732).

[0221] 27, when terminal 801 next transmits a data frame, it will have moved into the coverage area 713 of satellite receiving station 703, which is two stations behind satellite receiving station 701 that is the target receiving station for terminal 801, but based on the process by satellite receiving station 701 to determine which satellite receiving stations are available for reception, satellite receiving station 703 will be able to receive the next data frame from terminal 801. Furthermore, by receiving a notification from the subsequent satellite receiving station 703 on the same satellite orbit, satellite receiving station 701 can avoid performing unnecessary reception and demodulation processes after terminal 801 has passed out of its coverage area 711.

[0222] G-2.Frame configuration example Figure 28 shows an example of the frame structure of the data portion of a target terminal registration frame. The format of the portion other than the data portion depends on the communication method used. The target terminal registration frame is a frame in which a satellite receiving station instructs subsequent satellite receiving stations in the same satellite orbit to register the relevant terminal in its target terminal list.

[0223] The nSTA field stores the number of pieces of terminal information (STA Info) stored in the data portion. The nSTA field is followed by the same number of STA Info fields as listed in the nSTA field. Each STA Info field stores terminal information about a terminal that instructs the destination satellite receiving station to register in the target terminal list. In the frame configuration example shown in Figure 28, the nSTA field stores information indicating the value n, and n STA Info fields are stored.

[0224] Each STA Info field contains an ID field and a Data Tx Interval field. The ID field stores the ID of the terminal that is the receiving target. The Data Tx Interval field stores the data frame transmission interval of the terminal.

[0225] G-3. Processing operations of satellite receiving station FIG. 29 shows in the form of a flowchart the processing procedure for the satellite receiving station to receive the notification frame.

[0226] First, the satellite receiving station refers to the list of target terminals to receive the notification frame and calculates the radio resources (time and frequency) for receiving the notification frame from the registered terminal and the information required for demodulating the notification frame based on the above-mentioned rules 1 to 4 (step S2901).

[0227] Next, the satellite receiving station determines whether the notification frame reception time calculated in step S2901 has arrived (step S2902). When the notification frame reception time arrives (Yes in step S2902), the satellite receiving station detects the notification frame from the terminal using the preamble and synchronization information calculated in step S2901 (step S2903), and demodulates the received notification frame using the scrambling pattern calculated in step S2901 (step S2904). The satellite receiving station then determines whether demodulation of the notification frame was successful (step S2905). If demodulation of the notification frame fails (No in step S2905), the process returns to step S2901, and the satellite receiving station attempts to receive the next notification frame.

[0228] On the other hand, if the notification frame is successfully demodulated (Yes in step S2905), the satellite receiving station determines which satellite receiving stations can receive the next transmitted data frame based on the terminal ID and data transmission interval stored in the received notification frame (step S2906).The satellite receiving station then determines whether it can receive the next data frame transmitted from the terminal in question (step S2907).

[0229] If the satellite receiving station is capable of receiving the next data frame transmitted from the terminal (Yes in step S2907), the satellite receiving station registers information such as the terminal ID and data transmission interval stored in the received notification frame in the list of target terminals (step S2908).

[0230] If the satellite receiving station itself cannot receive the next data frame transmitted from the terminal in question (No in step S2907), the satellite receiving station generates a target terminal registration frame (step S2909) and transmits the target terminal registration frame to another satellite receiving station that can receive the next data frame transmitted from the terminal in question (step S2910).

[0231] Next, the satellite receiving station checks whether the terminal in question is present in its list of target terminals for reception (step S2911), and if present (Yes in step S2911), deletes the entry for the terminal in question from its list of target terminals for reception (step S2912).

[0232] 30 is a flowchart showing the processing steps for a satellite receiving station to receive a data frame. However, the satellite receiving station is capable of performing data frame reception processing in parallel for each terminal registered in the target terminal list.

[0233] First, the satellite receiving station acquires information about the target terminal, such as the terminal ID, from the list of target terminals (step S3001), and calculates the radio resources (time and frequency) for receiving data frames from the target terminal and the information necessary for demodulating the data frames based on the above-mentioned rules 1 to 4 (step S3002).

[0234] Next, the satellite receiving station determines whether the data frame reception time calculated in step S3002 has arrived (step S3003). When the data frame reception time arrives (Yes in step S3003), the satellite receiving station detects a data frame from the terminal using the preamble and synchronization information calculated in step S3002 (step S3004), and demodulates the received data frame using the scrambling pattern calculated in step S3002 (step S3005). The satellite receiving station then determines whether demodulation of the data frame was successful (step S3006). If demodulation of the data frame fails (No in step S3006), the process returns to step S3001, and the satellite receiving station attempts to receive the next notification frame.

[0235] On the other hand, if the data frame is successfully demodulated (Yes in step S3006), the satellite receiving station determines which satellite receiving stations can receive the next transmitted data frame based on the terminal ID and data transmission interval stored in the data frame (step S3007).The satellite receiving station then determines whether it can receive the next data frame transmitted from the terminal in question (step S3008).

[0236] Here, if the satellite receiving station itself is able to receive the next data frame transmitted from the terminal in question (Yes in step S3008), the satellite receiving station registers information such as the terminal ID and data transmission interval stored in the received data frame in the list of terminals to receive (step S3009).

[0237] If the satellite receiving station itself is not capable of receiving the next data frame transmitted from the terminal in question (No in step S3008), the satellite receiving station generates a target terminal registration frame (step S3010) and transmits the target terminal registration frame to another satellite receiving station that is capable of receiving the next data frame transmitted from the terminal in question (step S3011).

[0238] The satellite receiving station then checks whether the terminal in question is in its own list of target terminals for reception (step S3012), and if so (Yes in step S3012), deletes the entry for the terminal in question from its own list of target terminals for reception (step S3013).

[0239] FIG. 31 shows in the form of a flowchart the processing procedure for a satellite receiving station to receive a target terminal list registration frame.

[0240] First, the satellite receiving station determines whether or not it has received a target terminal list registration frame (step S3101). Then, when it receives a target terminal list registration frame (Yes in step S3101), it demodulates the received frame (step S3102) and determines whether or not the demodulation process was successful (step S3103).

[0241] If the satellite receiving station succeeds in demodulating the target terminal list registration frame (Yes in step S3103), it acquires nSTAs, which indicate the number of STA Info fields stored in the target terminal list registration frame (step S2204), and repeatedly executes the processing of each subsequent STA Info field the number of times equal to nSTAs. In this repeated processing, it registers terminal information, such as the terminal ID and data frame transmission interval stored in the STA Info field, in its own target terminal list (step S3105).

[0242] The satellite receiving station can register a new target terminal in its own target terminal list by processing the target terminal list registration frame according to the processing procedure shown in FIG.

[0243] Therefore, according to the fifth embodiment, the terminal does not need to transmit notification frames frequently, and even if the terminal moves into the reception range of a satellite receiving station several stations away during a long data transmission interval, the satellite receiving station that has the terminal in its reception range can receive and demodulate the data frame from the terminal.

[0244] H.Effect In this section H, the effects brought about by the above-mentioned first to fifth embodiments are summarized. According to the first to fifth embodiments, the following effects (1) and (2) can be obtained.

[0245] (1) The terminal does not need to transmit notification frames frequently. A satellite receiving station capable of receiving data frames periodically transmitted from the terminal can receive and demodulate the data frames. (2) It is possible to prevent a satellite receiving station from performing unnecessary reception and demodulation for a terminal that has passed through its coverage area.

[0246] The above (1) and (2) lead to the following additional effects:

[0247] (3) Lower power consumption and lower costs of terminals (4) Increase in the number of units accommodated per receiving station (5) Reducing the number of receiving stations required in the system (6) Lowering the cost of communication services [Example]

[0248] I. Sixth Example In the first to fifth embodiments described above, the terminal transmits a notification frame and then a data frame in the communication sequence, and the satellite receiving station basically targets the terminal that has received the notification frame. In contrast, in the sixth embodiment, the terminal transmits a data frame without transmitting a notification frame.

[0249] Figure 32 shows an example of a communication sequence between a terminal and a receiving station in a system in which a terminal can transmit data frames at will. The receiving station does not know the radio resources from which the terminal will transmit data frames. The radio resources here include the transmission time, transmission frequency, and code used for transmission. Therefore, the receiving station must perform reception and demodulation processing for all radio resources (time, frequency, and code).

[0250] However, if reception and demodulation processing is performed for all wireless resources, the resources required for reception processing at the receiving station (memory usage, amount of calculation, etc.) will become enormous, resulting in problems such as high cost, large size, and increased power consumption of the receiving station. In particular, when a receiving station is mounted on a low-earth orbit satellite, it is necessary to make the receiving station compact and low power consumption.

[0251] In contrast, in a sixth embodiment, the terminal adds information about the next data frame transmission to the data frame. The satellite receiving station then manages the radio resources for receiving and demodulating the next data frame based on the information added to the data frame. Therefore, according to the sixth embodiment, the satellite receiving station can limit the radio resources for receiving and demodulating the data frame, making it easier to achieve low cost, small size, and low power consumption for the receiving station.

[0252] I-1. System Configuration Fig. 33 shows a schematic configuration example of an LPWA wireless communication system according to the sixth embodiment. The example shown in the figure is composed of a plurality of receiving stations installed on the ground (hereinafter referred to as "ground stations"), a plurality of low-orbit satellite receiving stations (hereinafter simply referred to as "satellite receiving stations") that orbit the Earth in a low orbit, and numerous terminals scattered on the ground.

[0253] The terminal is a transmitter that periodically transmits information sensed by an onboard sensor, etc. The satellite receiving station receives the data transmitted by the terminal and performs demodulation processing. The satellite receiving station also transmits the demodulation results (user data) to an application server (not shown) on the cloud as necessary. The satellite receiving station also enables inter-satellite communication. There are no restrictions on the communication method between satellite receiving stations, but constant connection and high-speed communication are desirable. The ground station is a transmitter / receiver that communicates with the satellite receiving station. There are no restrictions on the communication method between the satellite receiving station and the ground station, but high-speed communication is desirable.

[0254] I-2. Communication sequence example 33, satellite receiving station 3301 and satellite receiving station 3302 are adjacent satellite receiving stations orbiting on the same satellite orbit. As satellite receiving station 3301 and satellite receiving station 3302 move on the satellite orbit, receivable range 3311 of satellite receiving station 3301 and receivable range 3312 of satellite receiving station 3302 also move on the ground.

[0255] FIG. 34 shows an example of a communication sequence between terminal 3401, which is included in either reception range 3311 or reception range 3312, and satellite receiving station 3301 and satellite receiving station 3302.

[0256] First, the terminal 3401 transmits (broadcasts) an initial data frame (SEQ 3401).

[0257] The initial data frame refers to a frame that terminal 3401 transmits for the first time, such as immediately after powering on. Terminal 3401 transmits using radio resources (time, frequency, and code) that are always targeted for reception by satellite receiving stations 3301 and 3302. Terminal 3401 also stores, in the initial data frame, information on the radio resources to be used for transmitting the next normal data frame.

[0258] 34, when terminal 3401 transmits the first data frame, the location where terminal 3401 is located is within receivable range 3311 of satellite receiving station 3301, so satellite receiving station 3301 successfully receives and demodulates the first data frame (SEQ3411). Next, satellite receiving station 3301 determines which satellite receiving station can receive the next normal data frame, based on the radio resource for transmitting the next normal data frame stored in the first data frame. Then, because satellite receiving station 3301 itself can receive the next normal data frame, satellite receiving station 3301 registers information about the radio resource for the next normal data frame to be transmitted by terminal 3401 in its own reception list (SEQ3412).

[0259] On the other hand, when terminal 3401 transmits the first data frame, the location of terminal 3401 is outside of coverage area 3312 of satellite receiving station 3302, so satellite receiving station 3302 cannot receive the first data frame.

[0260] Next, terminal 3401 transmits a normal data frame using the radio resource stored in the initial data frame (SEQ 3402). Furthermore, terminal 3401 stores, in the normal data frame, information on the radio resource to be used for transmitting the next normal data frame.

[0261] Satellite receiving station 3301 executes reception and demodulation processing based on the radio resources registered in its own reception list, thereby enabling pinpoint reception and demodulation of the normal data frame transmitted by terminal 3401 (SEQ 3413). However, at the time terminal 3401 transmits this normal data frame, the location of terminal 3401 is outside of receivable range 3312 of satellite receiving station 3302, so satellite receiving station 3302 cannot receive this normal data frame.

[0262] Furthermore, satellite receiving station 3301 determines which satellite receiving station can receive the next normal data frame based on the radio resource for transmitting the next normal data frame stored in the received normal data frame. Then, since satellite receiving station 3301 itself can receive the next normal data frame, satellite receiving station 3301 again registers terminal 3401 in its own reception list (SEQ3414).

[0263] Next, the terminal 3401 transmits the next normal data frame using the radio resource stored in the previous normal data frame (SEQ 3403). The terminal 3401 also stores, in the normal data frame, information on the radio resource to be used for transmitting the next normal data frame.

[0264] Satellite receiving station 3301 executes reception and demodulation processing based on the radio resources registered in its own reception list, thereby enabling pinpoint reception and demodulation of the normal data frame transmitted by terminal 3401 (SEQ 3415). However, at the time terminal 3401 transmits this normal data frame, the location of terminal 3401 is outside of receivable range 3312 of satellite receiving station 3302, so satellite receiving station 3302 cannot receive this normal data frame.

[0265] Furthermore, satellite receiving station 3301 determines which satellite receiving stations can receive the next normal data frame based on the radio resource for transmitting the next normal data frame stored in the received normal data frame. Since satellite receiving station 3301 cannot receive the next normal data frame, it transmits a reception target radio resource information notification frame to satellite receiving station 3302 that can receive it (SEQ3416).

[0266] The satellite receiving station 3302 registers the information on the radio resource stored in the reception target radio resource information notification frame received from the satellite receiving station 3301 in its own reception list (SEQ3421).

[0267] Next, the terminal 3401 transmits the next normal data frame using the radio resource stored in the previous normal data frame (SEQ 3404).

[0268] When terminal 3401 transmits the next normal data frame, its location falls within receivable range 3312 of satellite receiving station 3302. Satellite receiving station 3302 executes reception and demodulation processing based on the radio resources registered in its own reception list, thereby enabling it to pinpoint and demodulate the normal data frame transmitted by terminal 3401 (SEQ 3422). However, when terminal 3401 transmits this normal data frame, its location has moved outside receivable range 3312 of satellite receiving station 3301, and therefore satellite receiving station 3301 cannot receive this normal data frame.

[0269] The terminal may transmit the initial data frame periodically, rather than immediately after powering on. Even if the satellite receiving station fails to receive the normal data frame, the terminal will be registered in the satellite receiving station's reception list again from the point when it successfully receives the initial data frame, so it is desirable for the terminal to transmit the initial data frame periodically.

[0270] I-3. Equipment configuration In the sixth embodiment, the terminal configuration may be the same as that shown in FIG. 3, so in this section I, the explanation of the terminal configuration will be omitted.

[0271] Fig. 35 shows an example of the functional configuration of a satellite receiving station 3500 in a system according to the sixth embodiment. The satellite receiving station 3500 is used by being mounted on a low-earth orbit satellite that orbits the Earth in one of the satellite orbits shown in Fig. 33. The satellite receiving station 3500 includes an LPWA unit 3520 and an inter-satellite communication unit 3530.

[0272] The LPWA unit 3520 receives frames transmitted by a terrestrial terminal. In the LPWA unit 3520, the same components as those in the receiving station 200 shown in Fig. 4 are assigned the same reference numerals as in Fig. 4. The LPWA unit 3520 further includes a receivable receiving station determination unit 3526. The receivable receiving station determination unit 3526 determines receiving stations that can receive the next data frame based on next data frame transmission information stored in the data frame received from the terminal.

[0273] The inter-satellite communication unit 3530 includes a wireless communication unit 3531 , a wireless control unit 3532 , a frame generation unit 3533 , and a frame detection and demodulation unit 3534 .

[0274] The wireless communication unit 3531 transmits and receives wireless signals. Under the control of the wireless control unit 3532, the wireless communication unit 3531 receives radio waves, converts them into wireless signals, and passes them to the frame detection and demodulation unit 3534. Under the control of the wireless control unit 3532, the wireless communication unit 3531 also converts frames generated by the frame generation unit 3533 into wireless signals and transmits them.

[0275] The wireless control unit 3532 controls the wireless communication unit 3531 so that frames can be transmitted and received between satellite receiving stations.

[0276] The frame generation unit 3533 stores the next data frame transmission information acquired from the receivable receiving station determination unit 3526 on the LPWA unit 3520 side, and generates a frame according to a predetermined format.

[0277] The frame detection and demodulation unit 3534 detects and demodulates frames from the signal received by the wireless communication unit 3531. If the frame detection and demodulation unit 3534 successfully demodulates the frame, it passes the received data to the storage unit 205 in the LPWA unit 3520. Specifically, it stores information on the wireless resources of the target terminal received from a satellite receiving station ahead on the same orbit in a reception list in the storage unit 205.

[0278] I-4.Frame structure Figure 36 shows an example of the structure of a data frame transmitted and received between a terminal and a satellite receiving station. However, the frame structure of the initial data frame and the normal data frame is assumed to be the same. The data frame includes the fields ID, DATA, Time Interval, Ch, Code, and CRC.

[0279] The ID field stores an ID that is a unique identifier of the terminal 100 that is the sender. The DATA field stores the transmitted data. In the case of a data frame, data acquired from the sensor 104, etc. is stored. The Time Interval field stores information about the transmission interval from the transmission of the current data frame to the transmission of the next data frame. The Ch field stores information about the frequency to be used when transmitting the next data frame. The Code field stores information about the code to be used when transmitting the next data frame, specifically, information indicating a preamble, synchronization information (Sync), and four initial values ​​required to generate a scramble pattern. The CRC field stores a CRC value calculated from the information stored in the ID field, DATA field, Time Interval field, Ch field, and Code field. The receiving side uses the CRC value to determine whether demodulation was successful.

[0280] The sequence of the ID, DATA, Time Interval, Ch, Code, and CRC is FEC coded and rearranged (interleaved) to generate the payload. A preamble, a known pattern used for frame detection and synchronization acquisition, and synchronization information are then added to the beginning of the payload, and the frame is generated by performing an exclusive OR (XOR) with the scrambling pattern for each bit.

[0281] Within the system, rules are predetermined for determining the preamble and synchronization information required for frame generation, and the method for generating the scramble pattern. The methods for generating the preamble, synchronization information, and scramble pattern required for frame generation follow rules 3 and 4, respectively, shown in Figure 6. The preamble and synchronization information (Preamble / Sync) are determined by inputting two initial values, Seed(P)-1 and Seed(P)-2, used to calculate the preamble and synchronization information into rule 3. The scramble pattern is determined by inputting two initial values, Seed(S)-1 and Seed(S)-2, used to calculate the scramble pattern into rule 4.

[0282] Each initial value is determined in advance within the system and is stored in memory unit 106 within terminal 100 and memory unit 3525 within satellite receiving station 3500. Also, the initial values ​​that can be used for the initial data frame and the normal data frame are different.

[0283] 37 shows an example of the frame structure of the data portion of the reception target radio resource information notification frame. The format of the portion other than the data portion depends on the communication method used. The reception target radio resource information notification frame is a frame that notifies other satellite reception stations that can receive the next normal data frame of the radio resources for transmitting the next normal data frame when a satellite reception station determines that it cannot receive the next normal data frame itself.

[0284] The data portion of the reception target radio resource information notification frame includes an Rx Time field, a Ch field, and a Code field. The Rx Time field stores information about the reception time of the next data frame. The Ch field stores information about the reception frequency of the next data frame. The Code field stores information about the reception code of the next data frame, specifically, information indicating a preamble, synchronization information (Sync), and four initial values ​​required to generate a scramble pattern.

[0285] I-5. Terminal processing operations FIG. 38 shows the processing operations performed by the terminal in the form of a flowchart.

[0286] First, the terminal determines the radio resources (time, frequency, code) to be used for transmitting the initial data frame (step S3801).

[0287] Next, the terminal determines the radio resources (time, frequency, code) to be used for the next transmission of a normal data frame (step S3802).

[0288] Next, the terminal generates an initial data frame (step S3803). The Time Interval, Ch, and Code fields of the initial data frame store information about the radio resources to be used for transmitting the next normal data frame, as determined in step S3802.

[0289] Then, when the time to transmit the first data frame arrives (Yes in step S3804), the terminal transmits the first data frame generated in step S3803 using the transmission frequency calculated in step S3801 (step S3805).

[0290] Next, the terminal determines whether the frame to be transmitted the time after next is the first data frame (step S3806).

[0291] If the frame to be transmitted after next is not the initial data frame (No in step S3808), the terminal determines the radio resources (time, frequency, code) to be used for transmitting the normal data frame after next (step S3807).

[0292] Next, the terminal generates a normal data frame (step S3808). The Time Interval, Ch, and Code fields of the normal data frame store information about the radio resources to be used for transmitting the next normal data frame, as determined in step S3807. However, if the data frame to be transmitted next is the initial data frame (Yes in step S3806), the Time Interval, Ch, and Code fields of the normal data frame are padded with zeros.

[0293] Then, when the time to transmit the normal data frame arrives (Yes in step S3809), the terminal transmits the normal data frame generated in step S3803 using the transmission frequency calculated in step S3802 (step S3810).

[0294] Next, the terminal determines whether the next frame to be transmitted is a first data frame (step S3811). If the next frame to be transmitted is a first data frame (Yes in step S3811), the process returns to step S3801, and the terminal repeatedly executes the process for transmitting the first data frame. If the next frame to be transmitted is not a first data frame (No in step S3811), the process returns to step S3806, and the terminal repeatedly executes the process for transmitting a normal data frame.

[0295] I-6. Processing operations of satellite receiving station FIG. 39 shows in the form of a flowchart the processing operation for the satellite receiving station to receive the initial data frame.

[0296] First, the satellite receiving station performs reception and demodulation processing for all frequencies and codes assigned to the transmission of the initial data frame (step S3901).

[0297] If the reception and demodulation of the first data frame is successful (Yes in step S3902), the satellite receiving station calculates the expected reception time of the next normal data frame based on the transmission interval stored in the Time Interval field in the successfully demodulated first data frame (step S3903).

[0298] Next, the satellite receiving station determines whether it is the satellite receiving station that can receive the next normal data frame (step S3904).

[0299] If the satellite receiving station is the one that can receive the next normal data frame (Yes in step S3904), the satellite receiving station registers the predicted reception time calculated in step S3903 and the frequency and code stored in the initial data frame in its own reception list (step S3905).

[0300] On the other hand, if the satellite receiving station is not the one that can receive the next normal data frame (No in step S3904), the satellite receiving station transmits a reception target radio resource information notification frame to the satellite receiving station that can receive the next normal data frame (step S3906).

[0301] The processing of steps S3903 and S3904 in the flowchart shown in FIG. 39 will be described with reference to FIG.

[0302] For example, if the reception time of the first data frame that was successfully demodulated in step S3902 was 12:00:01.020 and the Time Interval was 00:01:00.000, the expected reception time of the next normal data frame would be 12:01:01.020. However, because the distance between the ground and the satellite receiving station is long, at several hundred kilometers, propagation delays occur. Furthermore, because the satellite receiving station moves, it is necessary to take into account that the amount of propagation delay varies for each data frame.

[0303] Figure 16 shows an example of the change over time in frequency error and propagation delay when the satellite is at an altitude of 600 km and has a frequency of 2 GHz. This is an example of a case where the satellite passes overhead of a terminal, and the satellite receiving station can receive signals from one terminal for six minutes. The frequency error was calculated using the model described in 3GPP TR 38.811 V15.1.0 (Non-Patent Document 1).

[0304] For example, suppose the estimated frequency error when receiving a data frame is 40 kHz. In this case, if the propagation delay is 3.5 milliseconds and the Time Interval is 00:01:00.000, the propagation delay when the next normal data frame is received will be 2.5 milliseconds. Therefore, the estimated time of reception of the next normal data frame will be 12:01:01.019.

[0305] Next, it is determined whether the satellite receiving station that can receive the next normal data frame is itself.

[0306] For example, in the example shown in FIG. 16, if the frequency error estimation result at the time of receiving a data frame is 40 kHz and the Time Interval is 00:01:00.000, the satellite receiving station that can receive the next normal data frame is itself.

[0307] On the other hand, if the estimated frequency error when receiving the data frame is -40 kHz and the time interval is 00:01:30.000, the satellite receiving station that can receive the next normal data frame will be the satellite receiving station one orbit behind in the same satellite orbit.

[0308] 40 is a flowchart showing the processing procedure for a satellite receiving station to receive a normal data frame. Note that the satellite receiving station executes this processing for each target radio resource for reception registered in the reception list.

[0309] First, the satellite receiving station acquires the radio resources (time, frequency, code) to be received from the reception list (step S4001), and then determines whether the target reception time has arrived (step S4002).

[0310] When the target reception time arrives (Yes in step S4002), the satellite receiving station performs reception and demodulation processing using the target reception code for the target reception frequency (step S4003).The satellite receiving station then determines whether demodulation of the normal data frame was successful (step S4004).

[0311] If demodulation of the normal data frame fails (No in step S4004), the satellite receiving station skips all subsequent processing steps and ends the reception processing of the normal data frame in the target radio resource for reception.

[0312] On the other hand, if the demodulation of the normal data frame is successful (Yes in step S4004), the satellite receiving station determines whether the demodulated normal data frame contains information about the radio resources to be used for transmitting the next normal data frame (step S4005).

[0313] If the demodulated normal data frame does not contain information about the wireless resource to be used for transmitting the next normal data frame (No in step S4005), the satellite receiving station skips all subsequent processing steps and terminates the normal data frame reception processing in the wireless resource to be received.

[0314] If the demodulated normal data frame contains information about the radio resources to be used for transmitting the next normal data frame (Yes in step S4005), the satellite receiving station calculates the expected reception time of the next normal data frame based on the reception time of the normal data frame and the transmission interval stored in the normal data frame (step S4006).

[0315] Next, the satellite receiving station determines whether it is the satellite receiving station that can receive the next normal data frame (step S4007).

[0316] If the satellite receiving station is the one that can receive the next normal data frame (Yes in step S4007), the satellite receiving station registers the predicted reception time calculated in step S4006 and the frequency and code stored in the normal data frame demodulated in step S4003 in its reception list (step S4008).

[0317] Also, if the satellite receiving station is not the one that can receive the next normal data frame (No in step S4007), the satellite receiving station transmits a reception target radio resource information notification frame to the satellite receiving station that can receive the next normal data frame (step S4009).

[0318] FIG. 41 shows, in the form of a flowchart, a processing procedure for a satellite receiving station to receive a reception target radio resource information notification frame.

[0319] First, the satellite receiving station determines whether or not it has received a target radio resource information notification frame from another satellite receiving station (step S4101). If it has received a target radio resource information notification frame (Yes in step S4101), it demodulates the target radio resource information notification frame (step S4102) and determines whether or not the demodulation of the frame was successful (step S4103).

[0320] If the reception target radio resource information notification frame is successfully demodulated (Yes in step S4103), the satellite receiving station determines whether the frame is addressed to the station itself (step S4104).

[0321] If the demodulated reception target radio resource information notification frame is addressed to the satellite receiving station (Yes in step S4104), the satellite receiving station registers the information stored in the frame in its own reception list (step S4105).

[0322] If the demodulated reception target radio resource information notification frame is not addressed to the satellite receiving station (No in step S4104), the satellite receiving station transfers the reception target radio resource information notification frame to the corresponding satellite receiving station (step S4106).

[0323] I-7.Effects The following summarizes the effects brought about by the sixth embodiment described in Section I. According to the sixth embodiment, the following effects (1) and (2) can be obtained.

[0324] (1) There is no need for signaling between the terminal and the satellite receiving station for allocating radio resources, and the satellite receiving station can limit the radio resources for performing reception and demodulation processing. (2) There is no need for signaling between the terminal and the satellite receiving station for wireless resource allocation, and it is possible to follow even if the satellite receiving station moves and the satellite receiving station that can receive the data frame transmitted by the terminal changes.

[0325] The above (1) and (2) lead to the following additional effects:

[0326] (3) Lower power consumption and lower costs of terminals (4) Increase in the number of units accommodated per receiving station (5) Smaller receiving stations and lower power consumption (6) Reduction in the number of receiving stations required for the system (7) Lowering the cost of communication services [Industrial Applicability]

[0327] Although the present disclosure has been described in detail above with reference to specific embodiments, it is obvious that those skilled in the art can make modifications or substitutions to the embodiments without departing from the spirit and scope of the present disclosure.

[0328] Although the present disclosure has been described in detail with reference to an embodiment in which the present disclosure is applied to an LPWA communication system, the gist of the present disclosure is not limited thereto. The present disclosure can be similarly applied to various types of communication systems in which communication is performed between a terrestrial terminal and a satellite receiving station orbiting the Earth. Furthermore, while the present disclosure has been described in detail with reference to an embodiment in which a specific satellite constellation is used for convenience, the present disclosure can also be applied to communication systems that use other satellite constellations and can accommodate any number of satellite receiving stations.

[0329] In short, the present disclosure has been described in the form of examples, and the contents of the specification should not be interpreted as limiting. To determine the gist of the present disclosure, the claims should be taken into consideration.

[0330] The present disclosure may also be configured as follows.

[0331] (1) Operates as one of the satellite receiving stations that orbits the Earth in a predetermined orbit and receives frames from a terminal on the ground; a receiving unit that receives and processes frames from the terminal; a determination unit that determines a satellite receiving station suitable for receiving the next frame transmitted by the terminal based on frame reception information when a frame is received from the terminal, a frame transmission interval of the terminal, and the positional relationship of surrounding satellite receiving stations; A communication device comprising:

[0332] (2) The frame reception information includes a frequency error estimation result and a propagation delay estimation result at the time of frame reception. The communication device according to (1) above.

[0333] (3) The frame reception information includes location information of the terminal. The communication device according to (1) above.

[0334] (4) Exchanging frame reception information with surrounding satellite receiving stations; A communication device according to any one of (1) to (3) above.

[0335] (5) The determination unit further determines a satellite receiving station suitable for receiving the next frame transmitted by the terminal based on frame reception information from surrounding satellite receiving stations. The communication device according to (4) above.

[0336] (6) storing information about the terminal determined by the determination unit as being capable of receiving the next frame to be transmitted by the own station in a list of target terminals; receiving and processing a frame to be transmitted next by the terminal based on the information stored in the target terminal list; The communication device according to (5) above.

[0337] (7) notifying the surrounding satellite receiving stations of information about terminals added to the target receiving terminal list based on frame reception information from the surrounding satellite receiving stations; The communication device according to (6) above.

[0338] (8) Based on the notification from the surrounding satellite receiving station, delete the information of the corresponding terminal from the receiving terminal list of the own station. The communication device according to (7) above.

[0339] (9) Exchange frame reception information including the station's own identification information with surrounding satellite receiving stations, notifying the satellite receiving station whose identification information is indicated in the frame reception information of the terminal that has been added to the target receiving terminal list based on the frame reception information from the surrounding satellite receiving station; The communication device according to (7) above.

[0340] (10) notifying the surrounding satellite receiving station that the determination unit has determined to be suitable for receiving the next frame transmitted from the terminal of the registration of the target receiving terminal; The communication device according to (1) above.

[0341] (11) The terminal that notified the surrounding satellite receiving station of its registration as a target terminal for reception is removed from the target terminal for reception by the own station. The communication device according to (10) above.

[0342] (12) The terminal that has been notified of the registration of the target terminal by the surrounding satellite receiving station is set as the target of reception by the own station. The communication device according to any one of (10) and (11) above.

[0343] (13) the frame reception information includes a frame transmission interval notified by the terminal; the determination unit estimates an expected reception time of the next frame transmitted from the terminal based on the frame transmission interval and the frequency error estimation result at the time of frame reception; The communication device according to (1) above.

[0344] (14) The determination unit determines a satellite receiving station suitable for receiving the next frame transmitted from the terminal based on the predicted reception time of the next frame transmitted from the terminal and the positional relationship of surrounding satellite receiving stations. The communication device according to (13) above.

[0345] (15) The terminal that the determination unit determines as being capable of receiving the next transmitted frame is set as the reception target of the next transmitted frame. The communication device according to (14) above.

[0346] (16) Notifying a nearby satellite receiving station that is determined to be suitable for receiving the next frame transmitted by the terminal of wireless resource information for receiving the frame from the terminal; The communication device according to (14) above.

[0347] (17) In response to receiving wireless resource information for receiving frames from a nearby satellite receiving station, the corresponding terminal is set as a reception target of the own station. The communication device according to (16) above.

[0348] (18) The surrounding satellite receiving stations include at least one of a satellite receiving station moving in the same orbit and a satellite receiving station moving in an adjacent orbit. A communication device according to any one of (1) to (17) above.

[0349] (19) A communication method that operates as a satellite receiving station that orbits the Earth in a predetermined orbit and receives frames from a terrestrial terminal, a receiving step of receiving and processing frames from the terminal; a determination step of determining a satellite receiving station suitable for receiving the next frame transmitted by the terminal based on frame reception information at the time of receiving a frame from the terminal, a frame transmission interval of the terminal, and the positional relationship of surrounding satellite receiving stations; A communication method comprising:

[0350] (20) It consists of a terminal installed on the ground and multiple satellite receiving stations each orbiting the Earth in a predetermined orbit, Each of the plurality of satellite receiving stations comprises a receiving unit that receives and processes frames from the terminal, and a determining unit that determines a satellite receiving station that is suitable for receiving the next frame transmitted by the terminal based on frame reception information when frames are received from the terminal, a frame transmission interval of the terminal, and a positional relationship between neighboring satellite receiving stations. Communication system. [Explanation of symbols]

[0351] 100... terminal, 101... wireless communication unit, 102... wireless control unit 103...frame generation unit, 104...sensor 105...Radio resource determination unit, 106...Storage unit 200: Receiving station, 201: Wireless communication unit, 202: Wireless control unit 203...frame detection and demodulation unit, 204...radio resource determination unit 205...Storage section 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 and demodulation unit 3500...Satellite receiving station, 3520...LPWA section 3526... Receivable receiving station determination unit 3531...wireless communication unit, 3532...wireless control unit 3533...frame generation unit, 3534...frame detection and demodulation unit

Claims

1. The satellite operates as one of the satellite receiving stations that orbits the Earth in a predetermined orbit and receives frames from a terminal on the ground; a receiving unit that receives and processes frames from the terminal; a determination unit that determines a satellite receiving station suitable for receiving the next frame transmitted by the terminal based on frame reception information relating to the frame received from the terminal, the frame transmission interval of the terminal included in the frame reception information, and the positional relationship of surrounding satellite receiving stations on the same orbit; A communication device comprising:

2. The frame reception information includes a frequency error estimation result and a propagation delay estimation result when the frame is received from the terminal. The communication device according to claim 1 .

3. The frame reception information includes location information of the terminal. The communication device according to claim 1 .

4. exchange frame reception information with surrounding satellite receiving stations; The communication device according to claim 1 .

5. the determination unit further determines a satellite receiving station suitable for receiving the next frame transmitted by the terminal based on frame reception information from surrounding satellite receiving stations. The communication device according to claim 4.

6. storing information about a terminal that the determination unit has determined to be capable of receiving the next frame to be transmitted by the own station in a list of target terminals; receiving and processing a frame to be transmitted next by the terminal based on the information stored in the target terminal list; The communication device according to claim 5 .

7. notifying the surrounding satellite receiving stations of information about the terminals added to the target receiving terminal list based on frame reception information from the surrounding satellite receiving stations; The communication device according to claim 6.

8. Based on the notification from the surrounding satellite receiving station, delete the information of the corresponding terminal from the receiving terminal list of the own station. The communication device according to claim 7.

9. The frame reception information including the station's own identification information is exchanged with surrounding satellite receiving stations, notifying the satellite receiving station whose identification information is indicated in the frame reception information of the terminal that has been added to the target receiving terminal list based on the frame reception information from the surrounding satellite receiving station; The communication device according to claim 7.

10. notifying a nearby satellite receiving station that the determining unit has determined to be suitable for receiving the next frame transmitted from the terminal of the registration of the target terminal; The communication device according to claim 1 .

11. removing the terminal that has notified the surrounding satellite receiving station of its registration as a target terminal for reception from the target terminal for reception of the own station; The communication device according to claim 10.

12. The terminal that has been notified of the registration of the target terminal from the surrounding satellite receiving station is set as the target of reception for the own station. The communication device according to claim 10.

13. the determination unit estimates an expected reception time of the next frame transmitted from the terminal based on a frame transmission interval of the terminal and a frequency error estimation result at the time of receiving a frame from the terminal; The communication device according to claim 1 .

14. the determination unit determines a satellite receiving station suitable for receiving the next frame transmitted by the terminal based on a positional relationship of surrounding satellite receiving stations on the same orbit as the predicted time of reception of the next frame transmitted from the terminal; 14. The communication device of claim 13.

15. The terminal that the determination unit determines to be able to receive the next transmitted frame is set as the reception target of the terminal.

15. The communication device of claim 14.

16. notifying a nearby satellite receiving station on the same orbit that is determined to be suitable for receiving the next frame transmitted by the terminal of radio resource information for receiving the frame from the terminal; 15. The communication device of claim 14.

17. In response to notification of wireless resource information for receiving frames from the terminal from a nearby satellite receiving station, the terminal is set as a reception target of the terminal.

17. The communication device of claim 16.

18. The surrounding satellite receiving stations further include satellite receiving stations traveling in adjacent orbits. The communication device according to claim 1 .

19. A communication method that operates as a satellite receiving station that orbits the Earth in a predetermined orbit and receives frames from a terminal on the ground, comprising: a receiving step of receiving and processing frames from the terminal; a determination step of determining a satellite receiving station suitable for receiving the next frame transmitted by the terminal based on frame reception information regarding the frame received from the terminal, the frame transmission interval of the terminal included in the frame reception information, and the positional relationship of surrounding satellite receiving stations on the same orbit; A communication method comprising:

20. It consists of a terminal installed on the ground and multiple satellite receiving stations that orbit the Earth in their own designated orbits. Each of the plurality of satellite receiving stations comprises a receiving unit that receives and processes frames from the terminal, and a determining unit that determines a satellite receiving station that is suitable for receiving the next frame transmitted by the terminal based on frame reception information regarding the frames received from the terminal, the frame transmission interval of the terminal included in the frame reception information, and the positional relationship of surrounding satellite receiving stations on the same orbit. Communication system.

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