KR20040029282A - Satellite communication method, and satellite communication apparatus, earth station, and gateway station for use with the satellite commnication method - Google Patents

Abstract

PURPOSE: A satellite communication method is provided to transmit conversion command information for directing a conversion of a communication line at handover timing, and to convert the communication line by a station receiving the information. CONSTITUTION: A gateway station(3) continuously transmits conversion command packets(8) when converting a communication line(5a) into a communication line(5b) of a communication satellite. The conversion command packets(8) are transmitted by the communication line(5a), and are transmitted to an earth station(4) by a communication line(6a) via another communication satellite. The earth station(4) receives the conversion indicate packets(8) by the communication line(6a), and converts into a communication line(6b) from the communication line(6a).

Description

SATELLITE COMMUNICATION METHOD, AND SATELLITE COMMUNICATION APPARATUS, EARTH STATION, AND GATEWAY STATION FOR USE WITH THE SATELLITE COMMNICATION METHOD}

The present invention relates to a satellite communication method for performing satellite communication between a gateway station and a ground station through a plurality of communication satellites sequentially flying in the ceiling direction, to a satellite communication device, a ground station and a gateway station used in the method. It is about.

There is a communication system such as iridium or a global star, for example, in a system that communicates using a satellite group on orbit. In the case of the iridium system, a total of 66 communication satellites are traversed on a low orbit, and each satellite itself includes an exchange function and an inter-satellite communication function, and each other via a communication between a plurality of adjacent satellites. It enables communication between remote devices. That is, each communication terminal on the ground communicates with a communication satellite that can communicate with each other, and communicates with a terminal on a far side that communicates with another communication satellite via communication between communication satellites.

Since the communication satellites traverse on the orbit, the communication satellites that communicate with each other from the communication terminals on the ground are not always the same, and move out of the cover area of one communication satellite to the cover area of the other communication satellites. At this time, each communication terminal on the ground breaks the communication link with one communication satellite and establishes a communication link with another satellite. This operation is called inter-satellite handover.

In the inter-satellite handover in such a satellite communication system, for example, a terrestrial communication terminal monitors a reception radio wave from a communication satellite, and when a reception radio wave reaches a predetermined value or less, a handover request signal is sent from the terrestrial communication terminal. A process is performed to transmit to a communication satellite and to cut this request signal from one communication satellite link and to establish a communication link with another communication satellite.

13 is a sequence diagram showing an inter-satellite handover process disclosed in, for example, Japanese Patent Laid-Open No. 2000-315972. Fig. 13 illustrates a handover from a first communication satellite to a second communication satellite that orbits on an orbit, and is a subscriber of a terrestrial communication terminal. In FIG. 13, first, for all communication satellites from the NOC (ground station), the physical location (latitude and longitude) immediately below the navigation satellites, the schedule indicating the time, and the front and rear ends of the communication satellites. The physical location (latitude, longitude) immediately below the navigation satellite located at, the schedule indicating the time, and the physical location (latitude, longitude) immediately below the navigation satellite adjacent to the communication satellite, A schedule representing the time is transmitted, and this information is registered at all communication satellites (A1, A2).

Based on the information on the communication satellite, the first communication satellite calculates the handover start time, calculates the handover completion time, and transmits to the second communication satellite which is the target of the handover in addition to the control signal. . When the second communication satellite receives the control signal and the additional information, handover between the first communication satellite and the second communication satellite is initiated (A3). In addition, a downlink message is transmitted to the subscriber from the first communication satellite to the second communication satellite (A4). The first communication satellite transmits the last communication data from the communication link establishing with the subscriber to the subscriber (A5), and then the second communication satellite transmits the subscriber with the newly established communication link with the subscriber. The first communication data to the furnace is transmitted (A6). Thereafter, an uplink communication link from the subscriber to the communication satellite is prepared, the last uplink A7 is performed for the first communication satellite, and the first uplink A8 is performed for the second communication satellite. .

In a conventional satellite communication system, a terrestrial communication terminal monitors a radio wave received from a communication satellite, and when a received radio wave reaches a predetermined value or less, a handover request signal is transmitted from the terrestrial communication terminal to the communication satellite. Communication link between communication satellites, handover control between communication satellites is performed, and then communication data is completed to a communication terminal on the ground, and a series of handover processes require transmission and reception of a large amount of data. There was this. Further, since handover processing is performed between communication satellites, each communication satellite needs a communication link transmitting and receiving device between communication satellites and a storage device for storing the handover processing calculation device and processing information. There has also been a problem that the size of the device is increased, which lowers the reliability of the communication satellite. In the inter-satellite handover method disclosed in Japanese Patent Laid-Open No. 2000-315972, the handover start time is estimated based on the positional information of the communication satellite, thereby eliminating the procedure of the handover processing request from the terrestrial communication terminal. However, the calculation of the handover processing start time in the communication satellite is required each time, resulting in an increase in the processing scale on the satellite side.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and in a communication system via a communication satellite that sequentially flies in the zenith direction, the time required for handover processing is shortened, and the size of the handover processing circuit is reduced. It is an object of the present invention to obtain a satellite communication method, a satellite communication device, a ground station, and a gateway station used in the method.

1 is a block diagram showing the overall configuration of a satellite communication system in a satellite communication method according to a first embodiment of the present invention.

2 is a schematic diagram showing an example of a trajectory in which a communication satellite is formed on the earth's surface in the satellite communication method according to the first embodiment of the present invention.

3 is a schematic diagram illustrating handover when switching a communication satellite in the satellite communication method according to the first embodiment of the present invention.

4 is a schematic diagram showing transmission and reception contents during handover between communication satellites in the satellite communication method according to the first embodiment of the present invention.

FIG. 5 is a schematic diagram showing transmission / reception contents during handover between communication satellites in the satellite communication method according to the first embodiment of the present invention. FIG.

Fig. 6 is a block diagram showing the configuration of a gateway station used in the satellite communication method according to the first embodiment of the present invention.

Fig. 7 is a configuration diagram showing the construction of a ground station used in the satellite communication method according to the first embodiment of the present invention.

8 is a schematic diagram showing transmission and reception contents during handover between communication satellites in the satellite communication method according to the second embodiment of the present invention.

9 is a schematic diagram showing transmission and reception contents during handover between communication satellites in the satellite communication method according to the third embodiment of the present invention.

Fig. 10 is a block diagram showing the configuration of a switch instruction packet in the satellite communication method according to the third embodiment of the present invention.

FIG. 11 is a schematic diagram showing transmission / reception contents during handover between communication satellites in the satellite communication method according to the third embodiment of the present invention. FIG.

12 is a schematic diagram showing time-division frames of transmission / reception signals during handover between communication satellites in the satellite communication method according to the fourth embodiment of the present invention.

13 is a sequence diagram showing handover processing in a conventional satellite communication system.

<Explanation of symbols for main parts of drawing>

1a, 1b, 1c: communication satellite

2: communication area

3a, 3b, 3c: gateway station

4a, 4b, 4c, 4d, 4e: ground station

5a, 5b: communication line

6a, 6b: communication line

7: data packet

8: switch indication packet

11: transmit antenna

12: receiving antenna

13: transmitter

14: packet sender

15: switch instruction packet generation unit

17: data packet generation unit

18: data packet storage unit

19: receiver

20: reception signal processing unit

21: satellite switching indicator

23, 24: switch indication packet

A satellite communication method according to a feature of the present invention is a satellite communication method in which communication is performed between a gateway station and a ground station via a communication satellite sequentially flying in the approximately ceiling direction, from communication via one communication satellite to the next. When switching to communication via another communication satellite that is flying, the gateway station or the ground station continuously transmits the switching indication information by a transmission line through the one communication satellite and transmits through the other communication satellite. Is to switch to communication.

A satellite communication apparatus according to a feature of the present invention includes a plurality of communication satellites sequentially flying in a substantially ceiling direction, and a gateway station and a ground station communicating via the communication satellite, wherein the gateway station communicates with one of the communication satellites. When switching from communication via satellite to communication via another communication satellite that follows, the switching instruction information is continuously transmitted to switch to communication via the other communication satellite, and the ground station transmits the switching instruction information. Receiving a switch from the communication through the one communication satellite to the communication through the other communication satellite.

A gateway station in accordance with a feature of the present invention includes a transmitter for communicating with a ground station via a plurality of communication satellites sequentially flying in the zenith direction, and the other one coming next from the communication via one of the communication satellites. A satellite switching instructing unit for instructing switching to communication via a communication satellite, and a switching instructing packet generating unit for generating a packet including switching instructing information based on the instruction from the satellite switching instructing unit, wherein the transmitting unit includes the switching instructing unit; The packet including the switching instruction information generated by the packet generator is continuously transmitted to the ground station.

In accordance with an aspect of the present invention, a ground station includes a transmitter that communicates with a gateway station through a plurality of communication satellites sequentially flying in a zenith direction, and one of the other stations coming next from the communication via one of the communication satellites. A satellite switching instructing unit for instructing switching to communication via a communication satellite, and a switching instructing packet generating unit for generating a packet including switching instructing information based on the instruction from the satellite switching instructing unit, wherein the transmitting unit includes the switching instructing unit; The packet including the switching instruction information generated by the packet generation unit is continuously transmitted to the gateway station.

Embodiment of the Invention

<First Embodiment>

The satellite communication method according to the first embodiment of the present invention, the satellite communication apparatus used in the method, the ground station and the gateway station will be described with reference to Figs. 1 is a configuration diagram showing an overall configuration of a satellite communication system in the satellite communication method according to the first embodiment. In Fig. 1, reference numerals 1a to 1c are communication satellites, reference numeral 2 is a communication area by the communication satellite 1a, reference numerals 3a to 3c are gateway stations, and reference numerals 4a to 4e are ground stations. The ground stations 4a to 4e are assumed to include fixed stations fixed on the ground or mobile stations mounted on vehicles, ships, aircrafts, and the like.

The communication satellites 1a to 1c are non-stationary communication satellites sequentially flying in the approximately ceiling direction of a specific area, and form a communication beam for the communication area 2 including this specific area. 1 shows Japan as a specific region. In this communication satellite group, for example, when the communication satellite 1a stays within a predetermined elevation angle range of a specific region for 8 hours, and the communication satellite 1a is within the predetermined elevation angle range, the following communication is performed. When the satellite 1b enters the predetermined elevation angle range and stays for 8 hours, and when the communication satellite 1b is within the predetermined elevation angle range, the next communication satellite 1c enters the predetermined elevation angle range and stays for 8 hours. The communication satellites 1a to 1c sequentially provide communication services so as to ensure communication at all times. The predetermined elevation angle range refers to an elevation angle range, for example, elevation 70 ° to 90 ° (ceiling), but the elevation angle range is set by individual communication satellite systems. In addition, satellites that fly in the circumferential direction, such as the communication satellites 1a to 1c, are, for example, a cycle of 24 hours, an orbital inclination angle of 45 °, an eccentricity of 0.139, an apogee altitude of 41650 km, and a perigee altitude of 29930 km. And an elliptical orbital satellite having in orbit. FIG. 2 shows an example of a trajectory formed on the earth's surface just below the satellite traveling in this orbit, also called a quasi-ceiling satellite. In addition, the number of communication satellites is three in the case of FIG. 1, but the number is set in each communication satellite system.

In Fig. 1, the gateway stations 3a to 3c respectively communicate with the client via a network, and communicate with the ground stations 4a to 4e via the communication satellites 1a to 1c. As a usage form of such a communication system, for example, when the client is a broadcaster and the ground stations 4a to 4e are vehicle-mounted ground stations (SNG stations: Satellite News Gathering), the video and audio data from the vehicle-mounted ground stations are received. Music or video data is transmitted to the broadcasting company via the gateway station after the communication satellites 1a to 1c, or similarly, when the client is the broadcasting company and the ground stations 4a to 4e are receiving antenna stations mounted on a general vehicle. May be broadcast from the broadcaster to the respective ground stations via the communication stations 1a to 1c via the gateway stations 3a to 3c. As another type of use, when the client is a hospital and the ground stations 4a to 4e are ambulances, the video and audio data from the ambulance which is the ground station are transmitted via the gateway satellites 1a to 1c. Various usage forms, such as when sending to a hospital, can be considered.

3 is a schematic diagram illustrating handover when switching a communication satellite from the gateway station 3 to the transmission line from the ground station 4 to the transmission line. In Fig. 3, reference numerals 5a and 5b denote communication lines used for transmission from the gateway station 3 to the communication satellites 1a and 1b, respectively, and reference numerals 6a and 6b denote the ground stations (the communication stations 1a and 1b respectively). It is a communication line used for transmission to 4).

During the communication service period of the communication satellite 1a (during the period in which the communication satellite 1a stays in a predetermined elevation range on a specific area), the gateway station 3 modulates the data packet to the carrier frequency f1, thereby providing a communication line. It transmits to the communication satellite 1a by 5a. By this communication line 5a, the communication satellite 1a receives the data packet from the gateway station 3, modulates the received data packet at carrier frequency f2, and transmits it by the communication line 6a. The ground station 4 receives the data packet by the communication line 6a. When the communication service period of the communication satellite 1a ends and reaches the communication service period of the next communication satellite 1b, the gateway station 3 modulates the data packet to the carrier frequency f1 and communicates by the communication line 5b. Transmit to satellite 1b. By this communication line 5b, the communication satellite 1b receives the data packet from the gateway station 3, modulates the received data packet at the carrier frequency f3, and transmits it by the communication line 6b. The ground station 4 receives the data packet by the communication line 6b.

Next, the handover process at the time of switching from the communication by this communication satellite 1a to the communication by the communication satellite 1b is demonstrated by FIG. 4 is a schematic diagram showing contents of transmission and reception during handover between communication satellites. In Fig. 4, reference numeral 7 denotes a data packet such as a video or audio signal, and is transmitted from the gateway station in the order of P1, P2, P3 .... Reference numeral 8 is a switching instruction packet for instructing the ground station 4, which is the receiving side, to switch the communication line. The gateway station (denoted as GW station in FIG. 3) 3 transmits data packets P1, P2, and P3 by the communication line 5a (frequency f1), and the communication line 6a by the communication satellite 1a ( It is transmitted to the ground station 4 by the frequency f2). The gateway station 3 grasps the time when the communication satellite 1b enters the predetermined elevation angle range and starts a communication service by notification from the communication satellite management station. Alternatively, the gateway station 3 calculates the time based on the orbital information of the communication satellite 1b, or grasps the time by the absolute time or period in which the communication satellite 1b is flying. The gateway station 3 continuously transmits the switching instruction packet 8 when switching the communicating communication line 5a to the communication line 5b (frequency f1) of the communication satellite 1b. This switching instruction packet 8 is transmitted by the communication line 5a, and is transmitted to the ground station 4 by the communication line 6a via the communication satellite 1a. The ground station 4 receives the switch instruction packet 8 by the communication line 6a. When the ground station 4 receives the switch instruction packet 8, the ground station 4 changes the communication line (switching frequency) based on the information in the packet, or changes to a predetermined communication line (for example, shifts by 1 ch). Etc.) That is, the ground station 4 switches from the communication line 6a to the communication line 6b (frequency f3) and receives it.

The satellite-to-satellite handover is basically performed as described above. However, in Fig. 4, the gateway station 3 also overlaps in both directions of the communication line 5a and the communication line 5b at the time of switching of the transmission communication line, indicating switching instruction. The case where the packet 8 is transmitted is shown. In this case, the ground station 4 can receive the switch instruction packet 8 after switching to the communication line 6b. When the ground station 4 receives the switch instruction packet 8 immediately after the switching of the communication line, the ground station 4 can determine that there was no reception loss of the data packet during the switching period of the communication line.

In contrast to the case of FIG. 4, the inter-satellite handover in the case where the ground station 4 becomes the transmitting side and the gateway station 3 becomes the receiving side will be described. In this case, the gateway station and the ground station of Fig. 4 are replaced with each other. In this case, a schematic diagram showing the contents of transmission and reception at the time of handover between communication satellites is shown in Fig. 5. In FIG. 5, the ground station 4, like the gateway station 3 in FIG. 4, grasps the time when the communication satellite 1b enters a predetermined elevation angle and starts a communication service by notification from the communication satellite management station. . Alternatively, the ground station 4 calculates the time based on the orbital information of the communication satellite 1b, or grasps the time by the absolute time or period in which the communication satellite 1b is flying. The transmission of the data packets P1, P2, ... from the ground station 4, the transmission of the switching instruction packet, the transmission of the data packets P4, P5, etc. and the reception of these at the gateway station 3 are shown in FIG. Same as the description. However, in consideration of the case where the ground station 4 and the gateway station 3 transmit and receive in both directions, in FIG. 5, the communication line 9a (frequency f4) and the communication line 9b between the ground station 4 and the communication satellite. (Frequency f4), the communication line 10a (frequency f5) is used between the communication satellite 1a and the gateway station 4, and the communication line 10b between the communication satellite 1b and the gateway station 4 is used. (Frequency f6).

Next, the configuration of the gateway station will be described. 6 is a configuration diagram showing the configuration of a gateway station. In Fig. 6, reference numeral 11 denotes a transmitting antenna and reference numeral 12 denotes a receiving antenna. Reference numeral 13 is a transmitter for communicating with the ground station by communicating with a communication satellite via the antenna 11, reference numeral 14 is a packet transmitter for transmitting data packets to be transmitted to the transmitter 13, and reference numeral 15 Is a switch instruction packet generator that generates a switch instruction packet. Reference numeral 16 denotes an interface with a communication network, reference numeral 17 denotes a data packet generator for generating a data packet from communication data from the communication network, and reference numeral 18 denotes a data packet that temporarily accumulates a data packet waiting to be sent out. It is an accumulation part. Reference numeral 19 is a receiver for receiving a transmission signal from the ground station 4 via a communication satellite when there is a transmission from the ground station 4, and reference numeral 20 denotes a signal from the ground station 4 received from the communication network. It is a reception signal processing unit that converts the transmission signal according to the protocol. Reference numeral 21 denotes a satellite switching instructing unit which instructs the transmitting unit 13 and the receiving unit 19 to switch satellites (change of communication line).

Next, the operation of the gateway station 3 will be described with reference to FIG. 6. Communication data from each client is input to the network I / F unit 16 via a communication network. The network I / F unit 16 sequentially outputs the input communication data to the data packet generation unit 17. The data packet generation unit 17 generates and outputs a data packet from the received communication data. When the packet format on the communication network side and the packet format on the satellite communication side are the same, the data packet generator 17 can be a through output. In addition, the data packet generation unit 17 compresses the communication data input from the network I / F unit 16 on the time axis with respect to the data of the stream system as necessary to generate a data packet. The packet sending section 14 receives a data packet from the data packet generating section 17 and a switching instruction packet from the switching instruction packet generating section 15. The packet sender 14 outputs the switch instruction packet to the transmitter 13 while the switch instruction packet is input, and outputs the data packet from the data packet generator 17 to the data packet accumulator 18. . The packet transmitter 14 outputs the data packet from the data packet generator 17 to the transmitter 13 while the switch instruction packet is not input, but the data packet is accumulated in the data packet accumulator 18. If so, the data packet is given priority to the transmission unit 13 and output. The transmitting unit 13 sequentially transmits data packets, but transmits a plurality of times in succession to the switching instruction packet. As described in FIG. 4, when the communication line is switched, the switching instruction packet is transmitted by overlapping both directions of the communication line 5a before switching and the communication line 5b after switching. The switching of the communication line is judged by the satellite switching instruction unit 21, and the transmission unit 13 sends a switching instruction of the communication line, and generates and outputs a switching instruction packet to the switching instruction packet generation unit 15. Instruct. In addition, the satellite switching instructor 21 grasps the time when the next communication satellite enters the predetermined elevation angle range and starts a communication service by notification from the communication satellite management station. Alternatively, the ground station 4 calculates the time based on the orbital information of the communication satellite 1b, or grasps it by the absolute time or period in which the communication satellite 1b is flying and performs a series of instructions for satellite switching. .

In addition, the gateway station 3 receives the transmission signal from the ground station 4 by the reception unit 19 via the reception antenna 12. The receiver 19 low frequency converts the RF signal and outputs the RF signal to the received signal processor 20. The received signal processor 20 distinguishes the data packet and the switch instruction packet from the signal after low frequency conversion, outputs the data packet to the network I / F unit 16, and sends the switch instruction packet to the satellite switch instruction unit 21. Output In addition, the reception signal processing unit 20 expands and reproduces the data of the stream system on the time axis as necessary and outputs the data to the network I / F unit 16. The network I / F unit 16 transmits a data packet from the reception signal processing unit 20 to a client on the communication network. On the other hand, when the satellite switching instructing unit 21 receives the switching instruction packet from the reception signal processing unit 20, the satellite switching instructing unit 21 instructs the reception unit 19 to switch the satellite (change of the communication line).

Next, the structure of the ground station 4 is demonstrated. 7 is a configuration diagram illustrating the configuration of the ground station 4. In Fig. 7, reference numeral 22 denotes an input / output I / F unit for inputting and outputting audio and video data and control data in the ground station 3. In Fig. 7, a circuit portion denoted by the same reference numeral as in Fig. 6 denotes a circuit portion that is the same as or equivalent to that portion of Fig. 6.

The configuration of the ground station 4 is almost the same as that of the gateway station 3. However, while the gateway station 3 transmits and receives communication data with a plurality of clients and transmits and receives these communication data with a plurality of ground stations 4, the signal throughput increases and the circuit scale becomes large. Since the ground station 4 is limited to the audio and video data handled by the ground station 4 and the like, the circuit scale is smaller than that of the gateway station 3. In addition, when the ground station 4 is a station that only performs reception, the ground station 4 can be composed of a reception antenna 12, a reception unit 19, a reception signal processing unit 20, a satellite switching instruction unit 21, and an input / output I / F unit 22. have.

As described above, according to the first embodiment, switching instruction information indicating an instruction to switch the communication line is transmitted to the receiving station at the timing of handover calculated by the transmitting station in advance, and the receiving station switches the communication line. Therefore, the time required for the handover process can be shortened, and the circuit scale required for this process can be reduced.

Second Embodiment

A satellite communication method according to a second embodiment of the present invention, a satellite communication device used in the method, a ground station and a gateway station will be described with reference to FIG. 8 is a schematic diagram showing contents of transmission and reception during handover between communication satellites according to the second embodiment. In Fig. 8, the same reference numerals as in Figs. 4 and 5 denote the same or equivalent parts as those in Figs. 4 and 5.

In FIG. 8, the gateway station 3 and the ground station 4 transmit and receive in both directions, and the use and transmission and reception of the communication line in the transmission of the GW station 3 and the reception of the ground station 4 are as described in FIG. In FIG. 8, the data packet 7 transmitted from the gateway station 3 is described as Pa1, Pa2, ... When the ground station 4 receives the switch instruction packet 8, it determines that a handover between communication satellites has occurred based on this reception, and starts the handover process of the ground station 4 transmission. First, the ground station 4 transmits data packets Pb1 and Pb2 by the communication line 9a (frequency f4), and these data packets are gateways via the communication line 10a (frequency f5) via the communication satellite 1a. It is transmitted to the station 3. As described above, when the ground station 4 determines that a handover between communication satellites has occurred, the ground station 4 transfers the communication line 9a in communication to the communication line 9b (frequency f4) of the communication satellite 1b. At the time of switching, the switching instruction packet 8 is transmitted continuously. This switching instruction packet 8 is transmitted by the communication line 9a, and is transmitted to the gateway station 3 by the communication line 10a (frequency f5) via the communication satellite 1a. The gateway station 3 receives the switch instruction packet 8 by the communication line 10a. When the gateway station 3 receives the switch instruction packet 8, the gateway station 3 changes the communication line based on the information in the packet (switch frequency) or changes to a predetermined communication line (for example, shifts by 1 ch). Etc.) That is, the gateway station 3 switches from the communication line 10a to the communication line 10b (frequency f6) and receives it.

FIG. 8 also shows a case where the ground station 4 overlaps in both directions of the communication line 10a and the communication line 10b and transmits a switching instruction packet when the transmission communication line is switched. In this case, the gateway station 3 can receive the switch instruction packet 8 after switching to the communication line 10b. When the gateway station 3 receives the switch instruction packet 8 immediately after the switching of the communication line, the gateway station 3 can determine that there was no reception loss of the data packet during the switching period of the communication line.

When the ground station 4 receives the switch instruction packet, the ground station 4 judges that a handover between communication satellites has occurred based on this reception, and starts the handover process for transmitting the ground station 4, but this process is shown in FIG. Is performed by the satellite switching instruction unit 21. In addition, the structure of the gateway station 3 and the ground station 4 in 2nd Example is the same as that of FIG.

As described above, according to the second embodiment, in response to the switching instruction information from the gateway station, the ground station switches the reception line and also transmits the switching instruction information instructing the switching of the reception line to the gateway station. Therefore, the ground station can shorten the time required for the handover process by omitting the processing such as the calculation of the handover time between the satellites.

Third Embodiment

The satellite communication method according to the third embodiment of the present invention, the satellite communication apparatus used in the method, the ground station and the gateway station will be described with reference to Figs. In the third embodiment, handover between communication satellites is performed by continuously transmitting the switch instruction packet having the data portion of the data packet already transmitted and set the switch instruction information in the header portion. 9 is a schematic diagram showing contents of transmission and reception during handover between communication satellites according to the third embodiment. In Fig. 9, reference numeral 23 denotes a switch instruction packet having a data portion in which data packets already transmitted are written and a header portion in which switch instruction information is written. In Fig. 9, the same reference numerals as those in Fig. 4 represent the same or equivalent parts as those in Fig. 4.

Next, in the handover process at the time of switching from the communication by the communication satellite 1a to the communication by the communication satellite 1b, the switch instruction packet 8 in FIG. It is implemented as shown in FIG. 4 except that the switching station packet 23 is replaced with the switching instruction packet 23 having the switching instruction packet 23 and the ground station 4 on the receiving side receives the switching instruction packet. 9 shows a case where the gateway station 3 transmits the switching instruction packet 23 by overlapping in both directions of the communication line 5a and the communication line 5b when the transmission communication line is switched. In this case, the ground station 4 can receive the switch instruction packet 23 after switching to the communication line 6b. When the ground station 4 receives the switch instruction packet 23 immediately after the switching of the communication line, the ground station 4 can determine that there was no reception loss of the data packet during the switching period of the communication line. In addition, even when the ground station 4 becomes the transmitting side and the gateway station 3 receives, the switching instruction packet 8 is replaced by the switching instruction packet 23 in FIG. 5, and communication is performed in the same manner as in FIG. 5. Handover between satellites is performed.

10 shows the configuration of the switch instruction packet 23 according to the third embodiment. The switch instruction packet 23 is composed of a header portion and a data portion, in which the serial number N and switch instruction information F assigned to the packet are stored. In addition, the serial number N of the switching instruction packet 23 indicates the serial number of the data packet transmitted before including the data stored in the data portion. In the case of Fig. 10, since the switch instruction packet 23 stores data of the data packet P3, the serial number of the switch instruction packet 23 is assumed to be the same as the serial number of the data packet P3. The value stored in the switching instruction information F is, for example, set to a value of '0' as information for not switching the communication line, and a value of '1' as information indicating to switch the communication line. Set it. The serial number N of the packet sets the serial number of the same packet as the packet already transmitted. Thereby, the receiving side can determine whether the switching instruction packet 23 is related to retransmission. The data portion stores the contents of the data portion of the packet already transmitted. This switching instruction information F is extracted by the received signal processing unit 20 in FIGS. 6 and 7 and output to the satellite switching instruction unit 21. The satellite switching instructing unit 21 performs the switching process of the communication line when there is a switching instruction (in the above example, F = 1). In addition, the reception signal processing unit 20 compares the serial number N of the switchover instruction packet 23 with the serial number of the packet which has already been received, and when the serial number N is the same as the serial number of the one normally received, the switchover instruction packet The data stored in the data portion of 23 is discarded. On the other hand, when the serial number N of the switching instruction packet 23 is the same as the serial number of the packet which was not normally received, the gateway station 3 uses the data stored in the data portion of the switching instruction packet 23 as retransmission data. ) Is output to the network I / F unit 16 (FIG. 6), and is output to the input / output I / F unit 22 (FIG. 7) in the case of the ground station 4.

Next, the case where the packet transmission and reception of FIG. 11 is performed as another example is demonstrated.

In Fig. 11, 24 is a switch instruction packet having a data portion to which a data packet already transmitted is written and a header portion to which switch instruction information is written, but as shown, the data content of the switch instruction packet 23 is the data packet P3. In contrast, the data content of the switching instruction packet 24 is that of the data packet P2. In Fig. 11, the same reference numerals as those in Fig. 4 represent the same or equivalent parts as those in Fig. 4.

When comparing FIG. 9 and FIG. 11, the difference is that FIG. 9 continuously transmits the switch instruction packet 23. In the case of FIG. 11, the switch instruction packet 24 and the switch instruction packet 23 are mixed. That's the point. In this manner, as with the packet data P2 and P3, the data portion and serial numbers of the plurality of data packets are transmitted together with the switching instruction, so that retransmission is possible not only for P3 but also for P2. The switch instruction packet 24 has the same configuration (Fig. 10) as the switch instruction packet 23, and has a header portion in which the serial number N and the switch instruction information F are stored, similarly to the switch instruction packet 23.

As described above, according to the third embodiment, each switch instruction packet has a data portion for storing previously transmitted data. Therefore, data retransmission can be performed during continuous transmission of the switching instruction packet instructing switching of the communication line.

Fourth Example

A satellite communication method according to a fourth embodiment of the present invention, a satellite communication device used in the method, a ground station and a gateway station will be described with reference to FIG. In the fourth embodiment, a method of handling and processing data and switching instruction information on a time division frame in the gateway station 3 and the ground station 4 will be described. 12 is a schematic diagram showing a time division frame of a transmission / reception signal during handover between communication satellites according to the fourth embodiment. In Fig. 12, reference numeral 25 denotes a frame containing meaningful data, and this type of frame is indicated by an empty box. Reference numeral 26 denotes a frame having switch indication information, and this type of frame is indicated by a diagonally marked box. Reference numeral 27 is a synchronization bit provided in each frame, reference numeral 28 is a switching instruction bit provided in each frame, and reference number 29 is data of each frame. In addition, in Fig. 12, there are cases where the transmitting station becomes a gateway station and the receiving station becomes a ground station, and the transmitting station becomes a receiving station and becomes a gateway station. In addition, a communication line is the same as that of FIG.

This transmitting station first transmits the frame 25 which stored significant data by the communication line 5a, and transmits the frame 26 at the time of satellite-to-satellite handover. The receiving station which has received this frame 26 by the communication line 6a switches to the communication line 6b, and thereafter receives it by the communication line 6b. The receiving station switches the reception frequency and resynchronizes the frame in switching the communication line. In the switching instruction bit included in each frame, for example, a value '0' is set as information indicating that the communication line is not switched, and a value '1' is used as information indicating that the communication line is switched. Set it. In addition, the frame 26 including the switching instruction information does not store meaningful data.

Fifth Embodiment

In the fifth embodiment of the present invention, in the first to fourth embodiments, a recovery method when the switch information such as the switch instruction packet, the switch instruction information, or the switch instruction bit from the transmitting station side cannot be received for some reason. It demonstrates.

If the reception station (the ground station or the gateway station may be the receiving station) fails to receive the switching information, the receiving station is shielded within a predetermined elevation angle range in the ceiling direction of the receiving station. It may be the same as entering a tunnel.

The receiving station then grasps, by notification from the communication satellite management station, the time at which the communication satellite flying in the ceiling direction enters the predetermined elevation angle and starts the communication service. Alternatively, the receiving station can calculate the time based on the orbital information of the communication satellite, or can grasp the time by the absolute time or period in which the communication satellite is flying. In this way, even when the grasping time arrives, when the switching information from the transmitting station side is not received, the communication line forcibly received may be switched. Alternatively, in the case of transmitting / receiving in both directions, when the receiving station cannot receive the switching information and the handover time elapsed, the receiving station transmits a retransmission request of the switching information to the transmitting station, and the retransmission is performed. The switching information may be transmitted again from the transmitting station that has received the request. In the processing of switching of the communication line, in FIG. 6 and FIG. 7, when the satellite switching instructing unit 21 cannot obtain the switching information even after the handover time has elapsed from the reception signal processing unit 20, the reception unit 19 is provided. Command to forcibly switch the communication line or to send the retransmission request of the switching information to the transmitting unit 13.

As described above, according to the fifth embodiment, when the ground station cannot receive the switch instruction information from the gateway station, it forcibly switches the communication line or requests retransmission of the switch instruction information. Therefore, even if reception loss of the switching instruction information occurs due to the shielding over the ground station or the like, the handover process between the satellites can be recovered.

According to the invention according to the characteristics of the present invention, at the timing of handover obtained as a calculation or the like, the switchover instruction information instructing the switching of the communication line is transmitted, and the station receiving the switch switches the communication line. The time processing can be shortened, and the circuit scale required for this processing can be reduced.

Claims (4)

A satellite communication method in which communication is performed between a gateway station and a ground station via a communication satellite sequentially flying in the approximately ceiling direction. When switching from communication via one communication satellite to communication via another communication satellite that follows, the gateway station or the ground station continuously transmits the switching indication information by a transmission line through the one communication satellite. To switch to communication via the other communication satellite. A plurality of communication satellites sequentially flying in the approximately ceiling direction, and a gateway station and a ground station communicating through the communication satellites, When the gateway station switches from communication via one communication satellite of the communication satellites to communication through another communication satellite that is next coming, the gateway station continuously transmits the switching indication information to communicate with the other communication satellite. To, And the ground station receives the switch indication information and switches from communication via the one communication satellite to communication via the other communication satellite. Transition from communication via one of the communication satellites to the ground station through a plurality of communication satellites sequentially flying in the circumferential direction, and communication from one communication satellite to the next communication satellite. And a switching instruction packet generator for generating a packet including switching instruction information based on the instructed satellite switching instruction unit and the instruction from the satellite switching instruction unit. And the transmitting unit continuously transmits a packet including the switching instruction information generated by the switching instruction packet generator to the ground station. Transmitting unit which communicates with a gateway station through a plurality of communication satellites sequentially flying in the approximately ceiling direction, and switching from communication through one communication satellite among the communication satellites to communication through another communication satellite next coming And a switching instruction packet generator for generating a packet including switching instruction information based on the instruction from the satellite switching instruction portion, the satellite switching instruction portion for indicating a; And the transmitting unit continuously transmits a packet including the switching instruction information generated by the switching instruction packet generator to the gateway station.