JP2024055309A - COMMUNICATION DEVICE AND COMMUNICATION METHOD - Google Patents

Abstract

An encryption key for preventing interception by spoofing is shared between a sending side and a receiving side without using another communication system.
[Solution] The system includes a first extra-troposphere communication unit 33A that communicates encrypted user data over a first extra-troposphere communication line 6 that is relayed to a first extra-troposphere mobile body 4 moving at a first altitude that is included outside the troposphere, which is an altitude higher than the troposphere, and a second extra-troposphere communication unit _33B that communicates communication control data with a communication partner _1/2 , the communication control data including at least one of an encryption key used by an encryption device 15 and a decryption key used by the communication partner _1/2 when decrypting the encrypted user data, and the encryption key used by the communication partner _1/2 and at least one of the decryption keys used by the decryption device ₁₅ when decrypting the encrypted user data, over a second extra-troposphere communication line 8 that is relayed to a _second extra-troposphere mobile body 5 moving at a second altitude before the first extra-troposphere communication unit _33A communicates the encrypted user data.
[Selected figure] Figure 2

Description

This disclosure relates to a communication device and a communication method that communicates over a communication line relayed by an artificial satellite or a mobile object moving in the stratosphere.

In mobile communications, technology to expand communication areas to include locations that are not on land is attracting attention. To this end, systems are being considered that integrate geostationary satellites (GEO, geostationary orbit), low Earth orbit satellites (LEO, low Earth orbit), and high altitude platform station (HAPS, high altitude pseudo satellites) with terrestrial mobile communications networks. Since geostationary satellites, low Earth orbit satellites, and high altitude pseudo satellites are all at different altitudes, the transmission speed and delay time for communications with the ground differ depending on the length of the communication path. Currently, communication systems are being deployed that make use of the advantages of each of geostationary satellites, low Earth orbit satellites, and high altitude pseudo satellites. Currently, communication services that use geostationary satellites, low Earth orbit satellites, and high altitude pseudo satellites are provided by different providers and are separated from each other in communication networks.

Satellite communications has excellent broadcasting capabilities, with a wide coverage area provided by a single satellite. However, because satellite communications has such a large coverage area, there is a problem that communications may be intercepted by spoofed terminals.

A method has been proposed that uses guard spot beams for authentication to prevent unauthorized persons requesting authentication from tracking signals (see Patent Document 1). With satellite communications, which are characterized by their wide-area and broadcast nature, it is difficult to prevent third parties from intercepting radio waves, so signal scrambling and encryption are common countermeasures. For example, an encryption method has been proposed that aims to protect terminal identification information, although it is not primarily intended for satellite communications (see Patent Document 2).

Patent No. 5976774 Special table 2020-532235

In satellite communications using artificial satellites or high-altitude pseudo satellites, when implementing encryption to prevent communications from being intercepted by spoofed terminals, there is an issue of how to share an encryption key between the sender and receiver. One possible method for sharing an encryption key is to send the encryption key over a terrestrial line and have the user enter the encryption key. However, as it is anticipated that this will be used in remote areas, islands, and mobile devices where it is difficult to connect to terrestrial lines (including mobile phone networks and terrestrial wireless relay networks), it may be difficult to share the encryption key using other communication systems, and there are issues with how to share the encryption key.

The present disclosure has been made to solve the problems described above, and aims to provide a communication device and a communication method that enable a sender and a receiver to share an encryption key without using another communication system, and that can communicate encrypted user data.

The communication device according to the present disclosure is an extra-troposphere communication line that is a communication line relayed to an extra-troposphere relay station that is a relay station mounted on an extra-troposphere mobile body that is a mobile body moving outside the troposphere at an altitude higher than the troposphere, and the first extra-troposphere communication line that is an extra-troposphere communication line relayed to a first extra-troposphere relay station that is an extra-troposphere relay station mounted on a first extra-troposphere mobile body that is an extra-troposphere mobile body moving at a first altitude included outside the troposphere, the first extra-troposphere communication line is an extra-troposphere communication line that is relayed to a first extra-troposphere relay station that is an extra-troposphere relay station mounted on a first extra-troposphere mobile body that is an extra-troposphere mobile body moving at a first altitude included outside the troposphere, and the first extra-troposphere communication unit communicates encrypted user data that is user data to be communicated with a communication partner, an encryption device that encrypts the user data to be transmitted with an encryption key to generate encrypted user data, a decryption device that decrypts the received encrypted user data with a decryption key to generate user data, and a decryption device that transmits the encrypted user data to the first extra-troposphere communication line. The communication control data is data communicated to communicate encrypted user data with a communication partner on a second extra-troposphere communication line that is relayed to a second extra-troposphere relay station that is an extra-troposphere relay station mounted on a second extra-troposphere mobile body that is an extra-troposphere mobile body that moves at a second altitude outside the troposphere different from the first altitude before the communication unit communicates, and the communication control data includes at least one of an encryption key used by the encryption device and a decryption key used by the communication partner when decrypting encrypted user data generated by the encryption device, and a second extra-troposphere communication unit communicates with the communication partner communication control data including an encryption key used by the communication partner and at least one of a decryption key used by the decryption device when decrypting encrypted user data generated by the communication partner.

The communication method according to the present disclosure is an extra-troposphere communication line that is a communication line relayed to an extra-troposphere relay station that is a relay station mounted on an extra-troposphere mobile body that is a mobile body moving outside the troposphere at an altitude higher than the troposphere, and includes a first extra-troposphere communication unit that communicates encrypted user data, which is data to be communicated, with a communication partner, and a communication unit that encrypts the user data to be transmitted using an encryption key and transmits the encrypted user data to a communication partner. The communication method includes a communication device having an encryption device that generates user data, a decryption device that decrypts received encrypted user data using a decryption key to generate user data, and a second extra-troposphere communication unit that communicates with a communication partner via a second extra-troposphere communication line that is an extra-troposphere communication line relayed to a second extra-troposphere relay station that is an extra-troposphere relay station mounted on a second extra-troposphere mobile body that is an extra-troposphere mobile body moving at a second altitude included outside the troposphere that is different from the first altitude, and a requesting communication terminal that is a communication terminal connected to one of the communication partners, and a requested communication terminal that is a communication terminal connected to the communication device and the other of the communication partners.
The communication method includes a procedure in which one of the communication device and the communication counterpart receives a request to start communication with the request destination communication terminal from a request source communication terminal; a procedure in which at least one of a self encryption key which is an encryption key used by the encryption device when encrypting user data to generate encrypted user data and a counterpart decryption key which is a decryption key used by the communication counterpart when decrypting the encrypted user data encrypted with the self encryption key is communicated with the communication counterpart by the second extra-troposphere communication unit; a procedure in which at least one of a counterpart encryption key which is an encryption key used by the communication counterpart when encrypting user data to generate encrypted user data and a self decryption key which is a decryption key used by the decryption device when decrypting the encrypted user data encrypted with the counterpart encryption key is communicated with the communication counterpart by the second extra-troposphere communication unit; a procedure in which the encryption device encrypts user data from the request source communication terminal with its own encryption key or the communication counterpart encrypts it with the counterpart encryption key to generate encrypted user data; and a procedure in which the first extra-troposphere communication unit transmits the encrypted user data from the encrypted request source communication terminal to the first extra-troposphere communication unit. the communication device decrypts the encrypted user data received by the communication device with its own decryption key, thereby generating user data from the requesting communication terminal; the communication device or the communication device transmits the decrypted user data from the requesting communication terminal to the requested destination communication terminal; the communication device encrypts the user data from the requested destination communication terminal with its own encryption key, thereby generating encrypted user data; the communication device communicates the encrypted encrypted user data from the requested destination communication terminal with the communication device via a first extra-tropospheric communication line; the decryption device decrypts the encrypted user data received by the first extra-tropospheric communication unit with its own decryption key, thereby generating user data from the requested destination communication terminal; and the communication device or the communication device transmits the decrypted user data from the requested destination communication terminal to the requesting communication terminal.

The communication device and communication method disclosed herein enable the sender and receiver to share an encryption key without using another communication system, enabling encrypted user data to be communicated.

1 is a diagram illustrating a schematic configuration of a satellite communication system including a communication device according to a first embodiment. 1 is a diagram illustrating a configuration of a communication device according to a first embodiment. 1 is a flowchart of a communication method in which a communication terminal connected to the communication device according to the first embodiment starts communication with a communication terminal connected to a communication partner. 11 is a continuation of the flowchart of the communication method in which a communication terminal connected to the communication device in accordance with the first embodiment starts communication with a communication terminal connected to a communication partner. 10 is a flowchart of a process for determining an encryption key and a decryption key to be used when a communication terminal connected to the communication device according to the first embodiment communicates with a communication terminal connected to a communication partner. 11 is a continuation of the flowchart of the process of determining the encryption key and the decryption key to be used when a communication terminal connected to the communication device in accordance with the first embodiment communicates with a communication terminal connected to a communication partner. 5 is a flowchart of a process in which the communication device according to the first embodiment encrypts user data and transmits the encrypted data to a low-earth orbit satellite. 10 is a flowchart of a process in which a communication party of a communication device according to the first embodiment decrypts encrypted user data received and transmits the decrypted data to a communication terminal. 10 is a flowchart of a process in which a communication partner of a communication device according to the first embodiment encrypts user data and transmits the data to a low-earth orbit satellite. 5 is a flowchart of a process in which the communication device according to the first embodiment decrypts encrypted user data received and transmits the decrypted data to the communication terminal; 5 is a flowchart of a process in which the communication device according to the first embodiment transmits communication control data to a geostationary satellite. 10 is a flowchart of a process in which a communication partner of a communication device according to the first embodiment receives communication control data. 10 is a flowchart of a process in which a communication partner of a communication device according to the first embodiment transmits communication control data to a geostationary satellite. 5 is a flowchart of a process in which the communication device according to the first embodiment receives communication control data. FIG. 13 is a diagram illustrating a schematic configuration of a satellite communication system including a communication device according to a second embodiment. FIG. 11 is a diagram illustrating a configuration of a communication device according to a second embodiment. 13 is a flowchart when a communication terminal connected to a communication device according to a second embodiment starts communication with a communication terminal connected to a communication partner. 13 is a continuation of the flowchart when a communication terminal connected to a communication device according to the second embodiment starts communication with a communication terminal connected to a communication partner. 13 is a flowchart of a process for determining an encryption key and a decryption key to be used when a communication terminal connected to a communication device according to a second embodiment communicates with a communication terminal connected to a communication partner. 13 is a continuation of the flowchart of the process of determining the encryption key and the decryption key to be used when a communication terminal connected to a communication device in accordance with embodiment 2 communicates with a communication terminal connected to a communication partner. 10 is a flowchart of a process in which a communication device according to a second embodiment encrypts user data and transmits the encrypted data to a high altitude pseudosatellite. 13 is a flowchart of a process in which a communication party of a communication device according to a second embodiment decrypts encrypted user data received and transmits the decrypted data to a communication terminal. 10 is a flowchart of a process in which a communication partner of a communication device according to the second embodiment encrypts user data and transmits the data to a high altitude pseudosatellite. 13 is a flowchart of a process in which a communication device according to a second embodiment decrypts encrypted user data received and transmits the decrypted data to a communication terminal. 11 is a flowchart of a process in which a communication device according to a second embodiment transmits communication control data to a low-earth orbit satellite. 13 is a flowchart of a process in which a communication partner of a communication device according to a second embodiment transmits communication control data to a low-earth orbit satellite. FIG. 11 is a diagram illustrating a configuration of a communication device according to a third embodiment. 13 is a flowchart when a communication terminal connected to a communication device according to a third embodiment starts communication with a communication terminal connected to a communication partner. 13 is a continuation of the flowchart when a communication terminal connected to a communication device according to embodiment 3 starts communication with a communication terminal connected to a communication partner. FIG. 13 is a diagram illustrating a configuration of a communication device according to a fourth embodiment. FIG. 13 is a diagram illustrating a schematic configuration of a satellite communication system including a communication device according to a fifth embodiment. FIG. 13 is a diagram illustrating a configuration of a communication device according to a fifth embodiment. 13 is a flowchart of a communication method in which a communication terminal connected to a communication device according to a fifth embodiment starts communication with a communication terminal connected to a communication partner communicating with the same high altitude pseudosatellite. 13 is a continuation of the flowchart of the communication method in which a communication terminal connected to a communication device according to the fifth embodiment starts communication with a communication terminal connected to a communication partner communicating with the same high altitude pseudosatellite. 13 is a flowchart of a communication method in which a communication terminal connected to a communication device according to a fifth embodiment starts communication with a communication terminal connected to a communication partner that communicates with a different high altitude pseudosatellite. 13 is a continuation of the flowchart of the communication method in which a communication terminal connected to a communication device according to the fifth embodiment starts communication with a communication terminal connected to a communication partner that communicates with a different high altitude pseudosatellite. 13 is a flowchart explaining a procedure from when a high altitude pseudo satellite receives radio waves to when the different high altitude pseudo satellite emits radio waves when a communication terminal connected to a communication device in accordance with a fifth embodiment communicates with a communication terminal connected to a communication partner that communicates with a different high altitude pseudo satellite. 13 is a flowchart explaining a procedure from when a communication terminal connected to a communication device in accordance with a fifth embodiment communicates with a communication terminal connected to a communication partner communicating with a different high altitude pseudo satellite to when the high altitude pseudo satellite receives radio waves and when the high altitude pseudo satellite emits radio waves. 13 is a flowchart of a communication method in which a communication terminal connected to a communication device in accordance with embodiment 5 starts communication with a communication terminal connected to a communication partner connected to a ground communication network. 13 is a continuation of the flowchart of the communication method in which a communication terminal connected to a communication device in accordance with embodiment 5 starts communication with a communication terminal connected to a communication partner connected to a ground communication network. 13 is a flowchart explaining the procedure from when a high-altitude pseudo satellite receives radio waves to when encrypted user data is transmitted through the terrestrial communications network when a communication terminal connected to a communication device in accordance with embodiment 5 communicates with a communication terminal connected to a communication partner connected to a terrestrial communications network. 13 is a flowchart explaining the procedure from when encrypted user data is transmitted through a terrestrial communication network to when a high altitude pseudo satellite emits radio waves when a communication terminal connected to a communication device in accordance with embodiment 5 communicates with a communication terminal connected to a communication partner connected to a terrestrial communication network.

Embodiment 1.
A schematic configuration of a satellite communication system according to a first embodiment is shown in Fig. 1. The satellite communication system 100 includes earth stations ₁₁ , ₁₂ , networks ₂₁ , ₂₂ , communication terminals ₃₁ , ₃₂ , low-earth orbit satellites ₄₁ , ₄₂ , and a geostationary satellite 5. The communication terminal ₃₁ connects to the earth station ₁₁ via the network _21. The communication terminal ₃₂ connects to the earth station ₁₂ via the network _22. The earth stations ₁₁ and ₁₂ have the same configuration. All earth stations, or an unspecified earth station, are referred to as an earth station 1. The same applies to the network 2, the communication terminal 3, the low-earth orbit satellite 4, and the like. The earth station 1 may be fixed to the surface of the earth, or may move on the ground, on the water surface, underground, underwater, or in the air.

In the satellite communication system 100, the communication terminal _3-1 and the communication terminal _3-2 communicate using a satellite communication line relayed by low-earth orbit satellites _4-1 and _4-2 and a satellite communication line relayed by a geostationary satellite 5. The network _2-1 may be a LAN (Local Area Network) or a WAN (Wide Area Network). The network _2-1 may be a dedicated network or a public network. The same applies to the network _2-2 . There are multiple communication terminals _3-1 connected to the earth station _1-1 . There are multiple communication terminals _3-2 connected to the earth station _1-2 . Here, a case will be described in which the communication terminal _3-1 connected to the earth station _1-1 starts communication with the communication terminal _3-2 connected to the earth station _1-2 , and communicates with them.

The earth station _1-1 and the earth station _1-2 can communicate with each other through low-earth orbit satellite communication links _6-1 and _6-2 relayed by low-earth orbit satellites _4-1 and _4-2 , and a low-earth orbit inter-satellite communication link 7. The low-earth orbit satellite communication link _6-1 is a satellite communication link used for communication between the earth station _1-1 and the low-earth orbit satellite _4-1 . The low-earth orbit satellite communication link _6-2 is a satellite communication link used for communication between the earth station _1-2 and the low-earth orbit satellite _4-2 . The low-earth orbit inter-satellite communication link 7 is an inter-satellite communication link connecting the low-earth orbit satellites _4-1 and _4-2 . If another low-earth orbit satellite 4- _N is interposed between the low-earth orbit satellites _4-1 and _4-2 , there will be a plurality of low-earth orbit inter-satellite communication links 7. If the low-earth orbit satellites _4-1 and _4-2 are the same, the earth station _1-1 and the earth station _1-2 communicate with each other without going through the low-earth orbit inter-satellite communication link 7.

Earth station _1-1 and earth station _1-2 can communicate using geostationary satellite communication links _8-1 and _8-2 relayed by geostationary satellite 5. Geostationary satellite communication link _8-1 is a satellite communication link used for communication between earth station _1-1 and geostationary satellite 5. Geostationary satellite communication link _8-2 is a satellite communication link used for communication between earth station _1-2 and geostationary satellite 5. The communication partner is a communication device with which earth station 1, which is a communication device, communicates. The communication partner of earth station _1-1 is earth station _1-2 . The communication partner of earth station _1-2 is earth station _1-1 .

Encrypted data (user data) and the like are communicated through the low-earth orbit satellite communication lines 6 ₁ , 6 ₂ and the low-earth orbit satellite communication line 7. Information necessary for using data communicated through the low- _earth orbit satellite communication lines 6 ₁ , 6 ₂ and the low-earth orbit satellite communication line ₇ , such as a decryption key for decrypting encrypted user data, is communicated through the geostationary satellite communication lines 8 1 , 8 2. In the satellite communication system according to the present disclosure, the communication between the communication terminal 3 ₁ and the communication terminal 3 ₂ is prevented from being intercepted by a third party by using two types of satellite communication lines. The user data that is the subject of the communication is not communicated through the geostationary satellite communication lines 8 ₁ , 8 _2. The user data communicated through the low-earth orbit satellite communication lines 6 ₁ , 6 ₂ and the low-earth orbit satellite communication line 7 is encrypted. Even if one of the geostationary satellite communication lines 8 ₁ , 8 ₂ or the low-earth orbit satellite communication lines 6 ₁ , 6 ₂ is intercepted, the user data communicated by the communication terminal 3 ₁ or the communication terminal 3 ₂ cannot be decrypted and obtained. In the first embodiment, the encryption method is a common key encryption method in which the encryption key used to encrypt data is the same as the decryption key used to decrypt the encrypted data.

The configuration of the earth station 1 will be described with reference to Fig. 2. The earth station 1 has antenna devices _11A , _11B , frequency converters _12A , _12B , modems _13A , _13B , a data processing device 14, an encryption device 15, and a network interface section 16 (abbreviated as network IF section). The data processing device 14 has a satellite communication interface section 50 (abbreviated as satellite communication IF section), a line control section 51, a tracking control section 52, a satellite position management section 53, a sequence control section 54, an encryption key/decryption key management section 55, an encryption device control section 56, a communication control data processing section 57, and a data storage section 58. Items common to the antenna devices _11A , _11B will be described with the reference numeral of the antenna device 11. The same applies to the frequency converter 12, etc. It is possible to consider that the earth station 1 as a communication device does not include the antenna devices _11A , _11B .

The antenna device 11 is an antenna whose direction of orientation is mechanically changed. The antenna device 11 also includes an amplifier for amplifying a transmission signal, an amplifier for amplifying a reception signal, and a mechanism for changing the direction of orientation of the antenna. The antenna device _11A transmits and receives radio waves to and from, for example, a low-orbit satellite 4. The antenna device _11B transmits and receives radio waves to and from, for example, a geostationary satellite 5. The antenna device 11 may be a phased array antenna whose direction of orientation is electrically changed. The antenna device 11 may be a phased array antenna supported by a mechanism for mechanically changing the direction of orientation. In some phased array antennas, the receiving antenna device and the transmitting antenna device are separate devices.

The frequency converter _12A converts the frequency of the transmission signal transmitted by the antenna device _11A to a radio wave frequency, and converts the frequency of the reception signal received by the antenna device _11A to an intermediate frequency or a baseband signal frequency. The frequency converter _12B converts the frequency of the transmission signal transmitted by the antenna device _11B to a radio wave frequency, and converts the frequency of the reception signal received by the antenna device _11B to an intermediate frequency or a baseband signal frequency. The modem _13A outputs the modulated transmission signal to the frequency converter _12A and demodulates the reception signal input from the frequency converter _12A . The modem _13B outputs the modulated transmission signal to the frequency converter _12B and demodulates the reception signal input from the frequency converter _12B . The antenna device _11A , the frequency converter _12A , and the modem _13A are referred to as the A-series satellite communication unit _33A . The antenna device _11B , the frequency converter _12B , and the modem _13B are referred to as the B-series satellite communication unit _33B . When the earth station 1 serving as a communication device does not include the antenna devices _11A and _11B , the frequency converter _12A and the modem _13A constitute the satellite communication section _33A . The frequency converter _12B and the modem _13B constitute the satellite communication section _33B .

A switch may be provided between the frequency converters _12A , _12B and the modulator-demodulators _13A , _13B so that the frequency converter _12A and the modulator-demodulator _13B are connected, and the frequency converter _12B and the modulator-demodulator _13A are connected. If the device can process multiple channels simultaneously, the frequency converters _12A , _12B may be combined into a single frequency converter. The modulator-demodulators _13A , _13B may be combined into a single modulator-demodulator.

The data processing device 14 causes the encryption device 15 to decrypt encrypted user data input from either the modulator/demodulator _13A or the modulator/demodulator _13B . The data processing device 14 outputs the decrypted user data or unencrypted data to the network IF unit 16. The data processing device 14 causes the encryption device 15 to encrypt the transmission data input from the network IF unit 16 if encryption is required. The data processing device 14 outputs the transmission data encrypted by the encryption device 15 or the transmission data not encrypted to the modulator/demodulator _13A or the modulator/demodulator _13B depending on the type of data. The encryption device 15 is an encryption device that encrypts user data to be transmitted using an encryption key to generate encrypted user data. The encryption device 15 is also a decryption device that decrypts received encrypted user data using a decryption key to generate user data.

The data processing device 14 may be provided with two terminals and a switch capable of selectively connecting the two terminals to the modulator/demodulators _13A and _13B . The two terminals are called an A-series terminal and a B-series terminal. The switch is in one of two states: the A-series terminal is connected to the modulator/demodulator _13A and the B-series terminal is connected to the modulator/demodulator _13B , and the A-series terminal is connected to the modulator/demodulator _13B and the B-series terminal is connected to the modulator/demodulator _13A . The state of the switch can be switched.

The network IF unit 16 outputs user data that is input from the network 2 and transmitted by the communication terminal 3 to the data processing device 14. The network IF unit 16 outputs user data that is output by the data processing device 14 and that should be received by the communication terminal 3 to the communication terminal 3 via the network 2. The network IF unit 16 is a terminal connection unit that exchanges user data with the communication terminal.

The satellite communication IF unit 50 exchanges packets with the satellite communication units 33 _A and 33 _B. The satellite communication IF unit 50 also exchanges data with the encryption device control unit 56, the communication control data processing unit 57, and the network IF unit 16.

The line control unit 51 manages the relayed satellite, transmission frequency, reception frequency, modulation/demodulation method, and error correction method for each of the satellite communication units _33A and _33B . The satellite communication unit 33 uses the same modulation/demodulation method and the same error correction method for transmission and reception. As the modulation/demodulation method and the error correction method, for example, the method specified in the public standard of digital television broadcasting or the public standard of mobile communication systems can be applied. The tracking control unit 52 controls the antenna devices _11A and _11B so that the antenna devices _11A and _11B face in the direction of the relayed satellite. Since the low-earth orbit satellite 4 moves relative to the surface of the earth, the low-earth orbit satellite 4 that can communicate with the earth station 1 changes over time. The tracking control unit 52 also controls the handover of the low-earth orbit satellite 4. When the low-earth orbit satellite 4 is handed over, the line control unit 51 also operates to change the relayed satellite, transmission frequency, reception frequency, modulation/demodulation method, and error correction method in the series of either the satellite communication unit _33A or _33B that communicates with the low-earth orbit satellite 4. The satellite position management unit 53 obtains orbit data of the low-earth orbit satellite 4 and the geostationary satellite 5 from an external source. The satellite position management unit 53 determines the positions of the satellites tracked by the antenna devices _11A and _11B based on the orbit data at a set period.

The series control unit 54 controls which of the satellite communication units _33A and _33B is used to communicate terminal management data (C-plane) and user data (U-plane) for each communication terminal 3 connected via the network 2. Separating the C-plane and the U-plane is similar to ^5th generation mobile communication systems (5G). In the communication device according to the present disclosure, the satellite communication line for communicating the C-plane and the satellite communication line for communicating the U-plane are separate.

The terminal management data includes communication control data. The communication control data is data communicated so that the communication device can communicate encrypted user data with the communication partner. The series control unit 54 is a communication control unit that controls the communication of encrypted user data by the satellite communication unit 33 on the U-plane side and the communication control data by the satellite communication unit 33 on the C-plane side.

A communication terminal 3 connected to an earth station 1, which is a communication device, is called the local communication terminal. A communication terminal 3 with which one of the local communication terminals 3 communicates is called a partner communication terminal. The partner communication terminal connects to another earth station 1 (communication partner). The encryption key and decryption key management unit 55 manages the encryption key to be used for each local communication terminal and for each series. The encryption key is the encryption key used when encrypting user data transmitted by the local communication terminal. The encryption key and decryption key management unit 55 manages the decryption key to be used for each partner communication terminal and for each series. The decryption key is the decryption key used when decrypting encrypted user data transmitted by the partner communication terminal.

The encryption key/decryption key management unit 55 determines and manages an encryption key for each communication terminal 3. Since a common key encryption method is used, the encryption key is also the decryption key. The encryption device control unit 56 provides the encryption key and the data to be encrypted to the encryption device 15 to encrypt the data. The encryption device control unit 56 provides the decryption key and the data to be decrypted to the encryption device 15 to decrypt the data. The communication control data processing unit 57 interprets the communication control data and causes other control units to perform the operations instructed by the communication control data. The communication control data processing unit 57 also creates communication control data to be sent to the communication partner.

The data storage unit 58 stores data necessary for the operation of the earth station 1. The data storage unit 58 stores communicating satellites _80A , _80B , receiving frequencies _81A , _81B , transmitting frequencies _82A , 82B, modulation/demodulation methods _83A , _83B , error correction methods _84A , _84B , the station's position 85, satellite positions _86A , _86B , satellite directions _87A , _87B , _a system used 88, an encryption key 89, and a decryption key 90.

The communicating satellite _80A is data that stores a satellite through which the communication line used by the satellite communication unit _33A is relayed. The communicating satellite _80B is data that stores a satellite through which the communication line used by the satellite communication unit _33B is relayed. The receiving frequency _81A is the frequency of radio waves received by the antenna device _11A . The receiving frequency _81B is the frequency of radio waves received by the antenna device _11B . The transmitting frequency _82A is the frequency of radio waves transmitted by the antenna device _11A . The transmitting frequency _82B is the frequency of radio waves transmitted by the antenna device _11B . The frequency converter _12A converts the frequency by referring to the receiving frequency _81A and the transmitting frequency _82A . The frequency converter _12B converts the frequency by referring to the receiving frequency _81B and the transmitting frequency _82B . The communicating satellites 80 _A and 80 _B , the receiving frequencies 81 _A and 81 _B and the transmitting frequencies 82 _A and 82 _B are set by the line control unit 51 .

The modulation/demodulation method _83A is data for storing the modulation/demodulation method used by the modulator/demodulator _13A . The modulation/demodulation method _83B is data for storing the modulation/demodulation method used by the modulator/demodulator _13B . The error correction method _84A is data for storing the error correction method used by the modulator/demodulator _13A . The error correction method _84B is data for storing the error correction method used by the modulator/demodulator _13B .

The own station position 85 is the position where the earth station 1 is located. If the earth station 1 does not move, the own station position 85 is a value that does not change. If the earth station 1 moves, the position of the mobile body on which the earth station 1 is mounted becomes the own station position 85. The position of the mobile body is input from outside the earth station 1. The satellite position _86A is the position where the communicating satellite _80A is located at the present time and at a future time within a predetermined range. The satellite position _86B is the position where the communicating satellite _80B is located at the present time and at a future time within a predetermined range. The satellite positions _86A and _86B are set by the satellite position management unit 53. The satellite position management unit 53 operates at a predetermined period and sets the satellite positions _86A and _86B from the time of operation to a future time within a predetermined range. The satellite existence direction _87A is the direction from the own station position 85 to the satellite position _86A . The satellite existence direction _87B is the direction from the own station position 85 to the satellite position _86B . The tracking control unit 52 controls the antenna device _11A so that the pointing direction of the antenna device 11A coincides with the satellite presence direction _87A . The tracking control unit 52 controls the antenna device _11B so that the pointing direction of the antenna device _11B coincides with _the satellite presence direction _87B .

The usage sequence 88 is data indicating which of the satellite communication units _33A and _33B is used for communication on the C-plane and the U-plane for each communication terminal 3. The assumed maximum number of communication terminals 3 that can be connected to the earth station 1 is represented by the variable _Nmax . The usage sequence 88 is data having a number of 2* _Nmax . The encryption key 89 is data for storing an encryption key used for encryption for each communication terminal 3 and for each sequence. The encryption key 89 is data having a number of 2* _Nmax . The decryption key 90 is data for storing a decryption key used for decrypting encrypted user data transmitted by the other communication terminal for each other communication terminal and for each sequence. The assumed maximum number of communication terminals 3 with which one communication terminal 3 communicates simultaneously is represented by the variable _KMAX . The decryption key 90 is data having a number of 2* _Kmax * _Nmax . Since it is a common key cryptosystem, the decryption key for decrypting data encrypted with an encryption key is the same as the encryption key. The usage sequence may be data for switching whether all communication terminals 3 use the satellite communication units _33A and _33B for communication in the U-Plane and C-Plane, respectively.

The data storage unit 58 is an encryption key storage unit that stores the encryption key used by the encryption device 15 for each of its own communication terminals that are communication terminals connected to the terminal connection unit. The encryption key used by the encryption device 15 is stored in the data storage unit 58 as an encryption key 89. The data storage unit 58 is also a corresponding decryption key storage unit that stores, for each of its own communication terminals, a corresponding decryption key that is a decryption key for decrypting data encrypted by the encryption device 15 with an encryption key. Since a common key encryption method is used, the corresponding decryption key that is a decryption key for decrypting data encrypted with an encryption key is the same as the encryption key. Therefore, the corresponding decryption key is stored in the data storage unit 58 as the encryption key 89. The data storage unit 58 is also a usage decryption key storage unit that stores, for each communication terminal that is the source of the encrypted user data, a usage decryption key that is a decryption key used by the encryption device 15 when decrypting received encrypted user data. The usage decryption key is stored in the data storage unit 58 as a decryption key 90.

In the data processing device 14, the C-plane packet from the network IF unit 16 is transferred to the communication control data processing unit 57. When the satellite communication IF unit 50 receives a C-plane packet from the communication control data processing unit 57, it outputs the packet to the modem 13 ( _13A or _13B) of the series set on the C-plane side in the usage series 88 of the communication terminal 3 corresponding to the source address written in the packet header. The communication terminal 3 corresponding to the source address written in the packet header is called the source communication terminal. The communication terminal 3 corresponding to the destination address written in the packet header is called the destination communication terminal.

When the satellite communication IF unit 50 receives a U-plane packet from the network IF unit 16, it outputs the packet to the modem 13 ( _13B or _13A ) of the series set on the U-plane side in the usage series 88 of the source communication terminal. Since the U-plane user data (packet) needs to be encrypted, the encryption device control unit 56 causes the encryption device 15 to encrypt the user data with the encryption key stored on the U-plane side of the source communication terminal in the encryption key 89 to generate encrypted user data. The satellite communication IF unit 50 outputs the encrypted user data to the modem 13 ( _13B or _13A ) of the series set on the U-plane side in the usage series 88 of the source communication terminal.

When the satellite communication IF unit 50 receives a packet from the modem 13 ( _13A or _13B ) of the series set on the C-plane side in the usage series 88 of the source communication terminal, it transfers it to the communication control data processing unit 57. The communication control data processing unit 57 interprets the C-plane packet (communication control data) and performs the processing instructed by the communication control data by itself or has another processing unit perform the processing.

When the satellite communication IF unit 50 receives a packet (encrypted user data) from the modem 13 ( _13B or _13A ) of the system set on the U-plane side in the usage system 88 of the source communication terminal, it transfers the packet to the encryption device control unit 56. The encryption device control unit 56 obtains the decryption key stored on the U-plane side in the usage system 88 of the source communication terminal from the decryption key 90, and has the encryption device 15 decrypt the data using the obtained decryption key to generate user data. The user data is sent to the source communication terminal via the network IF unit 16.

When explaining the functions of the encryption key/decryption key management unit 55 and the communication control data processing unit 57, the communication terminal that sent the communication start request is called the requesting communication terminal, and the communication terminal specified as the communication partner in the communication start request is called the requested communication terminal.

When the encryption key/decryption key management unit 55 receives a communication start request from the requesting communication terminal or the earth station 1, it determines an encryption key and stores it in the encryption key 89.

When the encryption key and decryption key management unit 55 receives a communication start request from the requesting communication terminal, it checks whether the encryption key of the requesting communication terminal on the U-Plane side is stored in the encryption key 89 in the usage sequence 88. If it is not stored, the encryption key and decryption key management unit 55 decides on an encryption key. The encryption key and decryption key management unit 55 stores the decided encryption key in the encryption key 89 in the usage sequence 88 as the encryption key of the requesting communication terminal on the U-Plane side. The encryption key of a certain terminal is the encryption key used when encrypting user data transmitted by that terminal.

When the encryption key decryption key management unit 55 receives communication control data of a communication start request transmitted from another earth station 1 (communication partner), it stores the decryption key of the requesting communication terminal included in the communication control data of the communication start request in the decryption key 90 as the decryption key of the requesting communication terminal on the U-Plane side in the usage sequence 88. The decryption key of a certain terminal is the decryption key used when decrypting encrypted user data in which the user data transmitted by that terminal is encrypted. Then, the encryption key decryption key management unit 55 checks whether the encryption key of the requested communication terminal specified in the communication start request is stored on the U-Plane side in the usage sequence 88 in the encryption key 89. If it is not stored, the encryption key decryption key management unit 55 determines an encryption key. The encryption key decryption key management unit 55 stores the determined encryption key in the encryption key 89 as the encryption key of the requested communication terminal on the U-Plane side in the usage sequence 88.

When the encryption key/decryption key management unit 55 receives communication control data for accepting the start of communication transmitted from another earth station 1 (communication partner), it stores the corresponding decryption key of the requested communication terminal included in the communication control data for accepting the start of communication in the decryption key 90 in the usage sequence 88 as the decryption key of the requested communication terminal on the U-Plane side.

If the encryption key of the requesting communication terminal is not stored in the encryption key storage unit, the encryption key/decryption key management unit 55 determines an encryption key and a corresponding decryption key, stores the determined encryption key in the encryption key storage unit as the encryption key of the requesting communication terminal, and stores the determined corresponding decryption key in the corresponding decryption key storage unit as the corresponding decryption key of the requesting communication terminal.

When the encryption key and decryption key management unit 55 receives communication control data for a communication start request, it stores the corresponding decryption key of the requesting communication terminal included in the received communication control data in the usage decryption key storage unit as the usage decryption key of the requesting communication terminal, and if the encryption key of the requested communication terminal is not stored in the encryption key storage unit, it determines an encryption key and a corresponding decryption key, stores the determined encryption key in the encryption key storage unit as the encryption key of the requested communication terminal, and stores the determined corresponding decryption key in the corresponding decryption key storage unit as the corresponding decryption key of the requested communication terminal.

When the encryption key and decryption key management unit 55 receives communication control data for accepting the start of communication, it stores the corresponding decryption key of the requested communication terminal included in the received communication control data in the usage decryption key storage unit as the usage decryption key of the requested communication terminal.

When the communication control data processing unit 57 receives communication control data of a communication start request from a requesting communication terminal, it creates communication control data of the communication start request including the requesting communication terminal, the requested communication terminal, and the encryption key of the requesting communication terminal determined by the encryption key/decryption key management unit 55, and outputs it to the satellite communication IF unit 50. The satellite communication IF unit 50 outputs the communication control data to the modem 13 on the C-Plane side via the usage series 88. Here, the encryption key of a certain terminal is the encryption key used when encrypting user data transmitted by that terminal. The satellite communication unit 33 including the modem 13 on the C-Plane side via the usage series 88 communicates the communication control data of the communication start request with the communication partner.

When the communication control data processing unit 57 receives communication control data of a communication start request sent from the communication partner, it creates communication control data of communication start acceptance including the requesting communication terminal, the requested communication terminal, and the encryption key of the requested communication terminal, and outputs it to the satellite communication IF unit 50. The satellite communication IF unit 50 outputs the communication control data to the C-Plane side modem 13 via the usage series 88. The satellite communication unit 33 including the C-Plane side modem 13 via the usage series 88 communicates the communication control data of communication start acceptance with the communication partner.

The communication control data processing unit 57 is a communication control data generation unit that generates communication control data for a communication start request including the requesting communication terminal, the requested communication terminal, and the corresponding encryption key of the requesting communication terminal when it receives a communication start request from its own communication terminal, the requesting communication terminal, which is a communication terminal connected to the communication partner via a network, and generates communication control data for a communication start acceptance including the corresponding encryption key of the requested communication terminal when it receives the communication control data for the communication start request from the communication partner.

The operation will be described. Figures 3 and 4 are flow charts for explaining the outline of the procedure of the communication method in which the communication terminal ₃₁ connected to the earth station ₁₁ communicates with the communication terminal _{32 connected to the earth station 12. Figure} 3 illustrates the process up to step S08, and Figure 4 illustrates the process from step S09. In the earth station ₁₁ and the earth station ₁₂ , it is assumed that the series A is the U-Plane and the series B is the C-Plane. In step S01, the communication terminal ₃₁ transmits a communication start request to the earth station ₁₁ to communicate with the communication terminal ₃₂ , and the network IF unit 16 of the earth station ₁₁ receives it. In step S02, the earth station ₁₁ and the earth station ₁₂ determine the encryption key and the decryption key to be used for the communication between the communication terminal ₃₁ and the communication terminal ₃₂ , and store them in the data storage unit 58. The process of S02 will be explained with reference to the flow charts shown in Figures 5 and 6. Here, the explanation will be given assuming that the earth station ₁₁ is the communication device and the earth station ₁₂ is the communication partner. Earth station ₁₂ may be the communications device and earth station ₁₁ may be the communication partner.

Step S01 is a procedure in which the earth station _1.1 receives a request from a request source communication terminal to start communication with a request destination communication terminal. Step S02 includes a procedure for determining an own encryption key _CK1 , which is an encryption key used by the encryption device 15 of the communication device (earth station _1.1 ) when encrypting user data to generate encrypted user data, and a counterpart decryption key _CK1, which is a decryption key used by the communication partner (earth station _1.2 ) when decrypting the encrypted user data encrypted with the own encryption key, and a procedure for determining a counterpart encryption key _CK2 , which is an encryption key used by the communication partner when encrypting user data to generate encrypted user data, and a procedure for determining an own decryption key _CK2, which is a decryption key used by the decryption device when decrypting the encrypted user data encrypted with the counterpart encryption key.

Step S03 and the following are processes for communicating user data and communication control data between the communication terminal _3-1 and the communication terminal _3-2 . Steps S03 to S05 are procedures for transmitting user data UD _-1 from the communication terminal _3-1 to the communication terminal _3-2 . Steps S06 to S08 are procedures for transmitting user data UD _-2 from the communication terminal _3-2 to the communication terminal _3-1 . Steps S09 to S11 are procedures for transmitting communication control data CC _-1 from the communication terminal _3-1 or the earth station _1-1 to the earth station _1-2 . Steps S12 to S14 are procedures for transmitting communication control data CC- ₂ from the communication terminal _3-2 or the earth station _1-2 to the earth station _1-1 . The processes from S03 to S05, the processes from S06 to S08, the processes from S09 to S11, and the processes from S12 to S14 are executed in parallel.

In step S03, the earth station ₁₁ converts the user data _UD1 transmitted from the communication terminal ₃₁ to the communication terminal ₃₂ into encrypted user data _CD1 , and transmits the data as radio waves _RU1 toward the low-earth orbit satellite _41. In step S04, the low-earth orbit satellite ₄₁ receives the radio waves _RU1 , frequency-converts and amplifies the radio waves _RU1 , and transmits the radio waves as radio waves _RC1 . The low-earth orbit satellite ₄₂ receives the radio waves _RC1 , frequency-converts and amplifies the radio waves _RC1 , and transmits the radio waves as radio waves _RD2 . In step S05, the earth station ₁₂ receives the radio waves _RD2 , and demodulates and decodes the radio waves _RD2 to generate the user data _UD1 . The earth station ₁₂ transmits the user data _UD1 to the communication terminal _32. The process in step S03 will be described with reference to the flowchart shown in FIG. 7. The process in step S05 will be described with reference to the flowchart shown in FIG. 8.

In _step S06, the earth station ₁₂ converts the user data _UD2 transmitted from the communication terminal 32 to the communication terminal ₃₁ into encrypted user data _CD2 , and transmits the data as radio waves _RU2 toward the low-earth orbit satellite _42. In step S07, the low-earth orbit satellite ₄₂ receives the radio waves _RU2 , frequency-converts and amplifies the radio waves _RU2, and transmits the radio waves _RC2 . The low-earth orbit satellite ₄₁ receives the radio waves _RC2 , frequency-converts and amplifies the radio waves _RC2 , and transmits the radio waves _RD1 . In step S08, the earth station ₁₁ receives the radio waves _RD1 , and demodulates and decodes the radio waves _RD1 to generate user data _UD2 . The earth station ₁₁ transmits the user data _UD2 to the communication terminal _31. The process of S06 will be described with reference to the flowchart shown in FIG. 9. The process of S08 will be described with reference to the flowchart shown in FIG. 10.

In step S09, the earth station ₁₁ transmits the communication control data _CC1 to the earth station ₁₂ as radio waves RU _C1 to the geostationary satellite 5. In step S10, the geostationary satellite 5 receives the radio waves RU _C1 , frequency-converts and amplifies the radio waves RU _C1 , and transmits them as radio waves RD _C2 . In step S11, the earth station ₁₂ receives the radio waves RD _C2 , demodulates the radio waves RD _C2 , and generates communication control data _CC1 . The earth station ₁₂ processes the communication control data _CC1 to control _the communication between the communication terminal ₃₁ and the communication terminal _32. The process of S09 will be described with reference to the flowchart shown in FIG. 11. The process of S11 will be described with reference to the flowchart shown in FIG. 12.

In step S12, the earth station ₁₂ transmits the communication control data _CC2 to the earth station ₁₁ , which is then radiated as radio waves RU- _C2 by the earth station ₁₂ toward the geostationary satellite 5. In step S13, the geostationary satellite 5 receives the radio waves RU- _C2 , frequency-converts and amplifies the radio waves RU- _C2 , and radiates them as radio waves RD- _C1 . In step S14, the earth station ₁₁ receives the radio waves RD- _C1 , demodulates the radio waves RD- _C1 , and generates communication control data CC _-2 . The earth station ₁₁ processes the communication control data CC _-2 to control the communication between the communication terminal _3-1 and the communication terminal _3-2 . The process of S12 will be described with reference to the flowchart shown in FIG. 13. The process of S14 will be described with reference to the flowchart shown in FIG. 14.

5 and 6, the procedure of the process in S02 in which the earth station _1.1 and earth station _1.2 decide the encryption key and decryption key to be used for the communication between the communication terminal _3.1 and the communication terminal _3.2 and store them in the data storage unit 58 will be described. In step S21, in the data processing device 14 of the earth station _1.1 , a communication start request from the communication terminal _3.1 is transferred to the communication control data processing unit 57. In step S22, the encryption key/decryption key management unit 55 started by the communication control data processing unit 57 checks whether the encryption key of the U-Plane side (series A) of the communication terminal _3.1 is set in the encryption key 89. If the encryption key is not set (NO in S22), in step S23, the encryption key/decryption key management unit 55 decides the encryption key _CK1 of the U-Plane side (series A) of the communication terminal _3.1 . The encryption key/decryption key management unit 55 stores the decided encryption key _CK1 in the encryption key 89. After execution of S23, and if the encryption key 89 of the communication terminal _3-1 on the U-Plane side (series A) is set (YES in S22), proceed to step S24. The encryption key _CK1 is the local encryption key used by the earth station _1-1 . The encryption key _CK1 is also the remote decryption key used by the earth station _1-2 .

In step S24, the communication control data processing unit 57 of the earth station 1 ₁ generates communication control _data CC _{1 for a communication start request including the encryption key CK 1 (also a decryption key) of the communication terminal 3 1 ,} the communication terminal _{3 2} , and the communication terminal 3 1, and transmits it to the satellite communication IF unit 50. The encryption key CK ₁ is obtained from the encryption key 89. In step S25, the satellite communication IF unit 50 transmits the communication control data CC ₁ to the satellite communication unit 33 _B , which is the C-Plane side (series B) of the communication terminal 3 _1. In step S26, the satellite communication unit 33 _B of the earth station 1 ₁ radiates the communication control data CC ₁ as radio waves RU ₁ toward the geostationary satellite 5. Specifically, the modem 13 _B of the satellite communication unit 33 _B of the earth station 1 ₁ modulates the communication control data CC ₁ to generate a transmission signal SS ₁ . The frequency converter _12B converts the frequency of the transmission signal _SS1 . The antenna device _11B radiates the frequency-converted transmission signal _SS1 toward the geostationary satellite 5 as radio waves _RU1 .

In step S27, the geostationary satellite 5 receives the radio wave _RU1 , frequency converts and amplifies it, and emits the radio wave _RD1 . In step S28, the satellite communication unit _33B of the earth station ₁₂ receives the radio wave _RD1 and generates communication control data _CC1 . The satellite communication IF unit 50 that has received the communication control data _CC1 transfers the communication control data _CC1 to the communication control data processing unit 57. In step S29, the communication control data processing unit 57 extracts the communication terminal ₃₁ , which is the requesting communication terminal, and the decryption key _CK1 from the communication control data _CC1 , and starts the encryption key/decryption key management unit 55.

In step S30, the encryption key decryption key management unit 55 stores the decryption key _CK1 extracted from the communication control data _CC1 in the decryption key 90 as the decryption key to be used on the U-Plane side (series A) of the communication terminal _31. In step S31, the encryption key decryption key management unit 55 checks whether the encryption key on the U-Plane side (series A) of the communication terminal ₃₂ , which is the request destination communication terminal, is set in the encryption key 89. If the encryption key is not set (NO in S31), in step S32, the encryption key decryption key management unit 55 determines the encryption key _CK2 on the U-Plane side (series A) of the communication terminal _32. The encryption key decryption key management unit 55 stores the determined encryption key _CK2 in the encryption key 89. After execution of S32 and if the encryption key on the U-Plane side (series A) of the communication terminal ₃₂ is set in the encryption key 89 (YES in S31), the process proceeds to step S33. The encryption key _CK2 is a peer encryption key used by the earth station _12. The encryption key _CK2 is also an own decryption key used by the earth station ₁₁ .

In step S33, the communication control data processing unit 57 of the earth station 1 ₂ generates communication control data CC 2 for accepting the start of communication, including the communication terminal 3 ₁ , the communication terminal 3 ₂ , and the encryption key CK ₂ (also a decryption key) of the communication terminal 3 ₂ acquired from the encryption key 89, and transmits it to the satellite communication IF unit 50. _In step S34, the satellite communication IF unit 50 transmits the communication control data CC ₂ to the satellite communication unit 33 _B , which is the C-Plane side (series B) of the communication terminal 3 _1. In step S35, the satellite communication unit 33 _B of the earth station 1 ₂ radiates the communication control data CC ₂ as radio waves RU ₂ toward the geostationary satellite 5. Specifically, the modem 13 _B of the satellite communication unit 33 _B of the earth station 1 ₂ generates a transmission signal SS ₂ by modulating it with the communication control data CC _2. The frequency converter 12 _B converts the frequency of the transmission signal SS ₂ . The antenna device _11B radiates the frequency-converted transmission signal _SS2 as a radio wave _RU2 toward the geostationary satellite 5.

In step S36, the geostationary satellite 5 receives the radio waves _RU2 , converts the frequency, amplifies them, and emits radio waves _RD2 . In step S37, the satellite communication unit _33B of the earth station ₁₁ receives the radio waves _RD2 and generates communication control data _CC2 . The satellite communication IF unit 50 that has received the communication control data _CC2 transfers it to the communication control data processing unit 57.

In step S38, the communication control data processing unit 57 extracts the communication terminal ₃₂ , which is the request destination communication terminal, and the decryption key _CK2 from the communication control data _CC2 , and starts the encryption key/decryption key management unit 55. In step S39, the encryption key/decryption key management unit 55 stores the decryption key _CK2 in the decryption key 90 as the decryption key for the U-Plane side (series A) of the communication terminal ₃₂ .

7, the procedure of the process in which the earth station _1.1 converts the user data _UD.1 to be transmitted from the communication terminal _3.1 to the communication terminal _3.2 in S03 into encrypted user data _CD.1 and radiates the data as radio waves _RU.1 toward the low-earth orbit satellite _4.1 will be described. In step S41, the communication terminal _3.1 transmits the user data _UD.1 to be transmitted to the communication terminal _3.2 to the earth station _1.1 , and the network IF unit 16 of the earth station _1.1 receives the user data UD.1. In step S42, the network IF unit 16 of the earth station _1.1 outputs the user data _UD.1 to the data processing device 14. In step S43, the encryption device control unit 56 refers to the encryption key 89 and obtains the encryption key _CK.1 of the communication terminal _3.1 . In step S44, the encryption device control unit 56 instructs the encryption device 15 to encrypt the user data _UD.1 with the encryption key _CK.1 , and the encryption device 15 generates encrypted user data _CD.1 . Step S44 is a procedure in which the encryptor encrypts the user data from the requesting communication terminal with its own encryption key _CK1 to generate encrypted user data.

In step _S45 , the encryption device control unit 56 inputs the encrypted user data _CD1 to the satellite communication unit _33A on the U-Plane side of the communication terminal 31. In step S46, the satellite communication unit _33A of the earth station ₁₁ radiates the encrypted user data _CD1 as radio waves _RU1 toward the low-earth orbit satellite _41. Specifically, the modem _13A of the satellite communication unit _33A of the earth station ₁₁ modulates the encrypted user data _CD1 to generate a transmission signal _SS1 . The frequency converter _12A converts the frequency of the transmission signal _SS1 . The antenna device _11A radiates the frequency-converted transmission signal _SS1 toward the low-earth orbit satellite ₄₁ as radio waves _RU1 .

8, the procedure of the process in which the earth station ₁₂ receives the radio wave _RD2 , demodulates and decodes the radio wave _RD2 to generate user data _UD1 and transmits it to the communication terminal ₃₂ in S05 will be described. In step S51, the satellite communication unit _33A of the earth station ₁₂ receives the radio wave _RD2 and generates encrypted user data _CD1 . Specifically, _the antenna device _11A of the satellite communication unit 33A of the earth station ₁₂ receives the radio wave _RD2 and generates a reception signal _RS2 . The frequency converter _12A converts the frequency of the reception signal _RS2 . The modem _13A demodulates the frequency-converted reception signal _RS2 to generate encrypted user data _CD1 .

In step S52, the satellite communication unit _33A outputs the generated encrypted user data _CD1 to the satellite communication IF unit 50. In step S53, the encryption device control unit 56 of the earth station ₁₂ refers to the decryption key 90 and obtains the decryption key _CK1 of the communication terminal _31. In step S54, the encryption device control unit 56 instructs the encryption device 15 to decrypt the encrypted user data _CD1 with the decryption key _CK1 , and the encryption device 15 generates user data _UD1 . In step S55, the data processing device 14 transmits the user data _UD1 to the communication terminal ₃₂ via the network IF unit 16 and the network ₂₂ , and the communication terminal ₃₂ receives it.

S54 is the procedure in which the communication partner decrypts the encrypted user data received by the communication partner with the partner's decryption key to generate user data. S55 is the procedure in which the communication partner sends the user data decrypted with the partner's decryption key to the request destination communication terminal.

9, the procedure of the process in which the earth station ₁₂ converts the user data _UD2 to be transmitted from the communication terminal ₃₂ to the communication terminal ₃₁ into encrypted user data _CD2 and radiates the data as radio waves _RU2 toward the low-earth orbit satellite ₄₂ in S06 will be described. FIG. 9 is the same as FIG. 7. In step S61, the communication terminal ₃₂ transmits the user data _UD2 to be transmitted to the communication terminal ₃₁ to the earth station ₁₂ , and the network IF unit 16 of the earth station ₁₂ receives the user data UD2. In step S62, the network IF unit 16 of the earth station ₁₂ outputs the user data _UD2 to the data processing device 14. In step S63, the encryption device control unit 56 refers to the encryption key 89 and obtains the encryption key _CK2 of the communication terminal _32. In step S64, the encryption device control unit 56 instructs the encryption device 15 to encrypt the user data _UD2 with the encryption key _CK2 , and the encryption device 15 generates encrypted user data _CD2 . Step S63 is a procedure in which the communication partner encrypts the user data from the request destination communication terminal with the partner's encryption key to generate encrypted user data.

In step S65, the satellite communication IF unit 50 inputs the encrypted user data _CD2 to the satellite communication unit _33A on the U-Plane side. In step S66, the satellite communication unit _33A radiates the encrypted user data _CD2 as radio waves _RU2 toward the low-earth orbit satellite _42. Specifically, _{the modem 13A of} the satellite communication unit _33A of the earth station 12 modulates the encrypted user data _CD2 to generate a transmission signal _SS2 . The frequency converter _12A converts the frequency of the transmission signal _SS2 . The antenna device _11A radiates the frequency-converted transmission signal _SS2 toward the low-earth orbit satellite ₄₂ as radio waves _RU2 .

With reference to Fig. 10, the procedure of the process in S08 in which the earth station _1.1 receives the radio wave _RD.1 , demodulates and decodes the radio wave _RD.1 to generate user data _UD.2 and transmits it to the communication terminal _3.1 will be described. Fig. 10 is similar to Fig. 8. In step S71, the satellite communication unit _33.A of the earth station _1.1 receives the radio wave _RD.1 and generates encrypted user data _CD.2 . Specifically, the antenna device _11.A of the satellite communication unit _33.A of the earth station _1.1 receives the radio wave _RD.1 and generates a received signal _RS.1 . The frequency converter _12.A converts the frequency of the received signal _RS.1 . The modem _13.A demodulates the frequency-converted received signal _RS.1 and generates encrypted user data _CD.2 .

In step S72, the satellite communication unit _33A outputs the generated encrypted user data _CD2 to the satellite communication IF unit 50. In step S73, the encryption device control unit 56 of the earth station ₁₁ refers to the decryption key 90 to obtain the decryption key _CK2 of the communication terminal _32. In step S74, the encryption device control unit 56 instructs the encryption device 15 to decrypt the encrypted user data _CD2 with the decryption key _CK2 , and the encryption device 15 generates user data _UD2 . In step S75, the data processing device 14 transmits the user data _UD2 to the communication terminal ₃₁ via the network IF unit 16 and the network ₂₁ , and the communication terminal ₃₁ receives it.

S74 is a procedure in which the decryption device decrypts the encrypted user data received by the first extratroposphere communication unit with its own decryption key to generate user data. S75 is a procedure in which the user data decrypted with its own decryption key is sent to the requesting communication terminal.

11, the procedure of the process in which the earth station ₁₁ transmits the communication control data _CC1 to the earth station ₁₂ as radio waves RU _C1 toward the geostationary satellite 5 in S09 will be described. In step S80, the communication terminal ₃₁ transmits a communication control request regarding communication with the communication terminal ₃₂ to the earth station ₁₁ , and the network IF unit ₁₆ of the earth station ₁₁ receives the communication control request. In step S81, the network IF unit 16 outputs the communication control request to the data processing device 14. In step S82, the data processing device 14 inputs the communication control request to the communication control data processing unit 57. In step S83, the communication control data processing unit 57 generates the communication control data _CC1 based on the communication control request. Note that the communication control data processing unit 57 may generate communication control data _CC1 that is not based on the communication control request from the communication terminal _31. In that case, the process starts from S83.

In step S84, the communication control data processing unit 57 of the earth station 1 ₁ outputs the communication control data CC ₁ to the satellite communication IF unit 50. In step S85, the satellite communication IF unit 50 outputs the communication control data CC ₁ to the satellite communication unit 33 _B on the C-Plane side of the communication terminal 3 _1. In step S86, the satellite communication unit 33 _B of the earth station 1 ₁ radiates the communication control data CC ₁ as radio waves RU _{C 1} toward the geostationary satellite 5. Specifically, the modem 13 _B of the satellite communication unit 33 _B of the earth station 1 ₁ modulates the communication control data CC ₁ with the communication control data CC 1 to generate a transmission signal SS _1. The frequency converter 12 _B converts the frequency of the transmission signal SS _1. The antenna device 11 _B radiates the frequency-converted transmission signal SS ₁ toward the geostationary satellite 5 as radio waves RU _{C 1} .

12, the procedure will be described in which, in S11, the earth station ₁₂ receives the radio wave RD _C2 , demodulates the radio wave RD _C2 , and processes the generated communication control data _CC2 to control the communication between the communication terminal ₃₂ and the communication terminal _31. In step S87, the satellite communication unit _33B of the earth station ₁₂ receives the radio wave RD _C2 and generates the communication control data _CC1 . Specifically, the antenna device _11B of the satellite communication unit _33B of the earth station ₁₂ receives the radio wave RD _C2 and generates the reception signal _RS2 . The frequency converter _12B converts the frequency of the reception signal _RS2 . The modem _13B demodulates the frequency-converted reception signal _RS2 and generates the communication control data _CC1 . In step S88, the satellite communication IF unit 50 receives the communication control data _CC1 and transfers it to the communication control data processing unit 57. In step S89, the communication control data processing unit 57 of the earth station ₁₂ controls the communication between the communication terminal ₃₁ and the communication terminal ₃₂ on the basis of the communication control data _CC1 .

With reference to Fig _. 13, the procedure of the process in which the earth station ₁₂ transmits the communication control data _CC2 to the earth station ₁₁ as radio waves RU- _C2 toward the geostationary satellite 5 in S12 will be described. Fig. 13 is the same as Fig. 11. In step S90, the communication terminal ₃₂ transmits a communication control request regarding communication with the communication terminal ₃₁ to the earth station ₁₂ , and the network IF unit 16 of the earth station ₁₂ receives it. In step S91, the network IF unit 16 outputs the communication control request to the data processing device 14. In step S92, the data processing device 14 inputs the communication control request to the communication control data processing unit 57. In step S93, the communication control data processing unit 57 generates the communication control data _CC2 based on the communication control request. Note that the communication control data processing unit 57 may generate communication control data _CC2 that is not based on the communication control request from the communication terminal _32. In that case, the process starts from S93.

In step S94, the communication control data processing unit 57 of the earth station ₁₂ outputs the communication control data _CC2 to the satellite communication IF unit 50. In step S95, the satellite communication IF unit 50 outputs the communication control data _CC2 to the satellite communication unit _33B on the C-Plane side of the communication terminal _32. In step S96, the satellite communication unit _33B of the earth station ₁₂ radiates the communication control data _CC2 as radio waves _RUC2 toward the geostationary satellite 5. Specifically, the modem _13B of the satellite communication unit _33B of the earth station ₁₂ modulates the communication control data _CC2 with the communication control data CC2 to generate a transmission signal _SS2 . The frequency converter _12B converts the frequency of the transmission signal _SS2 . The antenna device _11B radiates the frequency-converted transmission signal _SS2 toward the geostationary satellite 5 as radio waves _RUC2 .

14, the procedure will be described in which the earth station _1.1 receives the radio wave RD _C1 , demodulates the radio wave RD _C1 , and processes the generated communication control data _CC2 to control the communication between the communication terminal _3.1 and the communication terminal _3.2 in step S97. The satellite communication unit _33.B of the earth station _1.1 receives the radio wave RD _C1 and generates the communication control data _CC2 . Specifically, _the antenna device _11.B of the satellite communication unit 33.B of the earth station _1.1 receives the radio wave RD _C1 and generates the reception signal _RS1 . The frequency converter _12.B converts the frequency of the reception signal _RS1 . The modem _13.B demodulates the frequency-converted reception signal _RS1 and generates the communication control data _CC2 . In step S98, the satellite communication IF unit 50 receives the communication control data _CC2 and transfers it to the communication control data processing unit 57. In step S99, the communication control data processing unit 57 of the earth station _1-1 controls the communication between the communication terminal _3-1 and the communication terminal _3-2 on the basis of the communication control data CC _-2 .

The earth station 1 encrypts the user data and communicates it over the low-earth orbit satellite communication line 6. The earth station 1 communicates the encryption key and decryption key for encrypting the user data over the geostationary satellite communication line 8. Therefore, even if the user data communicated over the low-earth orbit satellite communication line 6 is intercepted, the contents of the user data will not be known because it has been encrypted. Since the encryption key and decryption key are communicated over the geostationary satellite communication line 8, the encryption key and decryption key will not be leaked even if the low-earth orbit satellite communication line 6 over which the user data is communicated is intercepted. Since the user data is not communicated over the geostationary satellite communication line 8, the contents of the user data will not be known even if the geostationary satellite communication line 8 is intercepted. In this embodiment 1, since a common key encryption method is used, the encryption key and the decryption key are the same. The encryption method may be a public key encryption method or a hybrid encryption method.

Meanwhile, satellite communication systems are characterized by their wide-area coverage, broadcasting capability, and disaster resistance. Because of these features, some satellite communication operators do not disclose information about wireless communication, such as the frequency, modulation/demodulation method, error correction method, transmission speed, and coding rate. Even if information about wireless communication is not disclosed, third parties can still intercept signals over a wide area within the communication area of the satellite. To prevent interception by spoofing, measures such as scrambling or encrypting data must be taken.

There are two general methods for encrypting data: public key cryptography and symmetric key cryptography. In public key cryptography, the encryption key used for encryption is different from the decryption key used for decryption. In public key cryptography, data encrypted with an encryption key (public key) is decrypted with a decryption key (private key). In public key cryptography, there is no need to share the decryption key, and data cannot be decrypted even if the public key is leaked. Public key cryptography requires a large amount of calculations for decryption, and takes a long time to process. On the other hand, symmetric key cryptography is an encryption method in which the encryption key used for encryption and the decryption key used for decryption are the same. Symmetric key cryptography requires fewer computer resources and takes less time to process than public key cryptography. When a symmetric key, which is both an encryption key and a decryption key, is shared between the sender and receiver, there is a possibility that the symmetric key (encryption key) may be leaked.

Satellite communications are also expected to be used in remote areas, islands, and mobile devices where it is difficult to connect to terrestrial lines (including mobile phone networks and terrestrial radio relay networks). For this reason, in satellite communications, it can be difficult to share a common key, which is the encryption key and decryption key for a common key cryptography method using a terrestrial communications system, and there are issues with how to share the common key. Even in communications systems that use communication lines relayed by mobile devices moving in the stratosphere, there are issues with how to share the common key.

The earth station 1, which is a communication device according to the present disclosure, does not require terrestrial infrastructure (terrestrial communication system). The earth station 1 can easily expand the communication area in a mobile communication system. The earth station 1 does not need to use a guard spot beam as in Patent Document 1.

Earth station 1 allows the sender and receiver to share an encryption key (including a decryption key) without using other communication systems. Earth station 1 can communicate encrypted user data.

Encryption keys and decryption keys are determined for each requesting communication terminal, so even if some of the encryption keys and decryption keys are known (leaked) to the outside, not all communications will be intercepted. Since encryption keys and decryption keys are determined each time communication begins, even if the encryption key and decryption key used at one time on a certain communication terminal are leaked, different encryption keys and decryption keys will be used the next time communication is made, so the leaked decryption key cannot decrypt the encrypted user data being communicated, and the contents of the communicated data will not be known to the outside.

Although a low-orbit satellite communication link 6 and a geostationary satellite communication link 8 are used, a high-altitude pseudo satellite communication link relayed by a high-altitude pseudo satellite moving in the stratosphere may also be used. A high-altitude pseudo satellite is a stratospheric mobile body that is a mobile body that moves in the stratosphere. A stratospheric mobile body other than a high-altitude pseudo satellite may also be used. Two or more types of satellite communication links relayed by communication satellites moving at two or more different altitudes lower than a geostationary satellite may also be used. Two types of extra-troposphere communication links may be selected from at least three types of extra-troposphere communication links and used as the first extra-troposphere communication link and the second extra-troposphere communication link.

The terms "outside the troposphere" and "communication lines outside the troposphere" will be explained. "Outside the troposphere" refers to an altitude higher than the troposphere from the Earth's surface. "Outside the troposphere" includes the stratosphere, mesosphere, thermosphere, exosphere, and outer space, in order of proximity to the Earth's surface. A mobile body moving at an altitude included in the outside troposphere is an outside troposphere mobile body. An outside troposphere mobile body moving at a first altitude included in the outside troposphere is a first outside troposphere mobile body. An outside troposphere mobile body moving at a second altitude different from the first altitude included in the outside troposphere is a second outside troposphere mobile body. A relay station mounted on an outside troposphere mobile body is an outside troposphere relay station. An outside troposphere relay station mounted on a first outside troposphere mobile body is a first outside troposphere relay station. An outside troposphere relay station mounted on a second outside troposphere mobile body is a second outside troposphere relay station. A communication line relayed by an outside troposphere relay station is an outside troposphere communication line. The extra-troposphere communication line relayed at the first extra-troposphere relay station is the first extra-troposphere communication line. The extra-troposphere communication line relayed at the second extra-troposphere relay station is the second extra-troposphere communication line.

There is one type of extra-troposphere communication line for each altitude at which the extra-troposphere mobile body moves. The at least three types of extra-troposphere communication lines are extra-troposphere communication lines that are relayed by extra-troposphere relay stations mounted on extra-troposphere mobile bodies that move at at least three mutually different altitudes included in the troposphere. Of the two types of extra-troposphere communication lines used, the extra-troposphere communication line that communicates encrypted user data is the first extra-troposphere communication line. The extra-troposphere communication line that communicates with the communication partner an encryption key used to encrypt user data and a decryption key to decrypt the encrypted user data before communication via the first extra-troposphere communication line is the second extra-troposphere communication line.

Selecting an extra-troposphere communication line means selecting an extra-troposphere mobile body equipped with a relay station that relays the extra-troposphere communication line. Each of the first extra-troposphere mobile body and the second extra-troposphere mobile body may be an extra-troposphere mobile body selected from at least three types of extra-troposphere mobile bodies that move at at least three mutually different altitudes included outside the troposphere.

Each of the first extra-tropospheric mobile body and the second extra-tropospheric mobile body may be an extra-tropospheric mobile body selected from a set of extra-tropospheric mobile bodies including a stratospheric mobile body that is a mobile body that moves in the stratosphere, a geostationary satellite, and an artificial satellite that moves at least two altitudes that are lower than the geostationary satellite and different from each other.

In the earth station 1, the low-earth orbit satellite communication line 6 and the low-earth orbit inter-satellite communication line 7 are the first extra-troposphere communication line. The geostationary satellite communication line 8 is the second extra-troposphere communication line. The satellite communication unit _33A is the first extra-troposphere communication unit that communicates encrypted user data obtained by encrypting user data with the communication partner in the first extra-troposphere communication circuit. The satellite communication unit _33B is the second extra-troposphere communication unit that communicates communication control data with the communication partner, including at least one of an encryption key (own encryption key) used by the encryption device and a decryption key (own decryption key) used by the communication partner when decrypting the encrypted user data generated by the encryption device, and communicates communication control data with the communication partner, including at least one of an encryption key (own encryption key) used by the communication partner and a decryption key (own decryption key) used by the decryption device when decrypting the encrypted user data generated by the communication partner.

The first extra-troposphere communication line may be a geostationary satellite communication line 8, and the second extra-troposphere communication line may be a low-earth orbit satellite communication line 6 and a low-earth orbit inter-satellite communication line 7.

When communicating via a non-troposphere communication line, the communicating satellite _80A stored in the data storage unit 58 is an extra-troposphere mobile body equipped with a relay station that relays the extra-troposphere communication line used by the satellite communication unit _33A . The communicating satellite _80B is an extra-troposphere mobile body equipped with a relay station that relays the extra-troposphere communication line used by the satellite communication unit _33B .

In the communication method, steps S26 to S28 shown in FIG. 5 are steps for communicating at least one of the own encryption key and the other party's decryption key with the communication partner through the second extra-troposphere communication unit. Steps S35 to S37 shown in FIG. 6 are steps for communicating at least one of the other party's encryption key and the own decryption key with the communication partner through the second extra-troposphere communication unit. Step S46 shown in FIG. 7 is a step in which the first extra-troposphere communication unit transmits encrypted user data encrypted with the own encryption key to the communication partner through the first extra-troposphere communication line. Step S51 shown in FIG. 8 is a step in which the communication partner receives the encrypted user data transmitted through the first extra-troposphere communication line. Step S66 shown in FIG. 9 is a step in which the communication partner transmits encrypted user data encrypted with the other party's encryption key through the first extra-troposphere communication line. Step S71 shown in FIG. 10 is a step in which the first extra-troposphere communication unit receives the encrypted user data transmitted by the communication partner through the first extra-troposphere communication line.

The communication device, which is an earth station 1 not including antenna devices _11A , _11B , includes two modulator-demodulators _13A , _13B and two frequency converters _12A , _12B . The sequence control unit 54 is a sequence allocation unit that assigns one frequency converter 12 and one modulator-demodulator 13 to be used as a first extra-troposphere communication unit, and assigns the other frequency converter 12 and the other modulator-demodulator 13 to be used as a second extra-troposphere communication unit.

The series control unit 54 causes one of the modems 13 to modulate and demodulate the encrypted user data, and causes one of the frequency converters 12 to perform frequency conversion between the frequency used in the first extratroposphere communication line and the frequency of the signal processed by the modem 12. The series control unit 54 causes the other of the modems 13 to modulate and demodulate the communication control data, and causes the other of the frequency converters 12 to perform frequency conversion between the frequency used in the second extratroposphere communication line and the frequency of the signal processed by the modem 13.

The tracking control unit 52 controls one antenna device 11 connected to one frequency converter 12 to track a first extratroposphere moving object, and controls the other antenna device 11 connected to the other frequency converter 12 to track a second extratroposphere moving object.

Since the earth station 1 uses a common key cryptosystem, the second extra-troposphere communication unit communicates with the communication partner communication control data including a decryption key used by the communication partner when decrypting the encrypted user data generated by the encryption device, and communicates communication control data including a decryption key used by the decryption device when decrypting the encrypted user data generated by the communication partner. When using a secret key cryptosystem, the second extra-troposphere communication unit communicates with the communication partner communication control data including an encryption key used by the encryption device, and communicates with the communication partner communication control data including an encryption key used by the communication partner.

The second extra-troposphere communication unit may communicate with the communication partner communication control data including at least one of an encryption key used by the encryption device and a decryption key used by the communication partner when decrypting encrypted user data generated by the encryption device, and communicate with the communication partner communication control data including at least one of an encryption key used by the communication partner and a decryption key used by the decryption device when decrypting encrypted user data generated by the communication partner via the second extra-troposphere communication line.

In the wireless communication system 100, the encryption key and decryption key are determined by the earth station 1 for each source communication terminal. The encryption key and decryption key may be determined for each pair of source communication terminal and destination communication terminal. The same encryption key and decryption key may be used regardless of the terminal, and the encryption key and decryption key may be changed depending on the time of day. If acceptable from a security standpoint, the encryption key and decryption key to be used may be determined for each earth station. The encryption method, unit for determining the encryption key and decryption key, and the period for changing the encryption key and decryption key may be determined in any way as long as the required security level is ensured.

When determining an encryption key and a decryption key for each pair of a source communication terminal and a destination communication terminal, the earth station 1 to which the source communication terminal is connected may determine the encryption key used by the communication partner when encrypting user data from the destination communication terminal. In this case, the communication control data of the communication start request in which the earth station 1 communicates with the communication partner earth station 1 includes the decryption key used by the communication partner when decrypting the encrypted user data generated by the encryption device, and the encryption key used by the communication partner. This communication control data of the communication start request is communication control data that includes at least one of the encryption key used by the encryption device and the decryption key used by the communication partner when decrypting the encrypted user data generated by the encryption device, and also includes at least one of the encryption key used by the communication partner and the decryption key used by the decryption device when decrypting the encrypted user data generated by the communication partner.

At the earth station 1, encrypted user data is communicated by the first extra-troposphere communication unit, and communication control data is communicated by the second extra-troposphere communication unit. The communication control data may be encrypted and communicated. The encrypted user data and encrypted communication control data may be allocated to the first extra-troposphere communication unit and the second extra-troposphere communication unit in some manner for communication.

The communication partner does not have to be a communication device according to the present disclosure. The communication partner may be, for example, a communication device connected to a terrestrial communication network.

The communication device according to this disclosure may communicate encrypted user data over a first extra-troposphere communication line and communicate communication control data over a second extra-troposphere communication line. The communication path over which encrypted user data is communicated may have a portion that is not the first extra-troposphere communication line. The communication path over which communication control data is communicated may have a portion that is not the second extra-troposphere communication line.

The earth station may not have a network IF unit 16 and may communicate user data with the other earth station.

The requesting communication terminal is a communication terminal connected to one of the communication device and the communication partner. The requested communication terminal is a communication terminal connected to the other of the communication device and the communication partner. The communication device has an encryption device (also a decryption device), a first extra-troposphere communication unit, and a second extra-troposphere communication unit. The communication method according to this disclosure may include the following procedure.
(A) A procedure in which either the communication device or the communication partner receives a request from a request source communication terminal to start communication with a request destination communication terminal.
(i) A procedure for communicating with a communication partner via a second extra-troposphere communication unit at least one of a self-encryption key, which is an encryption key used by the encryption device when encrypting user data to generate encrypted user data, and a partner-decryption key, which is a decryption key used by the communication partner when decrypting encrypted user data encrypted using the self-encryption key.
(c) A procedure for communicating with a communication partner via a second extra-troposphere communication unit at least one of a partner encryption key, which is an encryption key used by the communication partner when encrypting user data to generate encrypted user data, and a self-decryption key, which is a decryption key used by the decryption device when decrypting encrypted user data encrypted with the partner encryption key.
(iv) A procedure in which the encryptor encrypts user data from a requesting communications terminal with its own encryption key, or the communications partner encrypts the data with the communications partner's encryption key, to generate encrypted user data.
(E) A procedure in which the first extra-troposphere communication unit communicates encrypted user data from the encrypted request source communication terminal with a communication partner via the first extra-troposphere communication line.
(f) A procedure in which the communication partner decrypts encrypted user data received by the communication partner using the communication partner's decryption key, or the encryption device decrypts encrypted user data received by the communication device using its own decryption key, to generate user data from the requesting communication terminal.
(g) A procedure in which the communication partner or communication device transmits the decrypted user data from the requesting communication terminal to the requested communication terminal.
(h) A procedure in which the communication partner encrypts user data from a request destination communication terminal with the partner's encryption key, or the encryption device encrypts the data with its own encryption key, to generate encrypted user data.
(i) A procedure for communicating encrypted user data from the encrypted requested communication terminal with a communication partner via a first extratroposphere communication line.
(J) A procedure in which the decryption device decrypts the encrypted user data received by the first extratroposphere communication unit using its own decryption key, or the communication partner decrypts it using the partner's decryption key, to generate user data from the requested communication terminal.
(k) A procedure in which a communication device or a communication partner sends the decrypted user data from a requested communication terminal to a requesting communication terminal.
The above also applies to the other embodiments.

Embodiment 2.
The second embodiment is based on the first embodiment, but uses a communication line relayed by two mobile objects at altitudes selected from among three or more mobile objects that are outside the troposphere and move at altitudes, and changes the method for managing the encryption key and decryption key to a public key encryption method.

A schematic configuration of a satellite communication system according to the second embodiment is shown in FIG. 15. The differences between FIG. 1 and FIG. 1 of the first embodiment will be described with reference to FIG. 15. The satellite communication system 100C has earth stations _1C.sub.1 and _1C.sub.2 changed and has high altitude pseudosatellites _9.sub.1 and _9.sub.2 . The high altitude pseudosatellites _9.sub.1 and _9.sub.2 are also called HAPS (High Altitude Platform Station). The high altitude pseudosatellite 9 flies at an altitude of about 20 km and can communicate with earth stations present in a range of about 100 km in diameter on the earth's surface. The high altitude pseudosatellites 9 can communicate with each other. By forming a communication network in the stratosphere with several tens of high altitude pseudosatellites 9, communication can be made throughout Japan through communication lines relayed by the high altitude pseudosatellites 9. The artificial satellite or high altitude pseudosatellite 9 is an extratropospheric mobile object that moves outside the troposphere, which is at an altitude higher than the earth's troposphere.

The earth station 1C _-1 and earth station 1C- ₂ can communicate with each other through high altitude pseudosatellite communication links _21-1 and _21-2 relayed by high altitude pseudosatellites _9-1 and _9-2 , and a high altitude inter-pseudosatellite communication link 22. The high altitude pseudosatellite communication link _21-1 is a communication link used for communication between the earth station 1C _-1 and the high altitude pseudosatellite _9-1 . The high altitude pseudosatellite communication link _21-2 is a communication link used for communication between the earth station 1C _-2 and the high altitude pseudosatellite _9-2 . The high altitude inter-pseudosatellite communication link 22 is a communication link connecting the high altitude pseudosatellite _9-1 and the high altitude pseudosatellite _9-2 . When another high altitude pseudosatellite 9- _N is interposed between the high altitude pseudosatellite _9-1 and the high altitude pseudosatellite _9-2 , the number of high altitude inter-pseudosatellite communication links 22 becomes multiple. When the high altitude pseudo satellite _9-1 and the high altitude pseudo satellite _9-2 are the same, the earth station 1C- ₁ and the earth station 1C _-2 communicate with each other without passing through the high altitude inter-pseudo satellite communication link 22. The high altitude pseudo satellite communication link 21 and the high altitude inter-pseudo satellite communication link 22 are extratropical communication links that are communication links relayed by an extratropical mobile station that is a relay station mounted on an extratropical mobile body.

The configuration of earth station 1C will be described with reference to Figure 16. Figure 16 is a diagram showing the configuration of a communication device (earth station 1C) according to embodiment 2. Regarding Figure 16, differences from Figure 2 in the case of embodiment 1 will be described. Earth station 1C has a satellite selection input unit 59, and has modified line control unit 51C, encryption device 15C, tracking control unit 52C, satellite position management unit 53C, encryption key/decryption key management unit 55C, communication control data processing unit 57C, and data storage unit 58C.

Cryptographic device 15C differs from cryptographic device 15, which uses a common key cryptosystem, in that it encrypts and decrypts using a public key cryptosystem.

In the earth station 1C, the user selects and inputs the type of the extratropospheric mobile object to be used for communication by each of the satellite communication units _33A and _33B . The satellite selection input unit 59 accepts the type of the extratropospheric mobile object input by the user. The data storage unit 58C also has mobile object types _92A and _92B . The mobile object type _92A stores the type of the extratropospheric mobile object with which the satellite communication unit _33A communicates. The mobile object type _92B stores the type of the extratropospheric mobile object with which the satellite communication unit _33B communicates. The type of the extratropospheric mobile object is any of a geostationary satellite, a low-orbit satellite, and a high-altitude pseudo satellite. In addition, when a medium-orbit satellite or a plurality of low-orbit satellites at different altitudes can be used, the mobile object types are determined in advance so that all available types of extratropospheric mobile objects can be distinguished from each other.

The line control unit 51C manages the relayed extratropical mobile object, transmission frequency, and reception frequency for each of the satellite communication units _33A , _33B by referring to the mobile object types _92A , _92B . The tracking control unit 52C controls the antenna devices _11A , _11B so that they face the direction of the relayed _{extratropical} mobile object. The tracking control unit 52C can also track the high altitude pseudo satellite 9. The high altitude pseudo satellite 9 flies above a predetermined point on the Earth _'s surface. When the earth station 1C does not move, the high altitude pseudo satellite 9 that can communicate with the earth station 1C is determined.

The satellite position management unit 53C obtains from the outside orbit data of extra-tropospheric mobile bodies that can be used as the first extra-tropospheric mobile body and the second extra-tropospheric mobile body. The satellite position management unit 53C determines communicating satellites _80A , _80B for the extra-tropospheric mobile bodies of the types designated by the mobile body types _92A , _92B . The satellite position management unit 53C operates at a determined cycle, and determines the positions of the communicating satellites _80A , _80B from the time of operation based on the orbit data to a future time within a determined range, and sets the determined positions as satellite positions _94A , _94B .

The data storage unit 58C stores a decryption key 89C, an encryption key in use 90C, and a corresponding encryption key 91C. The decryption key 89C is data that stores a decryption key to be used for each communication terminal 3 and for each series. The decryption key is also called a secret key. The decryption key 89C is data of 2*N _max pieces. An encryption key used when encrypting encrypted data that can be decrypted with the decryption key is called a corresponding encryption key corresponding to the decryption key. The corresponding encryption key is also called a public key. The corresponding encryption key 91C is data that stores a corresponding encryption key for each decryption key stored in the decryption key 89C. The corresponding encryption key 91C is data of 2* _{N max} pieces. The encryption key in use 90C is data that stores an encryption key to be used for each communication terminal and for each series. The encryption key _in use of the communication terminal ...

The data storage unit 58C is a decryption key storage unit that stores a decryption key for decrypting the received encrypted user data for each of its own communication terminals that are communication terminals connected to the terminal connection unit. The decryption key used by the encryption device 15C is stored in the data storage unit 58C as decryption key 89C. The data storage unit 58C is a corresponding encryption key storage unit that stores, for each of its own communication terminals, a corresponding encryption key that is an encryption key for encrypting data that the encryption device 15C, which is a decryption device, decrypts with the decryption key. The corresponding encryption key is stored in the data storage unit 58C as corresponding encryption key 91C. The data storage unit 58C is a usage encryption key storage unit that stores, for each of the destination communication terminals, a usage encryption key that is an encryption key used by the encryption device 15C. The encryption key used by the encryption device 15C is stored in the data storage unit 58C as usage encryption key 90C.

The encryption key/decryption key management unit 55C determines and manages a decryption key and a corresponding encryption key for each communication terminal 3. When the encryption key/decryption key management unit 55C receives a communication start request from a requesting communication terminal, it determines a decryption key and a corresponding encryption key for each sending communication terminal. The encryption key/decryption key management unit 55C stores the determined decryption key and corresponding encryption key in the decryption key 89C and the corresponding encryption key 91C. When the encryption key/decryption key management unit 55C receives a communication start request from the communication partner (earth station 1C), it stores the encryption key included in the communication start request in the encryption key in use 90C as the encryption key in use for each requesting communication terminal.

When the encryption key decryption key management unit 55C receives a communication start request from the requesting communication terminal, it checks whether the decryption key of the requesting communication terminal on the U-Plane side is stored in the decryption key 89C in the usage sequence 88. If it is not stored, the encryption key decryption key management unit 55C determines the decryption key and the corresponding encryption key. The encryption key decryption key management unit 55C stores the determined compound key in the decryption key 89C in the usage sequence 88 as the decryption key of the requesting communication terminal on the U-Plane side. The encryption key decryption key management unit 55C stores the determined corresponding encryption key in the corresponding encryption key 91C in the usage sequence 88 as the corresponding encryption key of the requesting communication terminal on the U-Plane side.

When the encryption key decryption key management unit 55C receives communication control data of a communication start request transmitted from another earth station 1C (communication partner), it stores the corresponding encryption key of the request source communication terminal included in the communication control data of the communication start request in the usage sequence 88 as the usage encryption key of the request source communication terminal on the U-Plane side in the usage sequence 88 in the usage encryption key 90C. Then, the encryption key decryption key management unit 55C checks whether the decryption key of the request destination communication terminal specified in the communication start request is stored on the U-Plane side in the usage sequence 88 in the decryption key 89C. If it is not stored, the encryption key decryption key management unit 55C determines the decryption key and the corresponding encryption key. The encryption key decryption key management unit 55C stores the determined composite key in the decryption key 89C as the decryption key of the request destination communication terminal on the U-Plane side in the usage sequence 88. The encryption key decryption key management unit 55C stores the determined corresponding encryption key in the usage sequence 88 in the usage sequence 88 in the corresponding encryption key 90C as the corresponding encryption key of the request destination communication terminal on the U-Plane side.

When the encryption key decryption key management unit 55C receives communication control data for accepting the start of communication transmitted from another earth station 1C (communication partner), it stores the corresponding encryption key of the requested communication terminal included in the communication control data for accepting the start of communication in the encryption key usage sequence 88 in the encryption key usage 90C as the encryption key usage of the requested communication terminal on the U-Plane side.

If the decryption key of the requesting communication terminal is not stored in the decryption key memory unit, the encryption key decryption key management unit 55C determines an encryption key and a corresponding encryption key, stores the determined decryption key in the decryption key memory unit as the decryption key of the requesting communication terminal, and stores the determined corresponding encryption key in the corresponding encryption key memory unit as the corresponding encryption key of the requesting communication terminal.
When the encryption key/decryption key management unit 55C receives communication control data for a communication start request, it stores the corresponding encryption key of the requesting communication terminal included in the received communication control data in the usage encryption key memory unit as the usage encryption key of the requesting communication terminal, and if the decryption key of the requested communication terminal is not stored in the decryption key memory unit, it determines a decryption key and a corresponding encryption key, stores the determined decryption key in the decryption key memory unit as the decryption key of the requested communication terminal, and stores the determined corresponding encryption key in the corresponding encryption key memory unit as the corresponding encryption key of the requested communication terminal.
When the encryption key decryption key management unit 55C receives communication control data accepting the start of communication, it stores the corresponding encryption key of the requested communication terminal contained in the received communication control data in the encryption key usage memory unit as the encryption key usage of the requested communication terminal.

When the communication control data processing unit 57C receives communication control data of a communication start request from a requesting communication terminal, it creates communication control data of the communication start request including the requesting communication terminal, the requested communication terminal, and the corresponding encryption key of the requesting communication terminal determined by the encryption key/decryption key management unit 55C, and outputs it to the satellite communication IF unit 50. The satellite communication IF unit 50 outputs the communication control data to the modem 13 on the C-Plane side via the usage series 88.

When the communication control data processing unit 57C receives communication control data of a communication start request sent from the communication partner, it creates communication control data of communication start acceptance including the requesting communication terminal, the requested communication terminal, and the corresponding encryption key of the requested communication terminal, and outputs it to the satellite communication IF unit 50. The satellite communication IF unit 50 outputs the communication control data to the modem 13 on the C-Plane side via the usage series 88.

The communication control data processing unit 57C is a communication control data generation unit that generates communication control data for a communication start request including the requesting communication terminal, the requested communication terminal, and the corresponding encryption key of the requesting communication terminal when it receives a communication start request from its own communication terminal, the requesting communication terminal, which is a communication terminal connected to the communication partner via a network, and generates communication control data for a communication start acceptance including the corresponding encryption key of the requested communication terminal when it receives the communication control data for the communication start request from the communication partner.

The operation will be described. Figures 17 and 18 are flow charts for explaining the outline of the procedure when the communication terminal 3 ₁ connected to the earth station 1C ₁ communicates with the communication terminal 3 ₂ connected to the earth station 1C _2. Figure 17 illustrates the process up to step S08C, and Figure 18 illustrates the process from step S09C. In the earth station 1C ₁ and the earth station 1C ₂ , the satellite communication unit 33 _A of the series A communicates through a communication line relayed by the high altitude pseudo satellite 9, and the satellite communication unit 33 _B of the series B communicates through a communication line relayed by the low orbit satellite 4. In the earth station 1C ₁ and the earth station 1C ₂ , the series A is U-Plane, and the series B is C-Plane. In each earth station 1C, the U-Plane may be one of the series A and series B for each communication terminal, and the C-Plane may be the other.

In the wireless communication system 100C, the high altitude pseudo satellite 9 is the first extra-troposphere mobile body. The low orbit satellite 4 is the second extra-troposphere mobile body. The high altitude pseudo satellite communication link 21 and the high altitude inter-pseudo satellite communication link 22 are the first extra-troposphere communication link. The low orbit satellite communication link 6 and the low orbit inter-satellite communication link are the second extra-troposphere communication link. The satellite communication unit _33A is the first extra-troposphere communication unit. The satellite communication unit _33B is the second extra-troposphere communication unit. The first extra-troposphere communication link and the second extra-troposphere communication link are extra-troposphere communication links selected from at least three types of extra-troposphere communication links respectively relayed at extra-troposphere relay stations mounted on extra-troposphere mobile bodies moving at at least three mutually different altitudes included in the troposphere.

In step S01, the communication terminal _3.1 transmits a communication start request to the earth station _1C.1 to communicate with the communication terminal _3.2 , and the network IF unit 16 of the earth station _1C.1 receives the request. In step S02C, the earth stations _1C.1 and _1C.2 determine an encryption key and a decryption key to be used for communication between the communication terminals _3.1 and _3.2 , and store the determined keys in the data storage unit 58C. The process of S02C will be described with reference to the flowcharts shown in Figs. 19 and 20. The process of S02C differs from the process of S02 in that the communication is relayed by a low-orbit satellite 4, not a geostationary satellite 5. The process of S02C also differs in that an encryption key and a decryption key for a public key cryptosystem are determined.

Step S03C and after are the process of communicating user data and communication control data between communication terminal _3-1 and communication terminal _3-2 . Steps S03C to S05C are the procedure of transmitting user data UD _-1 from communication terminal _3-1 to communication terminal _3-2 . Steps S06C to S08C are the procedure of transmitting user data UD _-2 from communication terminal _3-2 to communication terminal _3-1 . Steps S09C to S11 are the procedure of transmitting communication control data CC _{-1 from communication terminal 3-1 or earth station 1C-1 to earth station 1C-2. S11 is the same process as in the case of earth station 1-1. Steps S12C to S14 are the procedure of transmitting communication control data CC-2 from communication terminal 3-2 or earth} station 1C _-2 to earth station 1C- ₁ . S14 is the same process as in the case of earth station _1-1 . The process from S03C to S05C, the process from S06C to S08C, the process from S09C to S11, and the process from S12C to S14 are executed in parallel.

The processing from S03C to S05C is similar to the processing from S03 to S05, except that it is relayed by a high altitude pseudo satellite 9. The processing from S06C to S08C is similar to the processing from S06 to S08, except that it is relayed by a high altitude pseudo satellite 9. The processing from S09C to S11 is similar to the processing from S09 to S11, except that it is relayed by a low altitude satellite 4. The processing from S12C to S14 is similar to the processing from S12 to S14, except that it is relayed by a low altitude satellite 4.

In step S03C, the earth station _1C1 converts the user data _UD1 transmitted from the communication terminal ₃₁ to the communication terminal ₃₂ into encrypted user data _CD1 , and transmits the data as radio waves _RU1 toward the high altitude pseudo satellite _91. In step S04C, the high altitude pseudo satellite ₉₁ receives the radio waves _RU1 , frequency-converts and amplifies the radio waves _RU1 , and transmits the radio waves as radio waves _RC1 . The high altitude pseudo satellite ₉₂ receives the radio waves _RC1 , frequency-converts and amplifies the radio waves _RC1, and transmits the radio waves as radio waves _RD2 . In step S05C, the earth station _1C2 receives the radio waves _RD2 , and demodulates and decodes the radio waves _RD2 to generate the user data _UD1 . The earth station _1C2 transmits the user data _UD1 to the communication terminal _32. The process in step S03C will be described with reference to the flowchart shown in FIG. 21. The process in step S05C will be described with reference to the flowchart shown in FIG. 22.

In step S06C, _the earth station _1C2 converts the user data _UD2 transmitted from the communication terminal 32 to the communication terminal ₃₁ into encrypted user data _CD2 , and transmits the data as radio waves _RU2 toward the high altitude pseudo satellite _91. In step S07C, the high altitude pseudo satellite ₉₂ receives the radio waves _RU2 , frequency-converts and amplifies the radio waves _RU2 , and transmits the radio waves as radio waves _RC2 . The high altitude pseudo satellite ₉₁ receives the radio waves _RC2 , frequency-converts and amplifies the radio waves _RC2, and transmits the radio waves as radio waves _RD1 . In step S08C, the earth station _1C1 receives the radio waves _RD1 , and demodulates and decodes the radio waves _RD1 to generate user data _UD2 . The earth station _1C1 transmits the user data _UD2 to the communication terminal _31. The process of S06C will be described with reference to the flowchart shown in FIG. 23. The process of S08C will be described with reference to the flowchart shown in FIG. 24.

In step S09C, the earth station _1C1 transmits the communication control data _CC1 to the earth station _1C2 , which is then radiated as radio waves _RUC1 by the earth station _1C1 toward the low-earth orbit satellite _41. In step S10C, the low-earth orbit satellite ₄₁ receives the radio waves _RUC1 , frequency-converts and amplifies the radio waves _RUC1 , and radiates them as radio waves _RDC1 . The low-earth orbit satellite ₄₂ receives the radio waves _RDC1 , frequency-converts and amplifies the radio waves _RDC1 , and radiates them as radio waves _RDC2 . In S11, the earth station _1C2 receives the radio waves _RDC2 , demodulates the radio waves _RDC2 , and generates the communication control data _CC1 . The earth station _1C2 processes the communication control data _CC1 to control the communication between the communication terminal ₃₁ and the communication terminal _32. The process in S09C will be described with reference to the flow chart shown in FIG. 25.

In step S12C, the earth station _1C2 transmits the communication control data _CC2 to the earth station _1C1 , which is then radiated as radio waves RU- _C2 by the earth station _1C2 toward the low-earth orbit satellite _4-2 . In step S13C, the low-earth orbit satellite _4-2 receives the radio waves RU- _C2 , frequency-converts and amplifies the radio waves RU- _C2 , and radiates them as radio waves RD- _C2 . The low-earth orbit satellite _4-1 receives the radio waves RD- _C2 , frequency-converts and amplifies the radio waves RD- _C2 , and radiates them as radio waves RD- _C1 . In step S14, the earth station _1C1 receives the radio waves RD- _C1 , demodulates the radio waves RD- _C1 , and generates communication control data CC _-2 . The earth station _1C1 processes the communication control data CC _-2 to control the communication between the communication terminal _3-1 and the communication terminal _3-2 . The process of S12C will be described with reference to the flow chart shown in FIG. 26.

With reference to Figures 19 and 20, the procedure of processing in S02C in which earth station _1-1 and earth station _1-2 determine the decryption key and encryption key to be used for communication between communication terminal _3-1 and communication terminal _3-2 and store them in data storage unit 58C in satellite communication system 100C will be described. Regarding Figures 19 and 20, the difference from Figures 5 and 6 in the case of satellite communication system 100 will be described. Since communication control data for a communication start request and communication start acceptance is communicated not through geostationary satellite communication line 8 relayed by geostationary satellite 5 but through low-earth orbit satellite communication line 6 relayed by low-earth orbit satellite 4 and low-earth orbit inter-satellite communication line 7, steps S26C, S27C, S28C and steps S35C, S36C, S37C have been changed. An encryption key/decryption key management section 55C in the earth station 1C manages decryption keys instead of encryption keys for each source communication terminal, and therefore steps S22C, S23C, S24C, S29C, S30C, S31C, S32C, S33C, S38C and S39C are modified.

In step S21, the data processing device 14 of the earth station _1C1 transfers a communication start request from the communication terminal _3.1 to the communication control data processing unit 57C. In step S22C, the encryption key/decryption key management unit 55C started by the communication control data processing unit 57C checks whether the decryption key of the U-Plane side (series A) of the communication terminal _3.1 is set in the decryption key 89C. If the decryption key is not set (NO in S22C), in step S23C, the encryption key/decryption key management unit 55C determines the decryption key _DK1 and the corresponding encryption key _CK1 of the U-Plane side (series A) of the communication terminal _3.1 . The encryption key/decryption key management unit 55C stores the determined decryption key _DK1 in the decryption key 89C and stores the corresponding encryption key _CK1 in the corresponding encryption key 91C. After execution of S23C and if the decryption key for the U-Plane side (series A) of the communication terminal ₃₁ is set in the decryption key 89C (YES in S22C), the process proceeds to step S24C.

In step S24C, the communication control data processing unit 57C of the earth station _1C1 generates communication control data _CC1 of a communication start request including the corresponding encryption key _CK1 of the communication terminal ₃₁ , the communication terminal ₃₂ , and the communication terminal 31 acquired from the corresponding encryption key _91C , and transmits it to the satellite communication IF unit 50. In step S25, the satellite communication IF unit 50 transmits the communication control data _CC1 to the satellite communication unit _33A , which is the C-Plane side (series A) of the communication terminal _31. In step S26C, the satellite communication unit _33A of the earth station _1C1 radiates the communication control data _CC1 as radio waves _RU1 toward the low-orbit satellite _41. Specifically, the modem _13A of the satellite communication unit _33A of the earth station _1C1 modulates the communication control data _CC1 to generate a transmission signal _SS1 . The frequency converter _12A converts the frequency of the transmission signal _SS1 . The antenna device _11A radiates the frequency-converted transmission signal _SS1 toward the low earth orbit satellite ₄₁ as a radio wave _RU1 .

In step S27C, the low-earth orbit satellite ₄₁ receives the radio wave _RU1 , frequency converts and amplifies it, and radiates the radio wave _RD1 . The low-earth orbit satellite ₄₂ receives the radio wave _RD1 , frequency converts and amplifies _it , and radiates it as radio wave _RD2 . In step S28C, the satellite communication unit _33A of the earth station _1C2 receives the radio wave _RD2 and generates communication control data _CC1 . The satellite communication IF unit 50 that receives the communication control data _CC1 transfers it to the communication control data processing unit 57C. In step S29C, the communication control data processing unit 57C extracts the communication terminal _31, which is the requesting communication terminal, and the encryption key _CK1 from the communication control data _CC1 , and starts the encryption key/decryption key management unit 55C.

In step S30C, the encryption key decryption key management unit 55C stores the encryption key _CK1 extracted from the communication control data _CC1 in the encryption key to be used 90C as the encryption key to be used on the U-Plane side (series A) of the communication terminal _31. In step S31C, the encryption key decryption key management unit 55C checks whether the decryption key on the U-Plane side (series A) of the communication terminal ₃₂ , which is the request destination communication terminal, is set as the decryption key 89C. If the decryption key is not set (NO in S31C), in step S32C, the encryption key decryption key management unit 55C determines the decryption key _DK2 and the corresponding encryption key _CK2 on the U-Plane side (series A) of the communication terminal _32. The encryption key decryption key management unit 55C stores the determined decryption key _DK2 in the decryption key 89C and stores the corresponding encryption key _CK2 in the corresponding encryption key 91C. After execution of S32C and if the decryption key for the U-Plane side (series A) of the communication terminal ₃₂ is set in the decryption key 89C (YES in S31C), the process proceeds to step S33C.

In step S33C, the communication control data processing unit 57C of the earth station _1C2 generates communication control data CC2 for accepting the start of communication, including the corresponding encryption key _CK2 of the communication terminal ₃₁ , the communication terminal _{32 ,} and the corresponding encryption key _91C of the communication terminal 32, and transmits the communication control data _CC2 to the satellite communication IF unit 50. In step S34, the satellite communication IF unit 50 transmits the communication control data _CC2 to the satellite communication unit _33A , which is the C-Plane side (series A) of the communication terminal 31. In step S35C, the satellite communication unit _33A of the earth station _1C2 radiates the communication control data _CC2 as radio waves _RU2 toward the low-orbit satellite _42. Specifically, the modem _13A of the satellite communication unit _33A of the earth station _1C2 modulates the communication control data _CC2 to generate a transmission signal _SS2 . The frequency converter _12A converts the frequency of the transmission signal _SS2 . The antenna device _11A radiates the frequency-converted transmission signal _SS2 toward the low earth orbit satellite ₄₂ as a radio wave _RU2 .

In step S36C, the low-earth orbit satellite ₄₂ receives the radio wave _RU2 , converts the frequency, amplifies it, and radiates the radio wave _RD2 . The low-earth orbit satellite ₄₁ receives the radio wave _RD2 , converts the frequency of the radio wave _RD2 , amplifies it, and radiates it as the radio wave _RD1 . In step S37C, the satellite communication unit _33A of the earth station _1C1 receives the radio wave _RD1 and generates the communication control data _CC2 . The satellite communication IF unit 50 that received the communication control data _CC2 transfers it to the communication control data processing unit 57C. In step S38C, the communication control data processing unit 57C extracts the communication terminal _{32 ,} which is the request destination communication terminal, and the encryption key _CK2 from the communication control data CC2, and starts the encryption key decryption key management unit 55C. In step S39, the encryption key decryption key management unit 55C stores the encryption key _CK2 in the encryption key used 90C as the encryption key of the U-Plane side (series A) of the communication terminal ₃₂ .

21, the procedure of the process in which the earth station 1C1 converts user data _UD1 to be transmitted from the communication terminal ₃₁ of S03C to the communication terminal ₃₂ into encrypted user data _CD1 and radiates the data as radio waves _RU1 toward the high altitude pseudo satellite ₉₁ will be described. The points in FIG. 21 that differ from FIG. 7 in the case of the earth station _{11 will} be described.

The earth station 1C determines and manages an encryption key for each source communication terminal. The earth station 1C determines and manages a decryption key for each source communication terminal. In step S43C, the encryption device control unit 56C refers to the encryption key in use 90C and obtains the encryption key _CK2 of the communication terminal _32. In step S44C, the encryption device control unit 56C instructs the encryption device 15C to encrypt the user data _UD1 with the encryption key _CK2 , and the encryption device 15C generates encrypted user data _CD1 .

In step S46C, the satellite communication unit _33A of the earth station _1C1 radiates the encrypted user data _CD1 as radio waves _RU1 toward the high altitude pseudo satellite _91. Specifically, the modem _13A of the satellite communication unit _33A of the earth station _1C1 generates a transmission signal _SS1 by modulating the encrypted user data _CD1 . The frequency converter _12A converts the frequency of the transmission signal _SS1 . The antenna device _11A radiates the frequency-converted transmission signal _SS1 toward the high altitude pseudo satellite ₉₁ as radio waves _RU1 .

22, a process procedure will be described in which the earth station _1C2 receives radio waves _RD2 , demodulates and decodes the radio waves _RD2 , generates user data _UD1 , and transmits the generated data to the communication terminal _32. The differences between the process shown in FIG. 22 and the process shown in FIG. 8 for the earth station ₁₁ will be described.

In step S53C, the encryption device control unit 56C of the earth station _1C2 refers to the decryption key 89C and acquires the decryption key _DK2 of the communication terminal _32. In step S54C, the encryption device control unit 56C instructs the encryption device 15C to decrypt the encrypted user data _CD1 with the decryption key _DK2 , and the encryption device 15C generates user data _UD1 .

With reference to Fig. 23, a process procedure will be described in which the earth station _1C2 converts user data _UD2 transmitted from the communication terminal ₃₂ to the communication terminal ₃₁ into encrypted user data _CD2 in S06C and radiates the data as radio waves _RU2 toward the high altitude pseudo satellite _92. Fig. 23 is similar to Fig. 21. Regarding Fig. 23, the differences from Fig. 9 in the case of the earth station ₁₁ will be described.

In step S63C, the encryption device control unit 56C refers to the encryption key in use 90C and obtains the encryption key _CK1 of the communication terminal _3.1 . In step S64C, the encryption device control unit 56C instructs the encryption device 15C to encrypt the user data _UD2 with the encryption key _CK1 , and the encryption device 15C generates encrypted user data _CD2 .

In step S66C, the satellite communication unit _33A radiates the encrypted user data _CD2 as radio waves _RU2 toward the high altitude pseudo satellite _92. Specifically, the modem _13A of the satellite communication unit _33A of the earth station _1C2 generates a transmission signal _SS2 by modulating the encrypted user data _CD2 . The frequency converter _12A converts the frequency of the transmission signal _SS2 . The antenna device _11A radiates the frequency-converted transmission signal _SS2 toward the high altitude pseudo satellite ₉₂ as radio waves _RU2 .

With reference to Fig. 24, the procedure of the process in S08C in which the earth station _1C1 receives the radio wave _RD1 , demodulates and decodes the radio wave _RD1 to generate user data _UD2 and transmits it to the communication terminal ₃₁ will be described. Fig. 24 is similar to Fig. 22. Regarding Fig. 24, the differences from Fig. 10 in the case of the earth station ₁₁ will be described.

In step S73C, the encryption device control unit 56C of the earth station _1C1 refers to the decryption key 89C and acquires the decryption key _DK1 of the communication terminal _31. In step S74C, the encryption device control unit 56C instructs the encryption device 15C to decrypt the encrypted user data _CD2 with the decryption key _DK1 , and the encryption device 15C generates user data _UD2 .

25, a process procedure _will be described in which the earth station _1C1 transmits the communication control data _CC1 to the earth station _1C2 in S09C as radio waves _RUC1 to the low earth orbit satellite _41. The points in FIG. 25 that are different from FIG. 11 for the earth station _1C1 will be described.

In step S86C, the satellite communication unit _33A of the earth station _1C1 radiates the communication control data _CC1 as radio waves _RUC1 toward the low earth orbit satellite _41. Specifically, the modem _13A of the satellite communication unit _33A of the earth station _1C1 modulates the communication control data _CC1 to generate a transmission signal _SS1 . The frequency converter _12A converts the frequency of the transmission signal _SS1 . The antenna device _11A radiates the frequency-converted transmission signal _SS1 toward the low earth orbit satellite ₄₁ as radio waves _RUC1 .

With reference to Fig. 26, the procedure of processing in S12C in _{which the earth station 1C2 transmits communication control data CC2 to the earth station 1C1 as radio waves RUC2 to the low earth orbit satellite 42 will be described . Fig} . 26 is similar to Fig. 25. Regarding Fig. 26, the differences from Fig. 13 in the case of the earth station ₁₁ will be described.

In step S96C, the satellite communication unit _33A of the earth station _1C2 radiates the communication control data _CC2 as radio waves _RUC2 toward the low-earth orbit satellite _42. Specifically, the modem _13A of the satellite communication unit _33A of the earth station _1C2 modulates the communication control data _CC2 to generate a transmission signal _SS2 . The frequency converter _12A converts the frequency of the transmission signal _SS2 . The antenna device _11A radiates the frequency-converted transmission signal _SS2 toward the low-earth orbit satellite ₄₂ as radio waves _RUC2 .

The earth station 1C encrypts the user data and communicates it over the high-altitude pseudo satellite communication line 21. The earth station 1C communicates the encryption key and decryption key for encrypting the user data over the low-altitude satellite communication line 6. Therefore, even if the user data communicated over the high-altitude pseudo satellite communication line 21 is intercepted, the contents of the user data will not be known because it has been encrypted. Since the encryption key and decryption key are communicated over the low-altitude satellite communication line 6, the encryption key and decryption key will not be leaked even if the high-altitude pseudo satellite communication line 21 over which the user data is communicated is intercepted. Since user data is not communicated over the low-altitude satellite communication line 6, the contents of the user data will not be known even if the low-altitude satellite communication line 6 is intercepted.

Earth station 1C does not require terrestrial infrastructure facilities. Earth station 1C can easily expand the communication area in a mobile communication system.

Earth station 1C allows the sender and receiver to share an encryption key (including a decryption key) without using other communication systems. Earth station 1C can communicate encrypted user data.

Earth station 1C uses public key cryptography and does not communicate the decryption key (private key). Earth station 1C can manage the decryption key more securely than earth station 1, which uses common key cryptography.

The earth station 1C can select a first extra-troposphere communication line and a second extra-troposphere communication line from at least three types of extra-troposphere communication lines relayed by relay stations mounted on extra-troposphere mobile bodies moving at at least three altitudes included in the troposphere, so that if there is a malfunction in the first extra-troposphere communication line or the second extra-troposphere communication line, communication can be performed using the other extra-troposphere communication line.

Embodiment 3.
The third embodiment is an embodiment in which the second embodiment is modified so that a set of a phased array antenna device and a satellite communication unit are used in a time-division manner. In a satellite communication system 100D, the earth station 1D is modified. The configuration of the earth station 1D will be described with reference to Fig. 27. Fig. 27 is a diagram showing the configuration of a communication device (earth station 1D) according to the third embodiment. Regarding Fig. 27, the points different from Fig. 16 in the second embodiment will be described. The first embodiment or other embodiments may be modified so that a set of a phased array antenna device and a satellite communication unit are used in a time-division manner.

The earth station 1D has a receiving antenna device 17 and a transmitting antenna device 18 instead of the antenna devices _11A and _11B . The receiving antenna device 17 and the transmitting antenna device 18 are phased array antennas. The phased array antenna can electrically change its direction of orientation at high speed. The receiving antenna device 17 and the transmitting antenna device 18 alternate between a period in which they track an extratropospheric mobile object (extratropospheric mobile object A) stored in the communicating satellite _80A and a period in which they track an extratropospheric mobile object (extratropospheric mobile object B) stored in the communicating satellite _80B . During the period in which they track the extratropospheric mobile object A, the earth station 1D communicates through an extratropospheric communication line A relayed by a relay station mounted on the extratropospheric mobile object A. During the period in which they track the extratropospheric mobile object B, the earth station 1D communicates through an extratropospheric communication line B relayed by a relay station mounted on the extratropospheric mobile object B. In the earth station _1D1 , the extra-tropospheric mobile body A is a high-altitude pseudo satellite ₉₁ , and the extra-tropospheric mobile body B is a low-earth orbit satellite _41. In the earth station _1D2 , the extra-tropospheric mobile body A is a high-altitude pseudo satellite ₉₂ , and the extra-tropospheric mobile body B is a low-earth orbit satellite _42. The extra-tropospheric mobile body A and the extra-tropospheric mobile body B may be selected from at least two types of extra-tropospheric mobile bodies. The extra-tropospheric mobile body A and the extra-tropospheric mobile body B may be interchanged.

To enable the earth station 1D to operate in a time-division manner, a time-division control unit 60 and transmission buffers _34A and _34B are added, and the frequency converter 12D, the modem 13D, the satellite communication IF unit 50D, the tracking control unit 52D, and the data storage unit 58D are modified. The receiving antenna unit 17, the transmitting antenna unit 18, the frequency converter 12D, and the modem 13D constitute a set of satellite communication unit 33D. The satellite communication unit 33D operates in a time-division manner as satellite communication unit _33A or satellite communication unit _33B .

During the period when the satellite communication unit 33D operates _as the satellite communication unit _33A , the satellite communication unit 33D operates to communicate through the high altitude pseudo satellite communication line _21-1 at the earth station 1D-1, and the satellite communication unit 33D operates to communicate through the high altitude pseudo satellite communication line _21-2 at the earth station 1D _-2 .

During the period when the satellite communication unit 33D operates as the satellite communication unit _33B , the satellite communication unit 33D operates so as to communicate with the earth station _1D1 via the low earth orbit satellite communication link ₆₁ , and the satellite communication unit 33D operates so as to communicate with the earth station _1D2 via the low earth orbit satellite communication link _62. The satellite communication unit 33D may be considered not to include the receiving antenna device 17 and the transmitting antenna device 18.

The time-division control unit 60 controls the receiving antenna device 17, the transmitting antenna device 18, the frequency converter 12D, and the modem 13D to operate in a time-division manner. The tracking control unit 52D controls the receiving antenna device 17 and the transmitting antenna device 18 to track the extratropical mobile object A during the period when communication is performed via the extratropical communication line A. The tracking control unit 52D controls the receiving antenna device 17 and the transmitting antenna device 18 to track the extratropical mobile object B during the period when communication is performed via the extratropical communication line B.

The data processor 14D operates in the same manner as the data processor 14. Since the modulator/demodulator 13D operates in a time-division multiplexing manner, transmission buffers _34A and _34B are provided between the output from the data processor 14D and the modulator/demodulator 13D.

The receiving antenna device 17 has a receiving antenna section 62 having multiple element receiving antennas 61, and an element receiving signal processing section 63 that processes element receiving signals received by the element receiving antennas 61. The transmitting antenna device 18 has a transmitting antenna section 65 having multiple element transmitting antennas 64, and an element transmitting signal generating section 66 that generates element transmitting signals transmitted by the element transmitting antennas 64.

The element reception signal processing unit 63 has an output terminal 67, a synthesis circuit 68, and a reception module 69 provided for each element reception antenna 61. The output terminal 67 is connected to the frequency converter 12D. In other words, the reception antenna device 17 is connected to the frequency converter 12D. The element reception signal generated by the element reception antenna 61 upon receiving radio waves is input to the reception module 69. The signals output by the multiple reception modules 69 are synthesized by the synthesis circuit 68 and output from the output terminal 67.

The element transmission signal generating unit 66 has an input terminal 70, a distribution circuit 71, and a transmission module 72 provided for each element transmission antenna 64. The input terminal 70 is connected to the frequency converter 12D. That is, the transmission antenna device 18 is connected to the frequency converter 12D. The transmission signal input to the input terminal 70 is distributed by the distribution circuit 71 and input to multiple transmission modules 72. The element transmission signal output by the transmission module 72 is input to the element transmission antenna 64. The element transmission antenna 64 radiates the input element transmission signal into space as a radio wave.

The element reception signal processing unit 63 synthesizes the element reception signals output by each element reception antenna 61 by changing the phase for each element reception antenna 61. The amount of phase change is determined according to the direction of orientation, the position of the element reception antenna 61 in the entire reception antenna unit 62, and the reception frequency. By changing the phase of multiple element reception signals and synthesizing them, the reception antenna unit 62 has directionality and can receive radio waves from the direction of orientation (reception direction). The reception antenna unit 62 can change its direction of orientation while remaining stationary. Changing the direction of orientation while the antenna remains stationary is called electronically changing the direction of orientation. To change the direction of orientation electronically, the reception module 69 has a phase shifter 73 and an amplifier 74. The amount of phase change (phase shift amount) by which the phase shifter 73 changes is input from the tracking control unit 52D.

By controlling the phase of the radio waves emitted by each of the multiple element transmitting antennas 63, the transmitting antenna unit 65 can emit radio waves in a determined directional direction (transmission direction). The phase of the element transmitting signal input to each element transmitting antenna 3 is determined according to the position of that element transmitting antenna 64 within the entire transmitting antenna unit 65 and the transmission frequency. The element transmitting signal generating unit 66 generates an element transmitting signal that can emit radio waves of the transmission frequency in a determined directional direction. The corresponding element transmitting antenna 3 emits the generated element transmitting signal into space as a radio wave. The transmitting module 72 has a phase shifter 75 and an amplifier 76. The amount of phase shift of the phase shifter 75 is input from the tracking control unit 52D.

The transmission buffers _34A and _34B are buffers for temporarily storing transmission data so that the modem 13D operates in a time-division manner. The transmission buffer _34A buffers transmission data transmitted through an extra-troposphere communication line relayed by an extra-troposphere mobile body A. The transmission buffer _34B buffers transmission data transmitted through an extra-troposphere communication line relayed by an extra-troposphere mobile body B.

The satellite communication IF unit 50D outputs the user data encrypted by the encryption device 15C or the communication control data that is not encrypted to the transmission buffer _34A or the transmission buffer _34B according to the type of data. The satellite communication IF unit 50D outputs the encrypted user data to the transmission buffer _34A . The satellite communication IF unit 50D outputs the communication control data to the transmission buffer _34B . The satellite communication unit 33D takes in the transmission data from the transmission buffer _34A while operating as the satellite communication unit _33A . The satellite communication unit 33D takes in the transmission data from the transmission buffer _34B while operating as the satellite communication unit _33B . The data decoded by the modem 13D is input to the satellite communication IF unit 50D. The satellite communication IF unit 50D judges whether the data packet is encrypted user data or communication control data based on the packet type stored in the data packet.

The data storage unit 58D also has time-division control data 93. The time-division control data 93 is data that indicates the period during which the satellite communication unit 33D and the tracking control unit 52D operate in a time-division manner. The time-division control unit 60 and the tracking control unit 52D refer to the time-division control data 93 and control the receiving antenna device 17, the transmitting antenna device 18, the frequency converter 12D, and the modem 13D to operate in a time-division manner.

The time division control unit 60 controls the frequency converter 12D and the modem 13D so as to communicate in a time division manner through the high altitude pseudo satellite communication line 21 and the low earth orbit satellite communication line 6. During a period (first communication period) during which communication is performed through the high altitude pseudo satellite communication line 21, which is the first extratroposphere communication line, the time division control unit 60 controls the frequency converter 12D to convert between the frequency used in the high altitude pseudo satellite communication line 21 and the frequency of the signal processed by the modem 13D. The signal demodulated by the modem 13D is input to the satellite communication IF unit 50D without buffering. During the first communication period, the time division control unit 60 controls the data modulated by the modem 13D to be obtained from the transmission buffer _34A . The first communication period is a period during which the modem 13D and the frequency converter 12D are used as the first extratroposphere communication unit. Also, the receiving antenna device 17, the transmitting antenna device 18, the frequency converter 12D and the modem 13D in the first communication period can be considered to constitute a satellite communication section _33A .

During a period (second communication period) during which communication is performed using the low-earth orbit satellite communication line 7, which is the second extratroposphere communication line, the time-division control unit 60 controls the frequency converter 12D to convert between the frequency used in the low-earth orbit satellite communication line 7 and the frequency of the signal processed by the modem 13D. During the second communication period, the time-division control unit 60 controls the frequency converter 12D to obtain data modulated by the modem 13D from the transmission buffer _34B . The second communication period is a period during which the modem 13D and the frequency converter 12D are used as the second extratroposphere communication unit. In addition, the receiving antenna device 17, the transmitting antenna device 18, the frequency converter 12D, and the modem 13D during the second communication period can be considered to constitute the satellite communication unit _33B .

The tracking control unit 52D controls the receiving antenna device 17 and the transmitting antenna device 18 to track the high altitude pseudo satellite 9, which is the first extratroposphere mobile body, during the first communication period, and controls the receiving antenna device 17 and the transmitting antenna device 18 to track the second extratroposphere mobile body, which is the first extratroposphere mobile body, during the second communication period.

In the first communication period, the tracking control unit 52D calculates the phase shift amount of the phase shifter _73A of the receiving module _69A that processes the element receiving signal received by the element receiving antenna 61 based on the satellite existence direction _87A , the receiving frequency _81A , and the arrangement of each element receiving antenna 61 in the entire receiving antenna unit 62, and controls each receiving module _69A to change the phase by the calculated phase shift amount. Here, the satellite existence direction _87A stores the direction in which the high altitude pseudo satellite 9 exists. The receiving frequency _81A and the transmitting frequency _82A store the receiving frequency and transmitting frequency used in the high altitude pseudo satellite communication line 21.

In the first communication period, the tracking control unit 52D calculates the amount of phase shift of the phase shifter 75 of the transmitting module _72A that outputs the element transmission signal input to the element transmitting antenna 63 based on the satellite presence direction _87A , the transmission frequency _82A , and the arrangement of each element transmitting antenna 63 within the entire transmitting antenna unit 64, and controls each transmitting module _72A to change the phase by the calculated amount of phase shift.

In the second communication period, the tracking control unit 52D calculates the phase shift amount of the phase shifter _73B of the receiving module _69B that processes the element receiving signal received by the element receiving antenna 61 based on the satellite presence direction _87B , the receiving frequency 81B, and the arrangement of each element receiving antenna ₆₁ within the entire receiving antenna unit 62, and controls each receiving module _69B to change the phase by the calculated phase shift amount. Here, the satellite presence direction _87B stores the direction in which the low earth orbit satellite 4 exists. The receiving frequency _81B and the transmitting frequency _82B store the receiving frequency and the transmitting frequency used in the low earth orbit communication line 6.

In the second communication period, the tracking control unit 52D calculates the amount of phase shift of the phase shifter _75B of the transmitting module _72B that outputs the element transmission signal input to the element transmitting antenna 63 based on the satellite presence direction _87B , the transmission frequency 82B, and the arrangement of each element transmitting antenna ₆₃ within the entire transmitting antenna unit 64, and controls each transmitting module _72B to change the phase by the calculated amount of phase shift.

28 and 29 are flow charts for explaining an outline of a procedure when a communication terminal _3-1 connected to an earth station 1D- ₁ communicates with a communication terminal _3-2 connected to an earth station 1D _-2 . Regarding Figs. 28 and 29, the points different from Figs. 17 and 18 in the case of the wireless communication system 100C will be explained.

Because it operates in a time-division manner, during the first communication period, the processes from S03C to S05C and the processes from S06C to S08C are executed in parallel. During the second communication period, the processes from S09C to S11 and the processes from S12C to S14 are executed in parallel.

Regarding the communication from earth station 1D- ₁ to earth station 1D- ₂ , step S15 is added between S03C and S09C to check whether the first communication period has ended. If the first communication period has not ended (NO in S15), return to S03C. If the first communication period has ended (YES in S15), proceed to S09C. After S11, step S16 is added to check whether the second communication period has ended. If the second communication period has not ended (NO in S16), return to S09C. If the first communication period has ended (YES in S16), return to S03C.

The operation in S03C is similar to that in the flowcharts of Figures 19 to 26 which explain the operation of the earth station 1C, except that satellite communication unit _33A is replaced with satellite communication unit 33D in the first communication period, and satellite communication unit _33B is replaced with satellite communication unit 33D in the first communication period.

Regarding the communication from earth station _1D2 to earth station _1D1 , step S17 is added between S06C and S12C to check whether the first communication period has ended. If the first communication period has not ended (NO in S17), return to S06C. If the first communication period has ended (YES in S17), proceed to S12C. After S14, step S18 is added to check whether the second communication period has ended. If the second communication period has not ended (NO in S18), return to S12C. If the first communication period has ended (YES in S18), return to S06C.

The earth station 1D operates in the same manner as the earth station 1C, except that it communicates in a time-division manner, and can provide the same effects.
The earth station 1D allows the sender and receiver to share an encryption key (including a decryption key) without using another communication system. The earth station 1D can communicate encrypted user data. Since the second extra-troposphere communication line for communicating the encryption key and the first extra-troposphere communication line for communicating the encrypted user data are separate, the contents of the user data will not be revealed even if only one of them is intercepted.

By using the receiving antenna device 17 and the transmitting antenna device 18, which are phased array antennas, the size of the earth station can be made more compact than when two mechanically driven antenna devices are used.

Embodiment 4.
The fourth embodiment is an embodiment in which the second embodiment is modified so as to use a pair of phased array antennas for transmitting and receiving radio waves in two directions that can be changed independently of each other. The encryption method is changed to a common key encryption method. In the satellite communication system 100E, the earth station 1E is changed. The configuration of the earth station 1E will be described with reference to Fig. 30. Fig. 30 is a diagram showing the configuration of a communication device (earth station 1E) according to the fourth embodiment. Regarding Fig. 30, the points different from Fig. 16 in the second embodiment will be described.

The earth station 1E has a receiving antenna device 17E and a transmitting antenna device 18E instead of the antenna devices _11A and _11B . The receiving antenna device 17E and the transmitting antenna device 18E are phased array antennas. The receiving antenna device 17E receives radio waves from two directions that can be changed independently of each other. The transmitting antenna device 18E transmits radio waves in two directions that can be changed independently of each other. The earth station 1E has a modified tracking control unit 52E in the data processing device 14E.

The receiving antenna device 17E has a receiving antenna section 62 having multiple element receiving antennas 61, and an element receiving signal processing section 63E that processes the element receiving signals received by the element receiving antennas 61.

The element reception signal processing unit 63E has output terminals _67A , _67B , synthesis circuits _68A , _68B , and two reception modules _69A , _69B provided for each element reception antenna 61. An element reception signal generated by the element reception antenna 61 receiving radio waves is input to each of the reception modules _69A , _69B . The signals output from the multiple reception modules _69A are synthesized by the synthesis circuit _68A and output from the output terminal _67A . The output terminal _67A is connected to the frequency converter _12A . The signals output from the multiple reception modules _69B are synthesized by the synthesis circuit _68B and output from the output terminal _67B . The output terminal _67B is connected to the frequency converter _12B . The reception module _69A has a phase shifter _73A and an amplifier _74A . The reception module _69B has a phase shifter _73B and an amplifier _74B . The amount of phase shift in each of the phase shifters _73A and _73B can be controlled. The amplification factor of each of the amplifiers _74A and _74B can be controlled.

In the element received signal processing unit 63E, the output terminal _67A , the combining circuit _68A , and the receiving module _69A are referred to as the series A element received signal processing unit 63E. The output terminal _67B , the combining circuit _68B , and the receiving module _69B are referred to as the series B element received signal processing unit 63E.

The receiving antenna device 17E outputs a receiving signal of a first receiving frequency from a first receiving direction that can be electronically changed by controlling the amount of phase shift in each phase shifter 73 _A. The receiving antenna device 17E outputs a receiving signal of a second receiving frequency different from the first receiving frequency from a second receiving direction that can be electronically changed independently of the first receiving direction by controlling the amount of phase shift in each phase shifter 73 _B.

The receiving antenna device 17E receives radio waves with different frequencies from two different directions. The receiving antenna device 17E can be considered to have two series of receiving antenna devices 17E. The receiving antenna device 17E of series A is composed of a receiving antenna section 62 and a series A element receiving signal processing section 63E. The receiving antenna device 17E of series B is composed of a receiving antenna section 62 and a series B element receiving signal processing section 63E.

The transmitting antenna device 18E has a transmitting antenna section 65 having a plurality of element transmitting antennas 64, and an element transmitting signal generating section 66E that generates element transmitting signals transmitted by the element transmitting antennas 64.

The element transmission signal generating unit 66E has input terminals _70A and _70B , distribution circuits _71A and _71B , and two transmission modules _72A and _72B provided for each element transmission antenna 64. The input terminal _70A is connected to the frequency converter _12A . The transmission signal input to the input terminal _70A is distributed by the distribution circuit _71A and input to the multiple transmission modules _72A . The input terminal _70B is connected to the frequency converter _12B . The transmission signal input to the input terminal _70B is distributed by the distribution circuit _71B and input to the multiple transmission modules _72B . The element transmission signals output by the transmission modules _72A and _72B are input to the element transmission antenna 64. The element transmission antenna 64 radiates the input element transmission signal into space as a radio wave. The transmission module _72A has a phase shifter _75A and an amplifier _76A . The transmitting module _72B has a phase shifter _75B and an amplifier _76B . The amount of phase shift in each of the phase shifters _75A and _75B can be controlled. The amplification factor of each of the amplifiers _76A and _76B can be controlled.

In the element transmission signal generation unit 66E, the input terminal _70A , distribution circuit _71A , and transmission module _72A are referred to as the series A element transmission signal generation unit 66E. The input terminal _70B , distribution circuit _71B , and transmission module _72B are referred to as the series B element transmission signal generation unit 66E.

The transmitting antenna device 18E can radiate radio waves of a first transmission frequency in a first transmission direction that can be electronically changed by controlling the amount of phase shift in each phase shifter 75 _A. The transmitting antenna device 18E can radiate radio waves of a second transmission frequency in a second transmission direction that can be electronically changed independently of the first transmission direction by controlling the amount of phase shift in each phase shifter 75 _B.

The transmitting antenna device 18E transmits radio waves with different frequencies in two different directions. The transmitting antenna device 18E can be considered to have two series of transmitting antenna devices 18E. The transmitting antenna device 18E of series A is composed of a transmitting antenna unit 64 and a series A element transmission signal generation unit 66E. The transmitting antenna device 18E of series B is composed of a transmitting antenna unit 64 and a series B element transmission signal generation unit 66E.

The receiving antenna device 17E and transmitting antenna device 18E of series A, the frequency converter _12A , and the modulator/demodulator _13A can be considered to constitute a set of satellite communication unit 33E _A. The receiving antenna device 17E and transmitting antenna device 18E of series B, the frequency converter _12B , and the modulator/demodulator _13B can be considered to constitute a set of satellite communication unit 33E _B.

The satellite existence directions _87A and _87B store the directions in which the extratropospheric mobile body A and the extratropospheric mobile body B exist. Here, in the earth station _1E1 and the earth station _1E2 , it is assumed that the sequence A is the U-Plane and the sequence B is the C-Plane. Since user data is communicated in the U-Plane, the extratropospheric mobile body A is the first extratropospheric mobile body. The extratropospheric mobile body B is the second extratropospheric mobile body. In addition, when the sequence A is the C-Plane and the sequence B is the U-Plane, the extratropospheric mobile body A is the second extratropospheric mobile body and the extratropospheric mobile body B is the first extratropospheric mobile body. The extratropospheric mobile body A and the extratropospheric mobile body B may be of different types. For example, the extratropospheric mobile body A may be a geostationary satellite 5 and the extratropospheric mobile body B may be a high altitude pseudo satellite 9.

The reception frequency and transmission frequency used in the first extra-troposphere communication line are stored in the reception frequency _81A and the transmission frequency _82A . That is, the first reception frequency is stored in the reception frequency _81A , and the first transmission frequency is stored in the transmission frequency _82A . The reception frequency and transmission frequency used in the first extra-troposphere communication line are stored in the reception frequency _81B and the transmission frequency _82B . That is, the second reception frequency is stored in the reception frequency _81B , and the second transmission frequency is stored in the transmission frequency _82B .

In the earth station 1E, the line control unit 51C is a frequency setting unit that sets the first reception frequency and the first transmission frequency to the reception frequency and transmission frequency of the first extra-troposphere communication line, respectively, and sets the second reception frequency and the second transmission frequency to the reception frequency and transmission frequency of the second extra-troposphere communication line, respectively.

The tracking control unit 52E controls the receiving antenna device 17E and the transmitting antenna device 18E to track the extra-troposphere mobile body A and the extra-troposphere mobile body B. That is, the tracking control unit 52E controls the first receiving direction and the first transmitting direction to match the direction in which the extra-troposphere mobile body A exists. The direction in which the extra-troposphere mobile body A exists is stored in the satellite presence direction _87A . The tracking control unit 52E controls the second receiving direction and the second transmitting direction to match the direction in which the extra-troposphere mobile body B exists. The direction in which the extra-troposphere mobile body B exists is stored in the satellite presence direction _87B .

Specifically, the tracking control unit 52E performs control as follows.
(a) The tracking control unit 52E calculates the amount of phase shift of the phase shifter 73A of each receiving module _69A so that the direction in which the extratroposphere moving body _A exists coincides with the first receiving direction, and inputs the calculated amount of phase shift to the phase shifter _73A . The tracking control unit 52E calculates the amount of phase shift in each receiving module _69A based on the first receiving direction, the first receiving frequency, and the arrangement, within the entire receiving antenna unit 62, of the element receiving antennas 61 that output the element receiving signals processed by each receiving module _69A .

(b) The tracking control unit 52E calculates the amount of phase shift of the phase shifter _75A of each transmitting module _72A so that the direction in which the extra-troposphere moving body A exists coincides with the first transmitting direction, and inputs the calculated amount of phase shift to the phase shifter _75A . The tracking control unit 52E calculates the amount of phase shift in each transmitting module _72A based on the first transmitting direction, the first transmitting frequency, and the arrangement, within the entire transmitting antenna unit 64, of the element transmitting antennas 63 that output the element received signals processed by each transmitting module _72A .

(c) The tracking control unit 52E calculates the amount of phase shift of the phase shifter _73B of each receiving module _69B so that the direction in which the extratroposphere moving body B exists coincides with the second receiving direction, and inputs the calculated amount of phase shift to the phase shifter _73B . The tracking control unit 52E calculates the amount of phase shift in each receiving module _69B based on the second receiving direction, the second receiving frequency, and the arrangement, within the entire receiving antenna unit 62, of the element receiving antennas 61 that output the element receiving signals processed by each receiving module _69B .

(d) The tracking control unit 52E calculates the amount of phase shift of the phase shifter _75B of each transmitting module 72B so that the direction in which the extra-troposphere moving body B exists coincides with the second transmitting direction, and inputs the calculated amount of phase shift to the phase _{shifter 75B} . The tracking control unit 52E calculates the amount of phase shift in each transmitting module _72B based on the second transmitting direction, the second transmitting frequency, and the arrangement, within the entire transmitting antenna unit 64, of the element transmitting antennas 63 that output the element received signals processed by each transmitting module _72B .

The earth station 1E operates in the same manner as the earth station 1C, and provides the same effects. However, the earth station 1E differs from the earth station 1C in that it uses a common key cryptosystem. Also, in the flowcharts of Figures 17 to 26 which explain the operation of the earth station 1C, the satellite communication units _33A and _33B are replaced with satellite communication units _33EA and _33EB .

Earth station 1E allows the sender and receiver to share an encryption key (including a decryption key) without using other communication systems. Earth station 1E can communicate encrypted user data. Since the second extra-troposphere communication line for communicating the encryption key and the first extra-troposphere communication line for communicating the encrypted user data are separate, the contents of the user data will not be known even if only one of them is intercepted.

By using the receiving antenna unit 17E and the transmitting antenna unit 18E, which are phased array antennas, the size of the earth station can be made more compact than when two mechanically driven antenna units are used.

The receiving antenna device 17E can output a reception signal of radio waves received from two directions that can be controlled independently. The transmitting antenna device 18E can transmit radio waves in two directions that can be controlled independently. Therefore, the receiving antenna device 17E and the transmitting antenna device 18E do not require time-division control. In the earth station 1E, control of the receiving antenna device and the transmitting antenna device is simpler than in the earth station 1D. The receiving antenna device 17E and the transmitting antenna device 18E can always communicate user data and communication control data in parallel.

Embodiment 5.
In the fifth embodiment, a high altitude pseudosatellite does not communicate with other high altitude pseudosatellites, but communicates with the communication device (earth station) according to the second embodiment, which has been changed to a common key cryptosystem. Figure 31 is a diagram showing a schematic configuration of a satellite communication system including a communication device according to the fifth embodiment. The points in Figure 31 that are different from Figure 15 in the second embodiment will be described.

In the satellite communication system 100F, earth stations _1F1 , _1F2 , and _1F3 have been changed, and a high altitude pseudo satellite 9 does not communicate with other high altitude pseudo satellites 9. The satellite communication system 100F has a terrestrial core network 40, terrestrial core network devices ₄₁₁ , ₄₁₂ , terrestrial networks ₄₂₁ , ₄₂₂ , a geostationary satellite earth station 43, a low earth orbit satellite earth station 44, high altitude pseudo satellite earth stations ₄₅₁ , ₄₅₂ , and an earth station 46. A communication terminal ₃₃ is connected to the earth station _1F3 via a network ₂₃ .

A communication terminal _3-4 is connected to the earth station 46 via a network _2-4 . The earth station 46 does not have an antenna device for communication through an extratroposphere communication line. The earth station 46 has an encryption device and can decrypt encrypted user data encrypted by the earth station 1F and generate encrypted user data that can be decrypted by the earth station 1F.

The earth station 1F ₁ can communicate with the earth stations 1F ₂ , 1F ₃ and the earth station 46. The earth station 1F ₂ communicates with the low-earth orbit satellite 4 ₁ using the low-earth orbit satellite communication link 6 _2. The earth station 1F ₂ communicates with the high-earth orbit pseudo satellite 9 ₁ using the high-earth orbit pseudo satellite communication link 21 _2. The earth station 1F ₃ communicates with the geostationary satellite 5 using the geostationary satellite communication link 8 _3. The earth station 1F ₃ communicates with the low-earth orbit satellite 4 ₂ using the low-earth orbit satellite communication link 6 _3. The earth station 1F ₃ communicates with the high-earth orbit pseudo satellite 9 ₂ using the high-earth orbit pseudo satellite communication link 21 ₃ .

The terrestrial core network 40 is a network of large-capacity communication lines laid on the ground. The terrestrial core network devices _41.sub.1 and _41.sub.2 connect the terrestrial core network 40 to other terrestrial networks _42.sub.1 and _42.sub.2 , respectively. The terrestrial network _42.sub.1 is connected to a geostationary satellite ground station 43, a low-earth orbit satellite ground station 44, and a high-altitude pseudo satellite ground station _45.sub.1 . The terrestrial network _42.sub.2 is connected to a high-altitude pseudo satellite ground station _45.sub.2 and an earth station 46.

The geostationary satellite ground station 43 enables communication between communication devices (such as earth stations 46) connected to the terrestrial network 42 (including those via the terrestrial core network 40) and the geostationary satellite 5. The geostationary satellite ground station 43 communicates with the geostationary satellite 5 using a geostationary satellite communication line _8-4 . The low-orbit satellite ground station 44 enables communication between communication devices connected to the terrestrial network 42 and the low-orbit satellite 4. The low-orbit satellite ground station 44 enables communication with the low-orbit satellite _4-1 using a low-orbit satellite communication line _6-4 . The high-orbit pseudosatellite ground station _45-1 enables communication between communication devices connected to the terrestrial network 42 and the high-orbit pseudosatellite _9-1 . The high-orbit pseudosatellite ground station _45-1 communicates with the high-orbit pseudosatellite _9-1 using a high-orbit pseudosatellite communication line _21-4 . The high-orbit pseudosatellite ground station _45-2 enables communication between communication devices connected to the terrestrial network 42 and the high-orbit pseudosatellite _9-2 . The high altitude pseudolite ground station 45 ₂ communicates with the high altitude pseudolite 9 ₂ using the high altitude pseudolite communication link 21 ₅ .

Because there is a low-earth-orbit satellite ground station 44, earth station 46 and earth station 1F can use the low-earth-orbit satellite communication line 6 to communicate an encryption key for encrypting and a decryption key for decrypting the user data to be communicated.

Earth station 1F modifies earth station 1C so that it uses a public key cryptosystem. The configuration of earth station 1F will be described with reference to FIG. 32. FIG. 32 is a diagram showing the configuration of a communication device (earth station 1F) according to embodiment 5. Regarding FIG. 32, the differences from FIG. 16 in embodiment 2 will be described. Earth station 1F modifies the encryption device 15, encryption key and decryption key management unit 55, communication control data processing unit 57, and data storage unit 58F. The encryption device 15, encryption key and decryption key management unit 55, and communication control data processing unit 57 are the same as those possessed by earth station 1.

The data storage unit 58F does not have a decryption key 89C, an encryption key in use 90C, or a corresponding encryption key 91C, but has an encryption key 89 and a decryption key 90. Compared to the data storage unit 58, the data storage unit 58F has moving object types _92A and _92B added thereto.

The operation will be described. First, a case will be described in which a communication terminal ₃₁ connected to an earth station _1F1 communicates with a communication terminal ₃₂ connected to an earth station _1F2 . The earth station _1F1 and the earth station _1F2 communicate with the same high altitude pseudo satellite _91. Figures 33 and 34 are flow charts for explaining an outline of a procedure in which a communication terminal ₃₁ connected to _an earth station 1F1 communicates with a communication terminal ₃₂ connected to an earth station _1F2 . Figure 33 illustrates the process up to step S08F, and Figure 34 illustrates the process from step S09C. The process from S09C shown in Figure 34 onwards is the same as that in Figure 18.

In earth station _1F1 and earth station _1F2 , satellite communication unit _33A of series A communicates through a communication line relayed by high altitude pseudo satellite 9, and satellite communication unit _33B of series B communicates through a communication line relayed by low earth orbit satellite 4. In earth station _1F1 and earth station _1F2 , series A is assumed to be the U-Plane and series B is assumed to be the C-Plane.

Regarding Figures 33 and 34, the differences from Figures 17 and 18 in the case of the earth station 1C will be described. In step S02F, the earth station _1F1 and earth station _1F2 determine the encryption key and decryption key to be used for the communication between the communication terminal ₃₁ and the communication terminal ₃₂ , and store them in the data storage unit 58. The process of S02F differs from S02C only in that an encryption key according to a common key cryptosystem is determined. The process of S02F is the same as the process of S02, except that a low-earth orbit satellite communication link 7 is used instead of a geostationary satellite communication link 8.

In step S03F, the earth station 1F1 transmits the encrypted user data _CD1 from the communication terminal ₃₁ , encrypted by the common key cryptosystem, as radio waves _RU1 toward the high altitude pseudo satellite _91. In step S04F, the high altitude pseudo satellite ₉₁ receives the radio waves _RU1 , frequency converts and amplifies _the radio waves _RU1 , and transmits them as radio waves _RD2 . In step S05F, the earth station _1F2 receives the radio waves _RD2 , demodulates and decodes the radio waves _RD2 to generate user data _UD1 . The earth station _1F2 transmits the user data _UD1 to the communication terminal _32. The process of S03F is almost the same as S03C. S03F differs from S03C in that it uses a common key cryptosystem. The process of S05F is almost the same as S05C. S05F differs from S05C in that it uses a common key cryptosystem.

In step S06F, the earth station _{1F2 transmits the encrypted user data CD2} from the communication terminal ₃₂ , encrypted by the common key cryptosystem, as radio waves _RU2 toward the high altitude pseudo satellite _91. In step S07F, the high altitude pseudo satellite ₉₁ receives the radio waves _RU2 , frequency converts and amplifies _the radio waves _RU2 , and transmits them as radio waves _RD1 . In step S08F, the earth station _1F1 receives the radio waves _RD1 , demodulates and decodes the radio waves _RD1 to generate user data _UD2 . The earth station _1F1 transmits the user data _UD2 to the communication terminal _31. The process of S06F is almost the same as S06C. S06F differs from S06C in that it uses the common key cryptosystem and that it transmits radio waves _RU2 toward the high altitude pseudo satellite _91. The process of S08F is almost the same as S08C. S08F differs from S08C in that it uses a common key cryptosystem.

The process of the earth station _1F1 and earth station _1F2 communicating communication control data is similar to the process of the earth station _1C1 and earth station _1C2 communicating communication control data. The difference is that the earth station _1F1 and earth station _1F2 communicate only by relaying to the low-earth orbit satellite _41. In step S10F, the low-earth orbit satellite ₄₁ receives the radio wave _RUC1 , frequency converts and amplifies the radio wave _RUC1 , and radiates it as a radio wave RD- _C2 . In step S11F, the earth station _1F2 receives the radio wave RD- _C2 radiated by the low-earth orbit satellite ₄₁ , demodulates the radio wave RD- _C2 , and generates communication control data CC- ₁ . The earth station _1F2 processes the communication control data CC _-1 to control the communication between the communication terminal ₃₁ and the communication terminal ₃₂ .

In step S12F, the earth station _1F2 transmits the communication control data _CC2 to the earth station _1F1 , which is then radiated as radio waves _RUC2 by the earth station _1F2 toward the low earth orbit satellite _41. In step S13F, the low earth orbit satellite ₄₂ receives the radio waves _RUC2 , frequency-converts and amplifies the radio waves _RUC2 , and radiates them as radio waves _RDC1 .

Even if a high altitude pseudo satellite 9 does not communicate with other high altitude pseudo satellites 9, encrypted user data can be communicated between two earth stations 1F that exist within the communication area of one high altitude pseudo satellite 9 using a high altitude pseudo satellite communication line 21.

Next, a case will be described in which a communication terminal ₃₁ connected to an earth station _1F1 communicates with a communication terminal ₃₃ connected to an earth station _1F3 which communicates with a different high altitude pseudo satellite. Here, the earth station _1F1 communicates with a high altitude pseudo satellite _91. The earth station _1F3 communicates with a high altitude pseudo satellite _92. The high altitude pseudo satellites ₉₁ and ₉₂ cannot communicate directly with each other.

Figures 35 and 36 are flow charts for explaining the outline of the procedure in which a communication terminal _{3_1} connected to an earth station _{1F_1} communicates with a communication terminal _{3_3} connected to an earth station _{1F_3} which communicates with a different high altitude pseudosatellite. Figure 35 shows the process up to step S08F, and Figure 36 shows the process from step S09C. The process from S09C onwards shown in Figure 36 is the same as that shown in Figure 18. Figure 36 differs from Figure 18 in that the earth station _{1F_3} , not the earth station _{1C_2} , carries out each procedure.

Regarding Fig. 35, differences from Fig. 33 will be described. In step S04G, the encrypted user data _CD1 passes through the high altitude pseudo satellite ₉₁ , the high altitude pseudo satellite ground station ₄₅₁ , the terrestrial network ₄₂₁ , the terrestrial core network device ₄₁₁ , the terrestrial core network 40, the terrestrial core network device ₄₁₂ , the terrestrial network ₄₂₂ , and the high altitude pseudo satellite ground station ₄₅₂ , and arrives at the high altitude pseudo satellite _92. The high altitude pseudo satellite ₉₂ emits radio waves _RD2 for communicating the encrypted user data _CD1 . The processing of S04G will be described with reference to the flowchart shown in Fig. 37.

In step S05G, the earth station _1F3 receives the radio wave _RD2 , and demodulates and decodes the radio wave _RD2 to generate user data _UD1 . The earth station _1F3 transmits the user data _UD1 to the communication terminal _33. S05G is the same process as S05F. S05G differs from S05F only in that it is performed by the earth station _1F3 and that it is transmitted to the communication terminal ₃₃ .

In step S06G, the earth station _1F3 converts the user data _UD2 transmitted from the communication terminal ₃₃ to the communication terminal ₃₁ into encrypted user data _CD2 , and transmits the data as radio waves _RU2 to the high altitude pseudo satellite _92. S06G is the same process as S06F. S06G differs from S06F only in that it is performed by the earth station _1F3 and that the user data _UD2 is transmitted by the communication terminal ₃₃ .

In step S07G, the encrypted user data _CD2 passes through the high altitude pseudo satellite ₉₂ , the high altitude pseudo satellite ground station ₄₅₂ , the terrestrial network ₄₂₂ , the terrestrial core network device ₄₁₂ , the terrestrial core network 40, the terrestrial core network device ₄₁₁ , the terrestrial network ₄₂₁ , and the high altitude pseudo satellite ground station ₄₅₁ , and reaches the high altitude pseudo satellite _91. The high altitude pseudo satellite ₉₁ emits radio waves _RD1 for communicating the encrypted user data _CD2 . The processing of S07G will be described with reference to the flowchart shown in FIG.

37, the process from when the high altitude pseudo satellite 9 ₁ receives the radio wave RU ₁ to when the high altitude pseudo satellite 9 ₂ emits the radio wave RD ₂ in order to communicate the encrypted user data CD ₁ in S04G will be described. In step S101, the high altitude pseudo satellite 9 ₁ receives the radio wave RU ₁ , frequency converts and amplifies the radio wave RU ₁ , and emits it as radio wave RD _1. In step S102, the high altitude pseudo satellite ground station 45 ₁ receives the radio wave RD ₁ and demodulates the radio wave RD ₁ to generate the encrypted user data CD ₁ .

In step S103, the high altitude pseudo satellite ground station 45 ₁ transmits a packet of encrypted user data CD ₁ to the communication terminal 3 ₂ to the terrestrial network 42 _1. In step S104, the packet of encrypted user data CD ₁ passes through the terrestrial network 42 ₁ , the terrestrial core network device 41 ₁ , the terrestrial core network 40, the terrestrial core network device 41 ₂ , and the terrestrial network 42 ₂ to reach the high altitude pseudo satellite ground station 45 _2. It is known that in the communication network (terrestrial communication network) on the ground of the communication system 100F, the packet to the communication terminal 3 ₂ is communicated from the high altitude pseudo satellite ground station 45 ₂ using the high altitude pseudo satellite communication line 21 _3. Also, the route from the high altitude pseudo satellite ground station 45 ₁ to the high altitude pseudo satellite ground station 45 ₂ is determined by some method.

In step S105, the high altitude pseudo satellite ground station ₄₅₂ radiates the packet of encrypted user data _CD1 as radio waves _RU1 toward the high altitude pseudo satellite _92. In step S106, the high altitude pseudo satellite ₉₂ receives the radio waves _RU1 , frequency-converts and amplifies the radio waves _RU1 , and radiates them as radio waves _RD2 .

38, the process from when the high altitude pseudo satellite 9 ₂ receives the radio wave RU ₂ to when the high altitude pseudo satellite 9 ₁ emits the radio wave RD ₁ in order to communicate the encrypted user data CD ₂ in S07G will be described. In step S111, the high altitude pseudo satellite 9 ₂ receives the radio wave RU ₂ , frequency converts and amplifies the radio wave RU ₂ , and emits it as radio wave RD _2. In step S112, the high altitude pseudo satellite ground station 45 ₂ receives the radio wave RD ₂ and demodulates the radio wave RD ₂ to generate the encrypted user data CD ₂ .

In step S113, the high altitude pseudo satellite ground station 45 ₂ transmits a packet of encrypted user data CD ₂ to the communication terminal 3 ₁ to the terrestrial network 42 _2. In step S114, the packet of encrypted user data CD ₂ passes through the terrestrial network 42 ₂ , the terrestrial core network device 41 ₂ , the terrestrial core network 40, the terrestrial core network device 41 ₁ , and the terrestrial network 42 ₁ to reach the high altitude pseudo satellite ground station 45 _1. It is known that in the communication network on the ground of the communication system 100F, a packet to the communication terminal 3 ₁ is communicated from the high altitude pseudo satellite ground station 45 ₁ using the high altitude pseudo satellite communication line 21 _1. Also, a route from the high altitude pseudo satellite ground station 45 ₂ to the high altitude pseudo satellite ground station 45 ₁ is determined by some method.

In step S115, the high altitude pseudosatellite ground station _45.1 radiates the packet of encrypted user data _CD.2 as radio waves _RU.1 toward the high altitude pseudosatellite _9.1 . In step S116, the high altitude pseudosatellite _9.1 receives the radio waves _RU.1 , frequency-converts and amplifies the radio waves _RU.1 , and radiates them as radio waves _RD.1 .

Even if a high altitude pseudo satellite 9 does not communicate with other high altitude pseudo satellites 9, encrypted user data can be communicated between two earth stations 1F that exist in the communication areas of different high altitude pseudo satellites 9 via a communication path that includes a high altitude pseudo satellite communication line 21 that passes through the two high altitude pseudo satellites 9 and the ground communication network.

Next, a case will be described in which a communication terminal ₃₁ connected to an earth station _1F1 communicates with a communication terminal ₃₄ connected to an earth station 46 connected to a terrestrial communication network. The earth station _1F1 communicates with a high altitude pseudo satellite _91. The earth station 46 communicates with the high altitude pseudo satellite ₉₁ via a communication path that passes through a high altitude pseudo satellite ground station _452. The earth station 46 communicates with a low altitude satellite ₄₂ via a communication path that passes through a low altitude satellite ground station 44.

39 and 40 are flow charts for explaining the outline of the procedure in which the communication terminal _3.1 connected to the earth station _1F.1 communicates with the communication terminal _3.4 connected to the earth station 46 connected to the terrestrial communication network. Fig. 39 shows the process up to step S08F, and Fig. 40 shows the process from step S09C.

Regarding Figures 39 and 40, the points different from Figures 33 and 40 will be described. In step S02H, the earth station _1F1 and the earth station 46 determine an encryption key and a decryption key to be used for communication between the communication terminal _3-1 and the communication terminal _3-4 , and store them in the data storage unit 58F. The earth station _1F1 and the earth station 46 communicate the decryption key through a communication path including the low-earth orbit satellite communication line 6 and the terrestrial communication network.

In step S04H, the encrypted user data _CD1 passes through the high altitude pseudo satellite ₉₁ , the high altitude pseudo satellite ground station ₄₅₁ , the ground network ₄₂₁ , the ground core network device ₄₁₁ , the ground core network 40, the ground core network device ₄₁₂ and the ground network ₄₂₂ , and arrives at the earth station 46. The processing in S04H will be explained with reference to the flow chart shown in FIG.

In step S05H, the earth station 46 receives the encrypted user data _CD1 and decrypts the encrypted user data _CD1 to generate user data _UD1 . The earth station 46 transmits the user data _UD1 to the communication terminal ₃₄ .

In step S06H, the earth station 46 converts the user data _UD2 transmitted from the communication terminal _3-4 to the communication terminal _3-1 into encrypted user data _CD2 and transmits it to the ground network _42-2 .

In step S07H, the encrypted user data _CD2 passes through the terrestrial network ₄₂₂ , the terrestrial core network device ₄₁₂ , the terrestrial core network 40, the terrestrial core network device ₄₁₁ , the terrestrial network ₄₂₁ , and the high altitude pseudo satellite ground station ₄₅₁ to reach the high altitude pseudo satellite _91. The high altitude pseudo satellite ₉₁ emits radio waves _RD1 for communicating the encrypted user data _CD2 . The processing of S07H will be described with reference to the flowchart shown in FIG.

In step S10H, the low-earth orbit satellite ₄₁ receives the radio wave RU _C1 , frequency-converts and amplifies the radio wave RU _C1 , and radiates it as a radio wave RD _C1 . The low-earth orbit satellite ₄₂ receives the radio wave RD _C1 , frequency-converts and amplifies the radio wave RD _C1 , and radiates it as a radio wave RD _C2 . The low-earth orbit satellite ground station 44 receives the radio wave RD _C1 , demodulates it, and generates communication control data CC _1. The low-earth orbit satellite ground station 44 transmits the communication control data CC ₁ to the terrestrial network 42 _1. The communication control data CC ₁ reaches the earth station 46 via the terrestrial network 42 ₁ , the terrestrial core network device 41 ₁ , the terrestrial core network 40, the terrestrial core network device 41 ₂ , and the terrestrial network 42 ₂ .

In step S11H, the earth station 46 receives the communication control data _CC1 from the terrestrial network _422. The earth station 46 processes the communication control data _CC1 to control the communication between the communication terminal _3-1 and the communication terminal _3-4 .

In step S12H, the earth station 46 transmits the communication control data _CC2 to the earth station ₁₁ to the terrestrial network _422. In step S13H, the communication control data _CC2 passes through the terrestrial network ₄₂₂ , the terrestrial core network device ₄₁₂ , the terrestrial core network 40, the terrestrial core network device ₄₁₁ , and the terrestrial network ₄₂₁ , and reaches the low-earth orbit satellite ground station 44. The low-earth orbit satellite ground station 44 transmits the communication control data _CC2 to the low-earth orbit satellite ₄₁ as radio waves RU _-C2 . The low-earth orbit satellite ₄₁ receives the radio waves RU- _C2 , frequency-converts and amplifies the radio waves RU- _C2 , and transmits them as radio waves RD- _C1 .

With reference to Fig. 41, the process from reception of radio wave _RU1 by high altitude pseudo satellite ₉₁ to transmission of encrypted user data _CD1 through the terrestrial communication network to earth station 46 in S04H will be described. The points in Fig. 41 that differ from Fig. 37 will be described.

In step S104H, the packet of encrypted user data CD ₁ is transmitted through the terrestrial network 42 ₁ , the terrestrial core network device 41 ₁ , the terrestrial core network 40 , the terrestrial core network device 41 ₂ and the terrestrial network 42 ₂ toward the earth station 46 .

With reference to Fig. 42, the process from when the earth station 46 transmits the encrypted user data _CD2 to the ground network ₄₂₁ in order to communicate the encrypted user data _CD2 in S07H until the high altitude pseudo satellite ₉₁ emits the radio wave _RD1 will be described. Regarding Fig. 42, the points different from Fig. 38 will be described.

In Fig. 42, the steps from S111 to S113 are omitted, and the process starts from S114. In S114, the packet of encrypted user data _CD2 transmitted by the earth station 46 passes through the terrestrial network ₄₂₂ , the terrestrial core network device ₄₁₂ , the terrestrial core network 40, the terrestrial core network device ₄₁₁ , and the terrestrial network ₄₂₁ , and arrives at the high altitude pseudosatellite earth station _451. S115 and S116 are the same as in Fig. 38.

In this way, the earth station 1F can communicate encrypted user data over a communication path including the high altitude pseudosatellite communication line 21 with any of the earth stations communicating with the same high altitude pseudosatellite 9, earth stations communicating with different high altitude pseudosatellites 9, and earth stations connected to a terrestrial communication network that cannot communicate with the high altitude pseudosatellite 9 by itself. The earth station 1F can communicate an encryption key for encryption and a decryption key for decryption with the communication partner over a communication path including the low altitude satellite communication line 6. Therefore, even if the user data communicated over a communication path including the high altitude pseudosatellite communication line 21 is intercepted, the contents of the user data will not be known because it is encrypted. Since the encryption key and decryption key are communicated over a communication path including the low altitude satellite communication line 6, the encryption key and decryption key will not be leaked even if the high altitude pseudosatellite communication line 21 through which the user data is communicated is intercepted. Since the user data is not communicated over the low altitude satellite communication line 6, the contents of the user data will not be known even if the low altitude satellite communication line 6 is intercepted.

The earth station 1F does not require any terrestrial infrastructure facilities. The earth station 1F can easily expand the communication area in a mobile communication system.

Earth station 1F allows the sender and receiver to share an encryption key (including a decryption key) without using other communication systems. Earth station 1F can communicate encrypted user data.

A communication device (earth station) according to any of the first to fourth embodiments can communicate encrypted user data with any of the earth stations communicating with the same high altitude pseudo satellite 9, with any of the earth stations communicating with different high altitude pseudo satellites 9, and with any of the earth stations connected to a terrestrial communication network that cannot communicate with the high altitude pseudo satellite 9 by itself, via a communication path including the high altitude pseudo satellite communication line 21.

The first extra-troposphere communication line for communicating encrypted user data may be an extra-troposphere communication line different from the high-altitude pseudo satellite communication line 21. The second extra-troposphere communication line for communicating encryption keys and the like may be an extra-troposphere communication line different from the low-orbit satellite communication line 6. The first extra-troposphere communication line and the second extra-troposphere communication line may be two types of extra-troposphere communication lines having different altitudes.

Although the preferred embodiments have been described above in detail, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

Various aspects of this disclosure are summarized below as appendices.

(Appendix 1)
an extra-troposphere communication line which is a communication line relayed to an extra-troposphere relay station which is a relay station mounted on an extra-troposphere mobile body which is a mobile body moving outside the troposphere at an altitude higher than the troposphere, and a first extra-troposphere communication unit which communicates encrypted user data, which is user data to be communicated, with a communication partner in the first extra-troposphere communication line which is an extra-troposphere communication line relayed to a first extra-troposphere relay station which is an extra-troposphere relay station mounted on a first extra-troposphere mobile body which is the extra-troposphere mobile body moving at a first altitude included in the troposphere;
an encryption device that encrypts the user data to be transmitted using an encryption key to generate the encrypted user data;
a decryption device that decrypts the received encrypted user data using a decryption key to generate the user data;
a second extra-troposphere communication unit that communicates with the communication partner the communication control data, the communication control data including at least one of the encryption key used by the encryption device and the decryption key used by the communication partner when decrypting the encrypted user data generated by the encryption device, and the second extra-troposphere communication unit that communicates with the communication partner the communication control data including at least one of the encryption key used by the communication partner and the decryption key used by the decryption device when decrypting the encrypted user data generated by the communication partner, before the first extra-troposphere communication unit communicates the encrypted user data, the second extra-troposphere communication line that is relayed to a second extra-troposphere relay station that is the extra-troposphere relay station mounted on a second extra-troposphere mobile body that is the extra-troposphere mobile body moving at a second altitude included outside the troposphere that is different from the first altitude, before the first extra-troposphere communication unit communicates the encrypted user data, the communication control data including at least one of the encryption key used by the communication partner and the decryption key used by the decryption device when decrypting the encrypted user data generated by the communication partner.
(Appendix 2)
a terminal connection unit for exchanging the user data with a communication terminal connected via a network;
an encryption key storage unit configured to store the encryption key used by the encryption device for each of the communication terminals connected to the terminal connection unit;
a corresponding decryption key storage unit that stores, for each of the communication terminals, a corresponding decryption key that is the decryption key for decrypting data that is encrypted by the encryption device with the encryption key;
a usage decryption key storage unit that stores a usage decryption key, which is the decryption key used when the encryption device decrypts the received encrypted user data, for each of the communication terminals that are transmission sources of the encrypted user data;
a communication control data generation unit which, when receiving a communication start request from a request source communication terminal which is the communication terminal itself and a request destination communication terminal which is the communication terminal connected to the communication partner via a network, generates the communication control data of the communication start request including the request source communication terminal, the request destination communication terminal, and the corresponding decryption key of the request source communication terminal, and generates the communication control data of the communication start acceptance including the corresponding decryption key of the request destination communication terminal when receiving the communication control data of the communication start request from the communication partner;
if the encryption key of the request source communication terminal is not stored in the encryption key storage unit, determine the encryption key and the corresponding decryption key, store the determined encryption key in the encryption key storage unit as the encryption key of the request source communication terminal, and store the determined corresponding decryption key in the corresponding decryption key storage unit as the corresponding decryption key of the request source communication terminal;
when receiving the communication control data of the communication start request, storing the corresponding decryption key of the request source communication terminal included in the received communication control data as the used decryption key of the request source communication terminal in the used decryption key storage unit, and if the encryption key of the requested destination communication terminal is not stored in the encryption key storage unit, determining the encryption key and the corresponding decryption key, storing the determined encryption key in the encryption key storage unit as the encryption key of the requested destination communication terminal, and storing the determined corresponding decryption key in the corresponding decryption key storage unit as the corresponding decryption key of the requested destination communication terminal;
an encryption key/decryption key management unit that, when receiving the communication control data for accepting the start of communication, stores the corresponding decryption key of the requested communication terminal included in the received communication control data in the usage decryption key storage unit as the usage decryption key of the requested communication terminal,
The communication device according to claim 1, wherein the second extra-troposphere communication unit communicates the communication control data of the communication start request and the communication control data of the communication start acceptance with the communication partner.
(Appendix 3)
a terminal connection unit for exchanging the user data with a communication terminal connected via a network;
a decryption key storage unit configured to store the decryption key for decrypting the received encrypted user data for each of the communication terminals connected to the terminal connection unit;
a corresponding encryption key storage unit that stores, for each of the communication terminals, a corresponding encryption key that is the encryption key used to encrypt data to be decrypted by the decryption device with the decryption key;
an encryption key storage unit for storing an encryption key used by the encryption device for each of the communication terminals of the destination;
a communication control data generating unit which, when receiving a communication start request from a request source communication terminal which is the communication terminal itself with a request destination communication terminal which is the communication terminal connected to the communication partner via a network, generates the communication control data of the communication start request including the request source communication terminal, the request destination communication terminal, and the corresponding encryption key of the request source communication terminal, and generates the communication control data of the communication start acceptance including the corresponding encryption key of the request destination communication terminal when receiving the communication control data of the communication start request from the communication partner;
if the decryption key of the request source communication terminal is not stored in the decryption key storage unit, determine the decryption key and the corresponding encryption key, store the determined decryption key in the decryption key storage unit as the decryption key of the request source communication terminal, and store the determined corresponding encryption key in the corresponding encryption key storage unit as the corresponding encryption key of the request source communication terminal;
when receiving the communication control data of the communication start request, storing the corresponding encryption key of the request source communication terminal included in the received communication control data as the used encryption key of the request source communication terminal in the used encryption key storage unit, and if the decryption key of the requested destination communication terminal is not stored in the decryption key storage unit, determining the decryption key and the corresponding encryption key, storing the determined decryption key in the decryption key storage unit as the decryption key of the requested destination communication terminal, and storing the determined corresponding encryption key in the corresponding encryption key storage unit as the corresponding encryption key of the requested destination communication terminal;
an encryption key decryption key management unit that, when receiving the communication control data for accepting the start of communication, stores the corresponding encryption key of the requested communication terminal included in the received communication control data in the encryption key usage storage unit as the encryption key usage of the requested communication terminal;
The communication device according to claim 1, wherein the second extra-troposphere communication unit communicates the communication control data of the communication start request and the communication control data of the communication start acceptance with the communication partner.
(Appendix 4)
4. The communication device according to claim 1, further comprising a communication control unit that controls communication of the encrypted user data by the first extra-troposphere communication unit and communication of the communication control data by the second extra-troposphere communication unit.
(Appendix 5)
A communication device described in any one of Appendix 1 to Appendix 4, wherein each of the first extra-troposphere moving body and the second extra-troposphere moving body is an extra-troposphere moving body selected from at least three types of extra-troposphere moving bodies each moving at at least three different altitudes included outside the troposphere.
(Appendix 6)
A communication device described in any one of Appendix 1 to Appendix 4, wherein each of the first extra-troposphere mobile body and the second extra-troposphere mobile body is an extra-troposphere mobile body selected from a set of extra-troposphere mobile bodies including a stratospheric mobile body that is a mobile body that moves in the stratosphere, a geostationary satellite, and an artificial satellite that moves at at least two different altitudes that are lower than the geostationary satellite and are included in the troposphere.
(Appendix 7)
Two modems;
Two frequency converters;
a sequence allocation unit that allocates one of the frequency converters and one of the modulator/demodulators to be used as the first extra-troposphere communication unit, and allocates the other of the frequency converters and the other of the modulator/demodulators to be used as the second extra-troposphere communication unit,
The sequence allocation unit,
causing one of said modulators/demodulators to modulate and demodulate said encrypted user data;
causing one of the frequency converters to convert between a frequency used in the first extratroposphere communication line and a frequency of a signal to be processed by the modem;
causing the other of the modulators/demodulators to modulate and demodulate the communication control data;
7. The communication device according to claim 1, wherein the other frequency converter converts a frequency between a frequency used in the second extratroposphere communication line and a frequency of a signal processed by the modem.
(Appendix 8)
A modem;
a frequency converter connected to the modem;
a time division control unit that controls the modem and the frequency converter so as to be used as the first extra-troposphere communication unit or the second extra-troposphere communication unit in a time division manner,
The time division control unit is
During a period in which the first extra-troposphere communication unit is used, the modulator/demodulator is caused to modulate and demodulate the encrypted user data, and the frequency converter is caused to convert a frequency between a frequency used in the first extra-troposphere communication line and a frequency of a signal processed by the modulator/demodulator;
7. The communication device according to claim 1, wherein, during a period in which the device is used as the second extra-troposphere communication unit, the modem is caused to modulate and demodulate the communication control data, and the frequency converter is caused to perform frequency conversion between a frequency used in the second extra-troposphere communication line and a frequency of a signal processed by the modem.
(Appendix 9)
Two antenna devices;
A communication device as described in Appendix 7, comprising a tracking control unit that controls one of the antenna devices connected to one of the frequency converters to track the first extra-troposphere moving body, and controls the other of the antenna devices connected to the other frequency converter to track the second extra-troposphere moving body.
(Appendix 10)
a receiving antenna device having a receiving antenna section having a plurality of element receiving antennas that receive radio waves and output element receiving signals; and an element receiving signal processing section that processes the plurality of element receiving signals to output a receiving signal of a first receiving frequency from a first receiving direction that can be electronically changed to one of the frequency converters, and to output a receiving signal of a second receiving frequency different from the first receiving frequency from a second receiving direction that can be electronically changed independently of the first receiving direction to the other of the frequency converters;
a transmitting antenna device comprising: a transmitting antenna section having a plurality of element transmitting antennas each receiving an element transmitting signal and transmitting radio waves; and an element transmitting signal generating section which receives a transmitting signal of a first transmitting frequency output from one of the frequency converters and a transmitting signal of a second transmitting frequency different from the first transmitting frequency output from the other of the frequency converters, and generates a plurality of the element transmitting signals to be input to the plurality of element transmitting antennas, respectively, so that the transmitting antenna section transmits radio waves of the first transmitting frequency in a first transmitting direction that can be electronically changed, and the transmitting antenna section transmits radio waves of the second transmitting frequency in a second transmitting direction that can be electronically changed independently of the first transmitting direction;
a frequency setting unit that sets the first reception frequency and the first transmission frequency to a reception frequency and a transmission frequency of the first extra-troposphere communication line, respectively, and sets the second reception frequency and the second transmission frequency to a reception frequency and a transmission frequency of the second extra-troposphere communication line, respectively;
and a tracking control unit that controls the first receiving direction and the first transmitting direction to track the first extra-troposphere moving body, and controls the second receiving direction and the second transmitting direction to track the second extra-troposphere moving body.
(Appendix 11)
a receiving antenna device which is a phased array antenna connected to the frequency converter;
a transmitting antenna device which is a phased array antenna connected to the frequency converter;
A communication device as described in Appendix 8, comprising a tracking control unit that controls the receiving antenna device and the transmitting antenna device to track the first extra-troposphere moving body during a period when the modem and the frequency converter are used as the first extra-troposphere communication unit, and controls the receiving antenna device and the transmitting antenna device to track the second extra-troposphere moving body during a period when the modem and the frequency converter are used as the second extra-troposphere communication unit.
(Appendix 12)
The extra-troposphere communication line is a communication line relayed to an extra-troposphere relay station that is a relay station mounted on an extra-troposphere mobile body that is a mobile body moving outside the troposphere at an altitude higher than the troposphere, and the first extra-troposphere communication line is an extra-troposphere communication line relayed to a first extra-troposphere relay station that is an extra-troposphere relay station mounted on a first extra-troposphere mobile body that is the extra-troposphere mobile body moving at a first altitude included in the troposphere, the extra-troposphere communication line including a first extra-troposphere communication unit that communicates encrypted user data obtained by encrypting user data that is data to be communicated with a communication partner, and an encryption unit that encrypts the user data to be transmitted with an encryption key to generate the encrypted user data. a decryption device that decrypts the received encrypted user data by a decryption key to generate the user data, and a second extra-troposphere communication unit that communicates with the communication partner through a second extra-troposphere communication line that is the extra-troposphere communication line relayed to a second extra-troposphere relay station that is the extra-troposphere relay station mounted on a second extra-troposphere mobile body that is the extra-troposphere mobile body moving at a second altitude included outside the troposphere and different from the first altitude, and a communication method for communicating between a communication device, a requesting communication terminal that is a communication terminal connected to one of the communication partners, and a requested communication terminal that is a communication terminal connected to the communication device and the other of the communication partners,
a step of receiving a request to start communication with the request destination communication terminal from the request source communication terminal by one of the communication device and the communication counterpart;
a step of communicating at least one of a local encryption key, which is an encryption key used by the encryption device when encrypting the user data to generate the encrypted user data, and a remote decryption key, which is a decryption key used by the communication remote device when decrypting the encrypted user data encrypted by the local encryption key, with the communication remote device through the second extra-troposphere communication unit;
a step of communicating at least one of a counterpart encryption key, which is the encryption key used by the counterpart when encrypting the user data to generate the encrypted user data, and a local decryption key, which is the decryption key used by the decryption device when decrypting the encrypted user data encrypted with the counterpart encryption key, with the second extra-troposphere communication unit;
a step of encrypting the user data from the request source communication terminal with the encryption device's own encryption key or encrypting the user data from the communication terminal with the other communication terminal's encryption key to generate the encrypted user data;
a step of communicating the encrypted user data from the request source communication terminal by the first extra-troposphere communication unit with the communication partner via the first extra-troposphere communication line;
a step of the communication partner decrypting the encrypted user data received by the communication partner with the partner decryption key, or the encryption device decrypting the encrypted user data received by the communication device with its own decryption key to generate the user data from the request source communication terminal;
a step of transmitting the decrypted user data from the request source communication terminal to the request destination communication terminal by the communication partner or the communication device;
a step of encrypting the user data from the request destination communication terminal with the other communication party's encryption key or encrypting the user data with the encryption device's own encryption key to generate the encrypted user data;
a step of communicating the encrypted user data from the request destination communication terminal with the communication partner through the first extratroposphere communication line;
a step of decrypting the encrypted user data received by the first extratroposphere communication unit with the decryption key of the decryption device or the communication partner with the partner's decryption key to generate the user data from the request destination communication terminal;
a procedure in which the communication device or the communication partner transmits the decrypted user data from the requested communication terminal to the requesting communication terminal.

100, 100C, 100D, 100E, 100F Satellite communication systems,
1, _{1 1} , 1 ₂ , 1C, 1D, 1E, 1F Earth station (communication device),
2, 2 ₁ , 2 ₂ , 2 ₃ , 2 ₄ network,
3, 3 ₁ , 3 ₂ , 3 ₃ , 3 ₄ communication terminals,
4, ₄₁ , ₄₂ low earth orbit satellites,
5 Geostationary satellite 6, ₆₁ , ₆₂ , ₆₃ , ₆₄ Low Earth orbit satellite communication link,
7. Low Earth Orbit Satellite Communication Links;
8, 8 ₁ , 8 ₂ , 8 ₃ , 8 ₄ Geostationary satellite communication lines,
9, ₉₁ , ₉₂ high altitude pseudosatellites,
11, _11A , _11B antenna device,
12, _12A , _12B , 12D Frequency converter,
13, _13A , _13B , 13D Modulator/Demodulator,
14, 14C, 14D, 14E, 14F Data processing device,
15, 15C Encryption device (decryption device),
16 network interface unit (network IF unit, terminal connection unit),
17, 17E Receiving antenna device,
18, 18E transmitting antenna device,
21, 21 ₁ , 21 ₂ , 21 ₃ , 21 ₄ , 21 ₅ High altitude pseudo satellite communication line,
22 High altitude pseudosatellite inter-communication links;
33, _33A , _33B , 33D Satellite communication unit (first extra-troposphere communication unit, second extra-troposphere communication unit),
33E _A , 33E _B satellite communication unit (first extratroposphere communication unit, second extratroposphere communication unit),
34, _34A , _34B transmit buffer,
40 terrestrial core network,
41, 41 ₁ , 41 ₂ terrestrial core network device,
42, 42 ₁ , 42 ₂ terrestrial network,
43 geostationary satellite ground stations;
44 low-earth orbit satellite ground stations;
45, 45 ₁ , 45 ₂ high altitude pseudo satellite ground station,
46 Earth stations,
50, 50D satellite communication interface unit (satellite communication IF unit),
51, 51C line control unit (frequency setting unit),
52, 52C, 52D, 52E tracking control unit,
53, 53C satellite position management unit,
54 sequence control unit (communication control unit, sequence allocation unit),
55, 55C encryption key/decryption key management unit,
56, 56C encryption device control unit,
57, 57C communication control data processing unit (communication control data generating unit),
58, 58E, 58F data storage unit (encryption key storage unit, corresponding decryption key storage unit, used decryption key storage unit),
58C, 58D data storage unit (decryption key storage unit, corresponding encryption key storage unit, used encryption key storage unit),
59 satellite selection input unit,
60 time division control unit,
61 element receiving antenna,
62 receiving antenna unit,
63, 63E element receiving signal processing unit,
64 element transmitting antenna,
65 transmitting antenna unit,
66, 66E element transmission signal generating unit,
67, _67A , _67B output terminals,
68, _68A , _68B synthesis circuit,
69, _69A , _69B receiving modules,
70, _70A , _70B input terminals,
71, _71A , _71B distribution circuit,
72, _72A , _72B transmission modules,
73, _73A , _73B phase shifters,
74, _74A , _74B amplifiers;
75, _75A , _75B phase shifters,
76, _76A , _76B amplifiers;
_80A , _80B : satellite in communication;
_81A , _81B receiving frequency,
_82A , _82B transmission frequency,
_83A , _83B modulation and demodulation method,
84 _A , 84 _B error correction method,
85 own station position,
86 _A , 86 _B satellite positions,
87 _A , 87 _B satellite presence direction,
88 Series of use,
89 encryption key,
89C Decryption key,
90 Decryption key,
90C Encryption key used,
91C corresponding encryption key,
92 _A , 92 _B mobile object type,
93 Time sharing control data.

Claims (17)

an extra-troposphere communication line which is a communication line relayed to an extra-troposphere relay station which is a relay station mounted on an extra-troposphere mobile body which is a mobile body moving outside the troposphere at an altitude higher than the troposphere, and a first extra-troposphere communication unit which communicates encrypted user data, which is user data to be communicated, with a communication partner in the first extra-troposphere communication line which is an extra-troposphere communication line relayed to a first extra-troposphere relay station which is an extra-troposphere relay station mounted on a first extra-troposphere mobile body which is the extra-troposphere mobile body moving at a first altitude included in the troposphere;
an encryption device that encrypts the user data to be transmitted using an encryption key to generate the encrypted user data;
a decryption device that decrypts the received encrypted user data using a decryption key to generate the user data;
a second extra-troposphere communication unit that communicates with the communication partner the communication control data, the communication control data including at least one of the encryption key used by the encryption device and the decryption key used by the communication partner when decrypting the encrypted user data generated by the encryption device, and the second extra-troposphere communication unit that communicates with the communication partner the communication control data including at least one of the encryption key used by the communication partner and the decryption key used by the decryption device when decrypting the encrypted user data generated by the communication partner, before the first extra-troposphere communication unit communicates the encrypted user data, the second extra-troposphere communication line that is relayed to a second extra-troposphere relay station that is the extra-troposphere relay station mounted on a second extra-troposphere mobile body that is the extra-troposphere mobile body moving at a second altitude included outside the troposphere that is different from the first altitude, before the first extra-troposphere communication unit communicates the encrypted user data, the communication control data including at least one of the encryption key used by the communication partner and the decryption key used by the decryption device when decrypting the encrypted user data generated by the communication partner. a terminal connection unit for exchanging the user data with a communication terminal connected via a network;
an encryption key storage unit configured to store the encryption key used by the encryption device for each of the communication terminals connected to the terminal connection unit;
a corresponding decryption key storage unit that stores, for each of the communication terminals, a corresponding decryption key that is the decryption key for decrypting data that is encrypted by the encryption device with the encryption key;
a usage decryption key storage unit for storing a usage decryption key, which is the decryption key used when the encryption device decrypts the received encrypted user data, for each of the communication terminals that are transmission sources of the encrypted user data;
a communication control data generation unit which, when receiving a communication start request from a request source communication terminal which is the communication terminal itself and a request destination communication terminal which is the communication terminal connected to the communication partner via a network, generates the communication control data of the communication start request including the request source communication terminal, the request destination communication terminal, and the corresponding decryption key of the request source communication terminal, and generates the communication control data of the communication start acceptance including the corresponding decryption key of the request destination communication terminal when receiving the communication control data of the communication start request from the communication partner;
if the encryption key of the request source communication terminal is not stored in the encryption key storage unit, determine the encryption key and the corresponding decryption key, store the determined encryption key in the encryption key storage unit as the encryption key of the request source communication terminal, and store the determined corresponding decryption key in the corresponding decryption key storage unit as the corresponding decryption key of the request source communication terminal;
when receiving the communication control data of the communication start request, storing the corresponding decryption key of the request source communication terminal included in the received communication control data as the used decryption key of the request source communication terminal in the used decryption key storage unit, and if the encryption key of the requested destination communication terminal is not stored in the encryption key storage unit, determining the encryption key and the corresponding decryption key, storing the determined encryption key in the encryption key storage unit as the encryption key of the requested destination communication terminal, and storing the determined corresponding decryption key in the corresponding decryption key storage unit as the corresponding decryption key of the requested destination communication terminal,
an encryption key/decryption key management unit that, when receiving the communication control data for accepting the start of communication, stores the corresponding decryption key of the request destination communication terminal included in the received communication control data in the usage decryption key storage unit as the usage decryption key of the request destination communication terminal,
The communication device according to claim 1 , wherein the second extra-troposphere communication unit communicates the communication control data of the communication start request and the communication control data of the communication start acceptance with the communication partner. a terminal connection unit for exchanging the user data with a communication terminal connected via a network;
a decryption key storage unit configured to store the decryption key for decrypting the received encrypted user data for each of the communication terminals connected to the terminal connection unit;
a corresponding encryption key storage unit that stores, for each of the communication terminals, a corresponding encryption key that is the encryption key used to encrypt data to be decrypted by the decryption device with the decryption key;
an encryption key storage unit for storing an encryption key used by the encryption device for each of the communication terminals of the destination;
a communication control data generating unit which, when receiving a communication start request from a request source communication terminal which is the communication terminal itself with a request destination communication terminal which is the communication terminal connected to the communication partner via a network, generates the communication control data of the communication start request including the request source communication terminal, the request destination communication terminal, and the corresponding encryption key of the request source communication terminal, and generates the communication control data of the communication start acceptance including the corresponding encryption key of the request destination communication terminal when receiving the communication control data of the communication start request from the communication partner;
if the decryption key of the request source communication terminal is not stored in the decryption key storage unit, determine the decryption key and the corresponding encryption key, store the determined decryption key in the decryption key storage unit as the decryption key of the request source communication terminal, and store the determined corresponding encryption key in the corresponding encryption key storage unit as the corresponding encryption key of the request source communication terminal;
when receiving the communication control data of the communication start request, storing the corresponding encryption key of the request source communication terminal included in the received communication control data as the used encryption key of the request source communication terminal in the used encryption key storage unit, and if the decryption key of the requested destination communication terminal is not stored in the decryption key storage unit, determining the decryption key and the corresponding encryption key, storing the determined decryption key in the decryption key storage unit as the decryption key of the requested destination communication terminal, and storing the determined corresponding encryption key in the corresponding encryption key storage unit as the corresponding encryption key of the requested destination communication terminal;
an encryption key decryption key management unit that, when receiving the communication control data for accepting the start of communication, stores the corresponding encryption key of the requested communication terminal included in the received communication control data in the encryption key usage storage unit as the encryption key usage of the requested communication terminal;
The communication device according to claim 1 , wherein the second extra-troposphere communication unit communicates the communication control data of the communication start request and the communication control data of the communication start acceptance with the communication partner. The communication device according to claim 1, further comprising a communication control unit that controls the communication of the encrypted user data by the first extratropical communication unit and the communication control data by the second extratropical communication unit. The communication device according to any one of claims 1 to 4, wherein each of the first extra-troposphere moving body and the second extra-troposphere moving body is an extra-troposphere moving body selected from at least three types of extra-troposphere moving bodies each moving at at least three mutually different altitudes included outside the troposphere. The communication device according to any one of claims 1 to 4, wherein each of the first extra-tropospheric mobile body and the second extra-tropospheric mobile body is an extra-tropospheric mobile body selected from a set of extra-tropospheric mobile bodies including a stratospheric mobile body that is a mobile body that moves in the stratosphere, a geostationary satellite, and an artificial satellite that moves at least two different altitudes that are lower than the geostationary satellite and are included in the troposphere. Two modems;
Two frequency converters;
a sequence allocation unit that allocates one of the frequency converters and one of the modulator/demodulators to be used as the first extra-troposphere communication unit, and controls the other of the frequency converter and the other of the modulator/demodulator to be used as the second extra-troposphere communication unit,
The sequence allocation unit,
causing one of said modulators/demodulators to modulate and demodulate said encrypted user data;
causing one of the frequency converters to convert between a frequency used in the first extratroposphere communication line and a frequency of a signal to be processed by the modem;
causing the other of the modulators/demodulators to modulate and demodulate the communication control data;
5. The communication device according to claim 1, further comprising a second frequency converter for converting a frequency between a frequency used in the second extratropical communication line and a frequency of a signal processed by the modem. Two modems;
Two frequency converters;
a sequence allocation unit that allocates one of the frequency converters and one of the modulator/demodulators to be used as the first extra-troposphere communication unit, and controls the other of the frequency converter and the other of the modulator/demodulator to be used as the second extra-troposphere communication unit,
The sequence allocation unit,
causing one of said modulators/demodulators to modulate and demodulate said encrypted user data;
causing one of the frequency converters to convert between a frequency used in the first extratroposphere communication line and a frequency of a signal to be processed by the modem;
causing the other of the modulators/demodulators to modulate and demodulate the communication control data;
6. The communication device according to claim 5, further comprising: a second frequency converter for converting a frequency between a frequency used in the second extratropical communication line and a frequency of a signal processed by the modem. A modem;
a frequency converter connected to the modem;
a time division control unit that controls the modem and the frequency converter so as to be used as the first extra-troposphere communication unit or the second extra-troposphere communication unit in a time division manner,
The time division control unit is
During a period when the signal is used as the first extra-troposphere communication unit, the modulator/demodulator is caused to modulate and demodulate the encrypted user data, and the frequency converter is caused to convert a frequency between a frequency used in the first extra-troposphere communication line and a frequency of a signal processed by the modulator/demodulator;
5. The communication device according to claim 1, wherein during a period in which the device is used as the second extra-troposphere communication unit, the modem is caused to modulate and demodulate the communication control data, and the frequency converter is caused to perform frequency conversion between a frequency used in the second extra-troposphere communication line and a frequency of a signal processed by the modem. A modem;
a frequency converter connected to the modem;
a time division control unit that controls the modem and the frequency converter so as to be used as the first extra-troposphere communication unit or the second extra-troposphere communication unit in a time division manner,
The time division control unit is
During a period when the signal is used as the first extra-troposphere communication unit, the modulator/demodulator is caused to modulate and demodulate the encrypted user data, and the frequency converter is caused to convert a frequency between a frequency used in the first extra-troposphere communication line and a frequency of a signal processed by the modulator/demodulator;
6. The communication device according to claim 5, wherein during a period when the device is used as the second extra-troposphere communication unit, the modem is caused to modulate and demodulate the communication control data, and the frequency converter is caused to perform frequency conversion between a frequency used in the second extra-troposphere communication line and a frequency of a signal processed by the modem. Two antenna devices;
The communication device described in claim 7, further comprising a tracking control unit that controls one of the antenna devices connected to one of the frequency converters to track the first extra-troposphere moving body, and controls the other of the antenna devices connected to the other frequency converter to track the second extra-troposphere moving body. Two antenna devices;
The communication device described in claim 8, further comprising a tracking control unit that controls one of the antenna devices connected to one of the frequency converters to track the first extra-troposphere moving body, and controls the other of the antenna devices connected to the other frequency converter to track the second extra-troposphere moving body. a receiving antenna device having a receiving antenna section having a plurality of element receiving antennas that receive radio waves and output element receiving signals; and an element receiving signal processing section that processes the plurality of element receiving signals to output a receiving signal of a first receiving frequency from a first receiving direction that can be electronically changed to one of the frequency converters, and to output a receiving signal of a second receiving frequency different from the first receiving frequency from a second receiving direction that can be electronically changed independently of the first receiving direction to the other of the frequency converters;
a transmitting antenna device comprising: a transmitting antenna section having a plurality of element transmitting antennas each receiving an element transmitting signal and transmitting radio waves; and an element transmitting signal generating section which receives a transmitting signal of a first transmitting frequency output from one of the frequency converters and a transmitting signal of a second transmitting frequency different from the first transmitting frequency output from the other of the frequency converters, and generates a plurality of the element transmitting signals to be input to the plurality of element transmitting antennas, respectively, so that the transmitting antenna section transmits radio waves of the first transmitting frequency in a first transmitting direction that can be electronically changed, and the transmitting antenna section transmits radio waves of the second transmitting frequency in a second transmitting direction that can be electronically changed independently of the first transmitting direction;
a frequency setting unit that sets the first reception frequency and the first transmission frequency to a reception frequency and a transmission frequency of the first extra-troposphere communication line, respectively, and sets the second reception frequency and the second transmission frequency to a reception frequency and a transmission frequency of the second extra-troposphere communication line, respectively;
The communication device of claim 7, further comprising a tracking control unit that controls the first receiving direction and the first transmitting direction to track the first extra-troposphere moving body, and controls the second receiving direction and the second transmitting direction to track the second extra-troposphere moving body. a receiving antenna device having a receiving antenna section having a plurality of element receiving antennas that receive radio waves and output element receiving signals; and an element receiving signal processing section that processes the plurality of element receiving signals to output a receiving signal of a first receiving frequency from a first receiving direction that can be electronically changed to one of the frequency converters, and to output a receiving signal of a second receiving frequency different from the first receiving frequency from a second receiving direction that can be electronically changed independently of the first receiving direction to the other of the frequency converters;
a transmitting antenna device comprising: a transmitting antenna section having a plurality of element transmitting antennas each receiving an element transmitting signal and transmitting radio waves; and an element transmitting signal generating section which receives a transmitting signal of a first transmitting frequency output from one of the frequency converters and a transmitting signal of a second transmitting frequency different from the first transmitting frequency output from the other of the frequency converters, and generates a plurality of the element transmitting signals to be input to the plurality of element transmitting antennas, respectively, so that the transmitting antenna section transmits radio waves of the first transmitting frequency in a first transmitting direction that can be electronically changed, and the transmitting antenna section transmits radio waves of the second transmitting frequency in a second transmitting direction that can be electronically changed independently of the first transmitting direction;
a frequency setting unit that sets the first reception frequency and the first transmission frequency to a reception frequency and a transmission frequency of the first extra-troposphere communication line, respectively, and sets the second reception frequency and the second transmission frequency to a reception frequency and a transmission frequency of the second extra-troposphere communication line, respectively;
The communication device of claim 8, further comprising a tracking control unit that controls the first receiving direction and the first transmitting direction to track the first extra-troposphere moving body, and controls the second receiving direction and the second transmitting direction to track the second extra-troposphere moving body. a receiving antenna device which is a phased array antenna connected to the frequency converter;
a transmitting antenna device which is a phased array antenna connected to the frequency converter;
The communication device described in claim 9, further comprising a tracking control unit that controls the receiving antenna device and the transmitting antenna device to track the first extra-troposphere moving body during a period when the modem and the frequency converter are used as the first extra-troposphere communication unit, and controls the receiving antenna device and the transmitting antenna device to track the second extra-troposphere moving body during a period when the modem and the frequency converter are used as the second extra-troposphere communication unit. a receiving antenna device which is a phased array antenna connected to the frequency converter;
a transmitting antenna device which is a phased array antenna connected to the frequency converter;
The communication device described in claim 10, further comprising a tracking control unit that controls the receiving antenna device and the transmitting antenna device to track the first extra-troposphere moving body during a period when the modem and the frequency converter are used as the first extra-troposphere communication unit, and controls the receiving antenna device and the transmitting antenna device to track the second extra-troposphere moving body during a period when the modem and the frequency converter are used as the second extra-troposphere communication unit. The extra-troposphere communication line is a communication line relayed to an extra-troposphere relay station that is a relay station mounted on an extra-troposphere mobile body that is a mobile body moving outside the troposphere at an altitude higher than the troposphere, and the first extra-troposphere communication line is an extra-troposphere communication line relayed to a first extra-troposphere relay station that is an extra-troposphere relay station mounted on a first extra-troposphere mobile body that is the extra-troposphere mobile body moving at a first altitude included in the troposphere, the extra-troposphere communication line including a first extra-troposphere communication unit that communicates encrypted user data obtained by encrypting user data that is data to be communicated with a communication partner, and an encryption unit that encrypts the user data to be transmitted with an encryption key to generate the encrypted user data. a decryption device that decrypts the received encrypted user data by a decryption key to generate the user data, and a second extra-troposphere communication unit that communicates with the communication partner through a second extra-troposphere communication line that is the extra-troposphere communication line relayed to a second extra-troposphere relay station that is the extra-troposphere relay station mounted on a second extra-troposphere mobile body that is the extra-troposphere mobile body moving at a second altitude included outside the troposphere and different from the first altitude, and a communication method for communicating between a communication device, a requesting communication terminal that is a communication terminal connected to one of the communication partners, and a requested communication terminal that is a communication terminal connected to the communication device and the other of the communication partners,
a step of receiving a request to start communication with the request destination communication terminal from the request source communication terminal by one of the communication device and the communication counterpart;
a step of communicating at least one of a local encryption key, which is an encryption key used by the encryption device when encrypting the user data to generate the encrypted user data, and a remote decryption key, which is a decryption key used by the communication remote device when decrypting the encrypted user data encrypted by the local encryption key, with the communication remote device through the second extra-troposphere communication unit;
a step of communicating at least one of a counterpart encryption key, which is the encryption key used by the counterpart when encrypting the user data to generate the encrypted user data, and a local decryption key, which is the decryption key used by the decryption device when decrypting the encrypted user data encrypted with the counterpart encryption key, with the second extra-troposphere communication unit;
a step of encrypting the user data from the request source communication terminal with the encryption device's own encryption key or encrypting the user data from the communication terminal with the other communication terminal's encryption key to generate the encrypted user data;
a step of communicating the encrypted user data from the request source communication terminal by the first extra-troposphere communication unit with the communication partner via the first extra-troposphere communication line;
a step of the communication partner decrypting the encrypted user data received by the communication partner with the partner decryption key, or the encryption device decrypting the encrypted user data received by the communication device with its own decryption key to generate the user data from the request source communication terminal;
a step of transmitting the decrypted user data from the request source communication terminal to the request destination communication terminal by the communication partner or the communication device;
a step of encrypting the user data from the request destination communication terminal with the other communication party's encryption key or encrypting the user data with the encryption device's own encryption key to generate the encrypted user data;
a step of communicating the encrypted user data from the request destination communication terminal with the communication partner through the first extratroposphere communication line;
a step of decrypting the encrypted user data received by the first extratroposphere communication unit with the decryption key of the decryption device or the communication counterpart with the counterpart decryption key to generate the user data from the request destination communication terminal;
a procedure in which the communication device or the communication partner transmits the decrypted user data from the request destination communication terminal to the request source communication terminal.

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