FR2756439A1 - SPACE BASED TELECOMMUNICATIONS SYSTEM - Google Patents

Abstract

In a space-based telecommunications system (10), a first satellite (22) orbit the Earth at a first altitude, while a second satellite (20) is coupled to the first satellite (22) via a telecommunications link and is in orbit around the Earth at a second altitude, different from the first. The first satellite (22) and the second satellite (20) communicate satellite control information to each other when the second satellite is in view of the first satellite. When there are multiple second satellites (20), the crosslinks between the second satellites (20) can therefore use all the available bandwidth to transfer voice and data signals between them.

Description

The present invention relates generally to

  space-based telecommunications and, in particular, satellites located in different orbits communicating with each other control information

satellites.

  Some satellites in conventional satellite communications systems have the ability to communicate with adjacent satellites sharing the same orbit altitude. These connections between satellites are called "cross links", and it is through them that voice signals and, or, data are transported from one satellite to another. If a base station on Earth transmits control information to a satellite other than the first satellite to receive the information, that control information may pass through many cross links before the satellite

  selected to receive the order information does not actually receive it.

  The retransmission of data or information from one satellite to another is what is commonly called hop transmission (the "hop" being taken here in the direction of direct connection between two nodes, that is to say - say two satellites). Hopping transmission consumes valuable energy and bandwidth, especially when control information is transmitted via many different satellites. Therefore, there is a need for a satellite communications system which reduces the number of hops that must be made before the receiving satellite receives command information or instructions from the satellite. In addition, the use of cross links for satellite control information can consume a cross link bandwidth which could be used to carry income-generating traffic. By traffic is meant, without limitation, voice information, data or faxes. Therefore, there is a need for a satellite communications system which minimizes the control information of the satellites carried on the cross links, thereby making

  maximum bandwidth available for revenue-generating traffic.

  The following description, intended to illustrate the invention, aims

  to allow a better understanding of its characteristics and advantages; it is based on the appended drawings: FIG. 1 is a high level diagram of a satellite telecommunications system according to a preferred embodiment of the invention; and

  Figure 2 is an example of a very simplified diagram of a satellite.

  The present invention is useful in that a network of satellites in geosynchronous orbit can communicate with a network of satellites in low Earth orbit. Since command information and instructions from satellites are transferred via geosynchronous satellites, there is no need for cross links in low Earth orbit to transfer this information. A base station (ie a satellite control installation) communicates directly with a geosynchronous satellite which in turn passes the communication directly to the respective satellites in low earth orbit and in medium earth orbit. A geosynchronous satellite will have visibility of several satellites in low Earth orbit at the same time and, therefore, will communicate directly with them. By binding with three or four geosynchronous satellites, each satellite of the finding in low Earth orbit becomes visible. FIG. 1 shows a very simplified diagram of a satellite telecommunications system 10. As shown in FIG. 1, the telecommunications system comprises at least two satellites 20 and 22, any number of subscriber units 30 and at least one base station 40. In general, satellites 20 and 22, the Subscriber units 30 and the base station 40 of the telecommunications system 10 can be considered as a network of nodes. All the nodes of the telecommunications system 10 are or may be in data communication with other nodes of the telecommunications system 10 via telecommunications links. In addition, all the nodes of the telecommunications system 10 are or can be in data communication with other telephone devices dispersed around the world via public telephone networks (PSTN) and, or alternatively, conventional terrestrial telecommunications devices to a PSTN via stations

classic land bases.

  The word "satellite" is used in this description to designate a

  a manufactured object or a vehicle intended to travel in an orbit around the Earth.

  The word "constellation" designates a certain number of satellites placed in certain orbits and intended to provide a specified coverage (for example radiocommunication, remote sensing, etc.) of a part, of several parts, or of the whole of the Earth. A constellation typically has multiple rings (or planes) of satellites and can have an equal number of satellites in

  each plan, although this is not essential.

  The invention can be applied to space-based telecommunications systems which assign particular regions of the Earth to specific cells defined on the Earth, and preferably systems which cause cells to move across the Earth. surface of the earth. The satellite 20 can be an isolated satellite or one of the many satellites 20 of a constellation of satellites orbiting the earth. The invention can also be applied to space-based telecommunications systems which have satellites orbiting the Earth at any angle of inclination, which includes

  models of polar orbits, equatorial orbits, inclined orbits or others.

  The invention can be applied to systems in which total coverage of the Earth is not achieved (ie where there are "holes" in the telecommunications coverage provided by the constellation) and to systems in which there is multiple coverage of certain parts of the Earth (i.e. more than one satellite is in view of a particular point on the surface

of the earth).

  In the preferred embodiment, the satellites 20 have a low Earth orbit, while the satellite 22 is a geosynchronous satellite. In another possible embodiment, the satellites 20 can be in medium earth orbit, while the satellite 22 is a geosynchronous satellite. According to another embodiment, the satellites 20 can be in a low Earth orbit, while the satellite 22 can be in a medium Earth orbit. There may be more than one satellite 22 serving the satellites 20, and these satellites 22 may be able to communicate with each other. A satellite in low Earth orbit will typically be in an altitude range from 700 km to 1,400 km (400 to 800 miles), while a satellite in medium Earth orbit will be at an altitude of about 2,000 km (6 200 miles), and that geosynchronous satellites are one

  elevation of approximately 36,000 kilometers (23,000 miles).

  Each satellite 20 communicates with other nearby satellites 20 via cross links. These cross links form the backbone of the space-based mobile telecommunications system 6. Thus, a call or a communication of a user, including, without limitation, data, voice signals and faxes, which comes from a subscriber unit 30 placed at any point on the surface of the Earth or in its vicinity can be routed via satellite 20 or a constellation of satellites to substantially any other point on the surface of the Earth. A call can be routed to a subscriber unit 31 (which receives the call) located on or near the Earth's surface from another satellite. The material means that the satellite 20 uses (for example spread spectrum technology) to communicate with subscriber units 30 and a base station 40 are indeed

known to those skilled in the art.

  The satellite 20 communicates with the satellite 22 via a cross link when the satellite 20 is in view of the satellite 22. The satellite 20 is not always in view of the satellite 22, but it is in view of the satellites 22 for a certain period of time. its orbit around the Earth. In other embodiments, there are numerous satellites 22, each satellite 20 being able to communicate with one of the satellites 22 regardless of where they are in their orbit around the Earth. In addition, each satellite 22 may be able to communicate with

adjacent satellites 22.

  The cross links between satellites 20 and 22 carry satellite control information, comprising, without limitation, instructions for the satellites, telemetry data, traffic routing vectors, traffic connection establishment data, line release messages, channel frequency of a cell, satellite operating instructions, cell shutdown programs. The satellite control information may also include radio link management data, such as time tag beam activation / deactivation tables, radio channel data associated with time tag beams such as allocation and the decommissioning of radio resources, and associated broadcast channel data

  to time tag beams.

  Satellite 29 receives satellite control information for one or more satellites from base station 40 and communicates it to the appropriate satellites 20. Since satellite 22 communicates satellite control information to satellites 20, the cross links between satellites 20 carry only user information (e.g. voice, fax and data) for transmission

  the communication of a subscriber unit 30 with another subscriber unit 30.

  Subscriber units 30 can be placed anywhere on the surface of the Earth or in the atmosphere above the Earth. The mobile telecommunications system 10 can process any number of subscriber units 30. The subscriber units 30 are preferably telecommunications devices capable of receiving voice signals and, well, data from satellites 20 and , or, of base stations 40. For example, the subscriber units 30 can be mobile cellular telephones of the manual type designed to transmit and receive communications in connection with satellites 20 and, or, base stations 40. In addition, the subscriber units 30 may be computers capable of sending E-mail messages, signals

  video, or fax signals, to name a few.

  The material means used by subscriber units 30 to transmit voice signals and, or, data to or from satellites 20 are well known in the art. In the preferred embodiment of the invention, the subscriber unit 30 communicates with a satellite 20 using a limited portion of the electromagnetic spectrum, which is divided into many channels. The channels will preferably be frequency channels belonging to the L band, to the K band, to the S band or to a combination of these, but may include communications of the frequency multiple access type (FDMA), of the access type. time multiple (TDMA) and, alternatively, of code access multiple access (CDMA) type, or using a combination of these types. Other methods can be used, as is well known from

one skilled in the art.

  The base station 40 communicates with the satellites 20 via the satellite 22 and controls them. For example, there may be a base station located in Honolulu, another base station located in Los Angeles and another base station in Washington, DC Base stations 40 may produce satellite signaling instructions for the satellite 22 so that the satellites 22 and 20 maintain their correct positions in orbit and perform other essential maintenance tasks. The base stations 40 may also be responsible for receiving voice signals and, or, data from satellites 20. The material means used by the base station 40 (for example spread spectrum) to communicate with the satellites

  22 and 20 and, alternatively, the subscriber units 30 are well known to those skilled in the art.

  FIG. 2 represents an example of a very simplified diagram of satellite 20 or 22. Satellite 20 comprises at least two transceivers ', a processor 34 and a memory 36. Certain transceivers 30' of satellite 20 are able to send satellite control information 20 and receive it, while other transceivers 30 'can send user information (e.g. voice, facsimile and data) to other adjacent satellites 20, to units base 30 and to base stations 40 to receive them. Certain transceivers 30 'of satellite 22 are able to send satellite control information to satellite 22 and to base station 40 and to receive it. The processor 34 controls the entire operation of the satellite 20 or 22 and may be responsible for the execution of software application programs. The memory 36 stores the programs executed by the processor 34. While a single processor 34 and a single memory unit 36 are shown in Figure 2, those skilled in the art will understand that more

  of a processor and more than one memory can be used in the satellite 20, 22.

  The number of processors and the memory size are unrelated to

the invention.

  The advantages of the invention are that it is thus possible to eliminate the need to use cross links between satellites in low Earth orbit to provide control information to other satellites in low Earth orbit. Another advantage is that a single hop is required to communicate satellite control information from satellite 22 to satellite 20. Thus, satellite control instructions can reach the designated low Earth orbit satellite much faster. Another advantage is that the bandwidth previously used for control information can be carried by the satellite 22, which leaves a greater bandwidth for the

income generating traffic.

  Variants are possible within the framework of the invention. For example, the following combinations are possible: a geosynchronous satellite 22 communicating with satellites 20 in medium orbit or low Earth orbit, or a satellite 22 in medium earth orbit communicating

  with 20 satellites in low Earth orbit.

  Of course, those skilled in the art will be able to imagine, from the

  system whose description has just been given by way of illustration only and

  in no way limiting, various variants and modifications not departing from the scope of the invention.

Claims (10)

  1. A space-based telecommunications system (10), characterized by: a first satellite (22) placed in orbit around the Earth at a first altitude; and a second satellite (20) coupled to the first satellite (22) via a telecommunications link and placed in orbit around the Earth at a second altitude, different from the first altitude, and in that the first satellite (22) and the second satellite (20)   communicate satellite control information to each other.   2. System according to claim 1, characterized in that the first   satellite (22) is in geosynchronous orbit around the Earth.   3. System according to claim 2, characterized in that the second   satellite (20) is in medium Earth orbit around the Earth.   4. System according to claim 2, characterized in that the second   satellite (20) is in low Earth orbit around the Earth.   5. System according to claim 1, characterized in that the connection of   telecommunications is a radio frequency link.   6. System according to claim 1, characterized in that the connection of   telecommunications is an optical link.   7. The system of claim 1, further characterized by: a base station (40) capable of transmitting and receiving first radio frequency signals; and at least one subscriber unit (30) capable of transmitting and receiving second radio frequency signals; further characterized in that the first satellite (22) has a first transceiver capable of receiving and transmitting the first signals of   radio frequency in connection with the base station (40); and a second transmitter-   receiver capable of receiving and transmitting third radio frequency signals in connection with the second satellite (20); and   in that the second satellite (20) comprises a first transmitter-   receiver capable of receiving and transmitting the third radio frequency signals in connection with the first satellite (22); and a second transceiver capable of receiving and transmitting the second radio frequency signals in conjunction with the unit subscriber (30).   8. The system of claim 1, further characterized by: a base station (40) capable of transmitting and receiving first radio frequency signals; and at least one subscriber unit (30) capable of transmitting and receiving second radio frequency signals; further characterized in that the first satellite (22) has a first transceiver capable of receiving and transmitting the first signals   radio frequency in connection with the base station (40); and a second transmitter-   receiver capable of receiving and transmitting optical signals in connection with the second satellite (20); and   in that the second satellite (20) comprises a first transmitter-   receiver capable of receiving and transmitting optical signals in connection with the first satellite (22); and a second transceiver capable of receiving and transmitting the second radio frequency signals in conjunction with the subscriber unit (30).   9. The system of claim 1, further characterized by: a base station (40) capable of transmitting and receiving optical signals; and at least one subscriber unit (30) capable of transmitting and receiving first radio frequency signals; further characterized in that the first satellite (22) has a first transceiver capable of receiving and transmitting the optical signals in connection with the base station (40); and a second transceiver capable of receiving and transmitting second radio frequency signals in conjunction with the second satellite (20); and   in that the second satellite (20) comprises a first transmitter-   receiver capable of receiving and transmitting the second radio frequency signals in conjunction with the first satellite (22); and a second transceiver capable of receiving and transmitting the first radio frequency signals in conjunction with the unit subscriber (30).   The system of claim 1, further characterized by: a base station (40) capable of transmitting and receiving first optical signals; and at least one subscriber unit (30) capable of transmitting and receiving radio frequency signals; further characterized in that the first satellite (22) has a first transceiver capable of receiving and transmitting the first signals   optics in connection with the base station (40); and a second transmitter-   receiver capable of receiving and transmitting second optical signals in connection with the second satellite (20); and   in that the second satellite (20) comprises a first transmitter-   receiver capable of receiving and transmitting the third optical signals in connection with the first satellite (22); and a second transceiver capable of receiving   and transmitting the radio frequency signals in connection with the subscriber unit (30).