System and method for reducing interference between satellites

• US 5,444,449 A
• Filed: 12/15/1993
• Issued: 08/22/1995
• Est. Priority Date: 12/15/1993
• Status: Expired due to Term

• Current Assignee: Inmarsat Two Company
• Original Assignee: International Mobile Satellite Organization
• Inventors: Poskett, Peter, Nomoto, Shimichi, Mullins, Dennis, Gosselin, Stephane
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US08/168,875
• Time in Patent Office: 615 Days
• Field of Search: 342/352, 342/354, 342/356, 342/357
• US Class Current: 342/354
• CPC Class Codes: H04B 7/18513 Transmission in a satellite or space-based system
• CPC Class Codes: H04B 7/2041 Spot beam multiple access

Abstract

A satellite system facilitates communications between earth stations and both geostationary satellites and non-geostationary satellites in an orbit at a lower altitude than that of said the geostationary satellites by preventing the non-geostationary satellite from transmitting signals that might possibly interfere with signals transmitted by the geostationary satellites. The non-geostationary satellite includes position acquisition subsystem for determining the position, and in particular the latitude, of the non-geostationary satellite relative to the surface of the earth. A data processor determines a forbidden band of locations on the surface of the earth all possible geostationary satellites and the non-geostationary satellite, at its determined position, are separated by less than a specified minimum discrimination angle. An antenna control subsystem in the non-geostationary satellite controls transmission of signal energy from the non-geostationary satellite in accordance with the satellites position so as to prevent transmission of signal energy from the non-geostationary satellite to said locations within the forbidden band.

Claims

1. A method of operation of a satellite system having a geostationary orbital band occupied by at least one geostationary satellite and a non-geostationary satellite in an orbit at a lower altitude than that of said at least one geostationary satellite, comprising the steps of:

determining position of said non-geostationary satellite relative to the surface of the earth;

calculating a minimum discrimination angle between said geostationary band and non-geostationary satellite at its determined position relative to a ground station on earth, wherein said minimum discrimination angle corresponds to a predefined threshold of interference between signals received by said ground station from said non-geostationary satellite and geostationary satellites in said geostationary orbital band;

defining a forbidden band of locations on the surface of the earth from which said geostationary orbital band and said non-geostationary satellite, at its determined position, are separated by less than said minimum discrimination angle; and

controlling transmission of signal energy from said non-geostationary satellite in accordance with said position thereof so as to prevent transmission of signal energy from said non-geostationary satellite to said locations within said forbidden band.

2. The method of operation of claim 1 wherein said step of controlling transmission further includes the step of adjusting an antenna beam pattern projected by said non-geostationary satellite such that energy therefrom is not incident upon said locations within said forbidden band.

3. The method of operation of claim 2 wherein said step of adjusting said antenna beam pattern further includes the step of projecting spot beams only to regions on the surface of the earth outside of said forbidden band of locations.

4. The method of operation of claim 1 wherein said step of defining a forbidden band of locations on the surface of the earth includes the step of specifying a forbidden band of latitude range on the surface of the earth from within which selected orbital positions proximate said geostationary orbit are separated from said non-geostationary satellite by less than said minimum discrimination angle.

5. The method of operation of claim 1 wherein said step of controlling transmission includes the step of preventing transmission of signals from said non-geostationary satellite within a field of view thereof encompassing said forbidden band.

6. The method of operation of claim 1 wherein said step of defining a forbidden band of locations on the surface of the earth includes the step of storing forbidden bands of locations corresponding to selected positions of said non-geostationary satellite in a memory on said non-geostationary satellite.

7. The method of operation of claim 6 wherein said step of controlling transmission of signal energy from said non-geostationary satellite includes the step of preventing transmission of signal energy from said non-geostationary satellite to said forbidden bands of locations stored in said memory in accordance with said determined position of said non-geostationary satellite.

8. A satellite system having a geostationary orbital band occupied by at least one geostationary satellite and a non-geostationary satellite in an orbit at a lower altitude than that of said at least one geostationary satellite, said non-geostationary satellite including an antenna control subsystem comprising:

position acquisition means for determining position of said non-geostationary satellite relative to the surface of the earth;

a data processor, coupled to said position acquisition means, that defines a forbidden band of locations on the surface of the earth from which said geostationary orbital band and said non-geostationary satellite, at its determined position, are separated by less than a specified minimum discrimination angle; and

means, coupled to said data processor, for controlling transmission of signal energy from said non-geostationary satellite in accordance with said position thereof so as to prevent transmission of signal energy from said non-geostationary satellite to said locations within said forbidden band.

9. The system of claim 8 wherein said means for controlling transmission further includes means for adjusting an antenna beam pattern projected by said second satellite such that energy therefrom is not incident upon said locations within said forbidden band.

10. The system of claim 9 wherein said means for adjusting said antenna beam pattern further includes means for projecting spot beams only to regions on the surface of the earth outside of said forbidden band of locations.

11. The system of claim 8 wherein said data processor includes means for specifying a forbidden band of latitude range on the surface of the earth from within which selected orbital positions proximate said geostationary orbit are separated from said second satellite by less than said minimum discrimination angle.

12. The system of claim 8 wherein said means for controlling transmission includes means for preventing transmission of signals from said second satellite within a field of view thereof encompassing said forbidden band.

13. The system of claim 8 wherein said data processor further includes a memory that stores forbidden bands of locations corresponding to selected positions of said non-geostationary satellite in a memory on said non-geostationary satellite.

14. The system of claim 13 wherein said means for controlling transmission of signal energy from said non-geostationary satellite includes means for preventing transmission of signal energy from said non-geostationary satellite to said forbidden bands of locations stored in said memory in accordance with said determined position of said non-geostationary satellite.

15. A method of operation of a satellite system having a geostationary orbital band occupied by at least one geostationary satellite and a non-geostationary satellite in an orbit at a lower altitude than that of said at least one geostationary satellite, comprising the steps of:

determining position of said non-geostationary satellite relative to the surface of the earth;

defining a forbidden band of locations on the surface of the earth from which said geostationary orbital band and said non-geostationary satellite, at its determined position, are separated by less than a specified minimum discrimination angle corresponding to a predefined threshold of interference at the surface of the earth between signals from said non-geostationary satellite and said geostationary satellites in said geostationary orbital band; and

controlling transmission of signal energy from said non-geostationary satellite in accordance with said position thereof so as to prevent transmission of signal energy from said non-geostationary satellite to said locations within said forbidden band.

16. The method of operation of claim 15 wherein said step of controlling transmission further includes the step of adjusting an antenna beam pattern projected by said non-geostationary satellite such that energy therefrom is not incident upon said locations within said forbidden band.

17. The method of operation of claim 16 wherein said step of adjusting said antenna beam pattern further includes the step of projecting spot beams only to regions on the surface of the earth outside of said forbidden band of locations.

18. The method of operation of claim 15 wherein said step of defining a forbidden band of locations on the surface of the earth includes the step of storing forbidden bands of locations corresponding to selected positions of said non-geostationary satellite in a memory on said non-geostationary satellite.

19. The method of operation of claim 18 wherein said step of controlling transmission of signal energy from said non-geostationary satellite includes the step of preventing transmission of signal energy from said non-geostationary satellite to said forbidden bands of locations stored in said memory in accordance with said determined position of said non-geostationary satellite.