Medium-earth-altitute satellite-based cellular telecommunications

• US 5,867,783 A
• Filed: 08/30/1996
• Issued: 02/02/1999
• Est. Priority Date: 04/22/1991
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Cress, Peter H., Rusch, Roger J., Horstein, Michael
• Primary Examiner(s): Urban, Edward F.
• Assistant Examiner(s): Ferguson, Keith
• Application Number:
  US08/705,976
• Time in Patent Office: 886 Days
• Field of Search: 455/427, 455/422, 455/424, 455/425, 455/428, 455/429, 455/430, 455/431, 455/12.1, 455/13.1, 455/13.2, 455/13.3, 342/356, 343/754, 359/867, 244/158 R, 244/159
• US Class Current: 455/427
• CPC Class Codes: B64G 1/1007 Communications satellites
• CPC Class Codes: B64G 1/1085 Swarms and constellations
• CPC Class Codes: B64G 1/242 Orbits and trajectories
• CPC Class Codes: H04B 7/195 Non-synchronous stations
• CPC Class Codes: H04B 7/2041 Spot beam multiple access

Abstract

A satellite-based cellular telecommunications system employing a constellation of telecommunications satellites in medium earth orbit to provide multibeam radio frequency (rf) communications links for worldwide cellular telephone service with a minimum number of satellites. The telecommunications satellites are placed in a plurality of inclined orbits about the earth at an altitude of between approximately 5600 and 10,000 nautical miles. The characteristics of the orbits, such as the number of orbits, the inclination of each orbit, the number of satellites in each orbit and the altitude of the satellites, are tailored to maximize the coverage area of the satellites and their related line-of-sight elevation angles, while minimizing propagation time delays, the number of beam-to-beam and satellite-to-satellites handovers, and the total number of satellites. The present invention also includes several additional features which essentially eliminate beam-to-beam and satellite-to-satellite handovers, thus dramatically reducing the likelihood of dropouts.

Claims

1. A method for deploying a full service constellation of satellites in a satellite based telecommunications system, whereby the satellites provide one of single and double coverage of at least a predetermined portion of the earth depending upon a number of satellites deployed, wherein single coverage constitutes continuous, 24-hour satellite visibility by mobile users of one satellite and double coverage constitutes continuous, 24-hour satellite visibility by mobile users of two satellites, each satellite being adjustable within a corresponding orbital plane to accommodate gain and loss of satellites from the corresponding orbital plane, comprising the steps of:

deploying a plurality of satellites in an original constellation of satellites providing single coverage;

distributing said original constellation of satellites along at least one orbital plane to provide single coverage of a desired portion of the earth;

providing rf communications links through said original constellation of satellites between mobile users and ground stations in an area of single coverage for the desired portion of the earth; and

deploying at least one additional satellite to said at least one orbital plane to provide a baseline constellation providing double coverage.

2. A method according to claim 1, further comprising the steps of:

after establishing double coverage, losing at least one satellite from the baseline constellation due to satellite failure, thereby temporarily preventing coverage of some region desired to have coverage by a faulty satellite orbital plane; and

adjusting a position of at least one remaining non-failing satellite within said faulty satellite orbital plane to provide at least single coverage of the desired portion of the earth until the satellite that failed is repaired or replaced.

3. A method according to claim 2, further comprising the steps of:

introducing into operation a new or repaired satellite within the faulty satellite orbital plane; and

adjusting a position of at least one satellite in the faulty satellite orbital plane to expand coverage afforded by satellites in the faulty satellite orbital plane from single coverage to double coverage.

4. A method according to claim 1, wherein the step of deploying at least one additional satellite includes deploying three additional satellites.

5. A method according to claim 1, wherein the original constellation includes six satellites that provides single hemispheric coverage of a predetermined latitude band.

6. A method according to claim 1, wherein the baseline constellation includes nine satellites that provide double hemispheric coverage of a predetermined band.

7. A method according to claim 1, wherein the original constellation includes nine satellites that provide whole earth coverage.

8. A method according to claim 1, wherein the baseline constellation includes twelve satellites that provide double whole earth coverage.

9. The method according to claim 1 further comprising the step of providing multi-beam communications links between the satellites and mobile users.

10. The method according to claim 1, further comprising receiving rf communications from mobile users via a multi-beam antenna over a first frequency band;

and

transmitting rf communications to the mobile users via a multi-beam antenna over a second frequency band.

11. The method according to claim 1, wherein each satellite uses at least two multi-beam antennas to provide multi-beam communications links with mobile users.

12. The method according to claim 1, wherein the satellites use at least two antennas to provide rf communications links with the ground stations.

13. The method according the claim 1, wherein the satellites utilize multi-beam antennas having a composite coverage area that determines the service region actually covered by each satellite.

14. The method according to claim 1, wherein each satellite utilizes a multi-beam antenna which includes 19 beams providing a composite footprint coverage area of about 23°

.

15. The method according to claim 1, wherein each satellite includes a multi-beam antenna having 37 beams providing a composite footprint coverage area of about 35°

.

16. The method according to claim 1, wherein each satellite includes a multi-beam antenna, each beam of the multi-beam antenna having a field of view of about 5°

and being capable of operating with mobile users having 1/2 watt of power and an omni directional antenna.

17. A method of forming a constellation of telecommunications satellites, comprising the steps of:

providing an original constellation of up to nine satellites which provide continuous, 24-hour satellite visibility by mobile users of one satellite in at least a predetermined latitude band;

evenly distributing said up to nine satellites among at least two inclined orbital planes;

operating said original constellation of satellites to provide telecommunications links between ground stations and mobile users in said predetermined latitude band; and

adding additional satellites to provide a full baseline satellite constellation of no more than 12 satellites which provides continuous, 24-hour satellite visibility by mobile users of two satellites in said at least a predetermined latitude band.

18. The method of claim 17, further comprising the step of:

after providing said original constellation and before providing said full baseline constellation, adding up to three additional satellites to provide a follow-on constellation of no more than nine satellites, said follow-on constellation including said no more than six satellites of said original constellation and said up to three additional satellites.

19. The method of claim 17, further comprising the step of arranging said original constellation of satellites in three circular orbital planes with two satellites per plane.

20. A method according to claim 17, further comprising the step of arranging said original constellation of satellites in up to three elliptical orbital planes, with at least two satellites per plane.

21. A method according to claim 17, wherein said full baseline constellation includes nine satellites arranged in no more than three elliptical orbital planes with at least three satellites in each elliptical orbital plane.

22. A method according to claim 17, wherein said follow-on constellation offers global land mass coverage of the earth of one satellite at all times with a minimum elevation angle of 10°

.

23. A method according to claim 17, wherein said full baseline satellite constellation offers global land mass coverage of the earth by at least two satellites at all times with a minimum elevation angle of 10°

.

24. A method according to claim 17, wherein said original constellation offers hemispheric coverage of the earth by at least one satellite at all times with a minimum elevation angle of 10°

.

25. A method according to claim 17, wherein said original constellation offers hemispheric coverage of the earth by at least two satellites at all times with a minimum elevation angle of 10°

.

26. A method according to claim 17, wherein said orbital planes are inclined at an inclination angle of at least 63°

.

27. A method according to claim 17, wherein said orbital planes are inclined at an inclination angle of at least 55°

.