Medium-earth-altitude satellite-based cellular telecommunications

• US 5,551,624 A
• Filed: 05/12/1995
• Issued: 09/03/1996
• 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: Rusch, Roger J., Cress, Peter H., Horstein, Michael
• Primary Examiner(s): BAREFOOT, GALEN L
• Application Number:
  US08/440,311
• Time in Patent Office: 480 Days
• Field of Search: 244/158 R, 343/754, 359/867, 375/1, 379/59, 379/60, 455/11.1, 455/12.1, 455/13.1, 455/13.2, 455/13.3, 344/352-358, 344/359, 344/360
• US Class Current: 455/12.1
• 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 constellation of telecommunication satellites which provides 24-hour cellular telephone communication coverage over a predetermined latitude range around the world for a cellular transceiver having an omni-directional antenna operating at a power level as low as 1/2 watt, comprising:

a plurality of less than 9 telecommunication satellites providing 24-hour cellular telephone communication coverage over a predetermined latitude range around the world which is less than whole earth coverage, each of said satellites having a plurality of multibeam antennas for enabling simultaneous bi-directional communication links with a plurality of cellular-based telecommunication devices;

each of said satellites residing in one of a plurality of predetermined orbits, with the number of said predeteremined orbits being different than the number of said satellites in each of said predetermined orbits; and

each of said predetermined orbits being related to the other orbits such that each of said predetermined orbits has a predetermined inclination angle with respect to the equator, a predetermined altitude of between approximately 5600 nmi and 7500 nmi, and a predetermined ascending node spacing between satellites in different orbital planes.

2. The constellation of telecommunication satellites according to claim 1, wherein there are a plurality of said satellites in each of said predetermined orbits.

3. The constellation of telecommunication satellites according to claim 2, wherein said satellites reside in three orbital planes and there are two satellites in each of said orbital planes.

4. The constellation of telecommunication satellites according to claim 1 wherein said predetermined inclination angle is between 50 and 55 degrees with respect to the equator.

5. The constellation of telecommunication satellites according to claim 1, wherein said predetermined altitude is approximately 5600 nautical miles above the earth.

6. A constellation of telecommunication satellites which provides 24-hour cellular telephone communication coverage over a predetermined latitude range around the world for a cellular transceiver having an omni-directional antenna operating at a power level as low as 1/2 watt, comprising:

a plurality of telecommunication satellites, each of said satellites having a plurality of multibeam antennas for enabling simultaneous bi-directional communication links with a plurality of cellular-based telecommunication devices;

each of said satellites residing in one of a plurality of predetermined orbits, with the number of said satellites in each of said orbits being different than the number of said orbits to provide 24-hour cellular telephone communication coverage over a predetermined latitude range around the world which is less than whole earth coverage; and

each of said predetermined orbits being related to the other orbits such that each of said predetermined orbits has a predetermined inclination angle with respect to the equator, a predetermined altitude of between approximately 5600 nmi and 7500 nmi, a predetermined ascending node spacing between satellites in different orbital planes, and a predetermined relative phase angle between satellites in different orbital planes such that an arriving satellite comes into view above a predetermined minimum elevation angle before a departing satellite disappears from view.

7. The constellation of telecommunication satellites according to claim 6, wherein there are a plurality of said satellites in each of said predetermined orbits.

8. The constellation of telecommunication satellites according to claim 7, wherein said satellites reside in three orbital planes and there are two satellites in each of said orbital planes.

9. The constellation of telecommunication satellites according to claim 6, wherein said predetermined inclination angle is between 50 and 55 degrees with respect to the equator.

10. The constellation of telecommunication satellites according to claim 6, wherein said predetermined altitude is approximately 5600 nautical miles above the earth.

11. A cellular telephone communication system having at least one planetary-based gateway station, a plurality of telecommunication satellites having a plurality of multibeam cellular communication antennas and at least one land-based mobile telecommunication device which is randomly located in a fixed cellular service region, said cellular telephone communication system being characterized by:

each antenna providing a predetermined field of view which is less than the field of view for any of said satellites limiting a maximum swing of the boresight angle of said antenna to approximately ±

4°

relative to NADIR for communication coverage with said land-based mobile telecommunication device to achieve 24-hour cellular telephone communication coverage over a predetermined latitude range around the world which is less than whole world coverage, and

an orbital configuration of said satellites in which each of said satellites resides in one of a plurality of predetermined altitude orbits of between approximately 5600 nmi and 7500 nmi, each of said predetermined orbits being related to the other orbits such that each of said predetermined orbits has a predetermined inclination angle with respect to the equator, a predetermined ascending node spacing between satellites in different orbital planes and a predetermined relative phase angle between satellites in different orbital planes.

12. A cellular telephone communication system having at least one planetary-based gateway station, a plurality of telecommunication satellites having a plurality of multibeam cellular communication antennas and at least one land-based mobile telecommunication device which is randomly located in a fixed cellular service region, said cellular telephone communication system being characterized by:

each antenna providing a predetermined field of view which is less than the field of view for any of said satellites, and

an orbital configuration of said satellites in which each of said satellites resides in one of a plurality of predetermined altitude orbits of between approximately 5600 nmi and 7500 nmi, with the number of said satellites in each of said orbits being different than the number of said orbits, each of said predetermined orbits being related to the other orbits such that each of said predetermined orbits has a predetermined inclination angle with respect to the equator, a predetermined ascending node spacing between satellites in different orbital planes, and a predetermined relative phase angle between satellites in different orbital planes;

the number of said satellites, the field of view of said satellites and said orbital configuration combining to provide 24-hour cellular telephone communication coverage over a predetermined latitude range around the world which is less than whole earth coverage.

13. A cellular telecommunications system, comprising:

at least one mobile cellular telephone station having an omnidirectional antenna, said mobile cellular telephone station including means for transceiving radio frequency energy (RF);

at least one additional mobile or fixed telephone station being spaced from said mobile cellular telephone station within a predetermined region of the earth, with the fixed telephone station being connected to a gateway station including an antenna for transceiving radio frequency energy (RF);

a satellite constellation located in space over the earth and including apparatus for transceiving radio frequency energy (RF) for providing a radio frequency energy communication link with said mobile cellular telephone station and said additional mobile or gateway station, said satellite constellation comprising;

a plurality of telecommunications satellites, said plurality of telecommunications satellites being spaced and moving in a plurality of orbits about the earth with the movement of said satellites being non-synchronous to the rotation of the earth, said plurality of orbits being circular;

all of said plurality of telecommunications satellites being at an altitude between approximately 5600 nmi and 7500 nmi above the earth; and

at least one of said telecommunications satellites being in the line of sight to both said mobile cellular telephone station and said additional mobile or gateway station at any instant of time, with said line of sight being at a minimum elevation angle of no less than 10°

;

wherein a radio frequency energy (RF) propagation time between said mobile cellular telephone station or said additional mobile or gateway station to said telecommunications satellite is less than 60 msec; and

wherein said telecommunications satellites have receiving antennas permitting reception at said altitude of signals emitted from said mobile cellular telephone station having an omni-directional antenna.

14. The cellular telecommunications system according to claim 13, wherein said orbits are substantially equally inclined at a predetermined angle relative to the equatorial plane of the earth.

15. The cellular telecommunications system according to claim 14, wherein an inclination angle of said orbits is 55°

.

16. The cellular telecommunications system according to claim 13, wherein said orbits are evenly spaced about the equator of the earth.

17. The cellular telecommunications system according to claim 13, wherein the mobile cellular telephone station transmits radio frequency signals with power levels as low as one half watt.

18. The cellular telecommunications system according to claim 13, wherein said telecommunications satellites within one orbit are evenly spaced from one another.

19. The cellular telecommunications system according to claim 13, wherein the number of said plurality of orbits is three, the number of said plurality of telecommunications satellites per orbit is three and wherein said three satellites are equally spaced in their orbit so as to insure that any telephone station is always within view of at least one satellite.

20. The cellular telecommunications system according to claim 13, wherein the number of telecommunications satellites per orbit is four;

and wherein said four satellites are equally spaced in their orbit to insure that any telephone station is always in view of at least two satellites.

21. A cellular telecommunications system, comprising:

at least one mobile cellular telephone station, said mobile cellular telephone station having an omni-directional antenna and including means for transceiving radio frequency energy (RF);

at least one additional mobile or fixed telephone station being spaced from said mobile cellular telephone station within a predetermined region of the earth, with the fixed telephone station being connected to a gateway station including an antenna for transceiving radio frequency energy (RF);

a satellite constellation located in space over the earth and including apparatus for transceiving radio frequency energy (RF) for providing a radio frequency energy communication link with said mobile cellular telephone station and said additional mobile or gateway station, said satellite constellation comprising;

a plurality of telecommunications satellites, said plurality of telecommunications satellites being spaced and moving in a plurality of orbits about the earth with the movement of said satellites being non-synchronous to the rotation of the earth, said plurality of orbits being circular;

all of said plurality of telecommunications satellites being at an altitude between approximately 5600 nmi and 7500 nmi above the earth;

at least one of said telecommunications satellites being in the line of sight to both said mobile cellular telephone station and said additional mobile or gateway station at any instant of time, with said line of sight being at a minimum elevation angle of no less than 10°

;

wherein a radio frequency energy (RF) propagation time between said mobile cellular telephone station or said additional mobile or gateway station to said telecommunications satellite is less than 60 msec;

wherein said telecommunications satellites have receiving antennas permitting reception at said altitude of signals emitted from said mobile cellular telephone station having an omni-directional antenna; and

wherein the number of orbits and the number of telecommunications satellites per orbit and the spacing of said satellites is sufficient to insure that said mobile cellular telephone station is always within view of at least two satellites.

22. A cellular telecommunications system, comprising:

at least one mobile cellular telephone station, said mobile cellular telephone station having an omni-directional antenna and including means for transceiving radio frequency energy (RF);

at least one additional mobile or fixed telephone station being spaced from said mobile cellular telephone station within a predetermined region of the earth, with the fixed telephone station being connected to a gateway station including an antenna for transceiving radio frequency energy (RF);

a satellite constellation located in space over the earth and including apparatus for transceiving radio frequency energy (RF) for providing a radio frequency energy communication link with said mobile cellular telephone station and said additional mobile or gateway station, said satellite constellation comprising;

a plurality of telecommunications satellites, said plurality of telecommunications satellites being spaced and moving in a plurality of orbits about the earth with the movement of said satellites being non-synchronous to the rotation of the earth, said plurality of orbits being circular;

all of said plurality of telecommunications satellites being at an altitude between approximately 5600 nmi and 7500 nmi above the earth; and

at least one of said telecommunications satellites being in the line of sight to both said mobile cellular telephone station and said additional mobile or fixed telephone station at any instant of time, with said line of sight being at a minimum elevation angle of no less than 10°

;

wherein a radio frequency energy (RF) propagation time between said mobile cellular telephone station or said additional mobile or gateway station to said telecommunications satellite is less than 60 msec;

wherein said telecommunications satellites have receiving antennas permitting reception at said altitude of signals emitted from said mobile cellular telephone station having an omni-directional antenna; and

wherein a predetermined relative phase separation between said telecommunications satellites in adjacent orbital planes ensures that, before a leaving telecommunications satellites disappears from view above said minimum elevation angle, at least one arriving telecommunications satellites comes into view above said minimum elevation angle.

23. A cellular telecommunications system, comprising:

at least one mobile cellular telephone station, said mobile cellular telephone station having an omni-directional antenna and including means for transceiving radio frequency energy (RF);

at least one additional mobile or fixed telephone station being spaced from said mobile cellular telephone station within a predetermined region of the earth, with the fixed telephone station being connected to a gateway station including an antenna for transceiving radio frequency energy (RF);

a satellite constellation located in space over the earth and including apparatus for transceiving radio frequency energy (RF) for providing a radio frequency energy communication link with said mobile cellular telephone station and said additional mobile or gateway station, said satellite constellation comprising;

a plurality of telecommunications satellites, said plurality of telecommunications satellites being spaced and moving in a plurality of orbits about the earth with the movement of said satellites being non-synchronous to the rotation of the earth, said plurality of orbits being circular and having an altitude of approximately 5600 nmi above the earth; and

at least one of said telecommunications satellites being in the line of sight to both said mobile cellular telephone station and said additional mobile or fixed telephone station at any instant of time, with said line of sight being at a minimum elevation angle of no less than 10°

;

wherein a radio frequency energy (RF) propagation time between said mobile cellular telephone station or said additional mobile or fixed telephone station to said telecommunications satellite being less than 60 msec; and

wherein said telecommunications satellites have receiving antennas permitting reception at said altitude of signals emitted from said mobile cellular telephone station having an omni-directional antenna.

24. A cellular telecommunications system, comprising:

at least one mobile cellular telephone station, said mobile cellular telephone station having an omni-directional antenna and including means for transceiving radio frequency energy (RF);

at least one additional mobile or fixed telephone station being spaced from said mobile cellular telephone station within a predetermined region of the earth, with the fixed telephone station being connected to a gateway station including an antenna for transceiving radio frequency energy (RF);

a satellite constellation located in space over the earth and including apparatus for transceiving radio frequency energy (RF) for providing a radio frequency energy communication link with said mobile cellular telephone station and said additional mobile or fixed telephone station, said satellite constellation comprising;

a plurality of telecommunications satellites, said plurality of telecommunications satellites being spaced and moving in a plurality of orbits about the earth with the movement of said satellites being non-synchronous to the rotation of the earth, said plurality of orbits being circular;

all of said plurality of telecommunications satellites being at an altitude between approximately 5600 nmi and 7500 nmi above the earth; and

at least one of said telecommunications satellites being in the line of sight to both said mobile cellular telephone station and said additional mobile or fixed telephone station at any instant of time, with said line of sight being at a minimum elevation angle of no less than 10°

;

wherein a radio frequency energy (RF) propagation time between said mobile cellular telephone station or said additional mobile or fixed telephone station to said telecommunications satellite satellites is less than 60 msec;

wherein said telecommunications satellites have receiving antennas permitting reception at said altitude of signals emitted from said mobile cellular telephone station having an omni-directional antenna; and

wherein each of said telecommunications satellites includes an antenna capable of transceiving over multiple radio frequency energy beams.

25. A method of providing cellular telecommunications, comprising the steps of:

establishing a satellite constellation having a plurality of telecommunications satellites spaced in a plurality of inclined orbits about the earth with the movement of said satellites being non-synchronous to the rotation of the earth, all of said plurality of telecommunications satellites being at an altitude between approximately 5600 nmi and 7500 nmi above the earth;

providing a plurality of mobile or fixed cellular telephone stations for users on the earth;

initiating a telephonic communications session with a mobile cellular telephone station, said mobile cellular telephone station including means for transceiving radio frequency energy (RF) and an additional mobile or fixed telephone station being spaced from said mobile cellular telephone station within a predetermined region of the earth, with the fixed telephone station being connected to a gateway station including an antenna for transceiving radio frequency energy (RF), by transmitting a radio frequency energy (RF) signal from said mobile cellular telephone station through an omni-directional antenna to be received by one satellite of said constellation of telecommunications satellites for providing an RF communication link between said mobile cellular telephone station and said additional mobile or fixed telephone station;

wherein at least one of said telecommunications satellites is in the line of sight to both said mobile cellular telephone stations and said additional mobile or gateway station at any instant of time, with said line of sight being at a minime elevation angle of no less than 10°

;

wherein the radio frequency energy (RF) propagation time between said mobile cellular telephone station or said additional mobile or gateway station to said telecommunications satellite is less than 60 msec; and

wherein said telecommunications satellites have receiving sensitivity and antennas permitting reception at said altitude of signals emitted from a mobile cellular telephone station having an omni-directional antenna with an RF power level of one half watt; and

retransmitting said RF signal through an antenna of said satellite to said additional mobile or gateway station to be received at said additional mobile or gateway station and establishing a communication link between said additional mobile or gateway station and said mobile cellular telephone station.

26. A medium-earth-orbit, satellite-based cellular telecommunications system comprising:

a plurality of mobile cellular telephone stations including at least one transceiver with an omni-directional antenna;

a constellation of telecommunications satellites providing a multibeam radio frequency (rf) communications link for said plurality of cellular telephone stations, the satellites being placed in a plurality of inclined orbits about the earth at an altitude of between approximately 5600 and 7500 nautical miles, wherein at least one satellite includes;

a multibeam antenna having a boresight; and

directing means for adjusting said antenna boresight to focus on a predetermined region of the earth as the satellite orbits said predetermined region.

27. The satellite-based cellular telecommunications system as set forth in claim 26, wherein the directing means adjusts the attitude of the satellite to maintain the antenna boresight on the predetermined region.

28. The satellite-based cellular telecommunications system as set forth in claim 26, wherein the directing means gimbals and rotates the antenna to maintain the antenna boresight on the predetermined region.

29. The satellite-based cellular telecommunications system as set forth in claim 26, wherein the orbits are approximately circular.

30. The satellite-based cellular telecommunications system as set forth in claim 26, wherein the constellation includes nine satellites arranged in three circular orbital planes, with three satellites in each orbital plane, the satellites being evenly spaced at 120°

intervals in each orbital plane at an altitude of 5600 nautical miles, each orbital plane being inclined at angle of 55°

relative to the equatorial plane to insure that each station is within view of at least one of said satellites at all times at a viewing angle to the earth of not less than 10°

.

31. The satellite-based cellular telecommunications system as set forth in claim 26, wherein the constellation includes twelve satellites arranged in three circular orbital planes, with four satellites in each orbital plane, the satellites being evenly spaced at 90°

intervals in each orbital plane at an altitude of 5600 nautical miles, each orbital plane being inclined at angle of 55°

relative to the equatorial plane to insure that each station is within view of at least two of said satellites at all times at a viewing angle to the earth of not less than 10°

.

32. The satellite-based cellular telecommunications system as set forth in claim 26, further including a gateway station in said predetermined region for establishing an RF communication link with a satellite.

33. The satellite-based cellular telecommunications system as set forth in claim 26, wherein each station is within view of at least one of said satellites at all times at a viewing angle of at least 10°

.