Method and system of frequency stabilization in a mobile satellite communication system

• US 6,356,740 B1
• Filed: 06/30/1995
• Issued: 03/12/2002
• Est. Priority Date: 06/30/1995
• Status: Expired due to Term

• Current Assignee: Hughes Network Systems LLC (Echostar Corporation)
• Original Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Inventors: Malcolm, James E., Marquart, Robert C.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): BANKS HAROLD, MARSHA DENISE
• Application Number:
  US08/497,333
• Time in Patent Office: 2,447 Days
• Field of Search: 455/10, 455/12.1, 455/13.1, 455/13.2, 455/33.1, 455/13.3, 455/54.1, 455/71, 455/68, 455/69, 455/70, 455/524
• US Class Current: 455/71
• CPC Class Codes: H03J 7/02 Automatic frequency control H03J7/18 takes precedence
• CPC Class Codes: H03L 1/00 Stabilisation of generator output against variations of physical values, e.g. power supply
• CPC Class Codes: H04B 7/18539 Arrangements for managing radio, resources, i.e. for establishing or releasing a connection

Abstract

The present invention relates generally to satellite communication systems, and more particularly to a method and system for stabilizing transmission frequencies in a mobile satellite communication system. The preferred embodiment of the invention involves adjusting the transmit frequency of the gateway to account for a frequency shift from the reference frequency on the link between the gateway and the satellite. The preferred method of stabilizing the transmission frequency of a mobile terminal in a mobile satellite communication system involves receiving frequency offset information transmitted by a gateway in the mobile satellite system, and adjusting a reference oscillator in a mobile terminal based on the frequency offset information. The preferred embodiment of the system includes a plurality of mobile terminals, a satellite adapted to communicate with the mobile terminals, and a gateway in communication with the satellite. Each mobile terminal has a mobile terminal reference oscillator, and the satellite has a satellite reference oscillator. The gateway has a high-stability reference oscillator and a digital processor. The digital processor includes a routine for calculating a frequency offset, such as reference oscillator drift. The gateway transmits the frequency offset to at least one of the mobile terminals via the satellite. At least one of the mobile terminals receives the frequency offset and adjusts the mobile terminal reference oscillator to compensate for the received frequency offset.

Claims

1. A method of stabilizing a transmission frequency in a mobile satellite communication system comprising the steps of:

adjusting a transmit frequency of a gateway terminal to compensate for a frequency shift between said gateway and a satellite;

calculating a frequency offset based on a geographical position of a mobile terminal and predetermined information related to movement of said satellite;

broadcasting the calculated frequency offset from said gateway terminal to the mobile terminal;

receiving said frequency offset information transmitted by said gateway in said mobile terminal; and

adjusting a reference oscillator in said mobile terminal based on said frequency offset information.

2. The method of claim 1, further comprising the steps of:

adjusting a transmit frequency of said mobile terminal to compensate for said frequency offset.

3. The method of claim 1, further comprising the steps of:

adjusting a receive frequency of said mobile terminal to compensate for said frequency offset.

4. The method of claim 1, further comprising the steps of:

transmitting a first signal from said mobile terminal to said gateway;

receiving a mobile terminal frequency offset from said gateway; and

adjusting said reference oscillator in said mobile terminal to compensate for said mobile terminal frequency offset.

5. The method of claim 4, wherein said mobile terminal frequency offset comprises mobile terminal motion offset.

6. The method of claim 4, wherein said mobile terminal frequency offset comprises mobile terminal reference oscillator offset.

7. The method of claim 1, further including the steps of:

placing a call between said mobile terminal and said gateway;

measuring a mobile terminal frequency offset at said gateway;

reporting said mobile terminal frequency offset to said mobile terminal;

adjusting said reference oscillator in said mobile terminal to compensate for said mobile terminal frequency offset.

8. The method of claim 7, further including the step of:

adjusting a transmit frequency of said mobile terminal to compensate for said mobile terminal frequency offset.

9. The method of claim 7, further including the step of:

adjusting a receive frequency of said mobile terminal to compensate for said mobile terminal frequency offset.

10. The method of claim 1, wherein said frequency offset information comprises satellite frequency translation offset.

11. The method of claim 1, wherein said frequency offset information comprises satellite motion offset.

12. The method of claim 1, further comprising the step of transmitting a doppler compensated signal from said gateway to said satellite.

13. The method of claim 12, wherein said doppler compensated signal comprises a signal having a frequency substantially equal to a nominal frequency minus a calculated uplink doppler offset.

14. The method of claim 13, further comprising the step of receiving the doppler compensated signal at the satellite, said doppler compensated signal having substantially the same frequency as the nominal frequency signal.

15. The method of claim 1, further comprising the steps of

transmitting a first signal from said gateway to a satellite;

translating the frequency of said first signal to produce a second signal;

transmitting said second signal from said satellite to a mobile terminal;

monitoring the transmission of the second signal at said gateway;

calculating a doppler offset for said first signal and for said second signal at said gateway; and

measuring a satellite frequency translation offset at said gateway by comparing the frequency of said first signal, the frequency of said second signal, and the doppler offset.

16. The method of claim 15, further including the step of:

adjusting a transmit frequency of said mobile terminal to compensate for said mobile terminal frequency offset.

17. The method of claim 16, further including the step of:

adjusting a recieve frequency of said mobile terminal to compensate for said mobile terminal frequency offset.

18. A mobile satellite communication system comprising:

a plurality of mobile terminals, each mobile terminal having a mobile terminal reference oscillator;

a satellite adapted to communicate with each of said mobile terminals, said satellite having a satellite reference oscillator;

at least one gateway in communication with said satellite, said gateway having a high-stability reference oscillator and a digital processor, said digital processor including a routine for calculating a frequency offset for each of the plurality of mobile terminals based on the geographical position of each of the plurality of mobile terminals and predetermined information related to movement of the satellite;

said gateway transmitting one of said frequency offsets to one of said mobile terminals, said one mobile terminal receiving said frequency offset and adjusting said mobile terminal reference oscillator to compensate for said received frequency offset.

19. The system of claim 18, wherein said mobile terminal frequency offset comprises mobile terminal motion offset.

20. The system of claim 18, wherein the one of said mobile terminal frequency offsets includes a mobile terminal reference oscillator offset.

21. The system of claim 18, wherein the one of said mobile terminal frequency offsets includes a mobile terminal reference oscillator drift, and said gateway periodically transmits said one frequency offset to said one of said mobile terminals.

22. The system of claim 18, wherein said satellite communicates with said mobile terminals by transmitting and receiving signals over a plurality of spot beams, each spqt beam having a coverage region and at least one control channel;

said routine calculates a plurality of frequency offsets, each calculated frequency offset associated with one of said spot beams and calculated based on the position of said coverage region for said associated spot beam; and

said gateway transmits said plurality of frequency offsets over said control channels to said mobile terminals.

23. The system of claim 18, wherein said gateway calculates a satellite frequency offset and transmits said satellite frequency offset to said satellite, said satellite adjusting said satellite reference oscillator to compensate for said received satellite frequency offset.

24. The system of claim 23, wherein said satellite frequency offset comprises satellite frequency translation offset.

25. The system of claim 23, wherein said frequency offset comprises satellite motion offset.

26. A gateway earth station in a mobile satellite communication system comprising:

an antenna for receiving and transmitting Ku-band signals;

a base transceiver station coupled to the antenna, said base transceiver station including a digital processor, said digital processor including a first routine for calculating a frequency offset based on a geographical position of a mobile terminal and on predetermined information pertaining to movement of a satellite, said base transceiver station transmitting said frequency offset to said satellite via the antenna; and

a high-stability reference oscillator coupled to the base transceiver station, said high-stability reference oscillator providing a reference frequency to the base transceiver station.