Frequency and timing synchronization and error correction in a satellite network

• US 20040234018A1
• Filed: 05/24/2004
• Published: 11/25/2004
• Est. Priority Date: 05/23/2003
• Status: Active Grant

• Current Assignee: Gilat Satellite Networks Limited
• Original Assignee: Gilat Satellite Networks Limited
• Inventors: Keschet, Daniel, Keshet, Arik, Ram, Uzi
• Granted Patent: US 7,471,720 B2
• Time in Patent Office: Days
• US Class Current: 375/354
• CPC Class Codes: H04B 7/18528 Satellite systems for providing two-way communications service to a network of fixed stations, i.e. fixed satellite service or very small aperture terminal [VSAT] system
• CPC Class Codes: H04B 7/208 Frequency-division multiple access [FDMA]
• CPC Class Codes: H04B 7/2125 Synchronisation

Abstract

An outgoing transmission carrier frequency at, for example, a remote terminal, may be adjusted based on a feature rate of an incoming transmission. The adjustment may compensate for error in the outgoing transmission carrier frequency. The incoming transmission may be from a satellite or hub, for example. The outgoing transmission may be the signal that is transmitted by an antenna, or the outgoing transmission may be converted to be at another carrier frequency such as a higher carrier frequency for ultimate transmission by an antenna. Also, a remote terminal may be synchronized to a satellite network with or without knowledge of the remote terminals'"'"' geographical location and with or without time stamps.

Claims

1. In a remote terminal of a satellite network, a method comprising a step of adjusting an outgoing transmission carrier frequency based on a feature rate of an incoming transmission.

2. The method of claim 1, further including steps of:

generating a reconstructed clock from the incoming transmission;

counting a predetermined number of pulses of the reconstructed clock to determine a period of time; and

counting a number of pulses of a locally-generated reference clock during the same period of time,

wherein the outgoing transmission carrier frequency is a function of at least the locally-generated reference clock.

3. The method of claim 2, further including a step of comparing the number of pulses counted of the reference clock to determine an error, wherein the step of adjusting includes adjusting the outgoing transmission carrier frequency to compensate for the error.

4. The method of claim 2, further including a step of comparing the number of pulses N counted of the reference clock to determine an error E=(N−

M)/M, wherein M is an expected number of pulses, and wherein the step of adjusting includes adjusting the outgoing transmission carrier frequency based on the error.

5. The method of claim 1, wherein the step of adjusting includes upconverting the outgoing transmission carrier frequency to a higher carrier frequency.

6. The method of claim 5, wherein the higher carrier frequency is in the C-band or the Ku-band.

7. The method of claim 1, wherein the outgoing transmission carrier frequency is in the L-band.

8. The method of claim 1, further including steps of:

generating a reconstructed clock from the incoming transmission;

counting a predetermined number of pulses of a locally-generated reference clock to determine a period time; and

counting a number of pulses of the reconstructed clock during the same period of time,

wherein the outgoing transmission carrier frequency is a function of at least the locally-generated reference clock.

9. The method of claim 8, further including a step of comparing the number of pulses counted of the reconstructed clock to determine an error, wherein the step of adjusting includes adjusting the outgoing transmission carrier frequency to compensate for the error.

10. The method of claim 8, further including a step of comparing the number of pulses N counted of the reconstructed clock to determine an error E such that N=R*(1/(1+E)), wherein R is an expected feature rate of the incoming transmission, and wherein the step of adjusting includes adjusting the outgoing transmission carrier frequency based on the error.

11. The method of claim 1, wherein the incoming transmission is from a hub of the satellite network.

12. The method of claim 1, wherein the feature rate is the baud rate of the incoming transmission.

13. The method of claim 1, wherein the feature rate is the data rate of the incoming transmission.

14. The method of claim 1, wherein the feature rate is a rate of MPEG blocks in the incoming transmission.

15. The method of claim 1, further including steps of:

providing a clock based on a locally-generated reference clock to a demodulator;

reading the feature rate value from the demodulator; and

comparing the feature rate value read from the demodulator to the nominal feature rate value.

16. In a remote terminal of a satellite network, a method comprising a step of adjusting an outgoing transmission carrier frequency based on a comparison of an incoming transmission with a locally-generated reference clock.

17. The method of claim 16, further including a step of generating a reconstructed clock from the incoming transmission, wherein the step of adjusting includes comparing the reconstructed clock with the reference clock.

18. The method of claim 16, wherein the outgoing transmission carrier frequency is in the L-band.

19. The method of claim 16, wherein the step of adjusting includes counting a predetermined number of first pulses associated with the incoming transmission and counting how many second pulses of the reference clock occur during a time required to count the first pulses.

20. The method of claim 19, further including determining an error based upon a comparison of the number of the second pulses counted with an expected number of the second pulses.

21. The method of claim 19, further including a step of generating a reconstructed clock from the incoming transmission, the first pulses being pulses of the reconstructed clock.

22. The method of claim 16, wherein the step of adjusting includes counting a predetermined number of first pulses associated with the reference clock and counting how many second pulses associated with the incoming transmission occur during a time required to count the first pulses.

23. The method of claim 22, further including determining an error based upon a comparison of the number of the second pulses counted with an expected number of the second pulses.

24. The method of claim 22, further including a step of generating a reconstructed clock from the incoming transmission, the second pulses being pulses of the reconstructed clock.

25. A remote terminal of a satellite network, comprising:

a receiver configured to receive an incoming transmission; and

a processor coupled to the receiver and configured to adjust a carrier frequency of an outgoing transmission based on a feature rate of the incoming transmission.

26. The remote terminal of claim 25, further including a modulator configured to generate the outgoing transmission under control from the processor.

27. The remote terminal of claim 26, further including an upconverter coupled to the modulator and configured to upconvert the outgoing transmission.

28. The remote terminal of claim 25, further including a local reference clock generator coupled to the processor and configured to generate a reference clock, wherein the processor is further configured to generate a reconstructed clock from the incoming transmission, count a predetermined number of pulses of the reconstructed clock to determine a period time, and count a number of pulses of the reference clock during the same period of time.

29. The remote terminal of claim 28, further including a modulator coupled to the processor and configured to generate the outgoing transmission, wherein the processor is further configured to determine an error based on the number of pulses counted of the reconstructed clock, and to control the modulator to adjust the carrier frequency of the outgoing transmission to compensate for the error.

30. The method of claim 28, further including a modulator coupled to the processor and configured to generate the outgoing transmission, wherein the processor is further configured to determine an error E based on the number of pulses N counted of the reconstructed clock such that N=R*(1/(1+E)), wherein R is an expected feature rate of the incoming transmission, and to control the modulator to adjust the outgoing transmission carrier frequency based on the error.

31. The remote terminal of claim 25, further including a reference clock generator coupled to the processor and configured to generate a reference clock, wherein the processor is further configured to generate a reconstructed clock from the incoming transmission, count a predetermined number of pulses of the reference clock to determine a period time, and count a number of pulses of the reconstructed clock during the same period of time.

32. The method of claim 31, further including a modulator coupled to the processor and configured to generate the outgoing transmission, wherein the processor is further configured to determine an error based on the number of pulses counted of the reconstructed clock, and to control the modulator to adjust the outgoing transmission carrier frequency to compensate for the error.

33. The method of claim 31, further including a modulator coupled to the processor and configured to generate the outgoing transmission, wherein the processor is further configured to determine an error E based on the number of pulses N counted of the reconstructed clock such that N=R*(1/(1+E)), wherein R is an expected feature rate of the incoming transmission, and to control the modulator to adjust the outgoing transmission carrier frequency based on the error.

34. A remote terminal of a satellite network, comprising:

a receiver configured to receive an incoming transmission;

a reference clock generator configured to generate a reference clock; and

a processor coupled to the receiver and the reference clock generator and configured to adjust an outgoing transmission carrier frequency based on a comparison of an incoming transmission with the reference clock.

35. The remote terminal of claim 34, wherein the processor is further configured to count a predetermined number of first pulses associated with the reference clock and count how many second pulses associated with the incoming transmission occur during a time required to count the first pulses.

36. The method of claim 35, wherein the processor is further configured to determine an error based upon a comparison of a number of second pulses counted with an expected number of the second pulses.

37. The remote terminal of claim 34, wherein the processor is further configured to count a predetermined number of first pulses associated with the incoming transmission and count how many second pulses associated with the reference clock occur during a time required to count the first pulses.

38. The method of claim 37, wherein the processor is further configured to determine an error based upon a comparison of the number of the second pulses counted with an expected number of the second pulses.

39. A method in a remote terminal, comprising steps of:

transmitting a first burst;

receiving a transmission including correction data responsive to the first burst; and

transmitting a second burst corrected in at least one of frequency or time in accordance with the correction data,

wherein the remote terminal does not receive time stamp transmissions.

40. The method of claim 39, further including a step of reconstructing slot and frame rates from a feature rate of the transmission.

41. The method of claim 39, wherein the correction data includes at least one of an amount of frequency adjustment or an amount of time adjustment.

42. The method of claim 39, wherein the remote terminal is part of a satellite network, the step of transmitting the first burst including transmitting the first burst within a predetermined window smaller in both time and frequency than a frame used by the satellite network.

43. The method of claim 39 wherein the remote terminal is unaware of its geographic location.

44. The method of claim 39, wherein the first burst is a link connect burst.

45. A remote terminal, comprising:

a transmission portion configured to transmit a first burst; and

a reception portion configured to receive a transmission including correction data responsive to the first burst,

wherein the transmission portion is further configured to transmit a second burst corrected in at least one of frequency or time in accordance with the correction data,

wherein the remote terminal does not receive time stamp transmissions.

46. The remote terminal of claim 45, further wherein slot and frame rates are reconstructed from a feature rate of the transmission.

47. The remote terminal of claim 45, wherein the correction data includes at least one of an amount of frequency adjustment or an amount of time adjustment.

48. The remote terminal of claim 45, wherein the remote terminal is part of a satellite network, the transmission portion being configured to transmit the first burst within a predetermined window smaller in frequency than an entire bandwidth used by the satellite network.

49. The remote terminal of claim 45, wherein the first burst is not aligned to slot and frame timing and does not require knowledge of geographic location.

50. A method in a hub, comprising steps of:

receiving a first burst from a remote terminal; and

transmitting correction data in response to the first burst,

wherein the hub does not transmit time stamps.

51. A hub configured to perform the method of claim 50.

52. A hub, comprising at least one receiver configured to detect an initial burst transmission with a frequency error of at least up to half of a frequency channel spacing.

53. The hub of claim 52, wherein the initial burst transmission is not aligned with predetermined frequency channels.

54. The hub of claim 52, further including a transmitter configured to transmit correction data in response to the initial burst transmission.

55. The hub of claim 54, wherein the hub is further configured to transmit time stamps.

56. The hub of claim 54, wherein the hub is further configured not to transmit time stamps.

57. The hub of claim 54, wherein the correction data includes at least one of an amount of frequency adjustment or an amount of time adjustment.

58. The hub of claim 54, wherein the hub is part of a satellite network, the initial burst transmission being transmitted within a predetermined window smaller in both time and frequency than a frame used by the satellite network.

59. A method in a remote terminal, comprising:

a transmission portion configured to transmit a first burst; and

a reception portion configured to receive a transmission including correction data responsive to the first burst,

wherein the transmission portion is further configured to transmit a second burst corrected in at least one of frequency or time in accordance with the correction data, and

wherein the remote terminal receives time stamp transmissions, and slot and frame rates are reconstructed from a feature rate of the transmission.

60. The remote terminal of claim 59, wherein the remote terminal is part of a satellite network, wherein the first burst is not aligned with a slot, and is aligned with frame timing with at least some timing error due to a difference of geographic delays within the satellite network, and wherein the remote terminal does not receive external information about a geographic location of the remote terminal.