Frequency and timing synchronization and error correction in a satellite network

• US 7,471,720 B2
• Filed: 05/24/2004
• Issued: 12/30/2008
• Est. Priority Date: 05/23/2003
• Status: Expired due to Fees

• Current Assignee: Gilat Satellite Networks Limited
• Original Assignee: Gilat Satellite Networks Limited
• Inventors: Ram, Uzi, Keschet, Daniel, Keshet, Arik
• Primary Examiner(s): Ahn; Sam K
• Application Number:
  US10/851,345
• Publication Number:
  US 20040234018A1
• Time in Patent Office: 1,681 Days
• Field of Search: 375/211, 375/214, 375/215, 375/219, 375/358, 375/354, 455/24, 455/69, 370/226, 370/274, 370/315, 370/316, 370/492, 370/501
• US Class Current: 375/211
• 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 for adjusting an outgoing transmission carrier frequency based on a feature rate of an incoming transmission comprising:

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;

counting a number of pulses N 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;

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

adjusting the outgoing transmission carrier frequency based on the error.

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

3. The method of claim 2, wherein the higher carrier frequency is in the C-band or the Ku-band.

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

5. The method of claim 1, wherein adjusting the outgoing transmission carrier frequency includes adjusting the outgoing transmission carrier frequency to compensate for the error.

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

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

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

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

10. The method of claim 1, further including:

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

reading the feature rate value from the demodulator.

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

a receiver configured to receive an incoming transmission;

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;

a modulator coupled to the processor and configured to generate the outgoing transmission; and

a local reference clock generator coupled to the processor and configured to generate a reference clock, wherein the processor is configured to;

generate a reconstructed clock from the incoming transmission,

count a predetermined number of pulses N of the reconstructed clock to determine a period time,

count a number of pulses of the reference clock during the same period of time,

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

control the modulator to adjust the outgoing transmission carrier frequency based on the error.

12. The remote terminal of claim 11, further including an upconverter coupled to the modulator and configured to upconvert the outgoing transmission.

13. The remote terminal of claim 11, wherein the processor is configured to control the modulator to adjust the carrier frequency of the outgoing transmission to compensate for the error.

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

a receiver configured to receive an incoming transmission;

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;

a modulator coupled to the processor and configured to generate the outgoing transmission; and

a local reference clock generator coupled to the processor and configured to generate a reference clock, wherein the processor is 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,

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

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

control the modulator to adjust the outgoing transmission carrier frequency based on the error.

15. A method in a remote terminal part of a satellite network, comprising:

transmitting a first burst from the remote terminal, wherein the first burst is aligned with frame timing with at least some timing error due to a difference of geographic delays within the satellite network;

receiving, at the remote terminal, a transmission including correction data responsive to the first burst;

receiving time stamp transmissions;

reconstructing, at the remote terminal, slot and frame rates from a feature rate of the transmission including correction data without the remote terminal receiving external information about a geographic location of the remote terminal; and

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