Terminal measurement based synchronization for mesh satellite communications

• US 8,675,634 B2
• Filed: 10/06/2009
• Issued: 03/18/2014
• Est. Priority Date: 10/06/2008
• Status: Active Grant

• Current Assignee: ViaSat Incorporated
• Original Assignee: ViaSat Incorporated
• Inventors: Agarwal, Anil
• Primary Examiner(s): Moore, Ian N
• Assistant Examiner(s): Alexander, Jenee
• Application Number:
  US12/574,064
• Publication Number:
  US 20100085908A1
• Time in Patent Office: 1,624 Days
• Field of Search: 370/350, 370/316, 370/324, 370/355, 455/12.1, 455/13.1, 455/13.2, 455/13.3
• US Class Current: 370/350
• CPC Class Codes: H04B 7/18513 Transmission in a satellite or space-based system
• CPC Class Codes: H04B 7/2125 Synchronisation

Abstract

Methods, systems, and devices are described for synchronization in mesh satellite communications. The arrival time of the gateway signal may be used to set a start of receive frame time for a terminal. A received control signal from the gateway may then be used to set a start of transmit frame time for the user terminal. The distance between the satellite and the gateway may change. Ephemeris data, various collections of terminal measurements, or terminal sync bursts may be used to modify start of transmit frame or start of receive frame settings for the terminal or gateway.

Claims

1. A system for synchronizing timing for mesh satellite communications, the system comprising:

a user terminal configured to;

transmit one or more first signals to the satellite;

receive the one or more first signals from the satellite via a mesh communication path; and

transmit a time measurement identifying transmit time between the user terminal and the satellite; and

a gateway, in communication with the user terminal via satellite, configured to;

receive the time measurement identifying transmit time between the user terminal and the satellite;

use the received time measurement to calculate a change in distance between the gateway and the satellite; and

adjust, responsive to the change in distance between the gateway and the satellite, one or more signals of;

a first set of control signals to set a start of receive frame for the user terminal;

or

a second set of control signals to set a start of transmit frame for the user terminal,

the adjustment set to synchronize timing for mesh satellite communications.

2. The system of claim 1, wherein the time measurement comprises a round trip time for the one or more first signals from the user terminal to the satellite and back to the user terminal.

3. The system of claim 1, wherein to use the received time measurement to calculate the change in distance, the gateway is configured to:

compare the received time measurement to a time measurement identifying a transmit time between the user terminal and the gateway.

4. The system of claim 3, wherein the gateway is further configured to:

calculate the time measurement identifying the transmit time between the user terminal and the gateway based on a round trip time of one or more second signals from the gateway to the user terminal and back to the gateway.

5. The system of claim 3, wherein the user terminal is further configured to:

transmit the time measurement identifying the transmit time between the user terminal and the gateway based on a transmit time of one or more second signals from the gateway to the user terminal.

6. The system of claim 1, wherein the gateway is configured to perform the adjustment by:

adjusting one or more signals of the first set to signal the user terminal to adjust start of receive frame timing at the user terminal; and

adjusting one or more signals of the second set to signal the user terminal to adjust start of transmit frame timing at the user terminal.

7. The system of claim 1, wherein the gateway is configured to perform the adjustment by:

delaying a transmission time for one or more signals of the first set,

wherein the received time measurement is used to determine that the distance between the satellite and the gateway decreased by a first amount, while the distance between the satellite and the user terminal decreased by a second amount less than the first amount.

8. The system of claim 1, wherein the gateway is configured to adjust the transmission timing to synchronize arrival, at the satellite, of the first set of signals and a third set of signals transmitted from the user terminal, the timing of the third set of signals set by the user terminal in response to receipt of the second set of signals.

9. The system of claim 1, wherein the gateway is configured to adjust the transmission timing to synchronize arrival, at the satellite, of the first set of signals and a third set of signals transmitted from the user terminal and a plurality of additional user terminals.

10. The system of claim 1, wherein,

the calculated change in distance between the gateway and the satellite comprises a change in one way trip time between the gateway and the satellite;

or

the calculated change in distance between the gateway and the satellite comprises calculating the distance between the gateway and the satellite.

11. A gateway for synchronizing timing for mesh satellite communications, the gateway comprising:

a memory module configured to;

store a first time measurement corresponding to a transmit time between a user terminal and a satellite;

store a second time measurement corresponding to a transmit time between the gateway and the user terminal via the satellite;

a distance determination module, communicatively coupled with the memory module, configured to calculate a change in distance between the gateway and the satellite based at least in part on the first and second timing measurements;

a synchronization module, communicatively coupled with the location determination module, and configured to adjust, responsive to the change in distance between the gateway and the satellite, one or more signals of;

a first set of control signals to set a start of receive frame for the user terminal;

or

a second set of control signals to set a start of transmit frame for the user terminal,

the adjustment set to synchronize timing for mesh satellite communications; and

a transmission module, communicatively coupled with the synchronization module, and configured to transmit the one or more signals with the adjusted transmission timing.

12. The gateway of claim 11, further comprising a receiver module, communicatively coupled with the memory module, and configured to:

receive, from the user terminal, the first time measurement corresponding to the transmit time between the user terminal and the satellite, the first time measurement calculated by the user terminal.

13. The gateway of claim 12, wherein the user terminal generates the first time measurement by calculating a round trip time for one or more signals from the user terminal to the satellite and back to the user terminal.

14. The gateway of claim 11, wherein the memory module is further configured to:

store additional time measurements, received from a plurality of additional user terminals, corresponding to the transmit time between at least a subset of the plurality of additional user terminals and the satellite,

wherein the additional time measurements are used by the distance determination module to calculate the change in distance between the gateway and the satellite.

15. The gateway of claim 11, wherein the distance determination module is further configured to:

calculate the change in distance between the gateway and the satellite by comparing the first and second timing measurements.

16. The gateway of claim 11, wherein the gateway further comprises a timing measurement module, communicatively coupled with the memory module, and configured to:

calculate the second time measurement identifying the transmit time between the user terminal and the gateway based on a round trip time of one or more signals from the gateway to the user terminal and back to the gateway.

17. The gateway of claim 11, further comprising a receiver module, communicatively coupled with the memory module, and configured to:

receive the second time measurement identifying the transmit time between the user terminal and the gateway based on a transmit time of one or more signals from the gateway to the user terminal.

18. The gateway of claim 11, wherein the synchronization module is configured to adjust the transmission timing to synchronize arrival, at the satellite, of the first set of signals and a third set of signals transmitted from the user terminal.

19. A method for synchronizing timing for mesh satellite communications, the method comprising:

obtaining a time measurement of a transmit time corresponding to a first distance between a user terminal and a satellite, the time measurement calculated based on a terminal-to-terminal communication on a mesh communication path;

identifying data corresponding to a second distance between a gateway and the user terminal;

using the time measurement and the data to calculate a change in distance between the gateway and the satellite; and

adjusting, responsive to the change in distance between the gateway and the satellite, timing for one or more signals of;

a first set of control signals to set a start of receive frame for the user terminal;

or

a second set of control signals to set a start of transmit frame for the user terminal,

the adjustment set to synchronize timing for mesh satellite communications.

20. The method of claim 19, further comprising:

receiving, from the user terminal, the time measurement.

21. The method of claim 19, further comprising:

receiving and storing additional data, received from each of a plurality of additional user terminals, corresponding to the transmit time between at least a subset of the plurality of additional user terminals and the satellite,

wherein the additional data is used to calculate the change in distance between the gateway and the satellite.

22. The method of claim 19, further comprising:

calculating the data based on a round trip time of one or more signals from the gateway to the user terminal and back to the gateway;

or

receiving the data from the user terminal.

23. A device for synchronizing timing for mesh satellite communications, the device comprising:

means for storing a first timing measurement identifying transmit time between a gateway and a user terminal communicating via satellite;

means for storing a second timing measurement identifying transmit time between the user terminal and the satellite;

means for identifying a change in distance between the gateway and the satellite based at least in part on the first and second timing measurements; and

means for adjusting, responsive to the change in distance between the gateway and the satellite, one or more signals of;

a first set of control signals to set a start of receive frame for the user terminal;

or

a second set of control signals to set a start of transmit frame for the user terminal,

the adjustment set to synchronize timing for mesh satellite communications.