Synchronization for satellite system

• US 10,411,362 B2
• Filed: 06/03/2016
• Issued: 09/10/2019
• Est. Priority Date: 03/29/2016
• Status: Active Grant

• Current Assignee: Maxar Space LLC (Galileo Parent, Inc.)
• Original Assignee: Space Systems/Loral Incorporated (Loral Space and Communications Incorporated)
• Inventors: Hreha, William, Wharton, Anne Elizabeth, Foulke, David Linford, Voreck, Richard Wallace, Shambayati, Shervin
• Primary Examiner(s): Dean, Raymond S
• Application Number:
  US15/172,859
• Publication Number:
  US 20170289939A1
• Time in Patent Office: 1,194 Days
• CPC Class Codes: H01Q 21/24 Combinations of antenna units polarised in different directions for transmitting or receiving circularly and elliptically polarised waves or waves linearly polarised in any direction circularly polarised patch antennas H01Q9/0428; circularly polarised horns H01Q13/0241; cross-polarised horns H01Q13/0258; polarisation converters H01Q15/242; cross-polarised rear feeds H01Q19/136; crossed polarisation dual antenna H01Q25/001
• CPC Class Codes: H01Q 3/2682 Time delay steered arrays
• CPC Class Codes: H04B 7/043 using best eigenmode, e.g. beam forming or beam steering
• CPC Class Codes: H04B 7/18513 Transmission in a satellite or space-based system
• CPC Class Codes: H04B 7/18515 Transmission equipment in satellites or space-based relays
• CPC Class Codes: H04B 7/18519 Operations control, administration or maintenance
• CPC Class Codes: H04B 7/18521 Systems of inter linked satellites, i.e. inter satellite service for optical links between satellites H04B10/118
• CPC Class Codes: H04B 7/18523 Satellite systems for providing broadcast service to terrestrial stations, i.e. broadcast satellite service arrangements specially adapted for satellite broadcast receiving H04H40/90; picture transmission via satellite H04N1/00103; television transmission via satellite H04N7/20
• CPC Class Codes: H04B 7/18534 for enhancing link reliablility, e.g. satellites diversity
• CPC Class Codes: H04B 7/18541 for handover of resources
• CPC Class Codes: H04B 7/18547 for geolocalisation of a station position fixing by direction or distance determination G01S5/00
• CPC Class Codes: H04B 7/18578 Satellite systems for providing broadband data service to individual earth stations for selecting H04W; provisions for broadband connection, H04Q11/0478
• CPC Class Codes: H04B 7/18584 Arrangements for data networking, i.e. for data packet routing, for congestion control data switching networks H04L12/00
• CPC Class Codes: H04B 7/18595 Arrangements for adapting broadband applications to satellite systems
• CPC Class Codes: H04B 7/19 Earth-synchronous stations
• CPC Class Codes: H04W 16/28 using beam steering
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 72/0446 Resources in time domain, e.g. slots or frames
• CPC Class Codes: H04W 72/0453 Resources in frequency domain, e.g. a carrier in FDMA
• CPC Class Codes: H04W 72/046 the resource being in the space domain, e.g. beams
• CPC Class Codes: H04W 72/21 : in the uplink direction of a wireless link, i.e. towards the network
• CPC Class Codes: H04W 72/23 : in the downlink direction of a wireless link, i.e. towards a terminal
• CPC Class Codes: H04W 84/18 : Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

Synchronization technology is implemented for a satellite communication system. Master clock information is accessed at a terrestrial location. A timing message based on the master clock information is transmitted from the terrestrial location to a satellite as the satellite is in orbit. The satellite is synchronized to the master clock based on the timing message. A beacon signal is transmitted from the satellite toward Earth. The beacon signal includes timing information. The beacon signal is received at a ground based gateway. The gateway is synchronized to the satellite based on the beacon signal. Communication is sent from the gateway to a terminal via the satellite. The communication includes timing data. The terminal is synchronized to the gateway based on the timing data.

Claims

1. A method of operating a satellite communications system, comprising:

accessing master clock information at a terrestrial location;

transmitting a timing message based on the master clock information from the terrestrial location to a satellite as the satellite is in orbit;

synchronizing the satellite to the master clock information based on the timing message;

transmitting a beacon signal from the satellite, the beacon signal includes timing information based on the synchronizing of the satellite, the transmitted timing information including pulses each representing timing of a respective one of data communication epochs of the satellite;

receiving the beacon signal at a ground based gateway;

synchronizing the gateway to the satellite based on the beacon signal;

sending communication from the synchronized gateway to a terminal via the satellite during one or more of the data communication epochs of the satellite, the communication includes timing data; and

synchronizing the terminal to the synchronized gateway based on the timing data.

2. The method of claim 1, wherein:

the timing message includes a command to set a clock on the satellite.

4. The method of claim 1, wherein:

the satellite receives the timing message as the satellites travels in orbit closest to the terrestrial location.

5. The method of claim 1, wherein:

the satellite is a non-geostationary satellite.

6. The method of claim 1, wherein:

the terminal synchronizes to the gateway while communicating user data with the gateway.

7. The method of claim 5, wherein said transmitting the beacon signal from the satellite comprises transmitting the beacon signal such that the beacon signal is received and can be processed at the gateway ahead of ability by the gateway to receive other signals beamed from the satellite, the method further comprising:

establishing further communication between the gateway and the satellite to implement connections between the gateway and a plurality of terminals via the satellite after the beacon signal is received and processed for synchronizing the gateway to the satellite for a current orbit.

8. The method of claim 1, wherein:

the sending communication from the gateway to the terminal includes sending a frame, the timing data is in the frame.

9. The method of claim 1, wherein:

the synchronizing the gateway to the satellite based on the beacon signal comprises using a location of the satellite and a location of the gateway to determine a transmission delay of the beacon signal and adjusting timing in the gateway based on the pulses in the timing information of the beacon signal and the determined transmission delay.

10. The method of claim 9, further comprising:

determining the location of the satellite including;

receiving GPS signals at a first ground based gateway;

receiving the beacon signal at the first ground based gateway;

determining time of receipt in GPS time of a predetermined part of the beacon signal at the first ground based gateway such that travel distance of the beacon signal from the satellite to the first ground based gateway can be determined based on said time of receipt in GPS time; and

calculating location of the satellite using the time of receipt in GPS time of the predetermined part of the beacon signal at the first ground based gateway and using the time of receipt in GPS time of the predetermined part of the beacon signal at multiple other ground based gateways.

11. The method of claim 9, further comprising

determining the Doppler to the satellite including receiving the beacon signal at the ground based gateway, determining frequency offset over time of the beacon signal at the ground based gateway;

and calculating Doppler to the satellite using the history of the beacon signal frequency offset.

12. The method of claim 9, further comprising determining the location of the satellite including:

respectively receiving GPS signals at respective ones of multiple ground based gateways;

respectively identifying GPS time at the multiple gateways based o the respectively received GPS signals;

receiving the beacon signal at the multiple ground based gateways;

determining respective times of receipt in GPS time of a predetermined part of the beacon signal at the respective multiple ground based gateways; and

calculating location of the satellite using the respective times of receipt in GPS time of the predetermined part of the beacon signal at the respective multiple ground based gateways.

24. The method of claim 1, wherein:

said sending of communication from the synchronized gateway to a terminal via the satellite and in accordance with the data communication epochs of the satellite includes allowing for switching of beams used for the communication between the epochs in accordance with a current time domain beam hopping plan of the satellite.

25. The method of claim 24, wherein:

said sending of communication from the synchronized gateway to a terminal via the satellite and in accordance with the data communication epochs of the satellite includes allowing for switching to a different current time domain beam hopping plan between the epochs.

26. The method of claim 1, wherein:

the master clock information is based on a predetermined system timing reference for the satellite communications system;

the transmitted timing information includes repeatedly inserted message blocks each indicating how far past the predetermined system timing reference are corresponding ones of the satellite epochs represented the pulses associated with the corresponding message block; and

said sending of communication from the synchronized gateway to a terminal via the satellite and in accordance with the data communication epochs of the satellite includes allowing for switching to different current time domain beam hopping plans between the epochs is based on how far past the predetermined system timing reference are corresponding ones of the satellite epochs.

3. A method of operating a satellite communications system, comprising:

accessing master clock information at a terrestrial location;

transmitting a timing message based on the master clock information from the terrestrial location to a satellite as the satellite is in orbit;

synchronizing the satellite to the master clock information based on the timing message;

transmitting a beacon signal from the satellite, the beacon signal includes timing information based on the synchronizing of the satellite;

receiving the beacon signal at a ground based gateway;

synchronizing the gateway to the satellite based on the beacon signal;

sending communication from the synchronized gateway to a terminal via the satellite, the communication includes timing data; and

synchronizing the terminal to the synchronized gateway based on the timing data;

wherein the satellite is a non-geostationary satellite having a plurality of non-articulating beam providing antennas whose operations are switched in accordance with a time domain beam hopping plan; and

wherein for each orbit, the beacon signal indicates timing of an epoch for the time domain beam hopping plan and indicates a quantity of epochs from a time reference.

13. A satellite communication system, comprising:

a non-geostationary satellite orbiting in a predetermined direction and comprising an antenna system configured to receive command information from a ground location and responsive to the command information, to synchronize itself to a predetermined system timing reference and to transmit a beacon signal in the predetermined direction toward a ground based gateway such that such that for each orbit the beacon signal is received at the gateway ahead of receiving other signals at the gateway from the satellite, the received beacon signal providing timing information for synchronizing the gateway to the predetermined system timing reference, the command information includes a command to adjust a clock on the satellite to synchronize the satellite to a master clock, the beacon signal including the timing information to synchronize the gateway to data communication epochs of the satellite and to the predetermined system timing reference before the gateway receives other signals from the satellite, the timing information including pulses each representing timing of a respective one of data communication epochs of the satellite and message blocks each indicating how far past the predetermined system timing reference are corresponding ones of the satellite epochs represented the pulses associated with the corresponding message block.

14. The satellite communication system of claim 13, wherein:

the non-geostationary satellite has a plurality of non-articulating beam providing antennas whose operations are switched in accordance with a time domain beam hopping plan;

the satellite clock is adjusted during a predetermined reconfiguration time; and

for each orbit, the beacon signal indicates timing of epochs between which switching between beams can be performed in accordance with the time domain beam hopping plan and indicates a quantity of epochs passed from the predetermined system timing reference.

15. The satellite communication system of claim 13, wherein:

the clock on the satellite is adjusted by the terrestrial location in bursts of small increments periodically while the satellite is in view for the terrestrial location.

16. The satellite communication system of claim 13, further comprising:

the gateway, and wherein said synchronizing of the gateway to the satellite includes using a location of the satellite and a location of the gateway to determine a transmission delay of the beacon signal and adjusting timing on the gateway based on the timing information in the beacon signal and the transmission delay.

17. The satellite communication system of claim 16, wherein:

the gateway is configured to determine the location of the satellite by working with other gateways to receive GPS signals at multiple ground based gateways, identify GPS time at the multiple gateways, receive the beacon signal at the multiple ground based gateways, determine respective times of receipt in GPS time of a predetermined part the beacon signal at respective ones of the multiple ground based gateways and calculate location of the satellite using the times of receipt in GPS time of the predetermined part the beacon signal at the multiple ground based gateways.

18. A satellite based communication system, comprising:

a ground-based gateway configured to communicate with a ground-based terminal via an in-view non-geostationary satellite orbiting in a predetermined direction and projecting a beacon signal for ground receipt ahead of other signals provided by the satellite, the beacon signal including pulses each representing timing of a respective one of data communication epochs of the satellite, the gateway is configured to receive the projected beacon signal from the satellite ahead of other signals provided by the satellite and to synchronize to the satellite based on the pulses in the beacon signal, the gateway being configured to send communication to the terminal via the satellite during one or more of the data communication epochs of the satellite and after being synchronized to the satellite, the communication with the terminal includes timing data for the terminal to synchronize to the synchronized gateway.

19. The satellite communication system of claim 18, wherein:

the non-geostationary satellite has a plurality of non-articulating beam providing antennas whose operations are switched in accordance with a time domain beam hopping plan; and

for each orbit, the beacon signal indicates timing of an epoch for the time domain beam hopping plan and indicates a quantity of epochs from a time reference.

20. The satellite communication system of claim 18, wherein:

the gateway is configured to establish communication between the gateway and the satellite to implement connections between the gateway and a plurality of terminals via the satellite, the gateway configured to synchronize to the satellite based on the beacon signal before the establishing communication for a current orbit.

21. The satellite communication system of claim 18, wherein:

the gateway is configured to synchronize to the satellite based on the beacon signal by using a location of the satellite and a location of the gateway to determine a transmission delay of the beacon signal and adjusting timing on the gateway based on the timing information in the beacon signal and the transmission delay.

22. The satellite communication system of claim 21, wherein:

the gateway is configured to determine the location of the satellite by working with other gateways to receive GPS signals at multiple ground based gateways, identify GPS time at the multiple gateways, receive the beacon signal at the multiple ground based gateways, determine times of receipt in GPS time of the beacon signal at the multiple ground based gateways and calculate location of the satellite using the times of receipt in GPS time of the beacon signal at the multiple ground based gateways.

23. The satellite communication system of claim 18, wherein:

an additional gateway is used, the gateway and the additional gateway are connected to the terminal via the satellite, the gateway and the additional gateway are configured to establish independent timing with the terminal.