APPARATUS AND METHOD FOR NETWORK LEVEL SYNCHRONIZATION IN MULTIPLE LOW EARTH ORBIT (LEO) SATELLITE COMMUNICATIONS SYSTEMS

• US 20150270890A1
• Filed: 03/19/2015
• Published: 09/24/2015
• Est. Priority Date: 03/19/2014
• Status: Active Grant

• Current Assignee: Hughes Network Systems LLC (Echostar Corporation)
• Original Assignee: Hughes Network Systems LLC (Echostar Corporation)
• Inventors: VASAVADA, Yash, RAVISHANKAR, Channasandra, ARUR, Deepak, PARR, Michael
• Granted Patent: US 9,749,035 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H04B 7/185 Space-based or airborne stations; Stations for satellite systemsH04B7/204 takes precedence
• CPC Class Codes: H04B 7/1851 Systems using a satellite or space-based relay H04B7/18508, H04B7/18521 take precedence; providing specific services H04B7/18523 - H04B7/18576
• CPC Class Codes: H04B 7/195 Non-synchronous stations
• CPC Class Codes: H04W 56/00 Synchronisation arrangements

Abstract

A synchronization approach is provided that compensates for the large Doppler offset of the satellites in a LEO satellite system by exploiting the predictable and deterministic nature of the Doppler component, and thereby simplifies the delay and the Doppler domain uncertainty ranges that the physical layer receivers have to resolve. The compensation is based on the known ephemeris information of the LEO satellite and the known positions of the gateway (GW) and the user terminal (UT) on the ground. Utilizing the deterministic component of the LEO Doppler, the synchronization process continually tracks and compensates for the time-varying offsets between the GW and UT frame timing, frame numbering (FN), symbol timings, and Doppler-induced scaling of center frequency and the signal bandwidth.

Claims

1. A method for synchronization in a satellite communications system comprising one or more satellites, wherein transmissions to each of at least a one of the satellites occur via a respective communications link with the satellite, the method comprising:

determining a system timing reference based on a global positioning system (GPS) timing reference and determining a system frequency reference;

periodically determining a timing delay factor and a frequency Doppler factor for each of the satellite(s) to which the transmissions occur based on respective satellite ephemeris data reflecting velocity and direction vector motion of the satellite;

dynamically adjusting the system timing reference based on the timing delay factor, and dynamically adjusting the system frequency reference based on the frequency Doppler factor, for each of the satellite(s) to which the transmissions occur; and

synchronizing timing and frequency of the transmissions to each of the satellites based on the respective adjusted system timing reference and the respective adjusted system frequency reference.

2. A method for synchronization in a satellite communications system comprising one or more satellites, wherein transmissions to each of at least a one of the satellites occur via a respective communications link with the satellite, the method comprising:

determining frame timing and frequency of downlink transmissions received from at least one of the satellites from which such transmissions are received;

receiving transmissions of ephemeris data reflecting velocity and direction vector motion of each of the satellites;

estimating a system timing reference and a system frequency reference by dynamically adjusting the frame timing and frequency for each of the satellites from which the downlink transmissions are received based on the ephemeris data for the respective satellite, and adjusting local timing and frequency references based on the adjusted frame timing and frequency; and

synchronizing timing and frequency of the transmissions to the satellites based on the estimated system timing and frequency references.