Apparatus and method for network level synchronization in multiple low earth orbit (LEO) satellite communications systems

• US 9,973,264 B2
• Filed: 08/28/2017
• Issued: 05/15/2018
• 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
• Primary Examiner(s): Faroul, Farah
• Application Number:
  US15/688,675
• Publication Number:
  US 20180013484A1
• Time in Patent Office: 260 Days
• Field of Search: None
• 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 method for synchronization of user terminal (UT) uplink data transmissions to a satellite in a satellite communications system is provided. The UT tracks frame timing and frequency of downlink data transmissions received by the UT from the satellite. The UT estimates a respective timing delay and frequency shift of the downlink data transmissions based on the tracked frame timing and frequency of the downlink data transmissions. The UT receives satellite ephemeris data broadcast by the satellite. The UT synchronizes uplink data transmissions to the satellite based on the estimated timing delay and frequency shift of the downlink data transmissions, the received satellite ephemeris data, and knowledge of a UT position and velocity vectors associated with any movement of the UT.

Claims

1. A method for synchronization of user terminal (UT) uplink data transmissions to a satellite in a satellite communications system, comprising:

tracking, by the UT, of frame timing and frequency of downlink data transmissions received by the UT from the satellite;

estimating a respective timing delay and frequency shift of the downlink data transmissions based on the tracked frame timing and frequency of the downlink data transmissions;

receiving, by the UT, satellite ephemeris data broadcast by the satellite; and

synchronizing uplink data transmissions by the UT to the satellite based on the estimated timing delay and frequency shift of the downlink data transmissions, the received satellite ephemeris data, and knowledge of a UT position and velocity vectors associated with any movement of the UT.

2. A satellite user terminal (UT), comprising:

a receiver configured to receive downlink data transmissions from a satellite in a satellite communications network, and to receive satellite ephemeris data broadcast by the satellite;

a transmitter configured to transmit uplink data transmissions to the satellite; and

a processor configured to track frame timing and frequency of the downlink data transmissions received from the satellite, to estimate a respective timing delay and frequency shift of the downlink data transmissions based on the tracked frame timing and frequency of the downlink data transmissions, and to synchronize the uplink data transmissions to the satellite based on the estimated timing delay and frequency shift of the downlink data transmissions, the received satellite ephemeris data, and knowledge of a UT position and velocity vectors associated with any movement of the UT.