# US 12,192,035 B2 · Feeder link synchronization > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,192,035 B2 - Document ID: US12192035B2 - Status: Granted - Kind: B2 - Application number: 18/304,369 - Filed: 2023-04-21 - Published: 2024-02-08 - Granted: 2025-01-07 - Earliest claimed: 2022-08-01 - Assignees: Hughes Network Systems, LLC - Applicants: Hughes Network Systems, LLC - Inventors: James Jehong Jong; Bin Chen; Tahereh Fazel - Web page: https://patentgrep.com/patent/US12192035B2 ## CPC - H04L 27/0014: {Carrier regulation (of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657)} - H04B 7/18513: {Transmission in a satellite or space-based system} - H04B 7/18519: {Operations control, administration or maintenance} - H04L 2027/0065: {Frequency error detectors (H04L2027/0067 takes precedence)} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - H04B: TRANSMISSION ## Abstract A method for frequency and time synchronization with respect to a satellite, the method including: calculating a frequency offset ({circumflex over (f)}B,e) due to an instability of a satellite oscillator from a beacon signal (fB,TXN); determining a Satellite Motion Doppler Correction for Ephemeris (SMDCe) of a satellite motion based on ephemeris data for the satellite; computing a Satellite Reference Drift Correction for Ephemeris (SRDCe) based on the frequency offset, the beacon signal and the SMDCe; setting a loopback TX frequency based on the SMDCe and the SRDCe; and transmitting a loopback TX signal to the satellite at the loopback TX frequency. ## Claims ### Claim 1 A method for frequency and time synchronization with respect to a satellite, the method comprising: calculating a frequency offset ({circumflex over (f)}B,e) due to an instability of a satellite oscillator from a beacon signal (fB,TXN); determining a Satellite Motion Doppler Correction for Ephemeris (SMDCe) of a satellite motion based on ephemeris data for the satellite; computing a Satellite Reference Drift Correction for Ephemeris (SRDCe) based on the frequency offset, the beacon signal and the SMDCe; setting a loopback TX frequency based on the SMDCe and the SRDCe; and transmitting a loopback TX signal to the satellite at the loopback TX frequency. ### Claim 2 (depends on 1) The method of claim 1, wherein the beacon signal comprises an unmodulated CW signal. ### Claim 3 (depends on 1) The method of claim 1, wherein the setting further comprises setting a loopback RX frequency based on the SMDCe and the SRDCe. ### Claim 4 (depends on 1) The method of claim 1, further comprising deriving a satellite to gateway delay (dGS), a gateway transmission delay and a receive frame delay from a loopback RX signal transmission time and a corresponding loopback TX signal reception time. ### Claim 5 (depends on 1) The method of claim 1, further comprising receiving a loopback RX signal based on the loopback TX signal; and estimating an uplink frequency offset and a downlink frequency offset from the loopback RX signal. ### Claim 6 (depends on 5) The method of claim 5, further comprising updating a Satellite Reference Drift Correction (SRDC) as SRDC′ and a Satellite Motion Doppler Correction (SMDC) as SMDC′ based on the SMDCe, the SMDCe and the downlink frequency offset. ### Claim 7 (depends on 6) The method of claim 6, further comprising adjusting traffic channel RX and TX frequencies based on the SRDC′ and the SMDC′. ### Claim 8 (depends on 1) The method of claim 1, further comprising: generating a timing reference signal at the satellite based on a reference clock from a Global Navigation Satellite System (GNSS) source at a Gateway (GW); and adjusting a transmission timing and a receive timing at the gateway to align signals with a frame boundary referenced at the satellite. ### Claim 9 (depends on 8) The method of claim 8, wherein the adjusting further comprises adjusting a loopback transmission timing and a receive loopback timing based on timing estimation measurement results. ### Claim 10 (depends on 8) The method of claim 8, further comprising generating a GNSS-aligned timecode to derive a system time reference. ### Claim 11 (depends on 10) The method of claim 10, further comprising deriving a system frame number from the GNSS-aligned timecode to achieve frame number synchronization. ### Claim 12 (depends on 11) The method of claim 11, further comprising cycling the system frame number based on a hyperframe duration. ### Claim 13 (depends on 11) The method of claim 11, further comprising calculating the system frame number at the gateway by adjusting for a satellite to gateway transit time and equipment delays for each direction. ### Claim 14 (depends on 11) The method of claim 11, further comprising multicasting a synchronization message comprising the system frame number. ### Claim 15 (depends on 1) The method of claim 1, further comprising interpolating the ephemeris data to a finer granularity. ### Claim 16 (depends on 15) The method of claim 15, wherein the interpolating comprises performing a third order Lagrange interpolation and a first order linear interpolation method to improve an accuracy of dGS values derived from the ephemeris data. ### Claim 17 (depends on 1) The method of claim 1, further comprising following variations of an SNR of a loopback RX signal with a first order filter; and adjusting a loopback transmit power based on the variations of the SNR. ### Claim 18 (depends on 1) The method of claim 1, further comprising tracking a last good beacon value and last good ephemeris data values; and restoring the last good beacon value when the beacon signal indicates an outage, or the last good ephemeris data values when the ephemeris data indicates an outage. ### Claim 19 (depends on 17) The method of claim 17, wherein the tracking further comprises tracking a last good loopback value from a loopback RX signal based on the loopback TX signal, and the restoring further comprises restoring the last good loopback value when the loopback RX signal indicates an outage. ### Claim 20 A system to synchronize frequency and time with respect to a satellite, the system comprising: a beacon receiver to receive a beacon signal (fB,TXN) and to calculate a frequency offset ({circumflex over (f)}B,e) due to an instability of a satellite oscillator from the beacon signal; an ephemeris module to determine a Satellite Motion Doppler Correction for Ephemeris (SMDCe) of a satellite motion based on ephemeris data for the satellite; a sync module to compute a Satellite Reference Drift Correction for Ephemeris (SRDCe) based on the frequency offset, the beacon signal and the SMDCe; a loopback transmitter to set a loopback TX frequency based on the SRDCe and the SMDCe, and to transmit a loopback TX signal to the satellite at the loopback TX frequency; and a loopback receiver to receive a loopback RX signal based on the loopback TX signal, and to estimate an uplink frequency offset and a downlink frequency offset from a loopback RX signal based on the loopback TX signal, wherein the sync module updates a Satellite Reference Drift Correction (SRDC) as SRDC′ and a Satellite Motion Doppler Correction (SMDC) as SMDC′ using the SRDCe, the SMDCe and the downlink frequency offset, and the sync module adjusts traffic channel RX and TX frequencies based on SRDC′ and SMDC′.