# US 12,119,922 B2 · System with modulated signal to compensate frequency errors in LTE signals > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,119,922 B2 - Document ID: US12119922B2 - Status: Granted - Kind: B2 - Application number: 18/101,353 - Filed: 2023-01-25 - Published: 2023-11-09 - Granted: 2024-10-15 - Earliest claimed: 2020-01-15 - Assignees: AST & Science, LLC - Applicants: AST & Science, LLC - Inventors: Huiwen Yao; Praveen Kumar Tangutoori - Web page: https://patentgrep.com/patent/US12119922B2 ## CPC - H04B 7/1858: {Arrangements for data transmission on the physical system, i.e. for data bit transmission between network components} - H04B 7/18513: {Transmission in a satellite or space-based system} - H04B 7/195: Non-synchronous stations - H04W 56/0035: {detecting errors in frequency or phase} - H04W 56/005: {compensating for timing error by adjustment in the receiver} - H04B: TRANSMISSION - H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72) ## Abstract A satellite communication system leverages the carrier offset detection capability of the demodulator contained in an on-board modem of M&C channel. The modem detects the frequency error Δf introduced in the signal path from the output of the base station at ground to the output of baseband conversion on the satellite, by analyzing the baseband signal at the baseband conversion to estimate the received carrier f′c and subtracting it the from the expected frequency (fc). ## Claims ### Claim 1 A communication ground station comprising: an antenna configured to receive a signal for a satellite, a compensator configured to compensate the signal for delay and Doppler variations; and a modem configured to determine, based on the signal compensated for delay and Doppler variations, a residual frequency error in the signal compensated for delay and Doppler variations, wherein the residual frequency error is estimated based on a received carrier frequency determined from the signal and an expected frequency determined from the signal, wherein the compensator is further configured to compensate the signal compensated for delay and Doppler variations for the residual frequency error. ### Claim 2 (depends on 1) The communication ground station of claim 1, wherein the signal comprises an uplink signal. ### Claim 3 (depends on 1) The communication ground station of claim 1, wherein the antenna is configured to receive the signal from a user equipment. ### Claim 4 (depends on 1) The communication ground station of claim 1, wherein the modem is configured to determine the residual frequency error by subtracting the received carrier frequency from the expected frequency. ### Claim 5 (depends on 1) The communication ground station of claim 1, wherein, to determine the received carrier frequency, the modem is configured to determine a frequency offset for a carrier signal of the signal compensated for delay and Doppler variations. ### Claim 6 (depends on 5) The communication ground station of claim 5, wherein to determine the frequency offset, the modem is configured to determine a sum of: (1) a difference in a clock source of the communication ground station and a clock source of a satellite, and (2) residual Doppler in response to compensating the signal for delay and Doppler variations. ### Claim 7 (depends on 1) The communication ground station of claim 1, wherein the signal comprises a monitor and control signal specifying one or more of a number of beams, beam frequencies, spectral allocation, or bandwidth. ### Claim 8 (depends on 1) The communication ground station of claim 1, further comprising: a de-multiplexer configured to apply a frequency shift equal to a negative of a frequency offset of the signal to provide a de-multiplexed signal. ### Claim 9 A method comprising: receiving, by a communication ground station, a signal for a satellite, compensating, by the communication ground station, the signal for delay and Doppler variations; determining, by the communication ground station and based on the signal compensated for delay and Doppler variations, a residual frequency error in the signal compensated for delay and Doppler variations, wherein the residual frequency error is determined based on a received carrier frequency determined from the signal and an expected frequency determined from the signal; and compensating, by the communication ground station, the signal compensated for delay and Doppler variations for the residual frequency error. ### Claim 10 (depends on 9) The method of claim 9, wherein receiving the signal comprises receiving an uplink signal. ### Claim 11 (depends on 9) The method of claim 9, wherein receiving the signal comprises receiving the signal from a user equipment. ### Claim 12 (depends on 9) The method of claim 9, wherein determining the residual frequency error comprises determining the residual frequency error by subtracting the received carrier frequency from the expected frequency. ### Claim 13 (depends on 9) The method of claim 9 wherein determining the received carrier frequency comprises determining a frequency offset for a carrier signal of the signal compensated for delay and Doppler variations. ### Claim 14 (depends on 13) The method of claim 13, wherein determining the frequency offset comprises determining a sum of: (1) a difference in a clock source of the communication ground station and a clock source of a satellite, and (2) residual Doppler in response to compensating the signal for delay and Doppler variations. ### Claim 15 (depends on 9) The method of claim 9, wherein the signal comprises a monitor and control signal specifying one or more of a number of beams, beam frequencies, spectral allocation, or bandwidth. ### Claim 16 (depends on 9) The method of claim 9, further comprising: applying, by the communication ground station, a frequency shift equal to a negative of a frequency offset of the signal to provide a de-multiplexed signal. ### Claim 17 A satellite system comprising: an antenna configured to receive, from a communication ground station, a signal for a user equipment, the signal compensated for delay and Doppler variations; a modem configured to determine, based on the signal compensated for delay and Doppler variations, a residual frequency error in the signal based on a received carrier frequency determined from the signal and an expected frequency determined from the signal; and a compensator configured to compensate the signal for the residual frequency error. ### Claim 18 (depends on 17) The satellite system of claim 17, wherein the signal comprises a downlink signal. ### Claim 19 (depends on 17) The satellite system of claim 17, wherein the modem is configured to determine the residual frequency error by subtracting the received carrier frequency from the expected frequency. ### Claim 20 (depends on 17) The satellite system of claim 17, further comprising: a de-multiplexer configured to apply a frequency shift equal to a negative of a frequency offset of the signal to provide a de-multiplexed signal.