Compensation of dynamic doppler frequency of large range in satellite communication systems
First Claim
1. A communication system providing a feeder link to an earth orbiting satellite transponder having a mobile link illuminating several spot beams with associated access, control and traffic channels for multiple user terminals on the earth, the system comprising:
- means for using the satellite transponder as a reference point to correct for dynamic Doppler caused by satellite motion;
means for performing Doppler correction for each of the channels of the feeder link to the satellite transponder;
means for calculating Doppler frequency shift in the mobile link between the satellite transponder and a median Doppler line of each spot beam on the earth;
means for using the calculated Doppler frequency shift in the mobile link to establish a forward link to the user terminals via the satellite transponder such that when the signal of each control channel is received by any user terminal on the median Doppler line of each spot beam, the carrier frequency of the control channel is received by the user terminal at a preassigned nominal frequency;
means for measuring the user terminal Doppler over the access channel and for deriving the Doppler frequency in the traffic channel from the measured Doppler in the access channel of the user terminals; and
means for facilitating a forward link and a return link over the traffic channel between the user terminal and a satellite base station via the satellite transponder for achieving minimal frequency error at the input of demodulators of the user terminal and the satellite base station.
13 Assignments
0 Petitions
Accused Products
Abstract
A communication system and a method of providing a feeder link to an earth orbiting satellite transponder having a mobile link illuminating spot beams with associated access channels, control channels and traffic channels for multiple user terminals (UTs) using the satellite transponder as the reference point to correct for dynamic frequency errors including the Doppler in the feeder link and in the mobile link caused by the satellite motion and the satellite translation error. A satellite access node (SAN) includes one or several radio frequency terminals (RFTs) and a satellite basestation subsystem (SBS). The RFT performs the center Doppler correction for each of the channels of the feeder link to the satellite transponder. The SBS corrects the feeder link residual Doppler and the satellite translation error for each channel and calculates the Doppler in the mobile link between the satellite transponder and the median Doppler line of each spot beam on the earth or each UT. The SBS measures the differential Doppler of the UT relative to the median Doppler line and derives its fractional Doppler, and uses the fractional Doppler to determine the position of the UT and calculate its Doppler of the traffic channels in the mobile link. The UT corrects the mobile link Doppler under the guidance of the SBS.
31 Citations
24 Claims
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1. A communication system providing a feeder link to an earth orbiting satellite transponder having a mobile link illuminating several spot beams with associated access, control and traffic channels for multiple user terminals on the earth, the system comprising:
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means for using the satellite transponder as a reference point to correct for dynamic Doppler caused by satellite motion; means for performing Doppler correction for each of the channels of the feeder link to the satellite transponder; means for calculating Doppler frequency shift in the mobile link between the satellite transponder and a median Doppler line of each spot beam on the earth; means for using the calculated Doppler frequency shift in the mobile link to establish a forward link to the user terminals via the satellite transponder such that when the signal of each control channel is received by any user terminal on the median Doppler line of each spot beam, the carrier frequency of the control channel is received by the user terminal at a preassigned nominal frequency; means for measuring the user terminal Doppler over the access channel and for deriving the Doppler frequency in the traffic channel from the measured Doppler in the access channel of the user terminals; and means for facilitating a forward link and a return link over the traffic channel between the user terminal and a satellite base station via the satellite transponder for achieving minimal frequency error at the input of demodulators of the user terminal and the satellite base station. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A communication system providing a feeder link to an earth orbiting satellite transponder having a mobile link illuminating several spot beams with associated access, control and traffic channels for multiple user terminals on the earth, the system comprising:
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a satellite access node (SAN) for using the satellite transponder as a reference point to correct for satellite motion, comprising; a radio frequency terminal (RFT) for performing center Doppler correction and up or down conversion for each of the channels of the feeder link to the satellite transponder; and a satellite basestation subsystem (SBS) for calculating Doppler frequency shift in the mobile link between the satellite transponder and a median Doppler line of each spot beam on the earth, wherein said SBS uses the calculated Doppler frequency shift in the mobile link to establish a forward link to the user terminals via the satellite transponder such that when the signal of each control channel is received by any user terminal on the median Doppler line of each spot beam, the carrier frequency of the control channel is received by the user terminal at a preassigned nominal frequency. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A communication method providing a feeder link to an earth orbiting satellite transponder having a mobile link illuminating several spot beams with associated access and control channels for multiple user terminals on the earth, the method comprising:
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using the satellite transponder as a reference point to correct for dynamic Doppler caused by satellite motion; performing Doppler correction for each of the channels of the feeder link to the satellite transponder; calculating Doppler frequency shift in the mobile link between the satellite transponder and a median Doppler line of each spot beam on the earth; using the calculated Doppler frequency shift in the mobile link to establish a forward link to the user terminals via the satellite transponder such that when the signal of each control channel is received by any user terminal on the median Doppler line of each spot beam, the carrier frequency of the control channel is received by the user terminal at a preassigned nominal frequency; broadcasting information over the control channel identifying an access channel frequency to the user terminals; broadcasting information over the control channel identifying the Doppler frequency shift in the mobile link relative to the median Doppler line for the user terminals; and facilitating a return link over the access channel from the user terminal via the satellite transponder using the identified access channel frequency and the calculated Doppler frequency shift in the mobile link with precompensation of the carrier frequency of the access channel by the user terminal for efficient use of the access channel bandwidth. - View Dependent Claims (19, 20, 21, 22, 23, 24)
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Specification