Accurate range and range rate determination in a satellite communications system
First Claim
1. An apparatus for determining the distance between a satellite and a user terminal and the rate of change of said distance, comprising:
- a user terminal receiver to receive at a user terminal a first signal from a satellite;
a user terminal demodulator to measure at said user terminal the frequency shift of said first signal to obtain a first Doppler shift, and to record the time of the frequency measurement to obtain a first timestamp;
a user terminal transmitter to transmit said first Doppler shift and said first timestamp to a gateway as a second signal;
a gateway demodulator to measure at said gateway a round trip delay between the transmission of said first signal from said satellite and the reception of said second signal at said gateway, to measure at said gateway the frequency shift of said second signal to obtain a second Doppler shift, and to record the time of the gateway measurements to obtain a second timestamp; and
a position determination module at said gateway to determine the distance between said satellite and said user terminal and the rate of change of said distance based on said round trip delay, said first and second Doppler frequency shifts, and said first and second timestamps.
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Abstract
The present invention is a system and method for accurately determining the distance (range) between one or more satellites and a user terminal and the rate of change (range rate) of that distance. When accurately determined according to the present invention, these quantities can be used to determine the location of the user terminal with a high degree of accuracy. When one satellite is available, the present invention determines the range and range rate based on the Doppler frequency shift that a signal experiences between the satellite and the user terminal, the round trip delay a signal experiences during transmission from the satellite to the user terminal and back via a satellite to a gateway, the Doppler frequency shift a signal experiences between the satellite and the gateway, and the timestamps of the measurements. When a second satellite is available, the present invention determines the range and range rate between the second satellite and the user terminal based on the round trip delay, the Doppler frequency shift that a signal experiences between the second satellite and the user terminal, and the difference in arrival times at the user terminal of the signals from the satellites.
79 Citations
10 Claims
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1. An apparatus for determining the distance between a satellite and a user terminal and the rate of change of said distance, comprising:
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a user terminal receiver to receive at a user terminal a first signal from a satellite; a user terminal demodulator to measure at said user terminal the frequency shift of said first signal to obtain a first Doppler shift, and to record the time of the frequency measurement to obtain a first timestamp; a user terminal transmitter to transmit said first Doppler shift and said first timestamp to a gateway as a second signal; a gateway demodulator to measure at said gateway a round trip delay between the transmission of said first signal from said satellite and the reception of said second signal at said gateway, to measure at said gateway the frequency shift of said second signal to obtain a second Doppler shift, and to record the time of the gateway measurements to obtain a second timestamp; and a position determination module at said gateway to determine the distance between said satellite and said user terminal and the rate of change of said distance based on said round trip delay, said first and second Doppler frequency shifts, and said first and second timestamps. - View Dependent Claims (2, 3, 4, 5)
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6. A method for determining the distance between a satellite and a user terminal and the rate of change of said distance, comprising:
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receiving at a user terminal a first signal from a satellite; measuring at said user terminal the frequency shift of said first signal to obtain a first Doppler shift; recording the time of the user terminal measurement to obtain a first timestamp; transmitting said first Doppler shift and said first timestamp to a gateway as a second signal; measuring at said gateway a round trip delay between the transmission of said first signal from said satellite and the reception of said second signal at said gateway; measuring at said gateway the frequency shift of said second signal to obtain a second Doppler shift; recording the time of the gateway measurement to obtain a second timestamp; and determining at said gateway the distance between said satellite and said user terminal and the rate of change of said distance based on said round trip delay, said first and second Doppler frequency shifts, and said first and second timestamps. - View Dependent Claims (7, 8, 9, 10)
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Specification