Patent ID: 6137441
Filing Date: 2000-10-24
Classification: G01S,H04B

Abstract:
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; anda 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.