Patent ID: 6816705
Filing Date: 2004-11-09
Classification: G01S,H04B

Abstract:
A satellite communications system wherein a user terminal is operable to transmit to more than one satellite and each of the satellites is operable to transmit to the user terminal and to send and receive signals from an earth station, wherein the earth station is operable to exchange signals with the user terminal through the satellites and thereafter be operable to analyze the signals to determine the position of the user terminal on the surface of the earth, wherein each of the satellites is operable to provide a broadcast message at predetermined times, the user terminal being operable to measure and record the time of arrival of each broadcast message, the user terminal being operable to report back to the earth station the time of arrival of each received broadcast message, the earth station being operable to compare the reported time of arrival with the predetermined times to calculate the propagation delay between the user terminal and each of the satellites, and the earth station is operable to calculate the position of the user terminal relative to each satellite, based on a knowledge of the actual position of each satellite at the predetermined times.