Satellite-based position-determining system

Claim 2

A satellite-based position-determining system comprising: a ground station equipped with a ground receiver, a ground transmitter and a ground clock coupled to said ground receiver and said ground transmitter for generating a ground clock signal; at least two satellites deployed in geostationary orbit and each equipped with a satellite receiver, a satellite transmitter and a satellite clock coupled to said satellite receiver and said satellite transmitter for generating a satellite clock signal; a user equipment of unknown position equipped with a user clock, a user receiver and a user transmitter for communicating with said satellites, wherein said satellite receiver and said satellite transmitter communicate with said user transmitter and said ground receiver, respectively; and means operably coupled to said user receiver for determining the position of said user equipment such that at least one of said satellite transmitters and said user transmitter both emit a range-finding signal toward each other based on respective clock time signals of said satellite clock and said user clock, each of said at least one of said satellite receiver and said user receiver receive each other's range-finding signal and measures each respective arrival time of said range-finding signals based on the respective clock time signals, and a time offset between the satellite and user clock signals is calculated from said measured arrival times to synchronize at least one of said satellite clock signals and said user clock signal and to determine the position of said user's equipment.

Claim 3

A satellite-based position-determining system according to claim 1, wherein said arrival times of the range-finding signals are measured at said ground station.

Claim 4

A satellite-based position-determining system according to claim 1, wherein said arrival times of the range-finding signals are measured in at least of said satellites.

Claim 5

A satellite-based position-determining system according to claim 1, wherein said arrival times of the range-finding signals are measured at said user's equipment itself.

Claim 6

A satellite-based position-determining system comprising: a ground station equipped with a ground receiver, a ground transmitter and a ground clock coupled to said ground receiver and said ground transmitter for generating a ground clock signal; at least two satellites deployed in geostationary orbit and each equipped with a satellite receiver, a satellite transmitter and a satellite clock coupled to said satellite receiver and said satellite transmitter for generating a satellite clock signal; a user equipment of unknown position equipped with a user clock, a user receiver and a user transmitter for communicating with said satellites, wherein said satellite receiver and said satellite transmitter communicate with said user transmitter and said ground receiver, respectively; and means operably coupled to said user receiver for determining the position of said user's equipment such that at least one of said satellite transmitters and said user transmitter both emit a range-finding signal toward each other based on respective clock time signals of said satellite clock and said user clock, each of said at least one of said satellite receiver and said user receiver receive each other's range-finding signal and measures each respective arrival time of said range-finding signals based on the respective clock time signals, and a time offset between the satellite and user clock signals is calculated from said measured arrival times to synchronize at least one of said satellite clock signals and said user clock signal and to determine the position of said users equipment; and means for automatically calibrating an error in the user clock signal by measuring the tendency of said clock signal to diverge while said user equipment is at a fixed position.

Claim 7

A satellite-based position-determining system comprising: a ground station equipped with a ground receiver, a ground transmitter and a ground clock coupled to said ground receiver and said ground transmitter for generating a ground clock signal; at least two satellites deployed in geostationary orbit and each equipped with a satellite receiver, a satellite transmitter and a satellite clock coupled to said satellite receiver and said satellite transmitter for generating a satellite clock signal; a user equipment of unknown position equipped with a user clock, a user receiver and a user transmitter for communicating with said satellites, wherein said satellite receiver and said satellite transmitter communicate with said user transmitter and said ground receiver, respectively; and means operably coupled to said user receiver for determining the position of said user's equipment such that at least one of said satellite transmitters and said user transmitter both emit a range-finding signal toward each other based on respective clock time signals of said satellite clock and said user clock, each of said at least one of said satellite receiver and said user receiver receive each other's range-finding signal and measures each respective arrival time of said range-finding signals based on the respective clock time signals, and a time offset between the satellite and user clock signals is calculated from said measured arrival times to synchronize at least one of said satellite clock signals and said user clock signal and to determine the position of said users equipment; and means for automatically calibrating an error in the user clock signal by measuring the tendency of said clock signal to diverge while said user equipment is at a fixed position.