Satellite-based position-determining system

• US 4,918,609 A
• Filed: 10/11/1988
• Issued: 04/17/1990
• Est. Priority Date: 10/11/1988
• Status: Expired due to Term

• Current Assignee: Koji Yamawaki
• Original Assignee: Koji Yamawaki
• Inventors: Yamawaki, Koji
• Primary Examiner(s): Chin, Gary
• Application Number:
  US07/255,248
• Time in Patent Office: 553 Days
• Field of Search: 364/443, 364/449, 364/569, 364/571.01, 73/178 R, 342/357, 342/358, 342/451
• US Class Current: 701/207
• CPC Class Codes: G01S 11/08 using synchronised clocks
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location

Abstract

A satellite-based position-determining system comprises at least two satellites deployed in geosynchronous orbit and equipped with a receiver, transmitter and clock and a user'"'"'s equipment of unknown position equipped with a clock and a receiver and transmitter for communications with said satellites. At least one satellite and the user'"'"'s equipment emit range-finding signals based on their own clocks, and each of them receives the other'"'"'s range-finding signal and measures the time period from the emission of its own range-finding signal to the reception of the other'"'"'s range-finding signal. Time errors of both clocks are calculated from the above time periods in order to synchronize both the clocks and the position of the user'"'"'s equipment is determined.

Claims

1. 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.

2. 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.

3. 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.

4. 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.

5. 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.