Geolocation method and apparatus for satellite based telecommunications system

• US 6,020,847 A
• Filed: 04/25/1996
• Issued: 02/01/2000
• Est. Priority Date: 04/25/1996
• Status: Expired due to Fees

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: TWR, Inc. (Veolia Environnement SA)
• Inventors: Stephens, Scott A., Upton, Eric L.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US08/638,066
• Time in Patent Office: 1,377 Days
• Field of Search: 342/353, 342/357, 342/457, 342/458, 342/453, 342/387, 455/54.1, 455/54.2, 455/456
• US Class Current: 342/357.78
• CPC Class Codes: G01S 19/00 Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
• CPC Class Codes: G01S 5/12 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial
• CPC Class Codes: H04B 7/1855 using a telephonic control signal, e.g. propagation delay variation, Doppler frequency variation, power variation, beam identification

Abstract

A method for determining the geolocation of a user terminal within a telecommunications system having a constellation of satellites which relay communications signals between earth stations and user terminals over preassigned channels. The method performs synchronization upon the telecommunications signals to calculate timing and frequency update information for the user terminals. The timing and frequency update information is also used within the earth station to calculate the geoposition of the user terminal. To do so, the earth station calculates a distance between the satellite and a user terminal based on the corresponding propagation time therebetween which is obtained from the timing information. Once the satellite to user terminal distance is obtained, a range solution line may be calculated therefrom. In addition, the frequency update information is used to calculate a Doppler solution line upon which the user terminal is positioned. Thereafter, the range and Doppler solution lines are combined to obtain points of intersection therebetween. These points of intersection represent potential geolocations of the user terminal. The earth station discriminates between these intersection points in one of several manners, such as the coverage beam spot or geographic cell assigned to the user terminal. Upon obtaining a single intersection point, the longitude and latitude of this point or output is the geolocation of the user terminal.

Claims

1. A method for determining a geolocation of a user terminal in a satellite based telecommunications system which passes communications signals along assigned channels between a user terminal, a satellite, and an associated earth station, said method comprising the steps of:

receiving a telecommunications signal over an assigned channel from a user terminal at an earth station;

determining a timing error offset representative of motion of said user terminal relative to said earth station and based on said telecommunications signal;

combining said timing error offset with a round trip propagation delay representing round trip propagation time of an RF signal through said user terminal, a satellite, and said earth station to obtain an updated round trip propagation delay through said user terminal, said satellite, and said earth station;

removing an earth station-to-satellite round trip delay from said updated round trip propagation delay, thereby determining a satellite-to-mobile terminal round trip propagation delay;

determining a range solution line based on said satellite-to-mobile terminal round trip propagation delay;

determining a Doppler solution line based on said telecommunications signal;

determining geographic points of intersection of said range and Doppler solution lines; and

outputting one of said geographic points of intersection as a geolocation of the user terminal.

2. The method of claim 1, wherein said step of outputting a geolocation comprises determining a geolocation for said user terminal based on said range solution line, said Doppler solution line, and a beam spot covering said user terminal.

3. The method of claim 1, wherein said step of outputting a geolocation comprises determining a geolocation for said user terminal based on said range solution line, said Doppler solution line, and a predefined geographic cell to which said user terminal is assigned.

4. The method of claim 1, wherein said step of determining a timing error offset comprises correlating said second telecommunications signal with a reference sync signal.

5. A method for determining a geolocation of a user terminal in a satellite based telecommunications system which passes communications signals along assigned channels between a user terminal, a satellite, and an associated earth station, said method comprising the steps of:

transmitting a first telecommunications signal over an assigned channel to a user terminal;

receiving a second telecommunications signal over an assigned channel from said user terminal at an earth station;

determining a round trip propagation delay through said user terminal, a satellite, and said earth station based on said first and second telecommunications signals;

receiving a subsequent telecommunications signal over the assigned channel from said user terminal at said earth station;

determining a timing error offset representative of motion of said user terminal relative to said earth station and based on said subsequent telecommunications signal;

combining said timing error offset with said round trip propagation delay to obtain an updated round trip propagation delay;

removing an earth station-to-satellite round trip delay from said updated round trip propagation delay, thereby determining a satellite-to-mobile terminal round trip propagation delay;

determining a range solution line based on said satellite-to-mobile terminal round trip propagation delay;

determining a Doppler solution line based on said subsequent telecommunications signal; and

determining geographic points of intersection of said range and Doppler solution lines; and

outputting one of said geographic points of intersection as a geolocation of the user terminal.