Method and system of determining user terminal position using a measured signal propagation delay and Doppler shift of a communications link

• US 6,307,503 B1
• Filed: 12/16/1998
• Issued: 10/23/2001
• Est. Priority Date: 05/07/1998
• Status: Expired due to Term

• Current Assignee: Hughes Network Systems LLC (Echostar Corporation)
• Original Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Inventors: Liu, Xiangdong
• Primary Examiner(s): Phan, Dao
• Application Number:
  US09/212,528
• Time in Patent Office: 1,042 Days
• Field of Search: 342/357.01, 342/357.04, 342/357.05, 455/12.1, 701/207
• US Class Current: 342/357.77
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• 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 system (20) and method (40) for determining a user terminal (23) location on the surface of the earth relies on the signal propagation delay and Doppler shift of radio frequency (RF) transmissions between the user terminal (UT) (23) and a satellite (22). An iterative procedure is employed to improve the accuracy of the location determination. Within the procedure, the position of the UT is estimated based on the propagation delay, Doppler shift, and a spherical approximation of the earth'"'"'s shape. The radius of the earth at the estimated UT position is adjusted using a predetermined model of the earth'"'"'s shape, such as an ellipsoid approximation. The adjusted radius value is then used to re-estimate the UT location using the spherical approximation. The iterative procedure continues until the estimated UT location converges to a predetermined accuracy. The position of the user terminal location can be determined based on a earth-central angle α and an azimuth angle β, which can be directly derived from the signal propagation delay and Doppler shift, respectively, using a set of closed-form equations.

Claims

1. A method of determining a user terminal location on the surface of the earth by referencing a satellite rotating the earth, comprising:

estimating the user terminal location using a spherical approximation of the shape of the earth; and

adjusting the estimated user terminal location using a refined approximation of the shape of the earth.

2. The method of claim 1, further comprising:

measuring a signal propagation delay and a Doppler shift of a carrier signal.

3. The method of claim 2, further comprising:

determining the signal propagation delay and the Doppler shift based on a random access channel (RACH) burst from the user terminal.

4. The method of claim 2, further comprising:

determining the user terminal location based on the signal propagation delay and the Doppler shift.

5. The method of claim 1, further comprising:

resolving ambiguity of the user terminal location.

6. The method of claim 5, further comprising:

resolving the ambiguity of the user terminal location based on a spot beam pilot signal emitted by the satellite.

7. The method of claim 1, further comprising:

converting the user terminal location to an earth-centered earth-fixed (ECEF) coordinate system.

8. The method of claim 1, further comprising:

tracking the position of the at least one satellite.

9. A system for determining a location of a user terminal on the surface of the earth, comprising:

a ground station for tracking a position of a satellite;

a receiver capable of determining a signal propagation delay and a Doppler shift of a radio frequency (RF) signal transmitted between the user terminal and the satellite;

a processor, in communication with the receiver, for determining the location of the user terminal, based on the signal propagation delay, the Doppler shift, and a spherical approximation of the shape of the earth in combination with an ellipsoid approximation of the shape of the earth.

10. The system of claim 9 further comprising:

means for resolving ambiguity of the location of the user terminal.

11. The system of claim 10, further comprising:

means for resolving the ambiguity of the location based on a spot beam pilot signal emitted by the satellite.

12. The system of claim 9, further comprising:

means for converting the location of the user terminal to an earth-centered earth-fixed (ECEF) coordinate system.

13. A computer-readable memory storing a program for directing a computing device to determine a user terminal location on the surface of the earth by estimating the user terminal location based on a signal propagation delay and a Doppler shift derived from a radio frequency (RF) signal transmitted between the user terminal and a satellite, and based on a spherical approximation of the shape of the earth and a predetermined refined approximation of the shape of the earth.

14. A method of determining a user terminal location on the surface of the earth by referencing a satellite rotating the earth, the method comprising the steps of:

measuring a signal propagation delay and a Doppler shift of a carrier signal;

determining an earth central angle α

between the user terminal and a sub-satellite point, the earth central angle being a function of the signal propagation delay;

determining an azimuth angle β

between the user terminal and the direction of motion of the satellite measured at sub-satellite points, the azimuth angle being a function of the Doppler shift;

determining an estimated user terminal location based on the earth central angle, the azimuth angle and a spherical approximation of the shape of the earth; and

adjusting the estimated user terminal location using a refined approximation of the shape of the earth.

15. A system for determining a location of a user terminal on the surface of the earth, the system comprising:

a ground station for tracking a position of a satellite;

a receiver adapted to determine a signal propagation delay and a Doppler shift of a radio frequency (RF) signal transmitted between the user terminal and the satellite;

a processor, in communication with the receiver, for determining the location of the user terminal, based on the signal propagation delay, the Doppler shift, and a spherical approximation of the shape of the earth in combination with an ellipsoid approximation of the shape of the earth;

said processor having means for determining an earth central angle α

between the user terminal and a sub-satellite point, the earth central angle being a function of the signal propagation delay;

said processor having means for determining an azimuth angle β

between the user terminal and the direction of the motion of the satellite, the azimuth angle being a function of the Doppler shift;

said processor having means for determining the user terminal location based on the earth central angle and the azimuth angle.