Azimuth determination for GPS/INS systems via GPS null steering antenna

• US 5,940,026 A
• Filed: 07/21/1997
• Issued: 08/17/1999
• Est. Priority Date: 07/21/1997
• Status: Expired due to Term

• Current Assignee: Teledyne Scientific & Imaging, LLC (Teledyne Technologies Incorporated)
• Original Assignee: Rockwell Science Center, Inc.
• Inventors: Popeck, Charles A.
• Primary Examiner(s): Tarcza, Thomas
• Assistant Examiner(s): Phan, Dao L.
• Application Number:
  US08/897,915
• Time in Patent Office: 757 Days
• Field of Search: 342/352, 342/451, 342/140, 342/357.01, 342/357.06, 342/357.11, 342/357.12, 701/213
• US Class Current: 342/357.36
• CPC Class Codes: G01S 5/0247 Determining attitude

Abstract

Illustrative embodiments of a method and apparatus are provided for determining azimuth for a system using signals from a constellation of satellites of the global navigation satellite system. The method includes the steps of identifying a direction of a selected satellite of the constellation of satellites and determining a azimuth by correlating the identified direction of the selected satellite with the location of the system.

Claims

1. A method of determining azimuth within an inertial navigation system using signals from a constellation of satellites of the global navigation satellite system where each satellite of the constellation of satellites provides positional information of the satellite, such method comprising the steps of:

acquiring a signal from at least some satellites of the constellation of satellites;

determining a location of the inertial navigation system from the acquired signals;

steering a null across a selected arc containing a selected satellite of the at least some satellites from which signals were acquired;

identifying a direction of the selected arc providing a relative minima in signal level from the selected satellite in response to the steered null; and

determining a azimuth by correlating the identified direction of the relative minima with an azimuth of the selected satellite from a perspective of the determined location.

2. The method of determining azimuth as in claim 1 further comprising decoding almanac/ephemeris data from each acquired satellite signal as provided satellite positional information.

3. The method of determining azimuth as in claim 1 wherein the step of acquiring a signal further comprises synchronizing a chip sequence of the inertial navigation system with a chip sequence from the at least some satellites.

4. The method of determining azimuth as in claim 1 wherein the step of determining location further comprises decoding navigational data from the acquired signal.

5. The method of determining azimuth as in claim 4 further comprising recovering emphemeris data from the navigational data.

6. The method of determining azimuth as in claim 5 further comprising determining a satellite position based upon the emphemeris data and a set of Keplerian equations or ECEF coordinates.

7. The method of determining azimuth as in claim 1 wherein the step of steering a null further comprises adding delay to signal values received from at least some elements of an antenna array of the inertial navigation system.

8. The method of determining azimuth as in claim 7 wherein the step of adding delay to signal values further comprising adding an incremental delay to signal values from antenna elements along a first axis of the antenna array.

9. The method of determining azimuth as in claim 7 wherein the step of adding delay to signal values further comprising adding an incremental delay to signal values from antenna elements along a second axis of the antenna array.

10. The method of determining azimuth as in claim 7 further comprising summing signal values at each steered null position and storing the sum in a signal value table along with indicia of the steered null direction.

11. The method of determining azimuth as in claim 10 further comprising comparing sums in the signal value table to determine a steered null direction providing the relative minima in signal level.

12. The method of determining azimuth as in claim 11 wherein the step of determining an azimuth by correlating the identified direction of the relative minima with the provided satellite positional information further comprises setting the direction of the steered null at the relative minima equal to the azimuth of the selected satellite as measured from the determined location.

13. Apparatus for determining azimuth within an inertial navigation system using signals from a constellation of satellites of the global position system where each satellite of the constellation of satellites provides positional information of the satellite, such apparatus comprising:

means for acquiring a signal from at least some satellites of the GPS system;

means for determining a location of the inertial navigation system from the acquired signals;

means for steering a null across a selected arc containing a selected satellite of the at least some satellites from which signals were acquired;

means for identifying a direction of the selected arc providing a relative minima in signal level from the selected satellite in response to the steered null; and

means for determining a azimuth by correlating the identified direction of the relative minima with an azimuth of the selected satellite from a perspective of the determined location.

14. The apparatus for determining azimuth as in claim 13 further comprising means for decoding almanac/ephemeris data from each acquired satellite signal as provided satellite positional information.

15. The apparatus for determining azimuth as in claim 13 wherein the means for acquiring a signal further comprises means for synchronizing a chip sequence of the inertial navigation system with a chip sequence from the at least some satellites.

16. The apparatus for determining azimuth as in claim 13 wherein the means for determining location further comprises means for decoding navigational data from the acquired signal.

17. The apparatus for determining azimuth as in claim 16 further comprising means for recovering emphemeris data from the navigational data.

18. The apparatus for determining azimuth as in claim 17 further comprising means for determining a satellite position based upon the emphemeris data and a set of Keplerian equations.

19. The apparatus for determining azimuth as in claim 13 wherein the means for steering a null further comprising means for adding delay to signal values received from at least some elements of an antenna array of the inertial navigation system.

20. The apparatus for determining azimuth as in claim 19 wherein the means for adding delay to signal values further comprises means for adding an incremental delay to signal values from antenna elements along a first axis of the antenna array.

21. The apparatus for determining azimuth as in claim 19 wherein the means for adding delay to signal values further comprises adding an incremental delay to signal values from antenna elements along a second axis of the antenna array.

22. The apparatus for determining azimuth as in claim 19 further comprising means for summing signal values at each steered null position and storing the sum in a signal value table along with indicia of steered null direction.

23. The apparatus for determining azimuth as in claim 22 further comprising means for comparing sums in the signal value table to determine the steered null direction providing the relative minima summed signal value and steered null direction.

24. The apparatus for determining azimuth as in claim 23 further comprising means for setting the direction of the steered null at the relative minima equal to the azimuth of the selected satellite as measured from the determined location.

25. Apparatus for determining azimuth within an inertial navigation system using signals from a constellation of satellites of the global position system where each satellite of the constellation of satellites provides positional information of the satellite, such apparatus comprising:

a cross-correlator which acquires a signal from at least some satellites of the GPS system;

a global position system processor which determines a location of the inertial navigation system from the acquired signals;

an antenna delay processor which steers a null across a selected arc containing a selected satellite of the at least some satellites from which signals were acquired;

a signal level comparator which identifies a direction of the selected arc providing a relative minima in signal level from the selected satellite in response to the steered null; and

a correlation processor which determines an azimuth by correlating the identified location of the relative minima with an azimuth of the selected satellite from the perspective of the determined location.

26. The apparatus for determining azimuth as in claim 25 further comprising a decoder processor which decodes almanac/ephemeris data from each acquired satellite signal as provided satellite positional information.

27. The apparatus for determining azimuth as in claim 25 wherein the antenna delay processor which steers a null further comprising a delay processor which adds delay to signal values received from at least some elements of an antenna array of the inertial navigation system.

28. The apparatus for determining azimuth as in claim 27 wherein the delay processor which adds delay to signal values further comprises a first antenna element weighting processor which adds an incremental delay to signal values from antenna elements along a first axis of the antenna array.

29. The apparatus for determining azimuth as in claim 27 wherein the a second antenna element delay processor which adds delay to signal values further comprises adding an incremental delay to signal values from antenna elements along a second axis of the antenna array.

30. The apparatus for determining azimuth as in claim 27 further comprising an accumulator which sums signal values at each steered null position and storing the sum in a signal value table along with indicia of steered null direction.

31. The apparatus for determining azimuth as in claim 30 further comprising a comparator which compares sums in the signal value table to determine the steered null direction providing the relative minima summed signal value and steered null direction.

32. The apparatus for determining azimuth as in claim 31 further comprises a coordinate position processor which sets the direction of the steered null at the relative minima equal to the azimuth of the selected satellite as measured from the determined location.