METHODS AND APPARATUS FOR GEOMETRY EXTRA-REDUNDANT ALMOST FIXED SOLUTIONS

• US 20090027262A1
• Filed: 07/23/2007
• Published: 01/29/2009
• Est. Priority Date: 07/23/2007
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Fries, Robert M., Wu, Shuwu, Shloss, Peter D., Peck, Stephen R.
• Granted Patent: US 7,768,451 B2
• Time in Patent Office: Days
• US Class Current: 342/357.270
• CPC Class Codes: G01S 19/04 providing carrier phase data
• CPC Class Codes: G01S 19/44 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method

Abstract

Methods and apparatus for providing high integrity probability of connect fix (PCF) in GPS navigation applications, such as precision approach and landing and airborne refueling. In an exemplary embodiment, an enlarged pull in region is used to compute protection levels. In an exemplary embodiment, geometric extra-redundancy is used to enhance PCF and PAF (probability of almost fixed). In an exemplary embodiment, geometric extra-redundancy almost fixed solutions provide superior accuracy and integrity for GPS navigation applications.

Claims

1. A method, comprising:

selecting almost fixed solutions with a correctly fixed solution to form an extended pull-in region (EPIR) so that a probability of almost fixed (PAF) over the EPIR an integrity allocation; and

computing protection levels including effects of incorrect fixes associated with the almost fixed solutions in the EPIR.

2. The method according to claim 1, further including meeting a probability of correct fix (PCF) threshold in integer ambiguity resolution.

3. The method according to claim 1, further including adding a position domain bias term due to incorrect fixes associated with the almost fixed solutions in the EPIR when calculating the protection levels.

4. The method according to claim 1, further including optimal selection of an EPIR by starting with the correctly-fixed solution and repeatedly adding the next almost fixed solution that has the least amount of resulting position domain bias to the EPIR until the probability of almost fixed (PAF) meets an integrity allocation.

5. A method, comprising:

generating a relative navigation solution by a fixed solution from the GPS observables;

computing protection levels by

selecting almost fixed solutions with a correctly fixed solution to form an extended pull-in region (EPIR) so that a probability of almost fixed (PAF) over the EPIR meets an integrity allocation;

computing protection levels including effects of incorrect fixes associated with the almost fixed solutions in the EPIR; and

outputting a relative navigation solution based upon the fixed solution and protection levels associated with the EPIR.

6. The method according to claim 5, further including using Least-squares AMBiguity Decorrelation Adjustment (LAMBDA) for integer ambiguity decorrelation.

7. The method according to claim 5, further including using bootstrapping for integer estimation.

8. The method according to claim 5, further including performing the relative navigation solution for an automated landing application.

9. The method according to claim 5, further including performing the relative navigation solution for autonomous airborne refueling.

10. A method, comprising:

collecting two or more sets of reference GPS information;

correcting the reference GPS information to a common reference point;

combining the two or more sets of reference GPS information with one or more sets of user GPS information to form GPS observables for relative positioning; and

using two or more sets of combined GPS observables for carrier phase integer ambiguity resolution for a common relative baseline vector.

11. The method according to claim 10, wherein the user GPS information is associated with an airborne user.

12. A method, comprising:

collecting two or more sets of reference GPS information;

correcting the reference GPS information to a common reference point;

combining the two or more sets of reference GPS information with one or more sets of user GPS information to form two or more sets of GPS observables for relative positioning;

using the two or more sets of combined GPS observables for carrier phase integer ambiguity resolution for a common relative baseline vector;

generating a relative navigation solution by a fixed solution from the GPS observables;

computing protection levels by

selecting almost fixed solutions with correctly fixed solution to form an extended pull-in region (EPIR) so that a probability of almost fixed (PAF) over the EPIR meets an integrity allocation; and

computing protection levels including effects of incorrect fixes associated with the almost fixed solutions in the EPIR.

outputting a relative navigation solution based upon the fixed solution and protection levels associated with the EPIR.

13. The method according to claim 12, further including generating double differenced observables for the GPS observables.

14. The method according to claim 13, further including decorrelating ambiguities for the double differenced observables.

15. The method according to claim 12, further including using bootstrap integer estimator for the integer fixing.

16. The method according to claim 12, further including using the fixed solution as the relative positioning solution when the PCF meets a threshold value and the PAF meets an integrity allocation.

17. A system, comprising:

a first module to select almost fixed solutions with a correctly fixed solution to form an extended pull-in region (EPIR) so that a probability of almost fixed (PAF) over the EPIR meets an integrity allocation; and

a second module to compute protection levels including effects of incorrect fixes associated with the almost fixed solutions in the EPIR.

18. The system according to claim 17, wherein the first module is capable of meeting a probability of connect fix (PCF) threshold in integer ambiguity resolution.

19. The system according to claim 17, further including a third module to add a position domain bias term due to incorrect fixes associated with the almost fixed solutions in the EPIR when calculating the protection levels.

20. The system according to claim 17, further including a fourth module for optimal selection of an EPIR by starting with the correctly-fixed solution and repeatedly adding the next almost fixed solution that has the least amount of resulting position domain bias to the EPIR until the probability of almost fixed (PAF) meets an integrity allocation.

21. A computer-readable storage medium having computer readable code, the medium comprising instructions for:

selecting almost fixed solutions with a correctly fixed solution to form an extended pull-in region (EPIR) so that a probability of almost fixed (PAF) over the EPIR meets an integrity allocation; and

computing protection levels including effects of incorrect fixes associated with the almost fixed solutions in the EPIR.

22. The computer-readable storage medium according to claim 21 further including instructions to enable meeting a probability of correct fix (PCF) threshold in integer ambiguity resolution.

23. The computer-readable storage medium according to claim 21 further including instructions for adding a position domain bias term due to incorrect fixes associated with the almost fixed solutions in the EPIR when calculating the protection levels.

24. The computer-readable storage medium according to claim 21, further including instructions for optimal selection of an EPIR by starting with the correctly-fixed solution and repeatedly adding the next almost fixed solution that has the least amount of resulting position domain bias to the EPIR until the probability of almost fixed (PAF) meets an integrity allocation.