Lock slip detection using inertial information

• US 6,720,913 B1
• Filed: 11/08/2002
• Issued: 04/13/2004
• Est. Priority Date: 11/08/2002
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Schipper, Brian W.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US10/290,992
• Time in Patent Office: 522 Days
• Field of Search: 342/357.04, 342/357.11, 342/357.06, 342/357.03, 342/357.12, 701/213
• US Class Current: 342/357.26
• CPC Class Codes: G01S 19/55 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method

Abstract

A method for detecting lock slip using inertial information is provided. The method involves an epoch comparison of a predicted delta phase range with a measured delta phase range. The predicted delta phase range is calculated by subtracting a previous inertial solution from a current inertial solution. The measured delta phase range is calculated by subtracting a previous carrier phase measurement from a current carrier phase measurement. If a difference between the predicted delta phase range and the measured delta phase range is greater than a threshold amount, a lock slip is declared. The method allows for lock slip detection in Global Positioning System (GPS) attitude determinations without relying on a lock slip notification from the GPS.

Claims

1. A method for detecting lock slip, comprising in combination:

comparing a predicted delta phase range with a measured delta phase range; and

declaring a lock slip if a difference between the predicted delta phase range and the measured delta phase range is greater than a threshold amount.

2. The method of claim 1, wherein the predicted delta phase range is calculated by subtracting a previous inertial solution from a current inertial solution.

3. The method of claim 2, wherein the previous inertial solution and the current inertial solution are determined by an Inertial Navigation System (INS).

4. The method of claim 2, wherein the previous inertial solution and the current inertial solution are positions of a satellite at a particular time.

5. The method of claim 2, wherein the previous inertial solution and the current inertial solution are calculated by taking an absolute value of a difference between an earth centered earth fixed position of a satellite and a position of an antenna based on an inertial solution.

6. The method of claim 5, wherein a lever arm correction may be performed in determining the position of the antenna.

7. The method of claim 1, wherein the measured delta phase range is calculated at a given frequency.

8. The method of claim 1, wherein the measured delta phase range is calculated by subtracting a previous carrier phase measurement from a current carrier phase measurement.

9. The method of claim 8, wherein the previous carrier phase measurement and the current carrier phase measurement are determined by a receiver.

10. The method of claim 1, wherein the threshold amount is a magnitude approximately half of a wavelength of a signal on which ambiguity resolution is being performed.

11. The method of claim 1, wherein the steps of comparing the predicted delta phase range with the measured delta phase range and declaring the lock slip are performed by a software algorithm stored in an Inertial Navigation System (INS).

12. A method for detecting lock slip, comprising in combination:

computing an inertially derived solution for predicted range between an antenna and a satellite;

computing an inertially derived solution for delta range by subtracting a previous inertial solution from a current inertial solution;

computing a carrier phase delta range by subtracting a previous carrier phase measurement from a current carrier phase measurement;

computing a delta range residual by subtracting the inertially derived solution for delta range from the carrier phase delta range; and

declaring a lock slip if the delta range residual is greater than a threshold amount.

13. The method of claim 12, wherein the inertially derived solution for predicted range is determined by an Inertial Navigation System (INS).

14. The method of claim 12, wherein the inertially derived solution for predicted range is calculated by taking an absolute value of a difference between an earth centered earth fixed position of the satellite and a position of the antenna based on an inertial solution.

15. The method of claim 14, wherein the inertial solution is a position of the antenna at a particular time.

16. The method of claim 12, wherein the previous carrier phase measurement and the current carrier phase measurement are determined by a receiver.

17. The method of claim 12, wherein the carrier phase delta range is calculated at a given frequency.

18. The method of claim 12, wherein the threshold amount is a magnitude approximately half of a wavelength of a signal on which ambiguity resolution is being performed.

19. A system for providing lock slip detection, comprising in combination:

a plurality of satellites providing position information;

a receiver operable to obtain the position information from the plurality of satellites, wherein the receiver produces carrier phase measurements based on the position information; and

an inertial navigational system (INS) operable to calculate an inertial solution of position, wherein the INS detects a lock slip by comparing the carrier phase measurements to the inertial solution.

20. The system of claim 19, wherein the lock slip is detected when a comparison of the carrier phase measurements to the inertial solution is greater than a threshold amount.

21. The system of claim 20, wherein the threshold amount is a magnitude approximately half of a wavelength of a signal on which ambiguity resolution is being performed.