Method of improving satellite reacquisition performance for integrated GP/IG navigational systems

• US 6,640,189 B2
• Filed: 09/19/2001
• Issued: 10/28/2003
• Est. Priority Date: 05/11/2001
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Fibersense Technology Corp. (Northrop Grumman Corporation)
• Inventors: Humphrey, Ian, Perlmutter, Michael S.
• Primary Examiner(s): Beaulieu, Yonel
• Application Number:
  US09/955,609
• Publication Number:
  US 20020169550A1
• Time in Patent Office: 769 Days
• Field of Search: 701/213, 701/214, 701/215, 701/216, 342/357.01, 342/357.02, 342/357.12, 342/357.15, 342/357.14, 342/387, 370/324, 370/350, 370/503, 375/136, 375/139, 368/28, 368/47, 455/12.1, 455/427, 455/428
• US Class Current: 701/214
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• CPC Class Codes: G01S 19/26 involving a sensor measurement for aiding acquisition or tracking
• CPC Class Codes: G01S 19/49 whereby the further system is an inertial position system, e.g. loosely-coupled
• CPC Class Codes: G01S 5/011 Identifying the radio environment

Abstract

A method of reacquiring a satellite signal within an integrated GP/IG navigation system includes detecting a loss of synchronization between a timing code in the satellite signal and a corresponding reference timing code. The method includes receiving position data from an inertial guidance unit. The position data is representative of an estimated position (and its associated uncertainty) of the navigation system. The method also includes estimating a distance from the navigation system to the satellite, as a function of the position data, and deriving an initial delay from the distance. The method includes delaying the reference timing code, with respect to the timing code embedded in the satellite signal, by an offset delay substantially equal to the initial delay. The method includes incrementally varying the offset delay until the timing code embedded in the satellite signal is synchronized with the reference timing code, or until the offset delay equals a predetermined end limit value.

Claims

1. A method of reacquiring a satellite signal within an integrated GP/IG navigation system, comprising:

detecting a loss of synchronization between a timing code embedded in the satellite signal and a corresponding reference timing code;

receiving position data from an inertial guidance unit, the position data being representative of an estimated position of the GP/IG navigation system;

estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the position data, and deriving an initial delay value from the distance value; and

delaying the reference timing code, with respect to the timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, including incrementally varying the offset delay value (i) until the timing code embedded in the satellite signal is synchronized with the reference timing code, or (ii) until the offset delay value equals a predetermined end limit value.

2. A method of reacquiring a satellite signal within an integrated GP/IG navigation system, comprising:

detecting a loss of synchronization between a timing code embedded in the satellite signal and a corresponding reference timing code;

receiving position data from an inertial guidance unit, the position data being representative of an estimated position of the GP/IG navigation system;

estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the position data, and deriving an initial delay value from the distance value; and

delaying the reference timing code, with respect to the timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, including increasing the offset delay value (i) until the timing code embedded in the satellite signal is synchronized with the reference timing code, or (ii) until the offset delay value equals a predetermined start limit value.

3. A method of reacquiring a satellite signal within an integrated GP/IG navigation system, comprising:

detecting a loss of synchronization between a timing code embedded in the satellite signal and a corresponding reference timing code;

receiving position data from an inertial guidance unit, the position data being representative of an estimated position of the GP/IG navigation system;

estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the position data, and deriving an initial delay value from the distance value; and

delaying the reference timing code, with respect to the timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, including decreasing the offset delay value (i) until the timing code embedded in the satellite signal is synchronized with the reference timing code, or (ii) until the offset delay value equals a predetermined start limit value.

4. A method of reacquiring a satellite signal within an integrated GP/IG navigation system, comprising:

detecting a loss of synchronization between a timing code embedded in the satellite signal and a corresponding reference timing code;

receiving position data from an inertial guidance unit, the position data being representative of an estimated position of the GP/IG navigation system;

estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the position data, and deriving an initial delay value from the distance value; and

delaying the reference timing code, with respect to the timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, further including incrementally varying the offset delay value within a search window, wherein the search window includes a first edge occurring at a predetermined start limit value and a second edge occurring at a predetermined end limit value, such that an amount of delay from the first edge to the second edge defines a window length.

5. A method according to claim 4, further including calculating an uncertainty estimate of the predicted position, and calculating an optimal width of the search window as a function of the uncertainty estimate.

6. A method according to claim 4, wherein the window length is a fixed value.

7. A method according to claim 6, wherein the fixed value is a predetermined function of one or more static parameters of the GP/IG navigation system.

8. A method according to claim 7, wherein the one or more static parameters are selected from the group consisting of the accuracy of an associated gyroscope set, the accuracy of an associated odometer, and combinations thereof.

9. A method according to claim 4, wherein the window length is a variable.

10. A method according to claim 9, wherein the variable is a predetermined function of one or more dynamic parameters associated with the GP/IG navigation system.

11. A method according to claim 10, wherein the one or more dynamic parameters are selected from the group consisting of (i) an amount of time the loss of synchronization has lasted, (ii) a figure of merit associated with the position data, (iii) a degradation value characterizing an associated gyroscope set, (iv) a degradation value characterizing an associated odometer, and combinations thereof.

12. A system for reacquiring a satellite signal within an integrated GP/IG navigation system, comprising:

a synchronization detector for detecting a loss of synchronization between a timing code embedded in the satellite signal and a corresponding reference timing code;

an inertial guidance unit for generating position data representative of an estimated position of the GP/IG navigation system;

a distance estimator for estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the position data;

a search controller for (i) deriving an initial delay value from the distance value, (ii) delaying the reference timing code, with respect to the timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, and (iii) incrementally varying the offset delay value until the timing code embedded in the satellite signal is synchronized with the reference timing code, or until the offset delay value equals a predetermined end limit value.

13. A system according to claim 12, wherein the search controller further decreases the offset delay value until the timing code embedded in the satellite signal is synchronized with the reference timing code, or until the offset delay value equals a predetermined start limit value.

14. A system according to claim 12, wherein the timing code includes a PR code.

15. A system according to claim 12, wherein the search controller further increases the offset delay value until the timing code embedded in the satellite signal is synchronized with the reference timing code, or until the offset delay value equals a predetermined end limit value.

16. A system according to claim 12, wherein the search controller further incrementally varies the offset delay value within a search window, the search window including a first edge occurring at a predetermined start limit value and a second edge occurring at a predetermined end limit value, such that an amount of delay from the first edge to the second edge defines a window length.

17. A system according to claim 16, wherein the search controller receives an uncertainty estimate of the predicted position, and calculates an optimal width of the search window as a function of the uncertainty estimate.

18. A system according to claim 16, wherein the window length has a fixed value.

19. A system according to claim 18, wherein the fixed value is a predetermined function of one or more static parameters of the GP/IG navigation system.

20. A system according to claim 19, wherein the one or more static parameters are selected from the group consisting of the accuracy of an associated gyroscope set, the accuracy of an associated odometer, and combinations thereof.

21. A system according to claim 16, wherein the window has a variable window length.

22. A system according to claim 21, wherein the variable window length is a predetermined function of one or more dynamic parameters associated with the GP/IG navigation system.

23. A system according to claim 22, wherein the one or more dynamic parameters are selected from the group consisting of (i) an amount of time the loss of synchronization has lasted, (ii) a figure of merit associated with the position data, (iii) a degradation value characterizing an associated gyroscope set, (iv) a degradation value characterizing an associated odometer, and combinations thereof.

24. A system according to claim 12, further including a correlator for correlating the timing code embedded in the satellite signal with the corresponding timing code, and providing a correlation output representative of an extent of correlation between the timing code embedded in the satellite signal and the corresponding timing code, wherein the search controller compares the correlation output to a predetermined threshold, and the synchronization detector detects the loss of synchronization when the correlation output is less than the predetermined threshold.

25. A system according to claim 12, further including one or more gyroscopes for providing gyroscope data, one odometer (or one or more accelerometers) for providing odometer data (or acceleration data), and a Kalman filter, wherein the inertial guidance unit generates the position data by combining the gyroscope data and the odometer data via the Kalman filter, such that the Kalman filter produces the position data as a function of the gyroscope data and the odometer data.

26. A system according to claim 25, wherein the Kalman filter receives position solution data from a GPS portion of the GP/IG navigation system, and combines the gyroscope data, the odometer data and the position solution data so as to produce the position data as a function of the gyroscope data, the odometer data and the position solution data.

27. A system according to claim 12, wherein the search controller derives the initial delay value by dividing the distance value by a propagation velocity of the satellite signal.

28. A method of acquiring a satellite signal within an integrated GP/IG navigation system, comprising:

receiving system position data from an inertial guidance unit, the position data being representative of an estimated position of the GP/IG navigation system;

acquiring satellite position data from an almanac (and the ephemeris data), the satellite position data being representative of a position of a satellite associated with the satellite signal;

estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the system position data and the satellite position data, and deriving an initial delay value from the distance value;

delaying a reference timing code associated with the satellite signal, with respect to a timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, including incrementally varying the offset delay value (i) until the timing code embedded in the satellite signal is synchronized with the reference timing code, or (ii) until the offset delay value equals a predetermined end limit value.

29. A method of acquiring a satellite signal within an integrated GP/IG navigation system, comprising:

receiving system position data from an inertial guidance unit, the position data being representative of an estimated position of the GP/IG navigation system;

acquiring satellite position data from an almanac (and the ephemeris data), the satellite position data being representative of a position of a satellite associated with the satellite signal;

estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the system position data and the satellite position data, and deriving an initial delay value from the distance value;

delaying a reference timing code associated with the satellite signal, with respect to a timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, including increasing the offset delay value (i) until the timing code embedded in the satellite signal is synchronized with the reference timing code, or (ii) until the offset delay value equals a predetermined start limit value.

30. A method of acquiring a satellite signal within an integrated GP/IG navigation system, comprising:

receiving system position data from an inertial guidance unit, the position data being representative of an estimated position of the GP/IG navigation system;

acquiring satellite position data from an almanac (and the ephemeris data), the satellite position data being representative of a position of a satellite associated with the satellite signal;

estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the system position data and the satellite position data, and deriving an initial delay value from the distance value;

delaying a reference timing code associated with the satellite signal, with respect to a timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, including decreasing the offset delay value (i) until the timing code embedded in the satellite signal is synchronized with the reference timing code, or (ii) until the offset delay value equals a predetermined start limit value.

31. A method of acquiring a satellite signal within an integrated GP/IG navigation system, comprising:

receiving system position data from an inertial guidance unit, the position data being representative of an estimated position of the GP/IG navigation system;

acquiring satellite position data from an almanac (and the ephemeris data), the satellite position data being representative of a position of a satellite associated with the satellite signal;

estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the system position data and the satellite position data, and deriving an initial delay value from the distance value;

delaying a reference timing code associated with the satellite signal, with respect to a timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, including incrementally varying the offset delay value within a search window, wherein the search window includes a first edge characterized by the start limit value and a second edge characterized by the end limit value, such that an amount of delay from the first edge to the second edge defines a window length.

32. A method according to claim 31, further including calculating an uncertainty estimate of the predicted position, and calculating an optimal width of the search window as a function of the uncertainty estimate.

33. A method according to claim 31, wherein the window length is a fixed value.

34. A method according to claim 33, wherein the fixed value is a predetermined function of one or more static parameters of the GP/IG navigation system.

35. A method according to claim 34, wherein the one or more static parameters are selected from the group consisting of the accuracy of an associated gyroscope set, the accuracy of an associated odometer, and combinations thereof.

36. A method according to claim 31, wherein the window length is a variable.

37. A method according to claim 36, wherein the variable is a predetermined function of one or more dynamic parameters associated with the GP/IG navigation system.

38. A method according to claim 37, wherein the one or more dynamic parameters are selected from the group consisting of (i) an amount of time the loss of synchronization has lasted, (ii) a figure of merit associated with the position data, (iii) a degradation value characterizing an associated gyroscope set, (iv) a degradation value characterizing an associated odometer, and combinations thereof.

39. A system for acquiring a satellite signal within an integrated GP/IG navigation system, comprising:

an inertial guidance unit for generating position data representative of an estimated position of the GP/IG navigation system;

ephemeris data for storing satellite position data representative of a position of a satellite associated with the satellite signal;

a distance estimator for estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the position data and the satellite position data; and

,

a search controller for (i) deriving an initial delay value from the distance value, (ii) delaying the reference timing code, with respect to the timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, and (iii) incrementally varying the offset delay value until the timing code embedded in the satellite signal is synchronized with the reference timing code, or until the offset delay value equals a predetermined end limit value.

40. A system for reacquiring a satellite signal within an integrated GP/IG navigation system, comprising:

detection means for detecting a loss of synchronization between a timing code embedded in the satellite signal and a corresponding reference timing code;

navigational means for generating position data representative of an estimated position of the GP/IG navigation system;

estimating means for estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the position data; and

,

controller means for (i) deriving an initial delay value from the distance value, (ii) delaying the reference timing code, with respect to the timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, and (iii) incrementally varying the offset delay value until the timing code embedded in the satellite signal is synchronized with the reference timing code, or until the offset delay value equals a predetermined end limit value.

41. A system for acquiring a satellite signal within an integrated GP/IG navigation system, comprising:

navigational means for generating position data representative of an estimated position of the GP/IG navigation system;

storage means for storing satellite position data representative of a position of a satellite associated with the satellite signal;

estimating means for estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the position data and the satellite position data; and

,

controller means for (i) deriving an initial delay value from the distance value, (ii) delaying the reference timing code, with respect to the timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, and (iii) incrementally varying the offset delay value until the timing code embedded in the satellite signal is synchronized with the reference timing code, or until the offset delay value equals a predetermined end limit value.

42. A method of acquiring a satellite signal within an integrated GP/IG navigation system, comprising:

generating position data representative of an estimated position of the GP/IG navigation system by (i) receiving position solution data from a GPS portion of the GP/IG navigation system, and (ii) combining gyroscope data, odometer data and the position solution data via a Kalman filter, such that the Kalman filter produces the position data as a function of the gyroscope data, the odometer data and the position solution data;

acquiring satellite position data representative of a position of a satellite associated with the satellite signal;

estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the system position data and the satellite position data, and deriving an initial delay value from the distance value;

delaying a reference timing code associated with the satellite signal, with respect to a timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, and

incrementally varying the offset delay value (i) until the timing code embedded in the satellite signal is synchronized with the reference timing code, or (ii) until the offset delay value equals a predetermined end limit value.

43. A system for acquiring a satellite signal within an integrated GP/IG navigation system, comprising:

an inertial guidance unit for generating position data representative of an estimated position of the GP/IG navigation system by (i) receiving position solution data from a GPS portion of the GP/IG navigation system, and (ii) combining gyroscope data, odometer data and the position solution data via a Kalman filter, such that the Kalman filter produces the position data as a function of the gyroscope data, the odometer data and the position solution data;

a distance estimator for estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the position data and satellite position data representative of a position of a satellite associated with the satellite signal; and

,

a search controller for (i) deriving an initial delay value from the distance value, (ii) delaying the reference timing code, with respect to the timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, and (iii) incrementally varying the offset delay value until the timing code embedded in the satellite signal is synchronized with the reference timing code, or until the offset delay value equals a predetermined end limit value.

44. A method of reacquiring a satellite signal within an integrated GP/IG navigation system, comprising:

detecting a loss of synchronization between a timing code embedded in the satellite signal and a corresponding reference timing code;

receiving position data from an inertial guidance unit, the position data being representative of an estimated position of the GP/IG navigation system;

calculating an uncertainty estimate of the predicted position, and calculating an optimal width of a search window as a function of the uncertainty estimate;

estimating a distance value, corresponding to the distance from the GP/IG navigation system to the satellite, as a function of the position data, and deriving an initial delay value from the distance value;

delaying the reference timing code, with respect to the timing code embedded in the satellite signal, by an offset delay value substantially equal to the initial delay value, and varying the offset delay value within the search window until the reference timing code matches the timing code embedded in the satellite signal.