Navigation System and Method of Obtaining Accurate Navigational Information in Signal Challenging Environments

• US 20090265104A1
• Filed: 04/22/2008
• Published: 10/22/2009
• Est. Priority Date: 04/22/2008
• Status: Active Grant

• Current Assignee: Harris Global Communications, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: ITT Manufacturing Enterprises, Inc. (ITT, Inc.)
• Inventors: Shroff, Diniar S.
• Granted Patent: US 8,725,327 B2
• Time in Patent Office: Days
• US Class Current: 701/216
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial

Abstract

A present invention embodiment includes a navigation system with a front-end GPS receiver, auxiliary sensors and a digital signal processor providing filtering and other processing. The navigation system enhances a UTC type architecture by employing an inertial compensation unit and a stochastic regulator. The inertial compensation unit compensates for inertial errors within the sensors, while the stochastic regulator applies an optimal stochastic control law to control system operation. The inertial compensation unit and stochastic regulator mitigate instability within the navigation system and provide: the functionality to attain high position accuracy in the sub-meter range that is stable and reliable; an optimal solution evident in the process of signal recovery time after loss and reacquisition, thereby resulting in signal-loss recovery with an order of magnitude improvement; and the ability to mitigate inertial errors that originate in the sensors. The navigation system provides navigation information for indoor and urban environmental conditions.

Claims

1. A navigation system comprising:

a receiver to receive location signals, correlate said received signals with generated signals to track said location signals and produce signal components based on said correlation;

a plurality of sensors to provide sensor measurements pertaining to said navigation system; and

a navigation unit to control said receiver to track said location signals and to produce a navigation solution based on said sensor measurements and said signal components, wherein said navigation unit includes a processor including;

an extended filter module to determine estimates of navigation information based on at least said signal components and measurements of said sensors;

a navigation module to determine navigation results based on said sensor measurements and to apply said estimates to said determined navigation results to produce said navigation solution;

an inertial compensation module to receive navigation solution information and produce compensation adjustments for said signal components to compensate for errors within said sensor measurements by bounding an inertial error growth rate of said sensors; and

a regulator module to receive navigation solution information and produce control adjustments for said signal components to apply a stochastic control law to control reliance by said navigation unit on said estimates and said determined navigation results for determining said navigation solution;

wherein said compensation and control adjustments are applied to said signal components provided to said navigation unit, and navigation solution information is provided to said receiver to control generation of said generated signals for tracking of said location signals.

2. The system of claim 1, wherein said location signals include satellite signals.

3. The system of claim 2, wherein said receiver includes a GPS receiver.

4. The system of claim 1, wherein said extended filter module includes:

a pre-filter module to determine estimates of errors pertaining to pseudorange information based on said signal components and said navigation information estimates.

5. The system of claim 4, wherein said extended filter module further includes:

a navigation filter module to produce said navigation information estimates based on said estimated errors of said pseudorange information, sensor measurements and navigation solution information, wherein said navigation information estimates include errors pertaining to said navigation results.

6. The system of claim 5, wherein said navigation filter module implements a Kalman filter with a dynamically adjustable system dynamics matrix.

7. The system of claim 1, further including an inertial measurement unit including one or more of said plurality of sensors, wherein said sensors within said inertial measurement unit include inertial sensors and said navigation module determines said navigation results based on measurements by said inertial sensors.

8. The system of claim 1, wherein said inertial compensation module employs a transfer function including a plurality of poles residing on real and imaginary axes of a complex S-plane, and wherein a distance from the origin for poles on the real axis is greater than the distance from the origin for poles on the imaginary axis.

9. The system of claim 8, wherein said transfer function includes two poles on each of the real and imaginary axes, and wherein said distance from the origin for said poles on said real axis is twice that of said distance from the origin for said poles on said imaginary axis.

10. The system of claim 1, wherein said regulator module includes:

an observer module to estimate states of said navigation unit; and

a control module to determine weight values to minimize a cost function associated with desired objectives and based on said estimated states, wherein said control adjustments are produced based on said determined weight values to apply said control law to said navigation unit.

11. The system of claim 10, wherein said cost function is based on deviations of said estimated states with desired values, and said desired objectives include stability and precision.

12. The system of claim 10, wherein said navigation filter module implements a Kalman filter and said regulator module dynamically adjusts a system dynamics matrix of said Kalman filter to reduce said cost function.

13. The system of claim 1, wherein said navigation solution includes one or more of position, velocity, orientation and time parameters.

14. The system of claim 1, wherein said regulator module controls said navigation unit to place greater reliance on said navigation results for determining said navigation solution in response to said location signals traversing a signal challenging environment or being unavailable.

15. The system of claim 1, wherein said regulator module controls said navigation unit to place greater reliance on said estimates for determining said navigation solution in response to said location signals being available.

16. A navigation system comprising:

a GPS receiver to receive satellite signals, correlate said received signals with generated signals to track said satellite signals and produce signal components based on said correlation;

a navigation unit to control said receiver to track said location signals and to produce a navigation solution based on said sensor measurements and said signal components, wherein said navigation unit includes a processor including;

a regulator module to receive navigation solution information and produce control adjustments for said signal components to apply a stochastic control law to control reliance by said navigation unit on navigation estimates and sensor measurements for determining said navigation solution, wherein said control adjustments are applied to said signal components provided to said navigation unit and navigation solution information is provided to said GPS receiver to control generation of said generated signals for tracking of said location signals.

17. The system of claim 16, wherein said regulator module includes:

an observer module to estimate states of said navigation system; and

a control module to determine weight values to minimize a cost function associated with desired objectives and based on said estimated states, wherein said control adjustments are produced based on said determined weight values to apply said control law to said navigation unit.

18. The system of claim 17, wherein said cost function is based on deviations of said estimated states with desired values, and said desired objectives include stability and precision.

19. The system of claim 16, wherein said regulator module controls said navigation unit to place greater reliance on said sensor measurements for determining said navigation solution in response to said satellite signals traversing a signal challenging environment or being unavailable.

20. The system of claim 16, wherein said regulator module controls said navigation unit to place greater reliance on said navigation estimates for determining said navigation solution in response to said satellite signals being available.

21. A sensor system comprising:

a plurality of inertial sensors to provide sensor measurements; and

a processor to receive inputs and produce outputs based on said measurements, said processor including;

an inertial compensation module to receive information pertaining to said outputs and produce compensation adjustments for said inputs to compensate for errors within said sensor measurements by bounding an inertial error growth rate of said sensors, wherein said compensation adjustments are applied to said inputs provided to said processor.

22. The system of claim 21, wherein said inertial compensation module employs a transfer function including a plurality of poles residing on real and imaginary axes of a complex S-plane, and wherein a distance from the origin for poles on the real axis is greater than the distance from the origin for poles on the imaginary axis.

23. The system of claim 22, wherein said transfer function includes two poles on each of the real and imaginary axes, and wherein said distance from the origin for said poles on said real axis is twice that of said distance from the origin for said poles on said imaginary axis.

24. A method of determining a navigation solution within a navigation system including a receiver, a plurality of sensors to provide sensor measurements pertaining to said navigation system and a processor to control said receiver to track said location signals and to produce said navigation solution, said method comprising:

(a) receiving location signals, correlating said received signals with generated signals to track said location signals and producing signal components based on said correlation;

(b) determining estimates of navigation information based on at least said signal components and measurements of said sensors;

(c) determining navigation results based on said sensor measurements and applying said estimates to said determined navigation results to produce said navigation solution;

(d) producing compensation adjustments for said signal components based on navigation solution information to compensate for errors within said sensor measurements by bounding an inertial error growth rate of said sensors; and

(e) producing control adjustments for said signal components based on navigation solution information to apply a stochastic control law to control reliance on said estimates and said determined navigation results for determining said navigation solution; and

(f) applying said compensation and control adjustments to said signal components and providing navigation solution information to said receiver to control generation of said generated signals for tracking of said location signals.

25. The method of claim 24, wherein said receiver includes a GPS receiver.

26. The method of claim 24, wherein step (b) further includes:

(b.1) determining estimates of errors pertaining to pseudorange information based on said signal components and said navigation information estimates.

27. The method of claim 26, wherein step (b) further includes:

(b.2) producing said navigation information estimates based on said estimated errors of said pseudorange information, sensor measurements and navigation solution information, wherein said navigation information estimates include errors pertaining to said navigation results.

28. The method of claim 27, wherein step (b.2) further includes:

(b.2.

     1) producing said navigation information estimates via a Kalman filter with a dynamically adjustable system dynamics matrix.

29. The method of claim 24, wherein step (d) further includes:

(d.1) compensating for errors within said sensor measurements by employing a transfer function including a plurality of poles residing on real and imaginary axes of a complex S-plane, wherein a distance from the origin for poles on the real axis is greater than the distance from the origin for poles on the imaginary axis.

30. The method of claim 29, wherein said transfer function includes two poles on each of the real and imaginary axes, and wherein said distance from the origin for said poles on said real axis is twice that of said distance from the origin for said poles on said imaginary axis.

31. The method of claim 24, wherein step (e) further includes:

(e.1) estimating states of said navigation system; and

(e.2) determining weight values to minimize a cost function associated with desired objectives and based on said estimated states, wherein said control adjustments are produced based on said determined weight values to apply said control law.

32. The method of claim 31, wherein said cost function is based on deviations of said estimated states with desired values, and said desired objectives include stability and precision.

33. The method of claim 31, wherein step (b) further includes:

(b.1) producing said navigation information estimates via a Kalman filter with a dynamically adjustable system dynamics matrix; and

step (e) further includes;

(e.3) dynamically adjusting said system dynamics matrix of said Kalman filter to reduce said cost function.

34. The method of claim 24, wherein said navigation solution includes one or more of position, velocity, orientation and time parameters.

35. The method of claim 24, wherein step (e) further includes:

(e.1) controlling said navigation system to place greater reliance on said navigation results for determining said navigation solution in response to said location signals traversing a signal challenging environment or being unavailable.

36. The method of claim 24, wherein step (e) further includes:

(e.1) controlling said navigation system to place greater reliance on said estimates for determining said navigation solution in response to said location signals being available.

37. A method of determining a navigation solution within a navigation system including a GPS receiver, a plurality of sensors to provide sensor measurements pertaining to said navigation system and a processor to control said receiver to track said location signals and to produce said navigation solution, said method comprising:

(a) receiving satellite signals, correlating said received signals with generated signals to track said satellite signals and producing signal components based on said correlation;

(b) determining a navigation solution and producing control adjustments for said signal components based on navigation solution information to apply a stochastic control law to control reliance by said navigation system on navigation estimates and sensor measurements for determining said navigation solution, wherein said control adjustments are applied to said signal components and navigation solution information is provided to said GPS receiver to control generation of said generated signals for tracking of said location signals.

38. The method of claim 37, wherein step (b) further includes:

(b.1) estimating states of said navigation system; and

(b.2) determining weight values to minimize a cost function associated with desired objectives and based on said estimated states, wherein said control adjustments are produced based on said determined weight values to apply said control law to said navigation system.

39. The method of claim 38, wherein said cost function is based on deviations of said estimated states with desired values, and said desired objectives include stability and precision.

40. The method of claim 37, wherein step (b) further includes:

(b.1) controlling said navigation system to place greater reliance on said sensor measurements for determining said navigation solution in response to said satellite signals traversing a signal challenging environment or being unavailable.

41. The method of claim 37, wherein step (b) further includes:

(b.1) controlling said navigation system to place greater reliance on said navigation estimates for determining said navigation solution in response to said satellite signals being available.

42. A method of compensating for sensor errors in a sensor system including a plurality of inertial sensors to provide sensor measurements and a processor to receive inputs and produce outputs based on said measurements, said method comprising:

(a) receiving information pertaining to said outputs and producing compensation adjustments for said inputs to compensate for errors within said sensor measurements by bounding an inertial error growth rate of said sensors, wherein said compensation adjustments are applied to said inputs.

43. The method of claim 42, wherein step (a) further includes:

(a.1) compensating for sensor errors by employing a transfer function including a plurality of poles residing on real and imaginary axes of a complex S-plane, and wherein a distance from the origin for poles on the real axis is greater than the distance from the origin for poles on the imaginary axis.

44. The method of claim 43, wherein said transfer function includes two poles on each of the real and imaginary axes, and wherein said distance from the origin for said poles on said real axis is twice that of said distance from the origin for said poles on said imaginary axis.