Method for fusing multiple GPS measurement types into a weighted least squares solution

• US 7,683,832 B2
• Filed: 08/13/2007
• Issued: 03/23/2010
• Est. Priority Date: 08/11/2006
• Status: Active Grant

• Current Assignee: Sierra Nevada Co. LLC
• Original Assignee: Sierra Nevada Corporation
• Inventors: Hansen, Joseph H. Jr., Wright, William G.
• Primary Examiner(s): Phan; Dao L
• Application Number:
  US11/838,133
• Publication Number:
  US 20080036654A1
• Time in Patent Office: 953 Days
• Field of Search: 342/357.04, 342/357.06, 342/357.12, 342/357.15, 701/207, 701/213, 701/215
• US Class Current: 342/357.48
• CPC Class Codes: G01S 19/15 Aircraft landing systems
• CPC Class Codes: G01S 19/51 Relative positioning

Abstract

A method of calculating position data for an airborne aircraft using a GPS-based airborne navigation system includes the processing of a position component of a relative state function by fusing a plurality of different types of measurement data available in the GPS-based system into a weighted least squares algorithm to determine an appropriate covariance matrix for the plurality of different types of measurement data.

Claims

1. A method for calculating position, velocity, and acceleration data for a moving craft using a GPS-based navigation system, comprising:

selecting a plurality of GPS-derived measurement data types that have the smallest variance for each of a plurality of GPS satellites;

processing position, velocity, and acceleration components of a relative state function by fusing the selected plurality of GPS-derived measurement data types from the GPS-based navigation system into a weighted least squares algorithm; and

determining an appropriate covariance matrix for the selected plurality of GPS-derived measurement data types, wherein errors in the position, velocity and acceleration data are minimized.

2. The method of claim 1, wherein at least one of the measurement data types is measured for a ship.

3. The method of claim 1, wherein at least one of the measurement data types is measured for an airborne aircraft.

4. The method of claim 1, wherein at least one of the measurement data types is measured for a stationary point.

5. The method of claim 1, wherein the processing includes the calculation of phase ambiguities.

6. An apparatus for calculating position velocity and acceleration data for a moving craft using a GPS based navigation system, comprising:

a data acquisition device operable to acquire a plurality GPS-based measurement data types using the GPS based navigation system; and

a calculating device operable to select, for each satellite, a GPS-based measurement data type having the smallest variance from the plurality of GPS-based measurement data types, and fuse the selected GPS-based measurement data types in a weighted least squares algorithm utilizing an appropriate covariance matrix for the selected GPS-based measurement data types.

7. The apparatus of claim 6, wherein at least one of the GPS-based measurement data types is acquired from the moving craft and at least one of GPS-based measurement data types is acquired from a reference location selected from the group consisting of a ship and a stationary point.

8. The apparatus of claim 6, wherein the calculating device is further operable to calculate phase ambiguities.

9. An airborne navigation system for calculating position, velocity and acceleration data for a moving craft using a GPS based navigation system, comprising:

a plurality of GPS data acquisition devices operable to determine a plurality of GPS-based position, velocity and acceleration data types of a reference location and the moving craft; and

a calculating component operable to select, for each satellite, a GPS-based measurement data type having the smallest variance from the plurality of GPS-based measurement data types, and fuse the selected GPS-based data types in a weighted least squares algorithm utilizing an appropriate covariance matrix for selected GPS-based data types, such that errors in the position, velocity and acceleration data are minimized.

10. The system of claim 9, wherein at least one of the data types is measured from the moving craft, and at least one of the data types is measured from the reference location selected from the group consisting of a ship and a fixed location.

11. The system of claim 9, wherein the calculating component is further operable to calculate phase ambiguities.

12. A method of calculating position data of a moving craft by fusing different types of GPS-based measurement data, comprising:

receiving GPS-based measurement data at the moving craft and a reference location;

computing position, velocity, and phase ambiguity data at the reference location;

transmitting the computed data from the reference location to the moving craft; and

combining, at the moving craft, the CPS-based measurement data and the computed data to produce a relative vector solution between the location of the moving craft and the reference location, the combining comprising selecting GPS-based measurement data having the lowest variance for each of a plurality of GPS satellites, calculating an appropriate weighting covariance matrix for the selected data, and fusing the selected data in a weighted least squared algorithm utilizing the calculated covariance matrix.

13. The method of claim 12, wherein the moving craft is an airborne aircraft.

14. The method of claim 12, wherein the reference location is a ship.

15. A method of calculating a Precision Relative State (PRS) solution for an airborne navigation system on a first moving craft by processing a plurality of different types of GPS-derived measurement data, comprising:

computing code range and phase range values from measurements and variances from data received from GPS satellites;

determining Wide Lane Float Ambiguities and a covariance value;

calculating Double-Difference measurements at a specified time based on a second moving craft;

determining first and second frequency float ambiguities and a covariance calculation from the Double-Difference measurements, the Wide Lane Float Ambiguities, and the covariance value;

selecting GPS-derived measurement data values having the smallest variance for each of the GPS satellites from the computed code range and phase range values;

building a covariance in matrix including calculating cross-correlation terms among the selected GPS-derived measurement data values; and

calculating the PRS solution and its covariance using the covariance matrix by a weighted least squares (WLS) algorithm.

16. The method of claim 15, wherein the step of calculating the PRS solution and its covariance includes repeating the calculation until the PRS solution converges.

17. The method of claim 15, wherein the data received from GPS satellites include data from at least four Global Positioning System (GPS) satellites.

18. A landing system for a moving craft, comprising:

a reference location having means for computing and transmitting reference location position, velocity, and estimated wide lane phase ambiguity data using a weighted least squares algorithm;

a receiver on the moving craft that is operable to receive GPS measurement data from a GPS satellite constellation and the computed data from the reference location; and

a calculating system associated with the receiver that is operable to calculate position data for the moving craft by fusing the measurement data and the reference data with a weighted least squares (WLS) algorithm.

19. The landing system of claim 18, wherein the moving craft has a navigation system operable to combine the GPS measurement data and the computed data for producing a relative vector solution between the moving craft'"'"'s location and the reference location.

20. The landing system of claim 18, wherein the reference location has a Relative Navigation (RelNav) system operable to calculate the estimated wide lane phase ambiguity data for the reference location.

21. The landing system of claim 20, wherein the estimated wide lane phase ambiguity data are transmitted to the moving craft by the reference location.

22. An Airborne Relative Navigation (RelNav) system for calculating a relative position and a velocity vector between a ship and an airborne aircraft and for providing this information as relative state to the aircraft, comprising:

a Measurement Management and Validation function that processes and validates incoming measurement data;

a Relative Measurements function that calculates Double-Difference measurements and

variance components from Single-Difference measurements;

a Wide Lane Ambiguities function that determines wide lane float ambiguities and a first covariance value;

an ambiguities function that determines first and second frequency float ambiguities and a second covariance value; and

a relative state function that computes a relative state and covariance solution from the wide lane float ambiguities, the first covariance value, the first and second frequency float ambiguities and the second covariance value, and that provides the solution to an avionic system on the aircraft using a weighted least squares algorithm.

23. The RelNav system of claim 22 wherein the covariance values include corrections for at least one of:

multi-path, noise, ionosphere, or troposphere errors.

24. The RelNav system of claim 22, wherein the covariance values are selected from the group consisting of at least one of multi-path, noise, ionosphere corrections, and troposphere corrections.

25. A Precision Relative State (PRS) computational module for calculating a PRS solution for a navigation system on a moving craft, employing a weighted least squares (WLS) algorithm for processing a plurality of different types of Global Positioning System (GPS)-derived measurement data, comprising:

an input computing module operable to compute a plurality of code range and phase range values from measurement and covariance data from a satellite;

a data selection module operable to select data based on measurement variances;

a covariance matrix-building module operable to assemble GPS-derived data for covariance matrix element calculation;

a covariance matrix element calculation module for determining values for the covariance matrix elements; and

PRS solution calculation module operable to calculate the PRS solution and its covariance using the covariance matrix by the WLS algorithm.

26. The PRS computational module of claim 25, wherein the input computing module includes measurement data from every available Global Positioning System (GPS) satellite.

27. The PRS computational module of claim 25, wherein the WLS algorithm includes:

an operation for calculating measurements and covariance;

an operation for calculating Line of Sight (LOS) vectors from a ship and an aircraft to a Satellite;

an operation for performing linearization of LOS vectors;

an operation for calculating WLS of relative position solutions; and

an operation for transforming each relative position solution and its covariance from World Geodetic System of 1984 coordinates to North-East-Down coordinates at a ship reference point.

28. The PRS computational module of claim 25, wherein the relative position solution calculation module operates iteratively until the PRS solution converges.

29. The PRS computational module of claim 26, wherein the data selection module is further operable to select data having the lowest measurement variances for each of the available GPS satellites.