GNSS Signal Processing to Estimate MW Biases

• US 20120163419A1
• Filed: 09/19/2010
• Published: 06/28/2012
• Est. Priority Date: 06/22/2007
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Seeger, Stephan
• Granted Patent: US 9,128,176 B2
• Time in Patent Office: Days
• US Class Current: 375/144
• CPC Class Codes: G01S 19/04 providing carrier phase data
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment
• CPC Class Codes: G01S 19/258 relating to the satellite constellation, e.g. almanac, ephemeris data, lists of satellites in view
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: G01S 19/43 using carrier phase measurements, e.g. kinematic positioning; using long or short baseline interferometry
• CPC Class Codes: G01S 19/44 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method

Abstract

Methods and apparatus are described for processing a set of GNSS signal data derived from code observations and carrier-phase observations at multiple receivers of GNSS signals of multiple satellites over multiple epochs, the GNSS signals having at least two carrier frequencies, comprising: forming an MW (Melbourne-Wübbena) combination per receiver-satellite pairing at each epoch to obtain a MW data set per epoch, and estimating from the MW data set per epoch an MW bias per satellite which may vary from epoch to epoch, and a set of WL (widelane) ambiguities, each WL ambiguity corresponding to one of a receiver-satellite link and a satellite-receiver-satellite link, wherein the MW bias per satellite is modeled as one of (i) a single estimation parameter and (ii) an estimated offset plus harmonic variations with estimated amplitudes.

Claims

1. A method of processing a set of GNSS signal data derived from code observations and carrier-phase observations at multiple receivers of GNSS signals of multiple satellites over multiple epochs, the GNSS signals having at least two carrier frequencies, comprising:

forming an MW (Melbourne-Wü

bbena) combination per receiver-satellite pairing at each epoch to obtain a MW data set per epoch, and

estimating from the MW data set per epoch an MW bias per satellite which may vary from epoch to epoch, and a set of WL (widelane) ambiguities, each WL ambiguity corresponding to one of a receiver-satellite link and a satellite-receiver-satellite link,

wherein the MW bias per satellite is modeled as one of (i) a single estimation parameter and (ii) an estimated offset plus harmonic variations with estimated amplitudes.

2. The method of claim 1, further comprising applying corrections to the GNSS signal data.

3. The method of claim 1, further comprising smoothing at least one linear combination of GNSS signal data before estimating an MW bias per satellite.

4. The method of claim 1, further comprising applying at least one MW bias constraint.

5. The method of claim 1, further comprising applying at least one integer WL ambiguity constraint.

6. The method of claim 1, further comprising using a spanning tree (ST) over one of an observation graph and a filter graph for constraining the WL ambiguities.

7. The method of claim 1, further comprising using a minimum spanning tree (MST) on one of an observation graph and a filter graph for constraining the WL ambiguities.

8. The method of claim 7, wherein the minimum spanning tree is based on edge weights, each edge weight derived from receiver-satellite geometry.

9. The method of claim 8, wherein the edge weight is defined with respect to one of (i) a geometric distance from receiver to satellite, (ii) a satellite elevation angle, and (iii) a geometric distance from satellite to receiver to satellite, and (iv) a combination of the elevations under which the two satellites in a single differenced combination are seen at a station.

10. The method of claim 7, wherein the minimum spanning tree is based on edge weights, with each edge weight based on WL ambiguity information, defined with respect to one of (i) difference of a WL ambiguity to integer, (ii) WL ambiguity variance, and (iii) a combination of (i) and (ii).

11. The method of claim 1, further comprising fixing at least one of the WL ambiguities as an integer value.

12. The method of claim 1, further comprising determining candidate sets of WL integer ambiguity values, forming a weighted combination of the candidate sets, and fixing at least one of the WL ambiguities as a value taken from the weighted combination.

13. The method of claim 11, wherein the estimating step comprises introducing fixed WL ambiguities so as to estimate MW biases which are compatible with fixed WL ambiguities.

14. The method of claim 13, wherein the estimating step comprises applying an iterative filter to the MW data per epoch and wherein introducing fixed WL ambiguities comprises one of (i) putting the fixed WL ambiguities as observations into the filter, (ii) putting the fixed WL ambiguities as observations into a copy of the filter generated after each of a plurality of observation updates, and (iii) reducing the MW combinations by the fixed WL ambiguities and putting the resulting reduced MW combinations into a second filter without ambiguity states to estimate at least one MW bias per satellite.

15. The method of claim 1, further comprising shifting at least one MW bias by an integer number of WL cycles.

16. The method of claim 1, further comprising shifting at least one MW bias and its respective WL ambiguity by an integer number of WL cycles.

17. The method of claim 1, wherein the navigation message comprises orbit information.

36. An article of manufacture comprising a tangible medium embodying instructions configured, when executed on a computer processing unit, to carry out the method according to claim 1.

18. (canceled)

19. Apparatus for processing a set of GNSS signal data derived from code observations and carrier-phase observations at multiple receivers of GNSS signals of multiple satellites over multiple epochs, the GNSS signals having at least two carrier frequencies, comprising:

an element adapted to form an MW (Melbourne-Wü

bbena) combination per receiver-satellite pairing at each epoch to obtain a MW data set per epoch, and

an element adapted to estimate from the MW data set per epoch an MW bias per satellite which may vary from epoch to epoch, and a set of WL (widelane) ambiguities, each WL ambiguity corresponding to one of a receiver-satellite link and a satellite-receiver-satellite link,

wherein the MW bias per satellite is modeled as one of (i) a single estimation parameter and (ii) an estimated offset plus harmonic variations with estimated amplitudes.

20. The apparatus of claim 19, further comprising an element adapted to apply corrections to the GNSS signal data.

21. The apparatus of claim 19, further comprising an element adapted to smooth at least one linear combination of GNSS signal data before an MW bias per satellite is estimated.

22. The apparatus of claim 19, further comprising an element adapted to apply at least one MW bias constraint.

23. The apparatus of claim 19, further comprising an element adapted to apply at least one integer WL ambiguity constraint.

24. The apparatus of claim 19, further comprising an element adapted to use a spanning tree (ST) over one of an observation graph and a filter graph to constrain the WL ambiguities.

25. The apparatus of claim 19, further comprising an element adapted to use a minimum spanning tree (MST) on one of an observation graph and a filter graph to constrain the WL ambiguities.

26. The apparatus of claim 25, wherein the minimum spanning tree is based on edge weights, each edge weight derived from receiver-satellite geometry.

27. The apparatus of claim 26, wherein the edge weight is defined with respect to one of (i) a geometric distance from receiver to satellite, (ii) a satellite elevation angle, and (iii) a geometric distance from satellite to receiver to satellite, and (iv) a combination of the elevations under which the two satellites in a single differenced combination are seen at a station.

28. The apparatus of claim 25, wherein the minimum spanning tree is based on edge weights, with each edge weight based on WL ambiguity information, defined with respect to one of (i) difference of a WL ambiguity to integer, (ii) WL ambiguity variance, and (iii) a combination of (i) and (ii).

29. The apparatus of claim 19, further comprising an element adapted to fix at least one of the WL ambiguities as an integer value.

30. The apparatus of claim 19, further comprising an element adapted to determine candidate sets of WL integer ambiguity values, form a weighted combination of the candidate sets, and fix at least one of the WL ambiguities as a value taken from the weighted combination.

31. The apparatus of claim 29, wherein the element adapted to estimate is further adapted to introduce fixed WL ambiguities so as to estimate MW biases which are compatible with fixed WL ambiguities.

32. The apparatus of claim 31, wherein the element adapted to estimate is further adapted to apply an iterative filter to the MW data per epoch and to introduce fixed WL ambiguities as one of (i) fixed WL ambiguities as observations in the filter, (ii) fixed WL ambiguities as observations in a copy of the filter generated after each of a plurality of observation updates, and (iii) MW combinations reduced by the fixed WL ambiguities and in a second filter without ambiguity states to estimate at least one MW bias per satellite.

33. The apparatus of claim 19, further comprising an element adapted to shift at least one MW bias by an integer number of WL cycles.

34. The apparatus of claim 19, further comprising an element adapted to shift at least one MW bias and its respective WL ambiguity by an integer number of WL cycles.

35. The apparatus of claim 19, wherein the navigation message comprises orbit information.

37. (canceled)