GNSS signal processing methods and apparatus

• US 7,755,542 B2
• Filed: 03/07/2007
• Issued: 07/13/2010
• Est. Priority Date: 03/07/2006
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Chen, Xiaoming, Vollath, Ulrich
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Mull; Fred H
• Application Number:
  US12/224,451
• Publication Number:
  US 20090027264A1
• Time in Patent Office: 1,224 Days
• Field of Search: 342/357.03, 342/357.04, 342/357.12, 342/358
• US Class Current: 342/357.24
• CPC Class Codes: G01S 19/04 providing carrier phase data

Abstract

Methods and apparatus for processing of data from a network of GNSS reference stations are presented. An ionosphere-free, federated geometry filter is employed so that computation time increases only linearly with the increase in number of reference stations, significantly reducing processing time as compared to a centralized filter approach.

Claims

1. A method of processing a set of GNSS signal data received from multiple satellites at multiple reference stations, comprising:

a. for each reference station,

applying to the GNSS signal data a station geometry filter to estimate values for local states representing parameters unique to that reference station and for common states representing parameters common to all reference stations,

providing values for the common states and their covariance to a master filter, and

preparing updated estimates for the local states when updated values for the common states are provided by the master filter, and

b. applying to the values for the common states and their covariances the master filter to estimate updated values for the common states, and to provide the updated values to the station geometry filters.

2. The method of claim 1, wherein

the common states comprise a satellite-clock error for each satellite and

the local states comprise a tropospheric scaling factor, a reference-station clock error, and an iono-free ambiguity for each satellite.

3. The method of claim 1, further comprising:

a. applying to the GNSS signal data from a subset of the reference stations a frame filter to estimate values for frame filter system states representing at least one of;

(i) a troposcaling vector having a troposcaling state for each reference station of a subset of the reference stations,

(ii) a receiver clock error vector having a receiver clock error state for each reference station of the subset,

(iii) an ambiguity vector having an ambiguity state for each satellite for each reference station of the subset,

(iv) a satellite clock error vector having a clock error state for each satellite, and

(v) an orbit error vector having a set of orbit error states for each satellite, and

b. supplying at least a subset of the estimated values for the frame filter states to the station geometry filters.

4. The method of claim 3, wherein the frame filter supplies estimated satellite-orbit error vector values to the station geometry filters.

5. The method of claim 4, wherein during each of a plurality of epochs the station geometry filters apply the satellite-orbit error values as a correction before estimating values for the local states and the common states.

6. The method of claim 3, wherein the frame filter supplies estimated troposcaling values to the station geometry filters.

7. The method of claim 3, wherein the frame filter supplies estimated troposcaling values to the station geometry filters during a number of initial epochs of operation of the station geometry filters.

8. The method of claim 1, further comprising combining state values from the station geometry filters to obtain an array of ionosphere-free ambiguity estimates and associated statistical information.

9. The method of claim 8, further comprising:

forming a geometry-free combination of the GNSS signal data;

applying a bank of geometry-free filters to the geometry-free combination to obtain geometry-free ambiguity estimates and associated statistical information; and

combining the ionosphere-free ambiguity estimates and associated statistical information with the geometry-free ambiguity estimates and associated statistical information to determine a combined array of ambiguity estimates and associated statistical information.

10. The method of claim 9, further comprising:

computing from the ambiguity estimates for all carrier phase observations a set of errors at the reference stations;

generating from the set of errors at the reference stations a set of virtual-reference-station data for use by a GNSS receiver at a mobile GNSS receiver location, and

transmitting the set of virtual-reference-station data for use by a GNSS receiver at the mobile GNSS receiver location.

11. The method of claim 9, further comprising:

combining the combined array of ambiguity estimates with the set of GNSS signal data to produce a set of network broadcast data for use by GNSS receivers within the network area, and

transmitting the network broadcast data for use by GNSS receivers within the network area.

12. The method of claim 8, further comprising:

forming a geometry-free combination of the GNSS signal data;

applying a bank of geometry-free filters to the geometry-free combination to obtain geometry-free ambiguity estimates and associated statistical information;

applying at least one code filter to the GNSS signal data using a plurality of geometry-free code-carrier combinations to obtain ambiguity estimates for the code-carrier combinations and associated statistical information; and

combining the ionosphere-free ambiguity estimates and associated statistical information with the geometry-free ambiguity estimates and associated statistical information and with the ambiguity estimates for all code-carrier combinations and associated statistical information to determine a combined array of ambiguity estimates and associated statistical information.

13. The method of claim 8, wherein the GNSS signal data is derived from at least three carrier frequencies received at the reference stations over multiple epochs, further comprising:

forming a geometry-free combination of the GNSS signal data;

applying a bank of geometry-free filters to the geometry-free combination to obtain geometry-free ambiguity estimates and associated statistical information;

applying at least one code filter to the GNSS signal data using a plurality of geometry-free code-carrier combinations to obtain ambiguity estimates for the code-cater combinations and associated statistical information;

applying at least one quintessence filter to the GNSS signal data using a plurality of geometry-free and ionosphere-free carrier-phase combinations to obtain geometry-free and ionosphere-free ambiguity estimates and associated statistical information; and

combining the ionosphere-free ambiguity estimates and associated statistical information with the geometry-free ambiguity estimates and associated statistical information and with the ambiguity estimates for the code-cater combinations and associated statistical information and with the geometry-free and ionosphere-free ambiguity estimates and associated statistical information to determine a combined array of ambiguity estimates and associated statistical information.

14. Apparatus for processing a set of GNSS signal data received from multiple satellites at multiple reference stations, comprising:

a. for each reference station, a station geometry filter having local states representing parameters unique to that reference station and common states representing parameters common to all reference stations,

wherein the station geometry filter is operative to estimate values for the local states and for the common states, to provide values for the common states and their covariance to a master filter, and to prepare updated estimates for the local states when updated values for the common states are provided by the master filter, and

b. the master filter having common states representing parameters common to all reference stations, the master filter being operative to receive values forte common states and their covariances from the station geometry filters, to estimate from the received values and their covariances updated values for the common states, and to provide the updated values to the station geometry filters.

15. The apparatus of claim 14, wherein the common states comprise a satellite-clock error for each satellite and the local states comprise a tropospheric scaling factor, a reference-station clock error, and an iono-free ambiguity for each satellite.

16. The apparatus of claim 14, further comprising:

c. a frame filter having frame filter system states representing at least one of;

(i) a troposcaling vector having a troposcaling state for each reference station of a subset of the reference stations,

(ii) a receiver clock error vector having a receiver clock error state for each reference station of the subset,

(iii) an ambiguity vector having an ambiguity state for each satellite for each reference station of the subset,

(iv) a satellite clock error vector having a clock error state for each satellite, and

(v) an orbit error vector having a set of orbit error states for each satellite,

 

wherein the frame filter is operative to estimate values for the frame filter system states from GNSS signal data received at a subset of the reference stations and to supply at least a subset of the estimated values for the frame filter system states to the station geometry filters.

17. The apparatus of claim 16, wherein the frame filter supplies estimated satellite-orbit error vector values to the station geometry filters.

18. The apparatus of claim 16, wherein during each epoch of operation the station geometry filters apply the satellite-orbit error values as a correction before estimating values for the local states and the common states.

19. The apparatus of claim 16, wherein the frame filter supplies estimated troposcaling values to the station geometry filters.

20. The apparatus of claim 16, wherein the frame filter supplies estimated troposcaling values to the station geometry filters during a number of initial epochs of operation of the station geometry filters.

21. The apparatus of claim 14, wherein the reference stations are distributed over a region and wherein the reference stations of the subset lie substantially about a perimeter of the region.

22. The apparatus of claim 14, wherein the master filter computes an optimal weighted least-square estimate of the common states and their covariance.

23. The apparatus of claim 14, further comprising:

a processing element to prepare a geometry-free combination of the GNSS signal data;

a filter to obtain from the geometry-free combination ambiguity estimates for the geometry-free carrier-phase combination and associated statistical information; and

a combiner to determine ambiguity estimates for all carrier phase observations and associated statistical information by combining the ionosphere-free ambiguity estimates and associated statistical information with the geometry-free ambiguity estimates and associated statistical information to determine a combined array of ambiguity estimates and associated statistical information.

24. The apparatus of claim 14, further comprising:

a processing element to prepare a geometry-free combination of the GNSS signal data;

a filter to obtain from the geometry-free combination ambiguity estimates for the geometry-free carrier-phase combination and associated statistical information;

at least one code filter using a plurality of geometry-free code-cater combinations of the GNSS signal data to obtain ambiguity estimates for the code-carrier combinations and associated statistical information; and

a combiner to determine ambiguity estimates for all cater phase observations and associated statistical information by combining the ionosphere-free ambiguity estimates and associated statistical information with the geometry-free ambiguity estimates and associated statistical information and with the code-cater combinations and associated statistical information to determine a combined array of ambiguity estimates and associated statistical information.

25. The apparatus of claim 14, wherein the GNSS signal data is derived from at least three carrier frequencies received at the reference stations over multiple epochs, further comprising:

a processing element to prepare a geometry-free combination of the GNSS signal data;

a filter to obtain from the geometry-free combination ambiguity estimates for the geometry-free carrier-phase combination and associated statistical information;

at least one code filter using a plurality of geometry-free code-carrier combinations of the GNSS signal data to obtain ambiguity estimates for the code-carrier combinations and associated statistical information;

at least one quintessence filter using a plurality of geometry-free and ionosphere-free carrier-phase combinations of the GNSS signal data to obtain ambiguity estimates for geometry-free and ionosphere-free carrier-phase combinations end associated statistical information; and

a combiner to determine ambiguity estimates for all carrier phase observations and associated statistical information by combining the ionosphere-free ambiguity estimates and associated statistical information with the geometry-free ambiguity estimates and associated statistical information and with the ambiguity estimates for the code-carrier combinations and associated statistical information and with the ambiguity estimates for geometry-free and ionosphere-free carrier-phase combinations and associated statistical information to determine a combined array of ambiguity estimates and associated statistical information.

26. The apparatus of claim 14, further comprising:

a resolver to compute from the ambiguity estimates for all cater phase observations a set of errors at the reference stations;

a processing element to generate from the set of errors at the reference stations a set of virtual-reference-station data for use by a GNSS receiver at a mobile GNSS receiver location.

27. The apparatus of claim 14, further comprising:

a combining element to combine the ambiguity estimates for all carrier phase observations with the set of GNSS signal data to produce a set of network broadcast data for use by GNSS receivers within the network area.