GNSS signal processing with clock difference modeling

• US 7,692,578 B2
• Filed: 03/31/2009
• Issued: 04/06/2010
• Est. Priority Date: 10/03/2005
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Vollath, Ulrich, Doucet, Kenneth Donald
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Mull; Fred H
• Application Number:
  US12/384,184
• Publication Number:
  US 20090237298A1
• Time in Patent Office: 371 Days
• Field of Search: 342/357.02, 342/357.04, 342/357.06, 342/357.12, 342/357.14, 342/357.15, 342/358
• US Class Current: 342/357.27
• CPC Class Codes: G01S 19/44 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method

Abstract

Three new methods are presented to improve floating solutions and ambiguity resolution for multiple global satellite navigation systems (GNSS), one of which may be an FDMA-based GNSS such as GLONASS: (1) modeling of the hardware-related differential clock error between two (or more) different GNSS, (2) modeling the frequency-dependent biases present in frequency-division multiple access (FDMA) GNSS, and (3) an ambiguity resolution method called Scoreboard Partial Fixing (SPF). The methods presented are independent of the number of carrier frequencies tracked for each satellite navigation system. Their application results in quicker and more reliable ambiguity resolution. The benefits of combining observations of multiple GNSS are exploited in a very efficient way, in contrast to known algorithms which often result in degraded performance with multiple GNSS. The frequency-dependent bias method has been found effective with GNSS observations from a combination of substantially dissimilar hardware, e.g., for processing signals from GNSS receivers of different manufacturers.

Claims

1. A method of processing signal data derived from signals received from satellites of two or more GNSS, each GNSS having a respective clock error, comprising:

eliminating satellite-specific clock errors from the signal data; and

applying to the signal data after elimination of the satellite-specific clock errors a filter defined by a state vector to estimate a set of carrier ambiguities, wherein the state vector comprises a first clock-error state representing clock error of a first GNSS, and a second clock-error state representing a difference between clock error of the first GNSS and clock error of a second GNSS.

2. The method of claim 1, wherein the state vector further comprises states representing position of each station and states representing carrier ambiguities for at least one carrier frequency combination, the method further comprising:

selecting one satellite of each GNSS as a reference satellite, and constraining the carrier ambiguities.

3. The method of claim 1, wherein the filter is a geometry filter of a set of factorized filters applied to the single-difference data.

4. The method of claim 1, wherein the state vector further comprises a third clock-error state representing a difference between clock error of the first GNSS and clock error of a third GNSS.

5. The method of claim 1, wherein at least one GNSS comprises a FDMA GNSS and wherein the state vector further comprises a state representing a wavelength/frequency-dependent factor for each band of each FDMA GNSS.

6. The method of claim 5, wherein the wavelength/frequency-dependent factor represents a difference to a reference wavelength.

7. The method of claim 6, wherein one GNSS comprises the GLONASS system and wherein the wavelength/frequency-dependent factor represents a difference to a GLONASS wavelength.

8. The method of claim 5, wherein each satellite of the FDMA GNSS has a unique carrier band, and wherein the wavelength/frequency-dependent factor for a given satellite is a coefficient based on the unique carrier band of the given satellite.

9. The method of claim 5, further comprising:

determining from the signal data a complete set of integer ambiguities for all satellites;

determining validity of the integer ambiguities of the complete set and at least one quality measure for the complete set;

for each subset of a plurality of subsets of the satellites, determining a partial set of integer ambiguities;

for each of the partial sets, determining validity of the integer ambiguities of the partial set and at least one quality measure for the partial set; and

from among those of the complete set and the partial sets determined to be valid, selecting as correct a set for which the quality measure is optimum.

10. The method of claim 9, wherein the set selected as correct comprises a partial set, the method further comprising:

augmenting the set selected as correct with integer ambiguities of another set or partial set.

21. A computer-readable medium in which a program is embodied, wherein the program comprises instructions adapted to cause a processor to execute the method of claim 1.

11. Apparatus comprising a processor for processing signal data derived from signals received from satellites of two or more GNSS, each GNSS having a respective clock error, comprising:

instructions for eliminating satellite-specific clock errors from the signal data; and

instructions for applying to the signal data after elimination of the satellite-specific clock errors a filter defined by a state vector to estimate a set of carrier ambiguities,

wherein the state vector comprises a first clock-error state representing clock error of a first GNSS, and a second clock-error state representing a difference between clock error of the first GNSS and clock error of a second GNSS.

12. The apparatus of claim 11, wherein the state vector further comprises states representing position of each station and states representing carrier ambiguities for at least one carrier frequency combination.

13. The apparatus of claim 11, wherein the filter is a geometry filter of a set of factorized filters applied to the single-difference data.

14. The apparatus of claim 11, wherein the state vector further comprises a third clock-error state representing a difference between clock error of the first GNSS and clock error of a third GNSS.

15. The apparatus of claim 11, wherein at least one GNSS comprises a FDMA GNSS and wherein the state vector further comprises a state representing a wavelength/frequency-dependent factor for each band of each FDMA GNSS.

16. The apparatus of claim 15, wherein the wavelength/frequency-dependent factor represents a difference to a reference wavelength.

17. The apparatus of claim 16, wherein one GNSS comprises the GLONASS system and wherein the wavelength/frequency-dependent factor represents a difference to a GLONASS wave-length.

18. The apparatus of claim 15 wherein each satellite of the FDMA GNSS has a unique carrier band, and wherein the wavelength/frequency-dependent factor for a given satellite is a coefficient based on the unique carrier band of the given satellite.

19. The apparatus of claim 15, further comprising instructions for:

determining from the signal data a complete set of integer ambiguities for all satellites;

determining validity of the integer ambiguities of the complete set and at least one quality measure for the complete set

for each subset of a plurality of subsets of the satellites, determining a partial set of integer ambiguities;

for each of the partial sets, determining validity of the integer ambiguities of the partial set and at least one quality measure for the partial set; and

from among those of the complete set and the partial sets determined to be valid, selecting as correct a set for which the quality measure is optimum.

20. The apparatus of claim 19, wherein the set selected as correct comprises a partial set, the instructions further comprising instructions for augmenting the set selected as correct with integer ambiguities of another set or partial set.