GNSS signal processing with ionospheric bridging for reconvergence

Patent metadata

Field	Value
Publication number	US-9651677-B2
Application number	US-201214002332-A
Country	US
Kind code	B2
Filing date	Mar 11, 2012
Priority date	Jan 14, 2008
Publication date	May 16, 2017
Grant date	May 16, 2017

Abstract

Methods and apparatus provide for positioning of a rover antenna from GNSS data derived from multi-frequency signals and correction data derived from a network of reference stations. Rover antenna position and multi-frequency ambiguities are estimated at each epoch. An ionospheric filter models variation in ionospheric bias per satellite. A set of ionospheric carrier-phase ambiguities is estimated at least when the multi-frequency ambiguities have attained a predetermined precision. The estimated ionospheric carrier-phase ambiguities are cached. After detecting interruption of signal at the rover antenna and determining reacquisition of signals at the rover antenna, an ionospheric bias per satellite over an interruption interval is predicted. For each satellite, a cached ionospheric carrier-phase ambiguity is combined with a predicted ionospheric bias to obtain a post-interruption ionospheric ambiguity estimate. The post-interruption ionospheric ambiguity estimates are used to aid estimation of rover antenna position after signal reacquisition.

First claim

The invention claimed is:

1. A method of estimating a position of a rover antenna using a computer processor, the method comprising:
receiving GNSS data derived from multi-frequency signals received at the rover antenna over a plurality of epochs;
receiving correction data for the GNSS data from a network of reference stations over the plurality of epochs;
at each of the plurality of epochs, estimating values defining a rover antenna position and a set of multi-frequency ambiguities using the GNSS data and the correction data;
modeling variation in ionospheric bias per satellite using an ionospheric filter;
estimating a set of ionospheric carrier-phase ambiguities;
upon determining that the set of ionospheric carrier-phase ambiguities have converged, caching the set of ionospheric carrier-phase ambiguities;
detecting an interruption of signal received at the rover antenna;
determining reacquisition of signals received at the rover antenna;
predicting an ionospheric bias per satellite over an interruption interval;
for each satellite, combining a cached ionospheric carrier-phase ambiguity with the predicted ionospheric bias to obtain a post-interruption ionospheric ambiguity estimate; and
estimating a position of the rover antenna subsequent to the reacquisition using the post-interruption ionospheric ambiguity estimates.

2. The method of claim 1 , wherein estimating the position of the rover antenna position subsequent to the reacquisition comprises, at each of a plurality of epochs after reacquisition of signals, using the GNSS data, the correction data, and the post-interruption ionospheric ambiguity estimates to estimate values defining an aided rover antenna position and an aided set of multi-frequency ambiguities.

3. The method of claim 2 , further comprising determining an accuracy of the post-interruption rover antenna position and an accuracy of each of the multi-frequency ambiguities.

4. The method of claim 3 , further comprising, upon determining that the accuracy of the post-interruption rover antenna position and the accuracy of each of the multi-frequency ambiguities has each achieved a predetermined level, terminating the estimation of the position of the rover antenna position subsequent to the reacquisition.

5. The method of claim 4 , wherein the values defining the rover antenna position are estimated in a filter, the method further comprising monitoring accuracies of the estimated values and terminating the estimation of the values when a predetermined accuracy level is achieved.

6. The method of claim 5 , further comprising continuing the estimation of the values defining a rover antenna position after terminating the estimation of the position of the rover antenna position subsequent to the reacquisition.

7. The method of claim 1 , wherein rover-satellite ionospheric biases are substantially uncorrelated with reference station-satellite ionospheric biases.

8. The method of claim 1 , wherein the ionospheric filter models an ionospheric bias per satellite which is single-differenced between rover data and correction data.

9. The method of claim 1 , wherein the set of ionospheric carrier-phase ambiguities comprises a single-differenced ionospheric ambiguity per satellite.

10. The method of claim 1 , wherein detecting the interruption comprises determining that fewer than four satellites are continuously observed over a predetermined interval.

11. The method of claim 1 , wherein determining the reacquisition comprises determining that at least four satellites are continuously observed over a predetermined interval.

12. The method of claim 1 , wherein the estimated rover antenna position subsequent to the reacquisition has a precision which is better than a precision that would be obtained without use of the post-interruption ionospheric ambiguity estimates.

13. The method of claim 1 , further comprising predicting a tropospheric bias, and wherein the predicted tropospheric bias is used in the estimation of the rover antenna position subsequent to the reacquisition.

14. The method of claim 1 , wherein the set of ionospheric carrier-phase ambiguities is estimated as a weighted average of integer ambiguity candidate sets.

15. The method of claim 1 , further comprising deferring caching of the estimated ionospheric phase ambiguities until satellite tracking is determined to be stable and within predetermined parameters.

16. The method of 1 , further comprising estimating time-wise variation of an ionospheric bias per satellite.

17. The method of claim 1 , further comprising estimating a change in ionospheric carrier-phase ambiguities after detecting an interruption of signal received at the rover antenna.

18. The method of claim 1 , wherein estimating the position of the rover antenna subsequent to reacquisition comprises combining the post-interruption ionospheric ambiguity estimates with estimates of other parameters from a set of factorized filters.

19. The method of claim 18 , wherein the post-interruption ionospheric ambiguity estimates are substituted for estimates from a bank of ionospheric filters.

20. An apparatus comprising:
a receiver configured to:
receive GNSS data derived from multi-frequency signals received at a rover antenna; and
receive correction data for the GNSS data derived from a network of reference stations; and

a processor coupled to the receiver, the processor configured to:
at each of a plurality of epochs, estimate values defining a rover antenna position and a set of multi-frequency ambiguities using the GNSS data and the correction data;
model variation in ionospheric bias per satellite using an ionospheric filter;
estimate a set of ionospheric carrier-phase ambiguities until the multi-frequency ambiguities have converged;
cache the estimated ionospheric carrier-phase ambiguities;
detect an interruption of signal received at the rover antenna;
determine reacquisition of signals received at the rover antenna;
predict an ionospheric bias per satellite over an interruption interval;
for each satellite, combine a cached ionospheric carrier-phase ambiguity with a predicted ionospheric bias to obtain a post-interruption ionospheric ambiguity estimate; and
estimate a position of the rover antenna subsequent to the reacquisition using the post-interruption ionospheric ambiguity estimates.

21. The apparatus of claim 20 , wherein estimating the position of the rover antenna subsequent to the reacquisition comprises, at each of a plurality of epochs after reacquisition of signals, using the GNSS data and the correction data and the post-interruption ionospheric ambiguity estimates to estimate values defining an aided rover antenna position and an aided set of multi-frequency ambiguities.

22. The apparatus of claim 21 , wherein the processor is further configured to determine an accuracy of the position of the rover antenna subsequent to the reacquisition and an accuracy of each of the multi-frequency ambiguities.

23. The apparatus of claim 22 , wherein the processor is further configured to terminate the estimation of the position of the rover antenna subsequent to the reacquisition when the accuracy of the position of the rover antenna subsequent to the reacquisition and the accuracy of each of the multi-frequency ambiguities has each achieved a predetermined level.

24. The apparatus of claim 23 , wherein the values defining the position of the rover antenna are estimated in a f

Assignees

• Leandro Rodrigo
• Vollath Ulrich
• Talbot Nicholas Charles
• Trimble Inc

Inventors

• Leandro Rodrigo
• Vollath Ulrich
• Talbot Nicholas Charles

Classifications

• G01S19/32

  Multimode operation in a single same satellite system, e.g. GPS L1/L2 · CPC title

• G01S19/072

  Ionosphere corrections · CPC title

• G01S19/44 Primary

  Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method · CPC title

• G01S19/43

  using carrier phase measurements, e.g. kinematic positioning; using long or short baseline interferometry · CPC title

• G01S19/09

  providing processing capability normally carried out by the receiver · CPC title