Satellite navigation receiver with improved ambiguity resolution

• US 10,379,225 B2
• Filed: 09/29/2016
• Issued: 08/13/2019
• Est. Priority Date: 03/18/2016
• Status: Active Grant

• Current Assignee: Deere & Company
• Original Assignee: Deere & Company
• Inventors: Dai, Liwen, Zeitzew, Michael
• Primary Examiner(s): Gregory, Bernarr E
• Application Number:
  US15/281,016
• Publication Number:
  US 20170269230A1
• Time in Patent Office: 1,048 Days
• CPC Class Codes: G01S 19/32 Multimode operation in a single same satellite system, e.g. GPS L1/L2
• CPC Class Codes: G01S 19/44 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method

Abstract

A satellite navigation receiver and associated methods are described that can provide improved integer ambiguity resolution and more accurate positioning information. A modified BIE process may be utilized to enable the receiver to perform the integer ambiguity resolution more optimally. The output of the modified BIE process may be time-domain smoothed to provide a solution which is smoother in ambiguity space, and therefore also provide a position solution that is smoother in time. Transitions between an ambiguity-determined solution to a float solution, when necessary, may be smoothed in time. A weighting scheme may dynamically blend the ambiguity-determined solution and the float solution to leverage the advantages of both solutions, such as faster pull-in, higher accuracy, and more stable and smooth performance.

Claims

1. A method for smoothing ambiguity values related to a position of a satellite navigation receiver, comprising:

determining estimated float narrow lane ambiguities based on received signals from one or more satellites, ionospheric-free float ambiguities, estimated integer wide lane ambiguities, and correction data;

applying the estimated float narrow lane ambiguities to a predictive filter with a least squares error minimization process to update ambiguity values;

calculating an ambiguity determined position solution based on the updated ambiguity values;

storing float ambiguity biases derived from the ambiguity determined position solutions;

determining the position of the satellite navigation receiver based the float ambiguity biases.

2. The method of claim 1, wherein applying the estimated float narrow lane ambiguities to update the ambiguity values comprises time-domain smoothing the determined ambiguity values.

3. The method of claim 2, wherein the time-domain smoothing is conducted at a regular interval and comprises:

removing unavailable satellites used in the time-domain smoothing, the unavailable satellites comprising the satellites that the receiver can no longer receive signals from;

determining whether a reference satellite used in the time-domain smoothing has changed to a new reference satellite;

if the reference satellite has changed, calculating the time-domain smoothed ambiguity values for the new reference satellite and the satellites other than the unavailable satellites;

determining whether new satellites should be used in the time-domain smoothing;

if the new satellites should be used;

adding the new satellites by initializing the time-domain smoothed ambiguity values for the new satellites, the new satellites comprising the satellites that were not utilized in a previous interval; and

adjusting the time-domain smoothed ambiguity values for the new satellites by a bias between the estimated float narrow lane ambiguities and time-domain smoothed ambiguity values from a previous interval;

updating the time-domain smoothed ambiguity values for the satellites and the new satellites, based on the determined ambiguity values, using a recursive estimator.

4. The method of claim 3, wherein determining whether the reference satellite has changed comprises:

determining whether the reference satellite is already defined;

if the reference satellite has not been defined, completing the processing of the change; and

if the reference satellite has been defined;

determining whether a new reference satellite has been used in a previous interval;

if the new reference satellite has not been used in the previous interval, initializing the time-domain smoothed ambiguity value for the new reference satellite, based on the estimated float narrow lane ambiguities; and

if the new reference satellite has been used in the previous interval, initializing the time-domain smoothed ambiguity value for the new reference satellite, based on a previous time-domain smoothed ambiguity value.

5. A method comprising:

calculating a float change vector as the difference of determined ambiguity values and float ambiguity values;

forming a design matrix representing a single-differencing operation, the design matrix having the same row dimensions as the float change vector and the same column dimensions as a state vector of a float solution;

computing a Kalman gain based on the design matrix and a covariance matrix of the float solution, using the float change vector as a constraint measurement;

forming a state correction term based on the Kalman gain and the float change vector;

forming a covariance correction term based on the Kalman gain, the design matrix, and the covariance matrix;

calculating an ambiguity determined position estimate based on the covariance correction term; and

updating a position of a satellite navigation receiver based on the ambiguity determined position estimate.

6. The method of claim 5, further comprising:

correcting the state vector by adding the state correction term to the state vector; and

correcting the covariance matrix by subtracting the covariance correction term from the covariance matrix.

7. A method of transitioning a position solution related to a position of a satellite navigation receiver, comprising:

determining whether the transitioning is needed, based on a transition condition;

if the transitioning is not needed, storing a position difference offset between an ambiguity determined position solution and a float solution;

if transitioning is needed, adjusting the position solution over a number of intervals from the ambiguity determined position solution to the float solution by an amount proportional to a previous difference offset until the position solution equals the float solution; and

update the position of the satellite navigation receiver based on the position solution.

8. The method of claim 7, wherein the transition condition comprises one or more of an age of PPP corrections, an availability of estimated integer wide lane ambiguities, a quality of estimated float narrow lane ambiguities, an availability of determined ambiguity values, a weighting of a second ambiguity determined position solution, or a detected jump in a second weighted ambiguity determined position solution.

9. The method of claim 7, wherein the transitioning is based on an estimate of an erroneous discrete jump in a first weighted ambiguity determined position solution.

10. The method of claim 9, further comprising determining the estimate of the erroneous discrete jump by comparing the position solution to a sum of previous position solutions and an estimate of a position change, the position change based on differences in consecutive carrier phase measurements.

11. A method for determining a position of a satellite navigation receiver, comprising:

determining estimated float narrow lane ambiguities of measured carrier phases associated with received signals from one or more satellites, based on estimated integer wide lane ambiguities and ionospheric-free float ambiguities;

at a regular interval, determining a weighted sum of candidate narrow lane integer ambiguities for the measured carrier phases, based on the estimated float narrow lane ambiguities, using a modified best integer equivariant (BIE) process;

during a search of the candidate narrow lane integer ambiguities, generating weighted sums of the candidate narrow lane integer ambiguities and a sum of weights, based on minimizing a mean-squared error (MSE) of the candidate narrow lane integer ambiguities and real valued parameters of a float solution comprising a state vector and a covariance matrix;

calculating determined ambiguity values based on the weighted sums of the candidate narrow lane integer ambiguities and the sum of weights;

forming a first constraint based on the determined ambiguity values;

applying the first constraint to a first copy of the float solution to calculate a first ambiguity determined position solution comprising a first ambiguity determined position estimate; and

determining the position of the satellite navigation receiver based on the first ambiguity determined position estimate.

12. The method of claim 11, further comprising:

time-domain smoothing the determined ambiguity values; and

forming a second constraint based on the time-domain smoothed ambiguity values, the second constraint for applying to a second copy of the float solution to calculate a second ambiguity determined position solution comprising a second ambiguity determined position estimate.

13. The method of claim 12, further comprising weighting the second ambiguity determined position solution to generate a second weighted ambiguity determined position solution by blending the float solution and the second ambiguity determined position solution.

14. The method of claim 13, wherein the blending comprises minimizing an error variance of a combination of the float solution and the second ambiguity determined position solution.

15. The method of claim 14, wherein the error variances are 3-D position variances that are computed as a trace of the corresponding 3-D position covariance matrix.

16. The method of claim 13, wherein the blending is based on an acceptability factor that indicates whether the second ambiguity determined position solution is acceptable.

17. The method of claim 16, where the acceptability factor is dependent on a quality of the second ambiguity determined position solution, the quality comprising a magnitude of the quadratic form of the second ambiguity determined position solution and a ratio test.

18. The method of claim 13, wherein the weighting is time-filtered or smoothed.

19. The method of claim 13, further comprising transitioning a position solution from the second weighted ambiguity determined position solution to the float solution.

20. The method of claim 19, wherein the transitioning is based on an estimate of an erroneous discrete jump in the first weighted ambiguity determined position solution.

21. The method of claim 20, further comprising determining the estimate of the erroneous discrete jump by comparing the position solution to a sum of previous position solutions and an estimate of a position change, the position change based on differences in consecutive carrier phase measurements.

22. The method of claim 12, further comprising transitioning a position solution from the second ambiguity determined position solution to the float solution.

23. The method of claim 22, wherein the transitioning is conducted at a regular interval and comprises:

determining whether the transitioning is needed, based on a transition condition;

if the transitioning is not needed, storing a position difference offset between the second ambiguity determined position solution and the float solution; and

if transitioning is needed, adjusting the position solution over a number of intervals from the second weighted ambiguity determined position solution to the float solution by an amount proportional to a previous difference offset until the position solution equals the float solution.

24. The method of claim 23, wherein the transition condition comprises one or more of an age of PPP corrections, an availability of the estimated integer wide lane ambiguities, a quality of the estimated float narrow lane ambiguities, an availability of the determined ambiguity values, a weighting of the second ambiguity determined position solution, or a detected jump in the second weighted ambiguity determined position solution.