Navigation System and Method for Resolving Integer Ambiguities Using Double Difference Ambiguity Constraints

• US 20120176271A1
• Filed: 11/17/2011
• Published: 07/12/2012
• Est. Priority Date: 01/12/2011
• Status: Active Grant

• Current Assignee: Deere & Company
• Original Assignee: Navcom Technology, Inc. (Deere & Company)
• Inventors: Dai, Liwen L., Hatch, Ronald R., Zhang, Yujie, Wang, Min
• Granted Patent: US 8,659,474 B2
• Time in Patent Office: Days
• US Class Current: 342/357.44
• CPC Class Codes: G01S 19/04 providing carrier phase data
• CPC Class Codes: G01S 19/072 Ionosphere corrections
• CPC Class Codes: G01S 19/073 involving a network of fixed stations
• CPC Class Codes: G01S 19/44 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method

Abstract

A system and method for providing improved correction information to navigation receivers includes receiving, from a plurality of reference stations at known locations, a plurality of satellite navigation measurements of signals from a plurality of global navigation satellites. A state of the plurality of global navigation satellites is computed based on the received satellite navigation measurements. Baselines, each corresponding to a pair of the reference stations, are identified. For each identified baseline, computing floating and integer values for a double-differenced integer ambiguity. Double-differenced integer ambiguities that satisfy a set of predefined conditions are identified, and the computed state of the plurality of global navigation satellites is adjusted in accordance with an integer value constraint applied to each double-differenced integer ambiguity that satisfies the set of predefined conditions. The correction information is computed from the adjusted computed state of the plurality of global navigation satellites.

Claims

1. A computer-implemented method, performed by a computer system that includes one or more processors and memory storing one or more programs, the one or more processors for executing the one or more programs, the method comprising:

receiving, from a plurality of reference stations at known locations, a plurality of satellite navigation measurements of signals from a plurality of global navigation satellites;

computing a state of the plurality of global navigation satellites based on the received satellite navigation measurements;

identifying a plurality of baselines, each baseline corresponding to a pair of the reference stations, and for each identified baseline, computing floating and integer values for a double-differenced integer ambiguity corresponding to the identified baseline;

identifying, in accordance with the computed floating and integer values for the double-differenced integer ambiguities corresponding to the plurality of identified baselines, a set of one or more double-differenced integer ambiguities that satisfy a set of predefined conditions; and

adjusting the computed state of the plurality of global navigation satellites, in accordance with an integer value constraint applied to each double-differenced integer ambiguity in the identified set of one or more double-differenced integer ambiguities that satisfy the set of predefined conditions, to produce an adjusted computed state of the plurality of global navigation satellites.

2. The method of claim 1, further including

computing correction information in accordance with the adjusted computed state of the plurality of global navigation satellites;

and

transmitting the correction information to a plurality of navigation receivers.

3. The method of claim 1, wherein the correction information includes correction values for each of the global navigation satellites in the plurality of global navigation satellites.

4. The method of claim 1, wherein the correction information includes correction values for two or more of the global navigation satellites in the plurality of global navigation satellites.

5. The method of claim 1 wherein the set of predefined conditions, for a respective double-differenced integer ambiguity, includes a requirement that a fractional difference between the integer and floating values of the respective double-differenced integer ambiguity does not exceed a first threshold.

6. The method of claim 5, including computing a variance and standard deviation of the respective double-differenced integer ambiguity, wherein set of predefined conditions for the respective double-differenced integer ambiguity includes a requirement that the standard deviation of the respective double-differenced integer ambiguity does not exceed a second threshold.

7. The method of claim 6, including computing a predefined W-ratio for the respective double-differenced integer ambiguity, wherein the W-ratio has a numerator corresponding to the fractional difference between the integer and floating values of the respective double-differenced integer ambiguity and a denominator corresponding to the standard deviation of the respective double-differenced integer ambiguity, and wherein set of predefined conditions for the respective double-differenced integer ambiguity includes a requirement that the W-ratio for the respective double-differenced integer ambiguity is greater than a third threshold.

8. The method of claim 7, wherein the first threshold is no greater than 0.25 cycles and the second threshold is no greater than 0.1 cycles.

9. The method of claim 1, wherein the identified baselines includes only mathematically independent baselines.

10. The method of claim 1, wherein identifying the set of one or more double-differenced integer ambiguities that satisfy the set of predefined conditions includes filtering the double-differenced integer ambiguities corresponding to the identified baselines so as to prevent any double-differenced integer ambiguities that fail to satisfy predefined filtering criteria from being included in the identified set.

11. The method of claim 1, wherein identifying the set of one or more double-differenced integer ambiguities that satisfy the set of predefined conditions and adjusting the computed state of the plurality of global navigation satellites comprises:

generating an ordered list of the double-differenced integer ambiguities by ordering the double-differenced integer ambiguities in accordance with a first parameter computed for each of the double-differenced integer ambiguities corresponding to the identified baselines,

selecting a first double-differenced integer ambiguity in the ordered list, and also selecting any other double-differenced integer ambiguities in the ordered list having a same value of the first parameter as the first double-differenced integer ambiguity in the ordered list,

determining which, if any, of the selected one or more double-differenced integer ambiguities satisfy the set of predefined conditions, to identify a set of fixed double-differenced integer ambiguities;

adjusting the computed state of the plurality of global navigation satellites, in accordance with the integer value constraint applied to each double-differenced integer ambiguity in the set of fixed double-differenced integer ambiguities;

removing the fixed double-differenced integer ambiguities from the ordered list;

re-computing floating and integer values for one or more of the double-differenced integer ambiguities remaining on the ordered list;

selecting a next double-differenced integer ambiguity in the ordered list, and also selecting any other double-differenced integer ambiguities in the ordered list having a same value of the first parameter as said next double-differenced integer ambiguity in the ordered list; and

repeating at least the determining and adjusting operations with respect to the selected one or more double-differenced integer ambiguities.

12. The method of claim 1, wherein the method is repeated for each of a sequence of measurement epochs.

13. The method of claim 1, wherein the state of the plurality of global navigation satellites includes a position of each global navigation satellite in the plurality of global navigation satellites, a velocity of each global navigation satellite in the plurality of global navigation satellites, and a time reported by each global navigation satellite in the plurality of global navigation satellites.

14. The method of claim 1, wherein computing the state of the plurality of global navigation satellites comprises computing the state of the plurality of global navigation satellites using a closed-form update equation.

15. A computer system, comprising:

one or more processors;

memory storing one or more programs for execution by the one or more processors, the one or more programs comprising instructions that when executed by the one or more processors cause the computer system to;

receive, from a plurality of reference stations at known locations, a plurality of satellite navigation measurements of signals from a plurality of global navigation satellites;

compute a state of the plurality of global navigation satellites based on the received satellite navigation measurements;

identify a plurality of baselines, each baseline corresponding to a pair of the reference stations, and for each identified baseline, computing floating and integer values for a double-differenced integer ambiguity corresponding to the identified baseline;

identify, in accordance with the computed floating and integer values for the double-differenced integer ambiguities corresponding to the plurality of identified baselines, a set of one or more double-differenced integer ambiguities that satisfy a set of predefined conditions; and

adjust the computed state of the plurality of global navigation satellites, in accordance with an integer value constraint applied to each double-differenced integer ambiguity in the identified set of one or more double-differenced integer ambiguities that satisfy the set of predefined conditions, to produce an adjusted computed state of the plurality of global navigation satellites.

16. The computer system of claim 15, wherein the one or more programs further comprise instructions which we executed by the one or more processors cause the computer system to:

compute correction information in accordance with the adjusted computed state of the plurality of global navigation satellites; and

transmit the correction information to a plurality of navigation receivers.

17. The computer system of claim 15, wherein the correction information includes correction values for each of the global navigation satellites in the plurality of global navigation satellites.

18. The computer system of claim 15, wherein the correction information includes correction values for two or more of the global navigation satellites in the plurality of global navigation satellites.

19. The computer system of claim 15, wherein the set of predefined conditions, for a respective double-differenced integer ambiguity, includes a requirement that a fractional difference between the integer and floating values of the respective double-differenced integer ambiguity does not exceed a first threshold.

20. The computer system of claim 15, wherein the one or more programs further comprise instructions which we executed by the one or more processors cause the computer system to compute a variance and standard deviation of the respective double-differenced integer ambiguity, wherein set of predefined conditions for the respective double-differenced integer ambiguity includes a requirement that the standard deviation of the respective double-differenced integer ambiguity does not exceed a second threshold.

21. The computer system of claim 20, wherein the one or more programs further comprise instructions which we executed by the one or more processors cause the computer system to compute a predefined W-ratio for the respective double-differenced integer ambiguity, wherein the W-ratio has a numerator corresponding to the fractional difference between the integer and floating values of the respective double-differenced integer ambiguity and a denominator corresponding to the standard deviation of the respective double-differenced integer ambiguity, and wherein set of predefined conditions for the respective double-differenced integer ambiguity includes a requirement that the W-ratio for the respective double-differenced integer ambiguity is greater than a third threshold.

22. A non-transitory computer readable storage medium, storing one or more programs configured for execution by a computer system, the one or more programs comprising instructions that when executed by the one or more processors cause the computer system to:

receive, from a plurality of reference stations at known locations, a plurality of satellite navigation measurements of signals from a plurality of global navigation satellites;

compute a state of the plurality of global navigation satellites based on the received satellite navigation measurements;

identify a plurality of baselines, each baseline corresponding to a pair of the reference stations, and for each identified baseline, computing floating and integer values for a double-differenced integer ambiguity corresponding to the identified baseline;

identify, in accordance with the computed floating and integer values for the double-differenced integer ambiguities corresponding to the plurality of identified baselines, a set of one or more double-differenced integer ambiguities that satisfy a set of predefined conditions; and

adjust the computed state of the plurality of global navigation satellites, in accordance with an integer value constraint applied to each double-differenced integer ambiguity in the identified set of one or more double-differenced integer ambiguities that satisfy the set of predefined conditions, to produce an adjusted computed state of the plurality of global navigation satellites.

23. The non-transitory computer readable storage medium of claim 22, wherein the one or more programs further comprise instructions which we executed by the one or more processors cause the computer system to:

compute correction information in accordance with the adjusted computed state of the plurality of global navigation satellites; and

transmit the correction information to a plurality of navigation receivers.

24. The non-transitory computer readable storage medium of claim 22, wherein the correction information includes correction values for each of the global navigation satellites in the plurality of global navigation satellites.

25. The non-transitory computer readable storage medium of claim 22, wherein the correction information includes correction values for two or more of the global navigation satellites in the plurality of global navigation satellites.

26. The non-transitory computer readable storage medium of claim 22, wherein the set of predefined conditions, for a respective double-differenced integer ambiguity, includes a requirement that a fractional difference between the integer and floating values of the respective double-differenced integer ambiguity does not exceed a first threshold.

27. The non-transitory computer readable storage medium of claim 22, wherein the one or more programs further comprise instructions which we executed by the one or more processors cause the computer system to compute a variance and standard deviation of the respective double-differenced integer ambiguity, wherein set of predefined conditions for the respective double-differenced integer ambiguity includes a requirement that the standard deviation of the respective double-differenced integer ambiguity does not exceed a second threshold.

28. The non-transitory computer readable storage medium of claim 27, wherein the one or more programs further comprise instructions which we executed by the one or more processors cause the computer system to compute a predefined W-ratio for the respective double-differenced integer ambiguity, wherein the W-ratio has a numerator corresponding to the fractional difference between the integer and floating values of the respective double-differenced integer ambiguity and a denominator corresponding to the standard deviation of the respective double-differenced integer ambiguity, and wherein set of predefined conditions for the respective double-differenced integer ambiguity includes a requirement that the W-ratio for the respective double-differenced integer ambiguity is greater than a third threshold.