SELECTING RAW MEASUREMENTS FOR USE IN POSITION COMPUTATION

• US 20110057833A1
• Filed: 08/31/2010
• Published: 03/10/2011
• Est. Priority Date: 01/14/2009
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Weisenburger, Shawn D., France, Peter
• Granted Patent: US 8,427,367 B2
• Time in Patent Office: Days
• US Class Current: 342/357.25
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/32 Multimode operation in a single same satellite system, e.g. GPS L1/L2
• CPC Class Codes: G01S 19/33 Multimode operation in different systems which transmit time stamped messages, e.g. GPS/GLONASS
• CPC Class Codes: G01S 19/423 by combining or switching between position solutions derived from different satellite radio beacon positioning systems
• CPC Class Codes: G01S 19/426 by combining or switching between position solutions or signals derived from different modes of operation in a single system
• CPC Class Codes: G01S 19/428 using multipath or indirect path propagation signals in position determination

Abstract

Raw measurements for a plurality of GNSS satellites are pruned based on signal to noise ratio (SNR) and elevation; with remaining unpruned raw measurements sorted by SNR into a sorted list of raw measurements. A first dilution of precision (DOP) based selecting process is performed to select an initial candidate list of raw measurements. The first DOP selecting process begins by using at least those of said pruned list of raw measurements which exceed an SNR quality threshold. The initial candidate list of raw measurements is sorted by elevation angle. A second DOP selecting process is performed to select a final candidate list of raw measurements. The second DOP selecting process begins by using at least those of the sorted initial candidate list which an elevation quality threshold. The final candidate list is used in position computation for a present epoch.

Claims

1. A method within a GNSS receiver of selecting raw measurements for use by said GNSS receiver in position computation, said method comprising:

accessing raw measurements for a plurality of GNSS satellites;

pruning those of said accessed raw measurements which are below a preset absolute minimum signal to noise ratio (SNR) threshold to achieve a first pruned list of raw measurements;

pruning those of first pruned list of raw measurements which are below a preset absolute minimum satellite elevation threshold to achieve a second pruned list of raw measurements;

sorting said second pruned list of raw measurements by SNR to achieve a sorted list of raw measurements;

performing first selecting process to achieve an initial candidate list of raw measurements, wherein said first selecting process involves selecting from said sorted list an incrementally increased plurality of raw measurements from best to worst SNR until a preset dilution of precision (DOP) quality threshold is met or said sorted list of raw measurements is exhausted, and wherein said first selecting process begins by using at least those of said sorted list of raw measurements which have a SNR value greater than a preset SNR quality threshold;

sorting said initial candidate list of raw measurements by elevation angle to achieve a sorted initial candidate list of raw measurements; and

performing a second selecting process to achieve a final candidate list of raw measurements, wherein said second selecting process involves selecting from said sorted initial candidate list an incrementally increased plurality of said raw measurements from highest to lowest elevation until said preset DOP quality threshold is met or said sorted initial candidate list of raw measurements is exhausted, and wherein said second selecting process begins by using at least those of said sorted initial candidate list of raw measurements which have an elevation value greater than a preset elevation quality threshold.

2. The method as recited in claim 1, further comprising:

utilizing said final candidate list of raw measurements in position computation for a present epoch.

3. The method as recited in claim 1, wherein said absolute minimum SNR and elevation thresholds are preset values that are differ based on a user selection of importance of availability or accuracy of a position determination.

4. The method as recited in claim 1, wherein said pruning those of said accessed raw measurements which are below a preset absolute minimum signal to noise ratio (SNR) threshold to achieve a first pruned list of raw measurements comprises:

pruning any of said accessed raw measurements that are below an absolute minimum SNR threshold of 12 dBHz.

5. The method as recited in claim 4, wherein said pruning those of first pruned list of raw measurements which are below a preset absolute minimum satellite elevation threshold to achieve a second pruned list of raw measurements comprises:

pruning any of said first pruned list of raw measurements that are below an absolute minimum satellite elevation threshold of 5 degrees.

6. The method as recited in claim 1, wherein said pruning those of said accessed raw measurements which are below a preset absolute minimum signal to noise ratio (SNR) threshold to achieve a first pruned list of raw measurements comprises:

pruning any of said accessed raw measurements that are below an absolute minimum SNR threshold of 28 dBHz.

7. The method as recited in claim 6, wherein said pruning those of first pruned list of raw measurements which are below a preset absolute minimum satellite elevation threshold to achieve a second pruned list of raw measurements comprises:

pruning any of said first pruned list of raw measurements that are below an absolute minimum satellite elevation threshold of 8 degrees.

8. The method as recited in claim 1 wherein said preset SNR quality threshold is preset at 37 dbHz.

9. The method as recited in claim 1, wherein said preset elevation threshold is set at 15 degrees.

10. The method as recited in claim 1, wherein said preset DOP quality threshold comprises a position DOP quality threshold.

11. The method as recited in claim 10, wherein said position DOP quality threshold is set at 6.0.

12. The method as recited in claim 10, wherein said DOP quality threshold is an horizontal DOP quality threshold.

13. The method as recited in claim 1, wherein said DOP quality threshold is a geometric DOP quality threshold.

14. The method as recited in claim 1, wherein said DOP quality threshold is a vertical DOP quality threshold.

15. The method as recited in claim 1, wherein said DOP quality threshold is a temporal DOP quality threshold.

16. A non-transitory computer readable storage medium having computer executable instructions stored thereon which, when executed cause a computer system to perform a method of selecting raw measurements for use by said GNSS receiver in position computation, said method comprising:

accessing raw measurements for a plurality of GNSS satellites;

pruning those of said accessed raw measurements which are below a preset absolute minimum signal to noise ratio (SNR) threshold to achieve a first pruned list of raw measurements;

pruning those of first pruned list of raw measurements which are below a preset absolute minimum satellite elevation threshold to achieve a second pruned list of raw measurements;

sorting said second pruned list of raw measurements by SNR to achieve a sorted list of raw measurements; and

performing first selecting process to achieve an initial candidate list of raw measurements, wherein said first selecting process involves selecting from said sorted list an incrementally increased plurality of raw measurements from best to worst SNR until a first preset dilution of precision (DOP) quality threshold is met or said sorted list of raw measurements is exhausted, and wherein said first selecting process begins by using at least those of said pruned list of raw measurements which have a SNR value greater than a preset SNR quality threshold.

17. The non-transitory computer readable storage medium of claim 16, wherein said method further comprises:

utilizing said initial candidate list of raw measurements in position computation for a present epoch.

18. The non-transitory computer readable storage medium as recited in claim 16, wherein said method further comprises:

sorting said initial candidate list of raw measurements by elevation angle to achieve a sorted initial candidate list of raw measurements; and

performing a second selecting process to achieve a final candidate list of raw measurements, wherein said second selecting process involves selecting from said sorted initial candidate list an incrementally increased plurality of said raw measurements from highest to lowest elevation until a second preset DOP quality threshold is met or said sorted initial candidate list of raw measurements is exhausted, and wherein said second selecting process begins by using at least those of said sorted initial candidate list of raw measurements which have an elevation value greater than a preset elevation quality threshold.

19. The non-transitory computer readable storage medium of claim 18, wherein said method further comprises:

utilizing said final candidate list of raw measurements in position computation for a present epoch.

20. The non-transitory computer readable storage medium of claim 16, wherein said preset DOP quality threshold is a preset position DOP quality threshold.

21. A non-transitory computer readable storage medium having computer executable instructions stored thereon which, when executed cause a computer system to perform a method of selecting raw measurements for use by said GNSS receiver in position computation, said method comprising:

accessing raw measurements for a plurality of GNSS satellites;

pruning those of said accessed raw measurements which are below a preset absolute minimum signal to noise ratio (SNR) threshold to achieve a first pruned list of raw measurements;

pruning those of first pruned list of raw measurements which are below a preset absolute minimum satellite elevation threshold to achieve a second pruned list of raw measurements;

sorting said second pruned list of raw measurements by elevation angle to achieve a sorted list of raw measurements; and

performing first selecting process to achieve an initial candidate list of raw measurements, wherein said first selecting process involves selecting from said sorted list an incrementally increased plurality of raw measurements from highest to lowest elevation until a first preset dilution of precision (DOP) quality threshold is met or said sorted list of raw measurements is exhausted, and wherein said first selecting process begins by using at least those of said pruned list of raw measurements which have an elevation value greater than a preset elevation quality threshold.

22. The non-transitory computer readable storage medium of claim 21, wherein said method further comprises:

utilizing said initial candidate list of raw measurements in position computation for a present epoch.

23. The non-transitory computer readable storage medium as recited in claim 21, wherein said method further comprises:

sorting said initial candidate list of raw measurements by SNR to achieve a sorted initial candidate list of raw measurements; and

performing a second selecting process to achieve a final candidate list of raw measurements, wherein said second selecting process involves selecting from said sorted initial candidate list an incrementally increased plurality of said raw measurements from best to worst SNR until a second preset DOP quality threshold is met or said sorted initial candidate list of raw measurements is exhausted, and wherein said second selecting process begins by using at least those of said sorted initial candidate list of raw measurements which have an SNR value greater than a preset SNR quality threshold.

24. The non-transitory computer readable storage medium of claim 23, wherein said method further comprises:

utilizing said final candidate list of raw measurements in position computation for a present epoch.

25. The non-transitory computer readable storage medium of claim 21, wherein said preset DOP quality threshold is a preset position DOP quality threshold.

26. A global navigation satellite system (GNSS) position determination system comprising:

an automated raw measurement selector module configured for automatically adjusting mask settings in order to select a final candidate list of raw measurements, from available raw measurements, in order to obtain the best quality position solution possible from a set of satellite measurements, wherein said automated raw measurement selector module comprises a plurality of preset thresholds used in determination of said final candidate list of raw measurements, and said plurality of preset thresholds include;

a preset absolute minimum signal-to-noise ratio (SNR) threshold;

a preset absolute minimum elevation threshold;

a preset SNR quality threshold set at a separate level from said absolute minimum SNR threshold;

a preset elevation quality threshold set at a separate level from said absolute minimum elevation threshold; and

at least one preset dilution of precision (DOP) threshold.

27. The GNSS position determination system of claim 26, wherein said automated raw measurement selector module is coupled with a navigation processor and configured for providing said final candidate list of raw measurements to a navigation processor for use in position computation for a present epoch.

28. The GNSS position determination system of claim 26, wherein said automated raw measurement selector module comprises an availability mode for emphasizing absolute availability of a position determination through automated selection of raw measurements.

29. The GNSS position determination system of claim 28, wherein said automated raw measurement selector module further comprises an accuracy mode for emphasizing absolute accuracy of a position determination through automated selection of raw measurements.

30. The GNSS position determination system of claim 29, wherein said availability mode utilizes different preset values of said thresholds than are used in said accuracy mode.