Fault detection and exclusion in a positioning system receiver

• US 6,515,618 B1
• Filed: 11/29/2000
• Issued: 02/04/2003
• Est. Priority Date: 11/29/2000
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Lupash, Lawrence O.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US09/726,994
• Time in Patent Office: 797 Days
• Field of Search: 342/357.12, 342/357.02, 701/214
• US Class Current: 342/357.29
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment

Abstract

A multi-stage process for detecting and excluding faulty measurements in a satellite positioning system receiver are described. Availability of fault detection is evaluated based on satellite geometry and satellite measurement quality. If fault detection is unavailable using only satellite measurements, an additional measurement is used, and fault detection availability is again evaluated. If fault detection is available, detection of a potential fault is performed. If a fault is detected, an exclusion/isolation process is activated. In that case, a fault exclusion operation is tested for availability. If fault exclusion is unavailable using only satellite measurements, an additional measurement is incorporated, and fault exclusion availability is again evaluated. If fault exclusion is available, an attempt is made to isolate and exclude the faulty measurement from a list of satellite measurements used for the navigation solution. The exclusion/isolation process is performed in several stages based on the elimination of the faulty satellite.

Claims

1. A method in a positioning system receiver of detecting and excluding a fault, the method comprising:

determining whether a fault detection operation is available, including periodically testing whether the fault detection operation is available at a first rate;

attempting to detect a fault while the fault detection operation is available, including periodically attempting to detect a fault at a second rate higher than the first rate;

determining whether a fault exclusion operation is available in response to a fault being detected; and

attempting to exclude the fault if the fault exclusion operation is available.

2. A method as recited in claim 1, wherein the positioning system receiver is used in an aircraft, the method further comprising:

in response to detection of a fault and prior to said determining whether the fault exclusion operation is available, attempting to confirm the fault by attempting to detect the fault at least one additional time, according to a current phase of flight of the aircraft.

3. A method as recited in claim 1, wherein the fault is in one of a set of measurements used by the receiver to compute a position, the method further comprising:

if the fault detection operation is not available, adding a new measurement to the set of measurements; and

repeating said determining whether the fault detection operation is available.

4. A method as recited in claim 3, wherein said determining whether the fault detection operation is available is based on the set of measurements.

5. A method as recited in claim 3, wherein the set of measurements comprises a plurality of satellite measurements.

6. A method as recited in claim 5, wherein the new measurement is not a satellite measurement.

7. A method as recited in claim 1, wherein the fault is in one of a set of measurements used by the receiver to compute a position, the method further comprising:

if the fault exclusion operation is not available, adding a new measurement to the set of measurements; and

repeating said determining whether the fault exclusion operation is available.

8. A method as recited in claim 7, wherein said determining whether the fault exclusion operation is available is based on the set of measurements.

9. A method as recited in claim 8, wherein the set of measurements comprises a plurality of satellite measurements.

10. A method as recited in claim 9, wherein the new measurement is not a satellite measurement.

11. A method as recited in claim 1, wherein the fault is in one of a set of measurements used by the receiver to compute a position, the method further comprising, if either the fault detection operation or the fault exclusion operation is not available, adding a new measurement to the set of measurements.

12. A method as recited in claim 11, wherein said determining whether the fault detection operation is available and said determining whether the fault exclusion operation is available are both based on the set of measurements.

13. A method as recited in claim 12, wherein the set of measurements comprises a plurality of satellite measurements.

14. A method as recited in claim 13, wherein the new measurement is not a satellite measurement.

15. A method of detecting and excluding a faulty measurement in a positioning system receiver, the method comprising:

performing a fault detection process, the fault detection process including

periodically determining whether a fault detection operation is available at a first rate, and

if the fault detection operation is available, periodically attempting to detect a fault at a second rate higher than the first rate; and

performing a fault exclusion process, the fault exclusion process including

determining whether a fault exclusion operation is available in response to a fault being detected, and

attempting to exclude the fault if the fault exclusion operation is available.

16. A method as recited in claim 15, further comprising, if fault detection is not available, adding a new measurement to the set of measurements and then repeating said determining whether the fault detection operation is available, wherein the new measurement is not a satellite measurement.

17. A method as recited in claim 15, further comprising, if the fault exclusion operation is not available, adding a new measurement to the set of measurements and then repeating said determining whether the fault exclusion operation is available, wherein the new measurement is not a satellite measurement.

18. A method as recited in claim 15, further comprising if either fault detection or the fault exclusion operation is not available, adding a new measurement to the set of measurements, wherein the new measurement is not a satellite measurement.

19. A method as recited in claim 15, wherein said determining whether the fault exclusion operation is available is performed at a rate equal to or approximately equal to the first rate.

20. A method of detecting and excluding a faulty satellite measurement in a satellite positioning system receiver, the method comprising:

determining at a first rate whether a fault detection operation is available based on a set of n measurements, the set of n measurements including a plurality of satellite measurements;

if the fault detection operation is available, attempting to detect a fault associated with one of the satellite measurements, at a second rate higher than the first rate;

if the fault detection operation is not available, adding a new measurement to the set of measurements and then repeating said determining whether the fault detection operation is available, wherein the new measurement is not a satellite measurement;

in response to detecting a fault, waiting for a delay period and then repeating said attempting to detect a fault; and

in response to a fault being detected a predetermined number of times within a defined period of time,

determining whether a fault exclusion operation is available at a rate equal to or approximately equal to the first rate,

if the fault exclusion operation is available, attempting to exclude the fault, and

if the fault exclusion operation is not available, adding a new measurement to the set of measurements and then repeating said determining whether the fault exclusion operation is available, wherein the new measurement is not a satellite measurement.

21. A method as recited in claim 20, wherein said determining whether the fault detection operation is available comprises:

computing a protection level; and

determining that the fault detection operation is available if the computed protection level has a predetermined relationship to a specified protection level.

22. A method as recited in claim 20, wherein said determining whether the fault exclusion operation is available comprises:

computing a protection level for each of n cases, wherein a different one of the n measurements is omitted in each case;

determining that the fault exclusion operation is available only if the computed protection level has a predetermined relationship to a specified protection level for each of the n cases.

23. A method as recited in claim 22, wherein said performing the fault exclusion operation comprises:

for each of the n cases, computing a test statistic and comparing the test statistic with a threshold to test for a predetermined condition;

ranking the measurements for only the cases in which the predetermined condition exists, based on the computed protection level for each of the measurements;

attempting to detect a fault, omitting one of the measurements based on said ranking;

if a fault is detected, repeating said attempting to detect a fault, omitting a different one of the measurements based on said ranking; and

if a fault is not detected, identifying the omitted measurement as the faulty satellite measurement.

24. A method of detecting and excluding a faulty satellite measurement in a satellite positioning system receiver, the method comprising:

(a) determining, at a first rate, whether a fault detection operation is available based on a set of n measurements, the set of n measurements including the plurality of satellite measurements, including

(a)(1) computing a protection level, and

(a)(2) determining that the fault detection operation is available if the computed protection level has a predetermined relationship to a specified protection level;

(b) if the fault detection operation is available, attempting to detect a fault associated with one of the satellite measurements, at a second rate higher than the first rate;

(c) if the fault detection operation is not available, adding a new measurement to the set of measurements and then repeating said determining whether the fault detection operation is available, wherein the new measurement is not a satellite measurement;

(d) in response to detecting a fault, waiting for a delay period and then repeating said attempting to detect a fault; and

(e) in response to a fault being detected a predetermined number of times within a period of time,

(e)(1) determining, at a rate equal to or approximately equal to the first rate, whether a fault exclusion operation is available, including

computing a protection level for each of n cases, wherein a different one of the n measurements is omitted in each case, and

determining that the fault exclusion operation is available only if the computed protection level has a predetermined relationship to a specified protection level for all of the n cases;

(e)(2) if the fault exclusion operation is not available, adding a new measurement to the set of measurements and then repeating said determining whether the fault exclusion operation is available, wherein the new measurement is not a satellite measurement; and

(e)(3) if the fault exclusion operation is available, attempting to exclude the fault, including

for each of the n cases, computing a test statistic and comparing the test statistic with a threshold to test for a predetermined condition,

ranking the measurements for only the cases in which the predetermined condition exists, based on the computed protection levels,

attempting to detect a fault, omitting one of the measurements based on said ranking,

if a fault is detected, determining that the omitted measurement is not the faulty satellite measurement and repeating said attempting to detect a fault, omitting a different one of the measurements based on said ranking, and

if a fault is not detected, identifying the omitted measurement as the faulty satellite measurement.

25. A satellite positioning system receiver comprising:

a receive module to receive and process signals from a plurality of satellites; and

a processor coupled to the receive module and configured to

generate a plurality of measurements based on the processed signals, the measurements for use in computing a navigational solution, and

execute a fault detection and exclusion routine to detect and exclude a fault in one of the measurements, the routine including

determining whether a fault detection operation is available, including periodically testing whether the fault detection operation is available at a background rate;

attempting to detect a fault while the fault detection operation is available, including periodically attempting to detect a fault at a foreground rate higher than the background rate;

determining whether a fault exclusion operation is available in response to a fault being detected; and

attempting to exclude the fault if the fault exclusion operation is available.

26. A satellite positioning system receiver as recited in claim 25, wherein the receiver is for use in an aircraft, wherein the processor is further configured to:

in response to detection of a fault and prior to determining whether the fault exclusion operation is available, attempt to confirm the fault by attempting to detect the fault at least one additional time, according to a current phase of flight of the aircraft.

27. A satellite positioning system receiver as recited in claim 25, wherein the fault is in one of a set of measurements used by the receiver to compute a position, the method further comprising:

if the fault detection operation is not available, adding a new measurement to the set of measurements; and

repeating said determining whether the fault detection operation is available.

28. A satellite positioning system receiver as recited in claim 27, wherein said determining whether the fault detection operation is available is based on the set of measurements.

29. A satellite positioning system receiver as recited in claim 27, wherein the set of measurements comprises a plurality of satellite measurements.

30. A satellite positioning system receiver as recited in claim 29, wherein the new measurement is not a satellite measurement.

31. A satellite positioning system receiver as recited in claim 25, wherein the fault is in one of a set of measurements used by the receiver to compute a position, the method further comprising:

if the fault exclusion operation is not available, adding a new measurement to the set of measurements; and

repeating said determining whether the fault exclusion operation is available.

32. A satellite positioning system receiver as recited in claim 31, wherein said determining whether the fault exclusion operation is available is based on the set of measurements.

33. A satellite positioning system receiver as recited in claim 31, wherein the set of measurements comprises a plurality of satellite measurements.

34. A satellite positioning system receiver as recited in claim 33, wherein the new measurement is not a satellite measurement.

35. A satellite positioning system receiver comprising:

means for receiving a plurality of signals, each from a different one of a plurality of satellites;

means for generating a set of measurements based on the plurality of signals;

means for performing a fault detection process, the fault detection process including

periodically determining whether a fault detection operation is available at a first rate, and

if the fault detection operation is available, periodically attempting to detect a fault in one of the measurements at a second rate higher than the first rate; and

means for performing a fault exclusion process, the fault exclusion process including

determining whether a fault exclusion operation is available in response to a fault being detected, and

attempting to exclude the fault if the fault exclusion operation is available.

36. A satellite positioning system receiver as recited in claim 35, further comprising, means for adding a new measurement to the set of measurements if the fault detection operation is not available and then repeating said determining whether the fault detection operation is available, wherein the new measurement is not a satellite measurement.

37. A satellite positioning system receiver as recited in claim 35, further comprising, means for adding a new measurement to the set of measurements if the fault exclusion operation is not available, and then repeating said determining whether the fault exclusion operation is available, wherein the new measurement is not a satellite measurement.

38. A satellite positioning system receiver as recited in claim 35, further comprising means for adding a new measurement to the set of measurements if either the fault detection operation or the fault exclusion operation is not available, wherein the new measurement is not a satellite measurement.

39. A satellite positioning system receiver as recited in claim 35, wherein said determining whether the fault exclusion operation is available is performed at a rate equal to or approximately equal to the first rate.