Method and apparatus for improving fault detection and exclusion systems

• US 20070139263A1
• Filed: 12/15/2005
• Published: 06/21/2007
• Est. Priority Date: 12/15/2005
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Xie, Gang, Jambulingam, Shreeram
• Granted Patent: US 7,286,083 B2
• Time in Patent Office: Days
• US Class Current: 342/357.580
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment

Abstract

A method for improving fault detection and exclusion of a GPS receiver is provided. The method determines pseudorange measurement residuals of tracked signals, divides the signals into two groups based on whether each signal has a higher or lower probability of being a failure, and estimates a residual bias using only the lower probability group of signals. The method further removes the residual bias from all calculated residuals, and compares each range residual to one of three different thresholds. A tighter threshold is applied to positive residuals of the group of signals with higher failure probability than to the group of signals with lower failure probability. A further tighter threshold is applied to negative residuals of the group of signals having higher failure probability. The method then determines PVT values of the GPS receiver utilizing range measurements of signals whose measurement residual magnitudes are less than their corresponding threshold values.

Claims

1. A method for improving signal fault detection and exclusion of a global positioning system (GPS) receiver, at a current epoch, the method comprising:

determining pseudorange measurements of a plurality of tracked signals between space vehicles and the GPS receiver;

predicting range values corresponding to the plurality of tracked signals;

dividing the plurality of tracked signals into two groups, a first group of signals comprising signals with prior epoch pseudorange measurements used in position, velocity and time (PVT) determinations, a second group of signals comprising signals with prior epoch pseudorange measurements not used in PVT determinations or that are newly acquired;

evaluating range residuals of tracked signals, the range residuals corresponding to differences between the pseudorange measurements and the predicted range values;

estimating a residual bias by utilizing the first group signals;

removing the residual bias from evaluated range residuals;

comparing each range residual of the first group of tracked signals to a first predetermined threshold value;

comparing each positive range residual of the second group of tracked signals to a second predetermined threshold value, and comparing a magnitude of each non-positive measurement residual of the second group of tracked signals to a third predetermined threshold value; and

determining PVT values of the GPS receiver position utilizing range measurements of signals whose corresponding range residual magnitudes are less than corresponding threshold values.

2. The method of claim 1, further comprising:

determining whether each of the plurality of tracked signals is newly acquired or corresponds to a range residual evaluated to be greater than the corresponding threshold value at prior epoch.

3. The method of claim 2, further comprising:

implementing the determined PVT values into navigational computations.

4. The method of claim 1, further comprising:

assigning a first probability to the first group of signals, and a second probability to the second group of signals, with the first probability being less than the second probability.

5. The method of claim 4, wherein the first probability indicates that corresponding signal measurements have a low probability to be excluded from PVT determinations.

6. The method of claim 1, further comprising:

determining that a negative measurement residual corresponds to a reflected signal.

7. The method of claim 1, further comprising:

moving all tracked signals into the first group when the division of all tracked signals renders the first group devoid of signals.

8. The method of claim 1, further comprising:

moving all tracked signals into the first group when the first group includes failed tracked signals.

9. A global positioning system (GPS) receiver system comprising:

a signal tracking and data decoder unit to track time-tagged ranging signals

broadcasted by space vehicles, and determine pseudorange measurements between the GPS receiver and the space vehicles;

a failure detection unit configured to divide the tracked signals into two groups, a first group comprising signals with prior epoch pseudorange measurements used in position, velocity and time (PVT) determinations, a second group comprising signals with prior epoch range measurements not used in PVT determinations or that are newly acquired, to evaluate range residuals of the tracked signals, the range residuals being a difference between the range measurements and the predicted range values, to estimate a residual bias by utilizing the first group of signals only, to compare each range residual of the first group of tracked signals to a first predetermined threshold value, to compare each positive range residual of the second group of tracked signals to a second predetermined threshold value, and to compare a magnitude of each non-positive range residual of the second group of tracked signals to a third predetermined threshold value; and

a PVT determination unit that uses range measurements of signals whose corresponding range residual magnitudes are less than corresponding threshold values to determine PVT values.

10. The GPS receiver system of claim 9, wherein the failure detection unit determines whether each one of the plurality of tracked signals is newly acquired or corresponds to a range residual evaluated to be greater than the corresponding threshold value at prior epoch.

11. The GPS receiver system of claim 9, wherein the failure detection unit assigns a first probability to the first group of signals, and a second probability to the second group of signals, with the first probability being less than the second probability.

12. The GPS receiver system of claim 11, wherein the first probability indicates that corresponding signal measurements have a low probability to be excluded from PVT determinations.

13. The GPS receiver system of claim 9, wherein the failure detection unit determines that a negative range residual corresponds to a reflected signal.

14. The GPS receiver system of claim 9, further comprising:

a navigational unit to determine navigational results using the determined PVT values.

15. The GPS receiver system of claim 9, wherein the failure detection unit moves all tracked signals into the first group when the division of all tracked signals renders the first group devoid of signals.

16. The GPS receiver system of claim 9, wherein the failure detection unit moves all tracked signals into the first group when the first group includes failed tracked signals.

17. A GPS navigational system comprising:

at least one processor;

a memory coupled to the processor, the memory comprising at least tracked signal data, decoding data, range measurement data, predicted range data, threshold data, position, velocity and time (PVT) data, epoch data, and residual data; and

a global positioning program operable to;

determine range measurements of a plurality of tracked signals between corresponding space vehicles and the GPS receiver;

predict range values of the plurality of tracked signals;

divide the plurality of signals into two groups of tracked signals, a first group comprising signals with prior epoch range measurements used in PVT determinations, a second group of signals being signals with prior epoch range measurements not used in PVT determinations or that are newly acquired;

evaluate range residuals of the tracked signals, the range residuals corresponding to differences between the range measurements and the predicted range values;

estimate a residual bias by utilizing the first group of signals;

remove the residual bias from the evaluated range residuals;

compare each positive range residual of the first group of tracked signals to a first predetermined threshold value, compare each positive range residual of the second group of tracked signals to a second predetermined threshold value, and compare a magnitude of each non-positive measurement residual of the second group of tracked signals to a third predetermined threshold value; and

determine PVT values of the GPS receiver position utilizing range measurements of signals whose corresponding range residual magnitudes are less than corresponding threshold values, wherein the at least one processor executes the global positioning program.

18. The GPS navigational system of claim 17, wherein the at least one processor determines whether each one of the plurality of tracked signals is newly acquired or corresponds to a range residual evaluated to be greater than the corresponding threshold value at prior epoch.

19. The GPS navigational system of claim 17, wherein the at least one processor assigns a first probability to the first group of signals, and a second probability to the second group of signals, with the first probability being less than the second probability.

20. The GPS navigational system of claim 17, wherein the at least one processor determines that a negative range residual corresponds to a reflected signal.