Methods and apparatus to detect and correct integrity failures in satellite positioning system receivers

• US 20070115171A1
• Filed: 06/08/2006
• Published: 05/24/2007
• Est. Priority Date: 11/18/2005
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Rahman, Mohammad, Gilkes, Alan
• Granted Patent: US 7,501,981 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

Methods and apparatus to detect integrity failures in satellite position system (SPS) receivers are disclosed. An example method comprises estimating a position fix from a plurality of pseudoranges, computing a zero-mean error vector based upon the position fix; and determining if an integrity failure has occurred based on the zero-mean error vector.

Claims

1. A method comprising:

estimating a position fix from a plurality of pseudoranges;

computing a first zero-mean error vector based upon the position fix; and

determining if an integrity failure has occurred based on the zero-mean error vector.

2. A method as defined in claim 1, further comprising:

updating the position fix based on the plurality of pseudoranges and a state vector;

computing a second zero-mean error vector based upon the updated position fix; and

computing a sum vector of the first and the second zero-mean error vectors, wherein determining if an integrity failure has occurred is based on the sum vector.

3. A method as defined in claim 2, further comprising computing a magnitude of the sum vector, wherein determining if an integrity failure has occurred comprises detecting if the magnitude exceeds a threshold.

4. A method as defined in claim 1, further comprising:

determining a starting position estimate based upon the position fix; and

estimating a second position fix from a second plurality of pseudoranges and the starting position estimate;

5. A method as defined in claim 4, wherein determining the starting position estimate based upon the position fix comprises computing an average of the position fix and at least one previous position fix.

6. A method as defined in claim 5, wherein the average is at least one of a weighted average or an unweighted average.

7. A method as defined in claim 4, wherein determining the starting position estimate based upon the position fix comprises:

computing a velocity based on the position fix and at least one previous position fix; and

computing the starting position estimate based on the computed velocity and the position fix.

8. A method as defined in claim 1, further comprising:

receiving a plurality of times from respective ones of a plurality of satellites; and

calculating the pseudoranges from the plurality of times based upon orbital locations of the plurality of satellites.

9. A method as defined in claim 1, wherein the pseudoranges include at least one of a correlated error or a common mode error.

10. An apparatus comprising:

a position fix engine to estimate a position fix from a plurality of pseudoranges;

error vector cleanup logic to compute a zero-mean error vector based upon a position fix error vector; and

an integrity failure detector to detect an integrity failure based on the zero-mean error vector.

11. An apparatus as defined in claim 10, further comprising a measurement engine to:

receive a plurality of times from respective ones of a plurality of satellites; and

calculate the pseudoranges from the plurality of times.

12. An apparatus as defined in claim 10, wherein the error vector cleanup logic comprises:

computing logic to compute a mean of the position fix error vector; and

a summer to subtract the mean from the position fix error vector.

13. An apparatus as defined in claim 10, wherein the integrity failure detector comprises:

an accumulator to compute a vector sum of the zero-mean error vector and a previous sum;

expected value computing logic to compute a magnitude of the vector sum; and

a comparator to compare the magnitude to a threshold.

14. An apparatus as defined in claim 10, further comprising an initial position estimator to estimate a starting position estimate based upon at least two previous position fixes estimated by the position fix engine.

15. An apparatus as defined in claim 10, wherein at least one of the position fix engine, the zero-mean computing logic or the integrity failure detector are implemented by a processor executing machine accessible instructions.

16. An article of manufacture storing machine accessible instructions which, when executed, cause a machine to:

estimate a position fix from a plurality of pseudoranges;

compute a first zero-mean error vector based upon the position fix; and

determine if an integrity failure has occurred based on the first zero-mean error vector.

17. An article of manufacture as defined in claim 16, wherein the machine accessible instructions, when executed, cause the machine to:

update the position fix based on the plurality of pseudoranges and a state vector;

compute a second zero-mean error vector based upon the updated position fix; and

compute a vector sum of the first and the second zero-mean error vectors, wherein determining if an integrity failure has occurred is based on the sum.

18. An article of manufacture as defined in claim 17, wherein the machine accessible instructions, when executed, cause the machine to compute a magnitude of the vector sum, wherein determining if an integrity failure has occurred comprises detecting if the magnitude exceeds a threshold.

19. An article of manufacture as defined in claim 16, wherein the machine accessible instructions, when executed, cause the machine to:

determining a starting position estimate based upon the position fix; and

estimating a second position fix from a second plurality of pseudoranges and the starting position estimate;

20. An article of manufacture as defined in claim 16, wherein the machine accessible instructions, when executed, cause the machine to:

receive a plurality of times from respective ones of a plurality of satellites; and

calculate the pseudoranges from the plurality of times based upon orbital locations of the plurality of satellites.