Search procedure for position determination system

• US 20040041729A1
• Filed: 08/29/2002
• Published: 03/04/2004
• Est. Priority Date: 08/29/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Rowitch, Douglas N.
• Granted Patent: US 6,825,805 B2
• Time in Patent Office: Days
• US Class Current: 342/357.15
• CPC Class Codes: G01S 19/28 Satellite selection

Abstract

A method of and system for performing a search for signals useful in determining the position of an entity. A first search is performed as part of a position determination attempt, and measurements are derived from the ensuing search results. Additional searching within the position determination attempt is avoided if the measurements satisfy one or more selected exit criteria. However, a second search is conducted if the measurements do not satisfy the one or more selected exit criteria.

Claims

1. A method of performing a search for signals useful in determining the position of an entity comprising:

performing a first search for signals useful in determining the position of the entity as part of a position determination attempt;

deriving one or more measurements from the ensuing search results;

determining whether the measurements satisfy one or more selected exit criteria;

avoiding additional searching within the position determination attempt if the measurements satisfy the one or more selected exit criteria; and

performing a second search for signals useful in determining the position of the entity if the measurements do not satisfy the one or more selected exit criteria.

2. The method of claim 1 wherein the measurements comprise peak signal to noise ratio and time measurements.

3. The method of claim 1 wherein the first search emphasizes speed rather than accuracy and sensitivity.

4. The method of claim 1 wherein the second search emphasizes accuracy and sensitivity rather than speed.

5. The method of claim 1 wherein the first search comprises searching for satellites in a first set.

6. The method of claim 5 wherein those satellites in the first set which satisfy a predetermined noise threshold form a second set.

7. The method of claim 6 wherein those satellites in the first set which satisfy a second threshold form a third set, and those satellites in the first set but excluding the third set form a fourth set.

8. The method of claim 7 wherein the second search is avoided if the number of satellites in the third set, equals the number of satellites in the first set.

9. The method of claim 8 wherein the measurements from the satellites in the second set define a polygon, and the second search is avoided if the area of the polygon, equals or exceeds a predetermined threshold.

10. The method of claim 9 wherein the second search is avoided if the number of satellites in the second set, equals or exceeds a predetermined threshold.

11. The method of claim 7 wherein the peak carrier signal to noise ratio for each of the measurements in the second set is summed, and the second search is avoided if the sum equals or exceeds a predetermined threshold.

12. The method of claim 7 wherein the second search is limited to those satellites in the fourth set.

13. The method of claim 1 wherein the entity is a subscriber station in a wireless communications system.

14. A memory storing a sequence of software instructions embodying a method for performing a search for signals useful in determining the position of an entity, the method comprising:

performing a first search for signals useful in determining the position of the entity as part of a position determination attempt;

deriving one or more measurements from the ensuing search results;

determining whether the measurements satisfy one or more selected exit criteria;

avoiding additional searching within the position determination attempt if the measurements satisfy the one or more selected exit criteria; and

performing a second search for signals useful in determining the position of the entity if the measurements from the first search do not satisfy the one or more selected exit criteria.

15. The memory of claim 14 wherein the measurements comprises peak signal to noise ratio and time measurements.

16. The memory of claim 14 wherein the first search emphasizes speed rather than accuracy and sensitivity.

17. The memory of claim 14 wherein the second search emphasizes accuracy and sensitivity rather than speed.

18. The memory of claim 14 wherein the first search comprises searching for satellites in a first set.

19. The memory of claim 18 wherein those satellites in the first set which satisfy a predetermined noise threshold form a second set.

20. The memory of claim 19 wherein those satellites in the first set which satisfy a second, second threshold form a third set, and those satellites in the first set but excluding the satellite of the third set form a fourth set.

21. The memory of claim 20 wherein the second search is avoided if the number of satellites in the third set, equals the number of satellites in the first set.

22. The memory of claim 21 wherein the measurements for the satellites in the second set define a polygon, and the second search is avoided if the area of the polygon, equal or exceed a predetermined threshold.

23. The memory of claim 21 wherein the second search is avoided if the number of measurements in the second set, equal or exceed a predetermined threshold.

24. The memory of claim 21 wherein the peak carrier signal to noise ratio is summed for each of the measurements in the second set, and the second search is avoided if the sum equals or exceeds a predetermined threshold.

25. The memory of claim 21 wherein the second search is limited to those satellites in the fourth set.

26. The memory of claim 14 wherein the entity is a subscriber station in a wireless communications system.

27. A system comprising a processor, the memory of claim 16, and a correlator, wherein the processor is configured to access and execute the software instructions stored in the memory, and, in combination with the correlator, perform the method embodied thereby.

28. A method of searching for signals useful in determining the position of an entity comprising:

a step for performing a first search for signals useful in determining the position of the entity as part of a position determination attempt;

a step for deriving one or more measurements from the ensuing search results;

a step for determining whether the measurements satisfy one or more selected exit criteria;

a step for avoiding additional searching within the position determination attempt if the measurements satisfy the one or more selected exit criteria; and

a step for performing a second search for signals useful in determining the position of the entity if the measurements do not satisfy the selected exit criteria.