Location estimation of wireless terminals based on combinations of signal strength measurements and geometry-of-arrival measurements

• US 20040180671A1
• Filed: 01/05/2004
• Published: 09/16/2004
• Est. Priority Date: 02/24/2003
• Status: Active Grant

• Current Assignee: Polaris Wireless Incorporated
• Original Assignee: Polaris Wireless Incorporated
• Inventors: Spain, David Stevenson Jr.
• Granted Patent: US 7,233,799 B2
• Time in Patent Office: Days
• US Class Current: 455/456.1
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A method and apparatus for estimating the location of a wireless terminal are disclosed. The location of the wireless terminal is estimated based on one or more signal strength measurements in conjunction with: (i) one or more angle-of-arrival measurements, (ii) one or more time-of-arrival measurements, or (iii) a combination of (i) and (ii). At each measurement time, the illustrative embodiment (a) determines the candidate locations for the wireless terminal, (b) computes a measurement likelihood function for any signal strength measurements that are available at that time, (c) computes a measurement likelihood function for any geometry-of-arrival measurements that are available at that time, (d) computes a joint likelihood function for all measurements available at that time, and (e) updates the location probability distribution for the wireless terminal with the joint measurement likelihood function. Estimates of the location of the wireless terminal are obtained from the location probability distribution.

Claims

1. A method comprising:

receiving

(i) a first signal measurement for a first signal as received by a wireless terminal, and

(ii) a second signal measurement for a second signal as transmitted by said wireless terminal; and

estimating the location of said wireless terminal based on said first signal measurement and said second signal measurement.

2. The method of claim 1 wherein said first signal measurement and said second signal measurement are made at substantially the same time.

3. The method of claim 1 wherein said first signal measurement is a signal strength measurement.

4. The method of claim 1 wherein said second signal measurement is an angle-of-arrival measurement.

5. The method of claim 1 wherein said second signal measurement is a time-of-arrival measurement.

6. The method of claim 1 wherein said second signal measurement is a time-of-arrival measurement.

7. The method of claim 1 wherein estimating the location of said wireless terminal comprises:

pruning a first list of candidate locations for said wireless terminal to a second list of candidate locations of said wireless terminal based on said first signal measurement; and

choosing an estimated location for said wireless terminal based on said second list of locations and said second signal measurement.

8. The method of claim 1 wherein estimating the location of said wireless terminal comprises:

pruning a first list of candidate locations for said wireless terminal to a second list of candidate locations of said wireless terminal based on said second signal measurement; and

choosing an estimated location for said wireless terminal based on said second list of locations and said first signal measurement.

9. The method of claim 1 wherein estimating the location of said wireless terminal comprises matching said first signal measurement and said second signal measurement against a database that associates locations with signal measurements.

10. The method of claim 1 wherein estimating the location of said wireless terminal comprises:

generating a first probability distribution for the location of said wireless terminal based on said first signal measurement;

generating a second probability distribution for the location of said wireless terminal based on said second signal measurement; and

choosing an estimated location of said wireless terminal based on said first probability distribution and said second probability distribution.

11. The method of claim 10 wherein said first probability distribution and said second probability distribution are multi-dimensional.

12. The method of claim 11 wherein said first probability distribution and said second probability distribution are defined for a surface.

13. The method of claim 1 wherein a unique location for said wireless terminal is mathematically indeterminate from only said first signal measurement.

14. The method of claim 1 wherein a unique location for said wireless terminal is mathematically indeterminate from only said second signal measurement.

15. A method comprising:

receiving

(i) a signal strength measurement for a first signal as received by a wireless terminal, and

(ii) a time-of-arrival measurement for a second signal as received by said wireless terminal; and

estimating the location of said wireless terminal based on said signal strength measurement and said time-of-arrival measurement.

16. The method of claim 15 wherein receiving further comprises (iii) a second signal strength measurement for a third signal as received by said wireless terminal;

and

wherein estimating the location of said wireless terminal is also based on said second signal strength measurement.

17. The method of claim 15 wherein receiving further comprises (iii) a second time-of-arrival measurement for a third signal as received by said wireless terminal;

and

wherein estimating the location of said wireless terminal is also based on said second time-of-arrival measurement.

18. The method of claim 15 wherein receiving further comprises (iii) an angle-of-arrival measurement for a third signal as transmitted by said wireless terminal;

and

wherein estimating the location of said wireless terminal is also based on said angle-of-arrival measurement.

19. The method of claim 15 wherein said signal strength measurement and said time-of-arrival measurement are made at substantially the same time.

20. The method of claim 15 wherein said first signal and said second signal are transmitted from different locations.

21. The method of claim 15 wherein said second signal is transmitted by an Earth satellite.

22. The method of claim 15 wherein estimating the location of said wireless terminal comprises:

pruning a first list of candidate locations of said wireless terminal to a second list of candidate locations of said wireless terminal based on said time-of-arrival measurement; and

choosing an estimated location of said wireless terminal based on said second list of locations and said signal strength measurement.

23. The method of claim 15 wherein estimating the location of said wireless terminal comprises:

pruning a first list of candidate locations of said wireless terminal to a second list of candidate locations of said wireless terminal based on said signal strength measurement; and

choosing an estimated location of said wireless terminal based on said second list of locations and said time-of-arrival measurement.

24. The method of claim 15 wherein said estimating the location of said wireless terminal comprises:

generating a first probability distribution for the location of said wireless terminal based on said signal strength measurement;

generating a second probability distribution for the location of said wireless terminal based on said time-of-arrival measurement; and

choosing an estimated location of said wireless terminal based on said first probability distribution and said second probability distribution.

25. The method of claim 24 wherein said first probability distribution and said second probability distribution are multi-dimensional.

26. The method of claim 25 wherein said first probability distribution and said second probability distribution are defined for a surface.

27. The method of claim 15 wherein a unique location for said wireless terminal is mathematically indeterminate from only said signal strength measurement.

28. The method of claim 27 wherein a unique location for said wireless terminal is also mathematically indeterminate from said signal strength measurement in combination with any other signal strength measurements received by said wireless terminal.

29. The method of claim 15 wherein a unique location for said wireless terminal is mathematically indeterminate from only said time-of-arrival measurement.

30. A method comprising:

receiving

(i) a signal strength measurement for a first signal as received by a wireless terminal,

(ii) a first time-of-arrival measurement for a second signal as received by said wireless terminal, wherein said second signal is transmitted by a first Earth satellite, and

(iii) a second time-of-arrival measurement for a third signal as received by said wireless terminal, wherein said third signal is transmitted by a second Earth satellite; and

estimating the location of said wireless terminal based on said signal strength measurement, said first time-of-arrival measurement, and said second time-of-arrival measurement.

31. The method of claim 30 wherein estimating the location of said wireless terminal comprises generating a time-difference-of-arrival measurement from said first time-of-arrival measurement and said second time-of-arrival measurement.

32. The method of claim 30 wherein receiving further comprises (iv) an angle-of-arrival measurement for a fourth signal as transmitted by said wireless terminal;

and

wherein estimating the location of said wireless terminal is also based on said angle-of-arrival measurement.

33. The method of claim 30 wherein said signal strength measurement, said first time-of-arrival measurement, and said second time-of-arrival measurement are made at substantially the same time.

34. The method of claim 30 wherein estimating the location of said wireless terminal comprises:

pruning a first list of candidate locations of said wireless terminal to a second list of candidate locations of said wireless terminal based on said first time-of-arrival measurement and said second time-of-arrival measurement; and

choosing an estimated location of said wireless terminal based on said second list of locations and said signal strength measurement.

35. The method of claim 30 wherein estimating the location of said wireless terminal comprises:

pruning a first list of candidate locations of said wireless terminal to a second list of candidate locations of said wireless terminal based on said signal strength measurement; and

choosing an estimated location of said wireless terminal based on said second list of locations, said first time-of-arrival measurement, and said second time-of-arrival measurement.

36. The method of claim 30 wherein said estimating the location of said wireless terminal comprises:

generating a first probability distribution for the location of said wireless terminal based on said signal strength measurement;

generating a second probability distribution for the location of said wireless terminal based on said first time-of-arrival measurement and said second time-of-arrival measurement; and

choosing an estimated location of said wireless terminal based on said first probability distribution and said second probability distribution.

37. The method of claim 36 wherein said first probability distribution and said second probability distribution are multi-dimensional.

38. The method of claim 37 wherein said first probability distribution and said second probability distribution are defined for a surface.

39. The method of claim 30 wherein a unique location for said wireless terminal is mathematically indeterminate from only said signal strength measurement.

40. The method of claim 39 wherein a unique location for said wireless terminal is also mathematically indeterminate from said signal strength measurement in combination with any other signal strength measurements received by said wireless terminal.

41. The method of claim 30 wherein a unique location for said wireless terminal is mathematically indeterminate from only said first time-of-arrival measurement and said second time-of-arrival measurement.

42. The method of claim 41 wherein a unique location for said wireless terminal is also mathematically indeterminate from said first time-of-arrival measurement and said second time-of-arrival measurement in combination with any other time-of-arrival measurements received by said wireless terminal.