Location Estimation of Wireless Terminals Through Pattern Matching of Signal-Strength Differentials

• US 20080299995A1
• Filed: 08/14/2008
• Published: 12/04/2008
• Est. Priority Date: 02/04/2003
• Status: Active Grant

• Current Assignee: Polaris Wireless Incorporated
• Original Assignee: Polaris Wireless Incorporated
• Inventors: Spain, David Stevenson
• Granted Patent: US 8,406,166 B2
• Time in Patent Office: Days
• US Class Current: 455/456.6
• CPC Class Codes: G01S 5/02521 using a radio-map
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A method of estimating the location of a wireless terminal is disclosed that is ideally suited for use with legacy systems. The illustrative embodiment of the present invention is based on the observation that the signal strength of a signal from a transmitter is different at some locations, and, therefore, the location of a wireless terminal can be estimated by comparing the signal strength it currently observes against a map or database that correlates locations to signal strengths. For example, if a particular radio station is known to be received well at a first location and poorly at a second location, and a given wireless terminal at an unknown location is receiving the radio station poorly, it is more likely that the wireless terminal is at the second location than it is at the first location.

Claims

1. A method for estimating a location of a wireless terminal, said method comprising:

receiving a first signal-strength measurement for a first signal at said wireless terminal and a second signal-strength measurement for a second signal at said wireless terminal; and

estimating the location of said wireless terminal based on the difference of said first signal-strength measurement minus said second signal-strength measurement.

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

3. The method of claim 1 wherein the task of estimating the location of said wireless terminal comprises generating a probability distribution for the location of said wireless terminal based on the difference of said first signal-strength measurement minus said second signal-strength measurement.

4. The method of claim 1 further comprising the task of receiving a third signal-strength measurement for a third signal at said wireless terminal.

5. The method of claim 4 further comprising the task of estimating the location of said wireless terminal is based on the difference of said first signal-strength measurement minus said third signal-strength measurement.

6. The method of claim 4 wherein said first signal-strength measurement and said third signal-strength measurement are made at substantially the same time and at substantially the same location.

7. The method of claim 4 wherein said third signal-strength measurement is at the maximum reportable value, and

wherein the task of estimating the location of said wireless terminal comprises restricting candidate locations to those where said third signal-strength measurement is expected to be at least equal to the maximum reportable value.

8. The method of claim 1 wherein said first signal is transmitted by a first transmitter at a first location and said second signal is transmitted by a second transmitter at a second location, wherein said first location is different than said second location.

9. The method of claim 1 wherein the task of estimating the location of said wireless terminal is performed at a location server.

10. A method for estimating a location of a wireless terminal, said method comprising:

receiving a first signal-strength measurement for a first signal at said wireless terminal and a second signal-strength measurement for a second signal at said wireless terminal; and

estimating the location of said wireless terminal by pattern matching the difference of said first signal-strength measurement minus said second signal-strength measurement against a signal-strength database that associates location with tuples of first signal signal-strength measurements and second signal signal-strength measurements.

11. The method of claim 10 wherein said first signal-strength measurement and said second signal-strength measurement are made at substantially the same time and at substantially the same location.

12. The method of claim 10 wherein the task of estimating the location of said wireless terminal comprises generating a probability distribution for the location of said wireless terminal is based on the difference of said first signal-strength measurement minus said second signal-strength measurement.

13. The method of claim 10 further comprising the task of receiving a third signal-strength measurement for a third signal at said wireless terminal.

14. The method of claim 13 further comprising the task of estimating the location of said wireless terminal by pattern matching the difference of said first signal-strength measurement minus said third signal-strength measurement against a signal-strength database that associates location with tuples of first signal signal-strength measurements and third signal signal-strength measurements.

15. The method of claim 13 wherein said first signal-strength measurement and said third signal-strength measurement are made at substantially the same time and at substantially the same location.

16. The method of claim 13 wherein said third signal-strength measurement is at the maximum reportable value, and

wherein the task of estimating the location of said wireless terminal comprises restricting candidate locations to those where said third signal-strength measurement is expected to be at least equal to the maximum reportable value.

17. The method of claim 10 wherein said first signal is transmitted by a first transmitter at a first location and said second signal is transmitted by a second transmitter at a second location, wherein said first location is different than said second location.

18. The method of claim 10 wherein the task of estimating the location of said wireless terminal is performed at a location server.