Using a derived table of signal strength data to locate and track a user in a wireless network

• US 6,839,560 B1
• Filed: 02/25/2000
• Issued: 01/04/2005
• Est. Priority Date: 02/25/1999
• Status: Expired due to Term

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Bahl, Paramvir, Padmanabhan, Venkata N.
• Primary Examiner(s): Nguyen, Lee
• Assistant Examiner(s): Persino, Raymond B.
• Application Number:
  US09/513,155
• Time in Patent Office: 1,775 Days
• Field of Search: 342/450, 342/457, 342/464, 342/451, 455/456.1, 455/456.2, 455/456.3, 455/456.4, 455/456.5, 455/456.6, 455/404.2, 455/67.11, 340/573.1, 701/208
• US Class Current: 455/456.1
• CPC Class Codes: G01C 21/206 specially adapted for indoor navigation
• CPC Class Codes: G01S 11/06 using intensity measurements
• CPC Class Codes: G01S 5/02521 using a radio-map
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

A method for locating a user in a wireless network is disclosed. A mobile computer seeking to determine its location within a building detects the signal strength of one or more wireless base stations placed at known locations throughout the building. The mobile computer uses this measured signal strength to determine its location via a signal-strength-to-location table look-up. A table of known locations within the building and the base station signal strength at those locations is searched to find the most similar stored signal strength to the signal strength detected. The location corresponding to the most similar stored signal strength is determined to be the current location of the mobile computer. Alternatively, a number of signal strengths from the table can be used and the corresponding locations can be spatially averaged to determine the location of the mobile computer. The table can be derived empirically, by placing a mobile computer at the known locations and detecting the signal strength of the wireless base stations at those locations, or the table can be derived mathematically by taking into account a reference signal strength, the distance between the reference point and the known location, and the number of walls between the reference point and the known location. As an alternative, the base stations can detect the signal strength of the mobile computer. In such a case, the table would relate a known position of the mobile computer to the signal strength of the mobile computer at that location as detected by the one or more base stations.

Claims

1. A method for determining a location of a mobile unit, comprising:

measuring a wireless signal strength;

comparing the measured wireless signal strength to a table of mathematically estimated wireless signal strengths and corresponding mobile unit locations;

finding a table entry whose mathematically estimated wireless signal strength is closest, by distance in signal space, to the measured wireless signal strength; and

determining the location of the mobile unit with reference to the found table entry;

wherein the mathematical estimates of base station wireless signal strengths at the corresponding mobile unit locations are derived by performing steps comprising;

determining an existing number of walls between the base station and the corresponding mobile unit locations; and

determining a wall attenuation factor.

2. The method of claim 1 wherein the determining the existing number of walls includes using a line clipping algorithm.

3. The method of claim 1 wherein the determining the existing number of walls includes determining a practical limit number of walls between the base station and the corresponding mobile unit locations.

4. A method for determining a location of a mobile unit comprising:

measuring at a base station, a wireless signal strength of the mobile unit;

comparing the measured wireless signal strength to a table of mathematically estimated wireless signal strengths and corresponding mobile unit locations that includes, for mobile units at the corresponding mobile unit locations, mathematical estimates of mobile unit wireless signal strengths at one or more base stations;

finding a table entry whose mathematically estimated wireless signal strength is closest, by distance in signal space, to the measured wireless signal strength; and

determining the location of the mobile unit with reference to the found table entry;

wherein the mathematical estimates of mobile unit wireless signal strengths at the one or more base stations locations are derived by performing steps comprising;

determining an existing number of walls between the one or more base stations and the corresponding mobile unit locations; and

determining a wall attenuation factor.

5. The method of claim 4 wherein the determining the existing number of walls includes using a line clipping algorithm.

6. The method of claim 4 wherein the determining the existing number of walls includes determining a practical limit number of walls between the one or more base stations and the corresponding mobile unit locations.

7. A computer-readable medium having computer-executable instructions for performing steps, comprising:

measuring at a mobile unit, a wireless signal strength of a base station;

comparing the measured wireless signal strength to a table of mathematically estimated wireless signal strengths and corresponding mobile unit locations including mathematical estimates of base station wireless signal strengths at the corresponding mobile unit locations;

finding a table entry whose mathematically estimated wireless signal strength is closest, by distance in signal space, to the measured wireless signal strength; and

determining the location of the mobile unit with reference to the found table entry;

wherein the mathematical estimates of base station wireless signal strengths at the corresponding mobile unit locations are derived by performing steps comprising;

determining an existing number of walls between the base station and the corresponding mobile unit locations; and

determining a wall attenuation factor.

8. The computer-readable medium of claim 7 wherein the determining the existing number of walls includes using a line clipping algorithm.

9. The computer-readable medium of claim 7 wherein the determining the existing number of walls includes determining a practical limit number of walls between the base station and the corresponding mobile unit locations.

10. A computer-readable medium having computer-executable instructions for performing steps, comprising:

measuring at a base station, a wireless signal strength of a mobile unit;

comparing the measured wireless sigal strength to a table of mathematically estimated wireless signal strengths and corresponding mobile unit locations, including for mobile units at the corresponding mobile unit locations, mathematical estimates of mobile unit wireless signal strengths at one or more base stations;

finding a table entry whose mathematically estimated wireless signal strength is closest, by distance in signal space, to the measured wireless signal strength and determining the location of the mobile unit with reference to the found table entry;

wherein the mathematical estimates of mobile unit wireless signal strengths at the one or more base stations locations are derived by performing steps comprising;

determining an existing number of walls between the one or more base stations and the corresponding mobile unit locations; and

determining a wall attenuation factor.

11. The computer-readable medium of claim 10 wherein the determining the existing number of walls includes using a line clipping algorithm.

12. The computer-readable medium of claim 10 wherein the determining the existing number of walls includes determining a practical limit number of walls between the one or more base stations and the corresponding mobile unit locations.

13. A mobile unit comprising:

a wireless interface hardware, wherein the wireless interface hardware obtains a wireless signal strength of a base station measured at the mobile unit;

a memory storage, storing a table of mathematically estimated wireless signal strengths and corresponding mobile unit locations, including mathematical estimates of base station wireless signal strengths at the corresponding mobile unit locations; and

a central processing unit wherein the central processing unit compares the obtained wireless signal strength to the table of mathematically estimated wireless signal strengths and corresponding mobile unit locations, finds a table entry whose mathematically estimated wireless signal strength is closest by distance in signal space, to the obtained wireless signal strength, and determines the location of the mobile unit with reference to the found table entry;

wherein further the mathematical estimates of base station wireless signal strengths at the corresponding mobile unit locations are derived by performing steps comprising;

determining an existing number of walls between the base station and the corresponding mobile unit locations; and

determining a wall attenuation factor.

14. The mobile unit of claim 13 wherein the determining the existing number of walls includes using a line clipping algorithm.

15. The mobile unit of claim 14 wherein the determining the existing number of walls includes determining a practical limit number of walls between the base station and the corresponding mobile unit locations.

16. A mobile unit comprising:

a wireless interface hardware, wherein the wireless interface hardware requests, from a base station, a wireless signal strength of the mobile unit measured at the base station a memory storage, storing a table of mathematically estimated wireless signal strengths and corresponding mobile unit locations, including for mobile units at the corresponding mobile unit locations, mathematical estimates of mobile unit wireless signal strengths at one or more base stations, and a central processing unit, wherein the central processing unit compares the obtained wireless signal strength to the table of mathematically estimated wireless signal strengths and corresponding mobile unit locations finds a table entry whose mathematically estimated wireless signal strength is closest, by distance in signal space, to the obtained wireless signal strength, and determines the location of the mobile unit with reference to the found table entry;

wherein further the mathematical estimates of mobile unit wireless signal strengths at the one or more base stations locations are derived by performing steps comprising;

determining an existing number of walls between the one or more base stations and the corresponding mobile unit locations; and

determining a wall attenuation factor.

17. The mobile unit of claim 16 wherein the determining the existing number of walls includes using a line clipping algorithm.

18. The mobile unit of claim 16 wherein the determining the existing number of walls includes determining a practical limit number of walls between the one or more base stations and the corresponding mobile unit locations.