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

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.

We claim: 
     
       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 mathematically estimated signal strengths in the table are determined without measurement of wireless signal strength at the corresponding mobile unit locations. 
     
     
       2. The method of  claim 1  wherein the determining the location of the mobile unit with reference to the found table entry includes determining the location of the mobile unit to be proximate to the found table entry's corresponding mobile unit location. 
     
     
       3. The method of  claim 1  wherein the measuring the wireless signal strength includes measuring, at the mobile unit, a wireless signal strength of a base station, and wherein the table of mathematically estimated wireless signal strengths and corresponding mobile unit locations includes mathematical estimates of base station wireless signal strengths at the corresponding mobile unit locations. 
     
     
       4. The method of  claim 1  wherein the measuring the wireless signal strength includes measuring, at a base station, a wireless signal strength of the mobile unit, and wherein the table of mathematically estimated wireless signal strengths and corresponding mobile unit locations includes, for mobile units at the corresponding mobile unit locations, mathematical estimates of mobile unit wireless signal strengths at one or more base stations. 
     
     
       5. The method of  claim 1  wherein the finding the table entry whose mathematically estimated wireless signal strength is closest to the measured wireless signal strength includes finding a plurality of table entries and wherein the determining the location of the mobile unit with reference to the found table entry includes determining the location of the mobile unit to be proximate to a spatial average of the found plurality of table entries' corresponding mobile unit locations. 
     
     
       6. The method of  claim 3  wherein the determining the location of the mobile unit to be proximate to a spatial average of the found plurality of table entries' corresponding mobile unit locations includes multiplying each found table entry's corresponding mobile unit location by a weighting factor prior to the spatial averaging. 
     
     
       7. A computer-readable medium having computer-executable instructions for performing steps, 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 mathematically estimated signal strengths in the table are determined without measurement of wireless signal strength at the corresponding mobile unit locations. 
     
     
       8. The computer-readable medium of  claim 7  wherein the determining the location of the mobile unit with reference to the found table entry includes determining the location of the mobile unit to be proximate to the found table entry's corresponding mobile unit location. 
     
     
       9. The computer-readable medium of  claim 7  wherein the measuring the wireless signal strength includes measuring, at the mobile unit, a wireless signal strength of a base station, and wherein the table of mathematically estimated wireless signal strengths and corresponding mobile unit locations includes mathematical estimates of base station wireless signal strengths at the corresponding mobile unit locations. 
     
     
       10. The computer-readable medium of  claim 7  wherein the measuring the wireless signal strength includes measuring, at a base station, a wireless signal strength of the mobile unit, and wherein the table of mathematically estimated wireless signal strengths and corresponding mobile unit locations includes, for mobile units at the corresponding mobile unit locations, mathematical estimates of mobile unit wireless signal strengths at one or more base stations. 
     
     
       11. The computer-readable medium of  claim 7  wherein the finding the table entry whose mathematically estimated wireless signal strength is closest to the measured wireless signal strength includes finding a plurality of table entries and wherein the determining the location of the mobile unit with reference to the found table entry includes determining the location of the mobile unit to be proximate to a spatial average of the found plurality of table entries' corresponding mobile unit locations. 
     
     
       12. The computer-readable medium of  claim 11  wherein the determining the location of the mobile unit to be proximate to a spatial average of the found plurality of table entries' corresponding mobile unit locations includes multiplying each found table entry's corresponding mobile unit location by a weighting factor prior to the spatial averaging. 
     
     
       13. A mobile unit comprising: a wireless interface hardware, wherein the wireless interface hardware obtains a wireless signal strength; a memory storage, storing a table of mathematically estimated wireless signal strengths and 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 the mathematically estimated signal strengths in the table are determined without measurement of wireless signal strength at the corresponding mobile unit locations. 
     
     
       14. The mobile unit of  claim 13  wherein the determining the location of the mobile unit with reference to the found table entry includes determining the location of the mobile unit to be proximate to the found table entry's corresponding mobile unit location. 
     
     
       15. The mobile unit of  claim 13  wherein the obtaining the wireless signal strength includes measuring, at the mobile unit, a wireless signal strength of a base station, and wherein the table of mathematically estimated wireless signal strengths and corresponding mobile unit locations includes mathematical estimates of base station wireless signal strengths at the corresponding mobile unit locations. 
     
     
       16. The mobile unit of  claim 13  wherein the obtaining the wireless signal strength includes requesting, from a base station, a wireless signal strength of the mobile unit as measured at the base station, and wherein the table of mathematically estimated wireless signal strengths and corresponding mobile unit locations includes, for mobile units at the corresponding mobile unit locations, mathematical estimates of mobile unit wireless signal strengths at one or more base stations. 
     
     
       17. The mobile unit of  claim 13  wherein the finding the table entry whose mathematically estimated wireless signal strength is closest to the obtained wireless signal strength includes finding a plurality of table entries and wherein the determining the location of the mobile unit with reference to the found table entry includes determining the location of the mobile unit to be proximate to a spatial average of the found plurality of table entries' corresponding mobile unit locations. 
     
     
       18. The mobile unit of  claim 17  wherein the determining the location of the mobile unit to be proximate to a spatial average of the found plurality of table entries' corresponding mobile unit locations includes multiplying each found table entry's corresponding mobile unit location by a weighting factor prior to the spatial averaging. 
     
     
       19. A device for locating a mobile device comprising:
 a processor;   at least one memory in communication with the processor;   an interface in communication with the processor and adapted to communicate with at least one wireless base station in a local area network;   a table stored in the at least a portion of the at least one memory wherein the table comprises a plurality of locations with corresponding signal strength values wherein the corresponding signal strength values are mathematically estimated without the need for measuring wireless signal strengths at the corresponding location;   computer instructions stored in at least another portion of the at least one memory, the computer instructions executable by the processor at least to:   receive measured signal strength values representative of signals received from the mobile device;   correlate the measured signal strength values with signal strength values corresponding to at least one location in said table; and   determine a location of said mobile device on a floor plan as a function of the at least one location in said table.   
     
     
       20. The device for locating a mobile device as recited in claim 19 wherein the measured signal strengths values representative of signals received from the mobile device are derived from signals received from the mobile device in communication with a wireless local area network. 
     
     
       21. The device for locating a mobile device as recited in claim 19 wherein the measured signal strengths values representative of signals received from the mobile device are derived from a plurality of signal measurements received from the mobile device. 
     
     
       22. The device for locating a mobile device as recited in claim 19 wherein the table further comprises corresponding signal strength values that are derived from measured signal strength values. 
     
     
       23. The device for locating a mobile device as recited in claim 19 wherein the computer instructions further comprise computer instructions to determine a position of the mobile device based on a weighting of a plurality of corresponding locations in the table. 
     
     
       24. The device for locating a mobile device as recited in claim 19 wherein the computer instructions to determine a position of the mobile device based on a weighting of a plurality of corresponding locations in the table computes a spatial average of the plurality of corresponding locations. 
     
     
       25. The device for locating a mobile device as recited in claim 19 further comprising computer instructions to determine a position of the mobile device based at least in part on a wall attenuation factor that accounts for the thickness of walls through which the signals from the mobile device travel. 
     
     
       26. A non-transitory computer readable storage device having stored thereon computer-readable readable instructions that upon execution on a computing device, at least cause a system to:
 receive measured signal strength values from a mobile device;   correlate the measured signal strength values with signal strength values corresponding to at least one location in a table stored in said memory wherein said table comprises a plurality of locations with corresponding signal strength values wherein the signal strengths are mathematically estimated without the need for measuring wireless signal strengths at the corresponding location in said table; and   determine a location of said mobile device on a floor plan as a function of the at least one location in said table.   
     
     
       27. The non-transitory computer readable storage device as recited in claim 26 wherein the measured signal strengths values from the mobile device are derived from signals received from the mobile device in communication with a wireless local area network. 
     
     
       28. The non-transitory computer readable storage device as recited in claim 26 wherein the measured signal strengths values from the mobile device are derived from a plurality of signal measurements received from the mobile device. 
     
     
       29. The non-transitory computer readable storage device as recited in claim 26 wherein the table further comprises corresponding signal strength values that are derived from measured signal strength values. 
     
     
       30. The non-transitory computer readable storage device as recited in claim 26 wherein the computer instructions further comprise computer instructions to determine a position of the mobile device based on a weighting of a plurality of corresponding locations in the table. 
     
     
       31. The non-transitory computer readable storage device as recited in claim 30 wherein the computer instructions to determine a position of the mobile device based on a weighting of a plurality of corresponding locations in the table computes a spatial average of the plurality of corresponding locations. 
     
     
       32. The non-transitory computer readable storage device as recited in claim 26 further comprising computer instructions to determine a position of the mobile device based at least in part on a wall attenuation factor that accounts for the thickness of walls through which the signals from the mobile device travel. 
     
     
       33. A method for locating a mobile computing device within a building, comprising:
 receiving measured signal strength values from the mobile computing device;   correlating the measured signal strength values with signal strength values corresponding to at least one location in a table stored in said memory wherein said table comprises a plurality of locations with corresponding signal strength values wherein the signal strengths are mathematically estimated without the need for measuring wireless signal strengths at the corresponding location in said table; and   determining a corresponding location on a floor plan of the building as a function of the at least one location in said table.   
     
     
       34. The method as recited in claim 33 wherein the measured signal strengths values from the mobile computing device are derived from signals received from the mobile device in communication with a wireless local area network. 
     
     
       35. The method as recited in claim 33 wherein the measured signal strengths values from the mobile computing device are derived from a plurality of signal measurements received from the mobile device. 
     
     
       36. The method as recited in claim 33 wherein the table further comprises corresponding signal strength values that are derived from measured signal strength values. 
     
     
       37. The method as recited in claim 33 further comprising determining a position of the mobile computing device based on a weighting of a plurality of corresponding locations in the table. 
     
     
       38. The method as recited in claim 37 further comprising computing a spatial average of the plurality of corresponding locations.