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 computer-implemented method for determining a location of a mobile unit, comprising: measuring a wireless signal strength of the signal received at a base station; comparing at a computing device the measured wireless signal strength to a table of mathematically estimated wireless signal strengths and corresponding mobile unit locations; finding a table entry whose stored in a memory, wherein the table entry has the 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 the 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 storage device 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 storage device 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 storage device 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 storage device 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 storage device 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 storage device 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 computer-readable storage device having stored thereon computer instructions that when executed carry out the acts comprising:
 populating a table comprising a plurality of values representative of locations within a circumscribed area and corresponding signal strength values representative of plurality of signal strengths received from a plurality of base stations wherein said table comprises at least one location derivable by signal strength values that are derived empirically without the need to measure signal strength at the at least one location;   receiving over at least one local area network a plurality of values representative of measured signal strengths from at least two of said plurality of base stations;   correlating the plurality of values representative of measured signal strengths from said at least two base stations to said plurality of values representative of base station signal strengths in said table to determine at least one value representative of location within the circumscribed area; and   estimating a location of a wireless device as a function of said at least one value.    
     
     
       20. The computer-readable storage device of claim 19 wherein the instruction for estimating the location of said wireless device comprises instructions for interpolating from at least two locations found in said table.  
     
     
       21. The computer-readable storage device of claim 19 wherein the instructions for estimating the location of said wireless device comprises instructions for finding at least two nearest neighbors in said table, where said nearest neighbors are locations having corresponding signal strength values that are most similar to the plurality of values representative of signal strength received from said wireless device.  
     
     
       22. The computer-readable storage device of claim 19 comprising instruction for populating said table by at least one of empirically estimating and mathematically estimating locations and corresponding signal strength values.  
     
     
       23. A system for locating a wireless device comprising:
 means for populating a data structure comprising a plurality of values representative of locations within a circumscribed area and corresponding signal strength values representative of plurality of signal strengths received from a plurality of base stations wherein at least one signal strength value is derived mathematically without the need for measuring signal strength at the corresponding location;   means for receiving over a local area network a plurality of values representative of measured signal strengths from at least two of said plurality of base stations;   means for correlating the plurality of values representative of measured signal strengths from said at least two base stations to said plurality of values representative of base station signal strengths in said data structure to determine at least one value representative of location within the circumscribed area; and   means for estimating a location of a wireless device as a function of said at least one value.    
     
     
       24. A system for locating a wireless device comprising:
 at least one local area network;   a plurality of wireless base stations are physically linked together and coupled to said at least one local area network;   a computer system comprising a processor and memory in communication with said plurality of wireless base stations by way of said at least one local area network;   a table stored in said memory wherein said table comprises a plurality of locations with corresponding signal strength values wherein at least some of the signal strengths are mathematically derived without the need for measuring wireless signal strengths at the corresponding location,   computer instructions stored in said memory; said computer instructions executable by said processor to receive measured signal strength values from said wireless device and to correlate the measure signal strength values with signal strength values corresponding to at least one location in said table; and   computer instructions stored in said memory; said computer instructions executable by said processor to determine a location of said mobile unit on a floor plan as a function of the at least one location in said table.    
     
     
       25. A system for locating a wireless device comprising:
 means for populating a data structure comprising a plurality of values representative of locations within a circumscribed area and corresponding signal strength values representative of plurality of signal strengths received from a plurality of base stations connected to at least one local area network wherein at least one of the signal strength values is mathematically derived without the need for measuring wireless signal strengths at the mathematically derived locations;   means for receiving from a wireless device a plurality of values representative of measured signal strengths from at least two of said plurality of base stations;   means for correlating the plurality of values representative of measured signal strengths from said at least two base stations to said plurality of values representative of base station signal strengths in said data structure to determine at least one value representative of location within the circumscribed area; and   means for estimating a location of a wireless device as a function of said at least one value.