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