Patent ID: 7130646

Claim:
A method of determining a position of a wireless device, the method including: identifying a first access point having a first known location and a predetermined radio propagation range of r, wherein the position of the wireless device is the first known location with an uncertainty of r; determining a first radio signal strength indicator (RSSI) of the first access point; correlating the first RSSI to a first stored distance, wherein the first stored distance represents a first relative distance from the first access point to the wireless device; identifying a second access point and a third access point having a second known location and a third known location, respectively; determining a second RSSI and a third RSSI of the second access point and the third access point, respectively; correlating the second RSSI and the third RSSI to a second stored distance and a third stored distance, respectively, wherein the second stored distance represents a second relative distance from the second access point to the wireless device, and wherein the third stored distance represents a third relative distance from the third access point to the wireless device; and computing a coordinate position of the wireless device using the first, second, and third known positions and the first, second, and third relative distances, wherein the first known position is (x 1 , y 1 , z 1 ) and the first relative position is r 1 , wherein the second known position is (x 2 , y 2 , z 2 ) and the second relative position is r 2 , wherein the third known position is (x 3 , y 3 , z 3 ) and the third relative position is r 3 , wherein the coordinate position of the wireless device is (x 0 , y 0 , z 0 ) and wherein computing the coordinate position includes using a set of equations: x 0 =( w 1 * x 1 )+( w 2 * x 2 )+( w 3 * x 3 ), y 0 =( w 1 * y 1 )+( w 2 * y 2 )+( w 3 * y 3 ), and z 0 =( w 1 * z 1 )+( w 2 * z 2 )+( w 3 * z 3 ), wherein w 1 =(1 /r 1 )/(1 /r 1 +1 /r 2 +1 /r 3 ), w 2 =(1 /r 2 )/(1 /r 1 +1 /r 2 +1 /r 3 ), and w 3 =(1 /r 3 )/(1 /r 1 +1 /r 2 +1 /r 3 ).