Patent ID: 8081991

Claim:
A method for determining a users position employing a wireless network, said method comprising: providing an edifice containing the wireless network comprised of a plurality of wireless access points throughout the edifice; providing a handheld device operable to transmit and receive transmissions from the plurality of wireless access points; transmitting location information from the at least three wireless access points to the handheld device; receiving said transmitted location information at the handheld device; processing said transmitted location information to determine location of handheld device within the edifice; wherein said transmitted location information includes determining the three dimensional spatial coordinates of each network access point by using a floor plan of the edifice, determining the radio signal power of each network access point at a fixed predetermined distance, encoding said spatial coordinate information and radio signal power, transmitting said encoded spatial coordinate information and radio signal power at a fixed predetermined distance, receiving said encoded information, and decoding and comparing said information for each access point with measured radio signal power of that access point at the location of the handheld device, wherein GPS information is used to determine the three dimensional spatial coordinate of one or more of the access points, and wherein said encoding and comparing further comprising: providing the measured radio signal power of two of the at least three access points and the predetermined radio power of each at a fixed predetermined distance to calculate a squared ratio of the estimated distances to two of the at least three access points being compared by the following, where Q ij = ( k i k j ) ⁢ ( P rj P ri ) ; providing the squared ratio of the estimated distances to the two of the at least three access points being compared and the three dimensional spatial coordinates of the two of the at least three access points being compared to calculate the three dimensional coordinates of the center and the radius of a sphere forming the locus of all points where the ratio of the estimated distances is constant: x cij = x i - Q ij ⁢ x j 1 - Q ij y cij = y i - Q ij ⁢ y j 1 - Q ij z cij = z i - Q ij ⁢ z j 1 - Q ij d cij 2 = Q ij ⁢ d ij 2 ( 1 - Q ij ) 2 ; providing these parameters to calculate the distance between a three dimensional spatial coordinate and the surface of the sphere defined by these parameters: Δ d ij =√{square root over (( x c ij −x ) 2 +( y c ij −y ) 2 +( z c ij −z ) 2 )}{square root over (( x c ij −x ) 2 +( y c ij −y ) 2 +( z c ij −z ) 2 )}{square root over (( x c ij −x ) 2 +( y c ij −y ) 2 +( z c ij −z ) 2 )}−√{square root over ( d c ij )}; determining the three dimensional spatial coordinates by minimizing the distance between a three dimensional spatial coordinate and the surface of the sphere and using the three dimensional coordinates as the estimate of the three dimensional spatial coordinates of the handheld device.