Patent ID: 7966021

Claim:
A method for estimating the location of a wireless node relative to a plurality of radio receivers operative to detect the strength of radio frequency (RF) signals, wherein a plurality of RF coverage maps are associated with the plurality of radio receivers, wherein each RF coverage map corresponds to one of the radio receivers, and characterizes the signal strength values for locations in a physical region for the corresponding radio receiver, comprising: collecting signal strength values, detected at a plurality of radio receivers, corresponding to signals transmitted by a wireless node; determining a differential error surface comprising, for all unique pairs of three or more radio receivers of the plurality of radio receivers, the sum of the squares of the difference between the signal strength values detected by each pair of radio receivers less the difference between the signal strength values in the RF coverage maps associated with the pair of radio receivers; and estimating the location of the wireless node using the differential error surface, wherein the wireless node comprises an RF ID tag.