Patent ID: 7346359

Claim:
A method of collecting reference radio frequency (RF) measurements to form RF fingerprints for a reference database to facilitate subsequent location determination of a mobile unit, the method comprising steps of: providing at least two transmitters that are detectable by said mobile unit at a first location in an area serviced by the at least two transmitters; collecting a plurality of measurements, each obtained at a respective successive time slice, the plurality of measurements indicative of RF signals transmitted between said mobile unit and a first transmitter of the at least two transmitters at the first location in said area; and determining a characteristic value based on at least some of the plurality of measurements, the characteristic value forming a first portion of a reference RF fingerprint associated with the first location, wherein determining the characteristic value comprises: determining if a transmitter of the at least two transmitters for which a plurality of measurements are being collected is out of range or temporarily unobservable for said mobile unit at a particular location in said area; applying a mathematical function to said plurality of measurements that are not temporarily unobservable or out of range and obtaining the characteristic value from said application of said mathematical function; and using the characteristic value to form a portion of a reference RF fingerprint to be applied to the database of reference RF fingerprints.