Method for RF fingerprinting

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 collecting the plurality of measurements comprises collecting a plurality of measurements at each of a plurality of orientations, and wherein determining the characteristic value comprises determining a characteristic value for each of the plurality of orientations based on at least some of the respective plurality of measurements, the characteristic values forming portions of respective reference RF fingerprints associated with the first location, and wherein the plurality of orientations includes a plurality of directions between the mobile unit and the first transmitter such that a plurality of measurements is collected at each of the plurality of directions at the first location, and wherein the plurality of orientations includes a plurality of elevations between the mobile unit and the first transmitter such that a plurality of measurements is collected at each of the plurality of elevations at the first location.

A method of determining a location of a mobile unit in an area serviced by a wireless network, the wireless network configured for wireless location determination of said mobile unit and capable of being accessed from within the area via at least one of a plurality of wireless transmitters, the wireless network having a database of reference radio frequency (RF) fingerprints indicative of RF signal levels at a plurality of locations in the area, the method comprising steps of:

• collecting a plurality of measurements from each of the plurality of wireless transmitters, the plurality of measurements for each of the plurality of wireless transmitters indicative of RF signal strengths transmitted between said mobile unit and a respective one of the plurality of wireless transmitters at a current location of the mobile unit in the area, each of the plurality of measurements for the respective one of the plurality of wireless transmitters obtained at a respective successive time slice;
• determining, for each of the plurality of measurements, a characteristic value based on at least some of the respective plurality of measurements, to form a plurality of characteristic values, each associated with a respective one of the plurality of wireless transmitters, the plurality of characteristic values forming, at least in part, a target RF fingerprint for the mobile device at the current location, wherein determining the characteristic value includes identifying transmitters determined to be out of range or temporarily unobservable by determining if the transmitter has not been observed in a selectable number of preceding time slices, and determining that the transmitter is temporarily unobservable if the transmitter has been observed in said selectable number of preceding time slices, but is not observable in a current time slice;
• and
• determining the location of the mobile device by, at least in part, comparing the target RF fingerprint with the database of reference RF fingerprints,
• wherein determining the characteristic value includes identifying which, if any, of the plurality of measurements is an outlier with respect to other of the plurality of measurements based on at least one statistical measurement, and determining the characteristic value based on at least some of the plurality of measurements not identified as outliers.