Patent ID: 6952158

Claim:
A method of geolocating a mobile appliance from a plurality of reference signal sources in disparate communication systems comprising the steps of: (a) establishing a locating station in a service area; (b) establishing the geophysical coordinates of the plurality of reference signal sources in the service area of the locating station irrespective of the communication system in which the reference signal sources are operative; (c) determining the reference signals emitted by each of the plurality of reference signal sources; (d) mapping the pattern of said reference signals and time differences between said reference signals emitted from the reference signal sources in the service area; (e) providing a mobile appliance the location of which is to be determined; (f) receiving at the mobile appliance energy from at least two of the plurality of disparate reference signal sources; (g) determining at the mobile appliance reference signals from the received energy; (h) determining at the mobile appliance the time difference of arrival between each pair of reference signals received from the plurality of disparate reference signal sources; (i) transmitting the determined time differences to the locating station; (j) receiving at the locating station the time differences transmitted by the mobile appliance; (k) determining at the locating station the pattern of received reference signals from the received time differences; (l) determining at the locating station an approximation of the location of the mobile appliance from a comparison of the determined pattern of received reference signals and the mapped pattern of reference signals to thereby determine the identity of the reference signal sources whose reference signals were received by the mobile appliance; and (m) geolocating at the locating station the mobile appliance from the time differences received from the mobile appliance by TDOA techniques from the identified reference signal sources.