Method and apparatus for a portable communication device to identify its own location

A system for identifying the location of a portable communication device in a radio network, at least a portion of which comprises:

• a plurality of at least three base stations in the radio network, each transmitting pilot signals which are offset in time by integral multiples of a substantially fixed duration with respect to pilot signals transmitted by each other base station in the network;
• a receiver in said portable communication device;
• a transmitter in said portable communication device;
• a relative delay calculation unit, disposed in said portable communication device and coupled to said receiver, for computing delays between the arrival time of a pilot signal transmitted from a primary base station and the arrival times of pilot signals transmitted from at least two other base stations, where said primary base station and said at least two other base stations are among said plurality of at least three base stations;
• a memory unit, disposed in said portable communication device and coupled to said receiver, for storing information indicative of the location of said primary base station and said at least two other base stations;
• and
• a processor, disposed in said portable communication device and coupled to said relative delay calculation unit and said memory unit, where said processor is programmed to identify the geographic location of said portable communication device.

A method of operating a portable communication device so as to identify its location in a radio network, the method comprising the steps of:

• receiving pilot signals from at least three base stations, where pilot signals transmitted by each base station are offset in time by integral multiples of a substantially fixed duration with respect to pilot signals transmitted by other base stations;
• computing the delays between the arrival time of a pilot signal transmitted from one of said base stations and the arrival times of pilot signals transmitted from at least two other of said base stations;
• receiving information indicative of the locations of the base stations whose pilot signals were received;
• specifying, for each pair of base stations corresponding to one of said delays, the geographic location of said portable communication device as being on a selected one of three curves thereby resulting in a plurality of selected curves;
• and
• identifying the geographic location of said portable communication device based upon points of intersection of said plurality of selected curves.