Patent ID: 8630656

Claim:
A method of determining the location of a mobile GSM receiver in one or more dimensions in a radio system which includes a network of GSM transmitters in which each of the transmitters transmit signals on a respective particular frequency and the positions of which transmitters are known, said GSM receiver configured to receive signals from said GSM transmitters, a mobile GSM and GSM network, the method comprising the steps of: a) detecting signals received by the mobile GSM receiver received from the transmitters that are visible in said network, a mobile GSM and GSM network, each of which visible signals is above a predetermined power level on its respective particular frequency and which can include signals from non-serving transmitters and a serving transmitter, said detecting including decoding from each of said received signals above said predetermined power level, information relating to the identity of the corresponding one of said transmitters in the network; b) compiling, in the mobile receiver, a list of the visible transmitters including information relating to the identity of said corresponding transmitters; c) sending said list to a calculation device; d) creating in the calculation device a further list of transmitters which are in said network of GSM transmitters but not detected by the mobile receiver; e) constructing a position function which relates to the probability that the receiver is at a given location, which has components corresponding to each transmitter in the list of visible transmitters, to each transmitter in the further list of transmitters not detected by the mobile receiver, each component including a predetermined probability function that relates to the probability that the receiver is at a particular location given the transmitters in said list and said further list; and f) evaluating said position function to determine a position that corresponds to the highest probability of location, and defining that position to be the location of the mobile receiver.