METHOD AND APPARATUS FOR DETERMINING THE POSITION OF A MOBILE COMMUNICATION DEVICE USING LOW ACCURACY CLOCKS

摘要

A position location communication system (10) determines the position of a master radio (12) using a round-trip messaging scheme in which the time of arrive (TOA) of ranging messages is accurately determined to yield the range estimates required to calculate the position of the master radio via trilateration. The master radio transmits outbound ranging messages to plura l reference radios (14, 16, 18, 20) which respond by transmitting reply rangin g messages. Upon reception of the reply ranging message, the master radio determines the range to the reference radio from the signal propagation time calculated by subtracting the far-end turn around time from the round-trip elapsed time. Any combination of fixed or mobile radios of known positions c an be used as the reference radios for another mobile radio in the system, thereby providing adaptability under varying transmission conditions. The individual radios do not need to be synchronized to a common time reference, thereby eliminating the need for highly accurate system clocks.