US Patent 7595755 Distance estimation

A method for estimating the distance between a transmitter and a receiver, the transmitter being arranged to transmit a signal as a series of bursts, and the carrier frequency of each burst being set according to a predetermined sequence, the method comprising: forming a first series comprising the measured differences between the phases of successive bursts as received at the receiver; forming a second series comprising estimated differences between the phases of successive bursts as received at a supposed time difference between the transmitter and the receiver; and determining the quality of fit between the first series and the second series.