Patent ID: 8199047

Claim:
A method for estimating a distance between an originator and a transponder, the method comprising: transmitting a first message from a first channel in said originator; receiving a second message on a second channel in said originator; calculating a coarse time measurement of the round-trip propagation time between said originator and said transponder, calculating a fine time adjustment in said originator comprising: calculating a plurality of peak error measurements of a correlator output in said second channel of said originator during a time period; calculating a rate of change of said plurality of peak error measurements during said time period; and estimating a peak error at a point after said time period by using said rate of change of said plurality of peak error measurements during said time period; calculating a round-trip propagation time using said coarse time measurement and said fine time adjustment; and calculating an estimated distance between said originator and said transponder using said round-trip propagation time.