US Patent 8000926 Method and system for positional measurement using ultrasonic sensing

A method for determining position and alignment is provided. The method includes monitoring a first and second sequence of ultrasonic signals transmitted from the first device to a second device, estimating a location of the first device from Time of Flight measurements of the ultrasonic signals at respective microphones on the second device, calculating a set of phase differences, weighting a difference of an expected location and estimated location of the first device with the set of phase differences to produce a relative displacement, and reporting a position of the first device based on the relative displacement.