Patent ID: 8614695

Claim:
A method comprising: selecting a plurality of pairs of digital ultrasonic signals to form two or more pairs of digital ultrasonic signals; estimating time difference of arrival(TDOA) for each of the two or more pairs of digital ultrasonic signals; determining an intersection of each pair of the TDOA estimated digital ultrasonic signals to form one or more intersections; determining a location of an ultrasonic signal generator corresponding to at least one of the one or more intersections at least in part based on a crosspower-spectrum of the two or more pairs of digital ultrasonic signals; and generating first and second pseudo random codes at a first generator and a second generator, respectively, and combining the first and second pseudo random codes based on a clock signal to generate pseudo random output codes, wherein the pseudo random output codes are to have correlation properties that are used in modulating the pseudo random output codes with ultrasonic signals generated by the ultrasonic signal generator.