Communication between a remote locator and a
transponder is used to determine the relative position of the
transponder. The
transponder and locator each include a
transmitter and a
receiver. The locator transmits an inquiry in the form of a relatively powerful cyclically encoded
signal with repetitive elements, uniquely associated with a target transponder. Periodically, each transponder correlates its coded ID against a possible inquiry
signal, determining frequency, phase and framing in the process. Upon a match, the transponder transmits a synthesized response coherent with the received
signal. The locator integrates multiple cyclical response elements, allowing low-power transmissions from the transponder. The locator correlates the integrated response, determines round-trip Doppler shift, time-of-flight, and then computes the distance and angle to the transponder. The transponder can be wearable, bionically implanted, or attached to, or embedded in, some object.