Phase-based ranging using dispersed channels

A method for determining a distance between a first radio transceiver device and a second radio transceiver device, the method comprising:

• sequentially transmitting, from the first radio transceiver device to the second radio transceiver device, radio frequency signals on a plurality of radio channels, each channel being non-uniformly spaced and representing a distinct continuous tone,
• sequentially transmitting, from the second radio transceiver device to the first radio transceiver device, radio frequency signals with distinct continuous tones on same channels as those received from the first radio transceiver device, as well as measured phase difference of the radio frequency signals on each radio channel received from the first radio transceiver device,
• on the first radio transceiver device,
• creating a first set of estimate candidates,
• repeatedly for the plurality radio channels, determining an optimal phase unwrapping vector candidate based on the first set of estimate candidates and the measured phase differences of signals received on the first and the second transceiver devices to determine a second set of candidates, and
• calculating the distance between the first radio transceiver device and the second radio transceiver device using the optimal phase unwrapping vector candidate and the second set of candidates.