US Patent 9261576 Navigation using range measurements to OFDM transmitters

A signal receiver receives a time-domain signal that includes a plurality of pilot tones at a plurality of corresponding frequencies. The time-domain signal is transmitted from a transmit location. The signal receiver extracts from the received time-domain signal pilot phase values corresponding to the pilot tones. The signal receiver computes a signal propagation time of the received time-domain signal by fitting an interpolation function to residual pilot phase values, corresponding to the extracted pilot phase values, and determines a slope of the interpolation function. The signal receiver computes a range between the transmit location and the signal receiver by multiplying the computed signal propagation time with the speed of light.