Patent ID: 8432536

Claim:
A system for determining velocity between first and second platforms, the first platform comprising: a receiver for receiving a signal from the second platform, the receiver including: multiple phase modulators (PMs), in which the PMs have phase angles different from each other, and each PM forms a signal having a time varying frequency, multiple mixers producing multiple fringe signals based on the time varying signals of the PMs and the received signal from the second platform, and a processor for counting the fringes in at least one of the fringe signals, wherein the fringes of the at least one fringe signal are counted when the frequency of the at least one fringe signal is below a predetermined frequency threshold; and the processor determines the velocity between the first and second platform based on a number of fringes counted in a time period; further comprising local oscillators input to the mixers, wherein the PMs modulate the local oscillators producing the time varying signals, and the time varying signals are mixed with the signal received from the second platform producing the fringe signals.