The optimum detector for passive detection is energy detector. Yet energy detector usually deteriorates due to fluctuation of background interference and a decrease in SNR.

Finally, a successive interference cancellation (SIC) scheme is proposed combined with minimum mean square error (MMSE) detection. Its performance is superior to simple SIC or MMSE detector.

The real time phase detector is constructed with a simple circuits. The amplitude and frequency of the vibrations are measured by synchronously detecting the phases in interference signal.