An experimental investigation of asynchronous demodulation of a phase-reversal modulated carrier

Abstract

The report considers an asynchronous (non-coherent) method of demodulating a carrier that is phase-reversal modulated by a two-level waveform. The comparatively simple demodulation technique treated relies on the conversion of a phase-modulated (PM) signal to an amplitude-modulated (AM) signal by appropriate filtering of the frequency components of the received phase-reversal modulated carrier. The resulting AM signal is then detected with a conventional envelope detector and the digital data is recovered with appropriate threshold and logic circuits. The experimental asynchronous demodulation system requires approximately 12 db greater signal-to-noise power ratio for the same probability of error relative to the optimum performance of the coherent demodulation system. Thus with a signal-to-noise ratio of 18 db or greater, the asynchronous demodulation system has a measured probability of error of 0.001 or less; a signal-to-noise ratio of 23 db provides a measured probability of error of about 0.0001. Apart from simplicity, the asynchronous demodulation system has the advantage of not requiring prior knowledge of the transmitted signal's precise characteristics as is required in some coherent demodulation systems. (Author)