Analysis of a Phase-Modulation Communications System

A communication system is analyzed which utilizes phase modulation (PM) and phase detection. The analysis shows that when the total radio frequency (RF) power level is significantly above the receiver threshold, a margin of safety exists which may be traded for additional signal-to-noise ratio (SNR) at the demodulated output of the receiver. In this respect the PM system is similar to FM communication systems which utilize an "FM improvement factor." Several examples are presented to indicate the magnitude of the PM improvement factor when the signal is a sine wave variable throughout the audio band. A novel type of closed-loop phase detector is suggested which is linear over a very wide range of phase angles.