Data Transmission by Combined AM and PM

Abstract

This paper presents theoretical analysis and experimental verification of the performance of a digital data modem which uses combined amplitude and phase modulation (AM–PM). The theoretical model assumes operation over the bandlimited additive Gaussian channel. The receiver used in the experiment, and for which theoretical results are presented, uses an envelope detector in parallel with a phase detector to recover the data. The criteria of error rate and communication efficiency (measured in bits per cycle of bandwidth) as functions of average signal-to-noise ratio (S/N) are used to make comparisons with other modulation schemes. The theory predicts a performance from 1 to 4 dB poorer than what can be realized from single sideband (SSB) modulation. We present experimental results which indicate excellent agreement with the theory.