COMPARISON OF DIGITAL MODULATION METHODS

Abstract

Important characteristics of a digital modulation technique are economy, efficiency, and quantizing distortion. As in most engineering situations, the choice of a specific digital modulation method for a practical application represents a compromise among cost and performance objectives. The purpose of this paper is to identify important design variables of digital modulators and to discuss the manner in which they influence cost and performance. In particular, we derive formulas that show the variation of quantizing noise with sampling rate and quantizer resolution in basic PCM and DPCM modulators. These formulas imply a conflict between economy and efficiency and we describe three current approaches to the resolution of this conflict. The first is efficiency oriented, the second economy oriented, and the third relies on digital signal processing to convert between efficient and economical modulation formats.