The role and scope of digital signal processing in communications systems

Trends in relative costs encourage sophisticated signal processing in order to make fuller use of the capacity of communications channels. This implies features of subtlety, adaptation, transformation and manipulation which are most expediently handled digitally. The variety, diversity and pervasive nature of these techniques in modern communications nets is illustrated, and their impact on overall system design is discussed. Three specific techniques are included for illustrative purposes: (1) The `design¿ of multi-valued discrete signals in the phase/amplitude plane. (2) The adaptation of Fourier analysis to equally-spaced narrow frequency `lines¿. (3) The compensation of tape recorders for both steady and transient differences in tape-speed between recording and replay.