Assessment of effects of delay distortion in data systems

An essential objective of a pulse transmission system is the preservation of some aspect of the pulse shape at the receiver. The phase characteristics of a system, which can generally be neglected in voice transmission, become important in pulse systems, since the shape of a pulse is influenced greatly by the phase of the energy components of the pulse spectrum. A quantity frequently used in describing this influence is the ¿group delay¿ or ¿envelope delay.¿ It is a measure of the relative phase shift experienced by neighboring components of the frequency spectrum and is equal to the slope of the tangent to the phase curve at any given frequency. If the phase shift changes linearly with frequency, the envelope delay is constant across the band, and there is no delay distortion. When the envelope delay varies with frequency, however, the shape of a pulse is degraded or distorted in transmission. This variational component of envelope delay will be called the delay distortion.