Coding for Error Protection and Security
Rodney F. W. Coates · 1982
In chapter 6, we studied the methods used to generate binary codewords from an analogue signal. A measure of system performance that is of great importance in such a context is the signal-to-quantising noise ratio. This quantity is a function only of the number of quantising levels used in the modulation system, not of the channel noise level. The channel noise is of concern to us in so far as it may cause errors in interpretation of the received binary digits. However, in most PCM systems, the error rate can be reduced to a low level by using repeater amplifiers in the transmission path at sufficiently frequent intervals that regeneration of a sharp-edged, noise-free version of the original signal is possible. The correspondingly rare noise components that occur in the decoded signal are unobjectionable.