On Signal-to-Noise Ratios in Communication Systems

Viterbi (1964) has given ratios (SNRs) after demodulation in digital lower bounds on maximum signal-to-noise communication systems. He computes the SNRs according to Yates-Fish and Fitch, and Mayer (his references [7] and [8]), namely, the signal energy as the variance of the signal in the absence of channel noise; the noise energy as the variance of the difference between the signal actually demodulated (perturbed by noise) and the desired output (as received in the absence of noise). This communication is intended to give another possible definition of SNR, which has been previously used by Battail (1962 & 1964) and looks more realistic from a certain point of view. Pointing out and discussing the discrepancy of both definitions involves, in fact, basic problems, which are of interest for digital, and even analog, communication systems.