On the Signal/Noise Ratio for a Channel with Additive Thermal Noise

A formalism for the understanding of additive thermal noise is presented which permits the construction of a quantum-mechanical picture of the additive interaction of signal and thermal noise. Under the assumption that the transmitter sends signals in such a way as to minimize the power losses related to the uncertainty principle, while the signals differ only in their mean values, probability distributions for various physical quantities in the presence of signals are presented. For a given mean signal power the best signal/noise ratio is found. In this connection irreversible changes, caused by the quantum system of measurement, are taken into account, and physical measurement is indicated which, with the use of “sinusoidal” signals, realizes the best signal/noise ratio.