Noise problems in pulse communication

Formulae for random noise in the audio-frequency output in pulse-communication receivers are given for pulse-length-, pulse-phase- and pulse-frequency-modulation systems in which the received pulses are sliced; they are also given for pulse-amplitude modulation. Noise resulting from random distribution of the i.f. phase at the onset of pulses is also considered. Optimum slicing level giving minimum output noise is evaluated. Signal/noise ratio and threshold formulae are obtained from these data for the pulse-modulation systems and are compared with those for conventional amplitude- and frequency-modulation systems having the same mean or peak power. Final conclusions as to the merits of all the above systems are drawn from graphs of output signal/noise ratio, in which the performance below threshold is also taken into account.