Compression, Filtering, and Signal-to-Noise Ratio in a Pulse-Modulated System

A proposed long distance waveguide system 1 will transmit a large number of wideband PCM channels via a single waveguide by means of a frequency multiplexing arrangement. In previous papers 2,8 an idealized frequency multiplex system was analyzed. These papers considered a system in which each channel signal, consisting of on-off carrier pulses, arrives at a detector together with three unwanted signals: (a) time crosstalk, due to leading and trailing edges of neighboring pulses; (b) frequency crosstalk, which is the interference from neighboring channels; and (c) thermal noise* generated essentially in the first amplifier of the receiver. Since these unwanted signals cause errors in the reading of the pulses, the filtering characteristics are closely related to the probability of errors. It has been shown that for any given probability of error it is possible to design the filters in such a way that a very desirable result is achieved--namely, the simultaneous minimization of time spacing between successive pulses, of frequency separation between neighboring channels, and of signal-to-noise ratio. * T h r o u g h o u t t h e p a p e r , when we t a l k about " n o i s e " we mean t h e r m a l noise. 1421