ABSTRACT
The channel is the communications medium in between the start ing point, the transmitter, and the finishing point, the receiver. The channel, shown in Fig. 5.1, may be free space, as in radio transmis sion or a more tangible medium such as copper or optical cable. Exactly what the channel is made of is not particularly relevant to communications theory; the fundamental mathematics and prob lems remain the same. Every communications channel is subject to unwanted noise.
