Information Channel Capacity

A communication channel consists of a transmitter, a receiver, and some medium between these two (possibly vacuum) that supports transmission of signals. In most cases, the transmitter and/or receiver have limited bandwidth, while the medium could transmit pulses of arbitrarily small time width. Hence, “channel capacity” is more a property of the transmitter and receiver, than of the signal-transmission medium. In simple pulse telegraphy, the presence of a pulse corresponds to a 1 and its absence to a 0. The number of levels is n = 2, in which case eq. (2) has the same form as eq. (1). If it is desired to transmit a digitized analog signal with n analog levels via simple pulse telegraphy, the bandwidth of the analog signal is limited to B/n, since a block of n two-level pulses is used to represent each n-level analog sample. Equivalently, if the analog sampling is performed to m-bit accuracy, then the analog bandwidth is limited to B/2.