Bounds of Communication

In comparing the performance of communication systems t h a t transmit information by means of signals of limited bandwidth, six quantities descriptive of the system and its environment are of particular importance: (i) t h e rate at which the system transmits information; (ii) the bandwidth occupied by the transmission signals; (Hi) a measure of the power of these signals; (iv) a measure of the ambient noise which perturbs the transmitted signals; (v) the delay time (caused by the transmitter and receiver) between the introduction of information at the input of the system and the emergence of useful information at the o u t p u t of the system; (vi) a measure of the fidelity with which the information at the o u t p u t of the system represents the information presented to the input of the system. To compare the performance of two communication systems in a meaningful manner, it is usually necessary to consider the values of at least these six quantities for the two systems. In general, such a comparison will not yield a simple ordering of the two systems. Two systems may utilize the same bandwidth, introduce the same delay, and operate 681