Principles of noise reduction in communication channels

THE development of communication theory has led to the introduction of concepts such as integration, correlation, matched filtering, comb filtering, probability of detection, etc. Much confusion centers about the significance of these concepts because of functional equivalence and because of inadequately defined purposes in using them. Thus, it may be overlooked that integration and correlation are equivalent operations, or that matched filtering and comb filtering are techniques of integration. The purpose in using these concepts can be understood properly only within frameworks of suitable criteria of performance. For example, it is frequently assumed that the end object of a filtering technique is to improve the signal-to-noise ratio. Actually, improvement in signal-to-noise ratio is not an end in itself, but a means to an end. This end is to increase the information rate over a communication channel by reducing the probability of error.