OVERVIEW

A primary function of electronic communication systems, including radar, is the transmission and reception of signals that contain the desired message. A message has broad meaning and is not restricted to electronic signals, although obviously this must be converted to such signals to be processed electronically. Examples of messages are spoken and written words, the liquid flow rate in a pipe, temperature changes in an industrial process, the pulse rate of an astronaut in space, and traffic flow on a highway.

A message that is completely predictable contains no additional information, for then one need only send a code number to identify the function and thereby disclose all its details. Thus a sine wave contains no further information once its amplitude, phase, and frequency are known, for it is now completely predictable over the infinite time interval.

This situation does not occur in practice, however, because associated with each desired message is some unwanted message, and this disturbance is designated "noise." An example of electrical noise is the familiar thermal noise. Furthermore, noise in one transmission channel may be the desired message in another channel, and vice versa. For example, a radio receiver tuned to station A may also receive audible music transmitted by station B. The music, in this case, is considered noise, whereas it is the desired message when the receiver is tuned to station B.

The basic signal processing problem is to determine the necessary operations on the received signal (message plus noise) to extract specific...