The Channel and Error Control

Abstract

Our information bits are transported from sender to receiver over a medium which we call a channel. The bits, or groupings of bits, are represented by waveforms and then either put directly onto a medium, as is the case with many local area networks, or sent through a modem (modulator/ demodulator) which generates and resolves waveforms designed for use on a specific channel. A communications engineer characterizes the behavior, not of bits through the channel, but of waveforms and signal processing algorithms that are used to decide which particular symbol is being sent. The need for this arises, of course, because of noise on the channel. Here we are concerned only with the bit stream as it is presented to us after the modem, after all the decisions regarding received waveform processing have been made.