Digital Transmission in the Presence of Impulsive Noise

The limiting noise with regard to transmitting digital data is impulsive in nature. Consisting of bursts of high amplitude, it occurs at random considerably more often than is predicted by the rms value of the Gaussian background noise. In this paper, an analysis is made of digital transmission, by various modulation procedures, in such a noise environment. * Taken from the dissertation submitted to the Faculty of the Polytechnic Institute of Brooklyn in partial fulfillment of the requirements for the degree of Doctor of Philosophy, 1964. 1699 1700 T H E BELL SYSTEM T E C H N I C A L J O U R N A L , OCTOBER 1965 The block diagram of a generalized data transmission system including a telephone channel is shown in Fig. 1. The data signal consists of a train of either ideal impulses or square pulses, each pulse having either positive or negative polarity depending 011 whether it represents a mark or a space. The transmitter consists of a low-pass filter, which band limits the data signal, followed by a modulator and a band-pass filter. The low-pass filter is required to prevent "foldover" distortion in modulation. The band-pass filter restricts the transmitted signal to the range of frequencies passed by the channel. It avoids the waste of transmitted power in signal components which will not be received and also includes the channel splitting filters which prevent crosstalk into frequencies reserved for other channels. The low-pass and band-pass filters also shape the signal, giving it the form desired for transmission.