Modified duobinary repeatered span line

Abstract

An end-office repeater accepts a high-speed bipolar signal, converts the bipolar signal into a unipolar signal, scrambles the unipolar signal, and encodes the scrambled unipolar signal into a modified duobinary signal for transmission over a cable pair. Before cable loss would severely degrade the duobinary signal, line repeaters and/or inter-office repeaters are installed at predetermined intervals so as to equalize and regenerate the modified duobinary signal. By so doing, the signal is recovered with acceptable phase jitter, which permits recovery of the original high-speed bipolar signal at the distant end of a repeatered span line. The receiving-end office repeater equalizes and regenerates the modified duobinary signal, decodes the signal to obtain a unipolar signal, descrambles the unipolar signal, and converts the unipolar signal into a bipolar signal. Detection of errors in the modified duobinary signal may be obtained without adding redundant digits. However, errors which may occur during transmission may be lost by the decoding to a unipolar signal. Thus, errors detected from violations of the coding rule of the modified duobinary signal are inserted, by means of an error transfer network, into the bipolar signal and appear as violations of the bipolar code.