Abstract: An incoming bit stream is digitally processed to obtain both in-phase and quadrature-phase 7-level correlative signals. The two 7-level correlative signals are separately band limited to a passband having a bandwidth that is about 1/8th of the bit rate of the original bit stream, and these band limited signals are then separately analog modulated, respectively, using in-phase and quadrature-phase components derived from a line carrier oscillator. The modulation products are then combined in a summing circuit to derive a signal-sideband 7-level correlative signal.

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.

Abstract: In PCM transmission, it is well known to transmit 24 voice-grade channels at a bit rate of 1.544 Megabits per second (Mb/s). The number of channels which may be transmitted in about the same bandwidth is doubled by the use of correlative level coding, such as the modified duobinary technique. Because of the degradation experienced by the modified duobinary signal in passing over cable pairs, periodic regeneration of the signals is required for effective transmission. The present invention is directed to a regenerative repeater which equalizes, amplifies, reshapes, and retimes the received modified duobinary signal so as to provide a regenerated signal which is nearly identical with that originally transmitted.

Abstract: A binary signal is first digitally transformed to obtain both an altered binary signal and its complement. The altered and altered complementary signals are next each delayed by two bit intervals of the original waveform to obtain both delayed altered and delayed altered complementary signals in binary form. Then, the altered and delayed altered complementary signals are gated to obtain the first gated binary output signal wherein a second level output signal is obtained whenever the two input signals are both first level signals and the first gated signal is a first level signal for all other input combinations. The altered complementary and delayed altered signals are similarly gated to obtain a second gated output signal in binary form. Finally, the first and second gated output signals are compared to obtain a three-level digital modified duobinary signal.