US 4,053,713 AGranted

Multi-channel multiplex data transmission system

AssigneeOki Electric Industry Co., Ltd.

InventorKazuhiko Nitadori

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Abstract

The sum and difference signals of a pair of data channels are applied to a pair of roll-off filters, respectively. The outputs of said roll-off filters are modulated by a pair of carrier signals which have the phase difference (.pi./2) to each other. The modulated signals are added to each other in an adder and a single output signal is provided from the output of said adder. Said output signal and another output signal relating to another pair of data channels, and some pilot signals are applied to an adder, the output of which is transmitted to a receiving station in the form of a multi-channel multiplex data signal. At the receiving station, the received signal is demodulated with the inverse process of the above modulation steps and the demodulated data signals are applied to an automatic equalizer. The present invention described above provides high speed data transmission through a narrow-band-line which has only almost the Nyquist band width.

Claims10

Dependent claims

A mutli channel multiplex orthogonal VSB transmission system comprising a modulator, a demodulator and a transmission means arranged between the modulator and the demodulator;

said modulator comprising at least a two-channel modulator, means for generating a plurality of carrier waves at the frequency interval f.sub.c where f.sub.c is the pulse repetition frequency in each channels;
and wherein said two-channel modulator comprises;
means connected to each input channel for obtaining the sum and the difference of PAM signals of each pair of input channels, a pair of roll-off filters connected to the output of said means for the sum and the difference respectively, said roll-off filters having the equal amplitude roll-off characteristic less than 50%, a predetermined equal fixed delay and the phase characteristics of 45% and -45.degree. respectively in the amplitude roll-off region, a variable phase shifter for shifting the phase of said carrier waves, a fixed phase shifter for delaying the phase of the output of said variable phase shifter by 90.degree., a first multiplying means inputs of which being connected to the output of one of said roll-off filters and the output of said fixed phase shifter, a second multiplying means inputs of which being connected to the output of the other roll-off filter and the output of said variable phase shifter, and means for adding the outputs of said first and second multiplying means and providing the output of the two-channel modulator.

Dependencies are inferred from the claim text.