Method for two-track digital signal transmission in an unbalanced band-limited channel by means of quadrature amplitude modulation

摘要

To economise on bandwidth, only one sideband and a residual part of the other sideband of a double-sideband signal generated with a digital input pulse sequence in a conventional manner through multi-stage QAM are transmitted following additional transmission filtering. The normal and quadrature components of a demodulated single pulse are thereby present at the receiving end following conventional coherent demodulation with two orthogonal carrier oscillations in each case on one of the two outputs of the demodulator, and are thus no longer accessible for conventional decoding. However, by means of reception filtering combined with the transmission filtering, the normal component for the symbol sequence frequency and the quadrature component for the half symbol sequence frequency fulfil the 1st Nyquist criterion. Under this condition, the digital input pulse sequence can be decoded from the two demodulated sequences of residual sideband QAM signal components with the aid of detectors which operate according to Maximum Likelihood Sequence Estimation (MLSE) methods. If two binary signals are used to activate the QAM modulator and if the received pulse is furthermore formed in such a way that the quadrature component of a demodulated single pulse fulfils the 1st Nyquist criterion for the half symbol rate in such a way that it ... only one symbol period immediately before and after the ... Original abstract incomplete. IMAGE