A receiver structure is described, for use in pulseamplitude modulation (PAM) data communication systems, which combines null-zone detection and maximum likelihood (ML) processing to improve upon the performance of a conventional decision-feedback equalizer (DFE) while retaining a manageable level of complexity. If the output of the equalizer does not fall in the null zone, the receiver operates a...

We report on the performance of band-limited staggered quadrature amplitude modulation (SQAM) in the presence of phase jitter and additive Gaussion noise. It is demonstrated that offsetting, or staggering, the in-phase and quadrature data streams by a fraction of a symbol interval improves the phase-jitter immunity of a conventional QAM data transmission system. For example, with a raised cosine p...

In this concise paper we have developed a new carrier recovery system for vestigial sideband amplitude modulation (VSB-AM) data sets. Neither dc restoration nor extra bandwidth is required for the proposed system. A pilot tone is transmitted at the carrier frequency and the phase jitter is derived from the quadrature chnnnel. "Artificial" phase jitter which is introduced by the data signal can be eliminated by properly shaping the transmitted signal. We have also shown that even in the presence of channel distortion and white Gaussian noise, the proposed system can faithfully track up to 60-Hz phase jitter.

A new approach to the automatic equalization of differentially phase-modulated data signals passing through a linear distorting medium is presented. The equalizer, which is of the transversal filter type, operates in the frequency passband and contains two sets of taps — in-phase and quadrature. A tap-rotation property of the equalizer is used to establish an absolute phase reference at the equalizer output, and once this crucial step is taken, the passband equalizer output can be used to automatically (as well as adaptively) adjust the tap weights so as to minimize a mean-square distortion function. The resulting algorithm requires correlating an error signal with the tap voltages, and thus it is possible to use a structure similar to that employed when equalizing baseband PAM. The generality of the approach makes it applicable to the equalization of any double-sideband data signal.