A FAST-INITIAL2ING DIGITAL EQUALIZER WITH ON-LINE TRACKING FOR DATA COMMUNICATIONS

摘要

A theory is developed for a digital equalizer for use in reducing intersymbol interference (ISI) on high¬-speed data communications channels. The equalizer is initialized with a single isolated transmitter pulse, provided the signal-to-noise ratio (SNR) is not unusually low, then switches to a decision-directed, on-line mode of operation that allows tracking of channel variations. Conditions for optimal tap-gain settings are obtained first for a transversal equalizer structure by using a mean-squared error (MSE) criterion, a first-order gradient algorithm to determine the adjustable equalizer tap-gains, and a sequence of isolated initializing pulses. Since the rate of tap-gain convergence depends on the eigenvalues of a channel-output correlation matrix A convergence can be improved by making a linear transformation on A to obtain a new correlation matrix A. The corresponding change in equalizer structure results in a set of parallel trans¬versal filter-sections, the weighted outputs of which are summed to produce the equalizer output. It is shown that by properly selecting the tap-gains of each transversal filter-section, the equalizer can be adjusted to minimize the MSE on the first iteration of the algorithm.