Equalization system with preshaping filter

In an equalizer, a method of eliminating the effects of precursor and postcursor interference from a train of incoming digital signals to be sampled at successive instants separated by a predetermined period T, comprising the steps of:

• (a) preshaping each incoming signal, having a peak value at instant t(0), with reduction of its amplitude to a value close to a zero at instant t(0)+T;
• (b) transmitting the preshaped signal to a first decision stage of said equalizer;
• (c) deriving from the output of said first decision stage a feed-forward pulse adapted to compensate for precursor interference with a succeeding signal;
• (d) delaying the purged signal from step (b) by a time sufficient to let the delayed signal coincide with the feed-forward pulse derived in step (c);
• (e) algebraically combining the feed-forward pulse from step (c) with the delayed signal from step (d) to produce a resulting signal;
• and
• (f) transmitting the resulting signal from step (e) to a second decision stage of said equalizer to produce a decided signal.

An equalizer for eliminating the effects of postcursor and precursor interference from a train of incoming digital signals, comprising:

• preshaping means connected to a transmission path carrying said incoming signals;
• first threshold means connected to said preshaping means for converting a given incoming signal, sampled at uniform intervals, into a first decided pulse having one of several predetermined signal levels;
• filter means connected to said first threshold means for deriving from said first decided pulse a feedback pulse adapted to correct postcursor interference and a feed-forward pulse adapted to compensate for precursor interference;
• first summing means inserted between said preshaping means and said first threshold means, said first summing means being connected to said filter means for algebraically combining said feedback pulse with a subsequent incoming signal;
• second summing means having an input connected to said filter means for receiving said feed-forward pulse therefrom;
• delay means connecting said preshaping means to another input of said second summing means for enabling an algebraic combination of said given signal with a concurrently arriving feed-forward pulse derived by said first threshold means and said filter means form said subsequent signal;
• and
• second threshold means connected to said second summing means for converting an output pulse of the latter into a second decided pulse;
• said preshaping means including circuitry for reducing the amplitude of each incoming signal from a peak at an instant t(0) to at least near-zero at an instant t(0)+Tm T being a sampling interval.

An equalization system for eliminating the effects of postcursor and precursor interference from a train of incoming signals in the form of digital pulses, comprising:

• a transmission path with a receiving end carrying said incoming signals, the latter having a recurrence period T;
• timing means connected to said receiving end for extracting said recurrence period T and establishing a succession of discrete intervals T related thereto;
• pulse-shaping means connected to said receiving end and controlled by said timing means for deriving from said incoming signals a compensating wave whose absolute amplitude at instants t.sub.0 +T substantially equals that of incoming signals, t.sub.0 being the instants at which said digital pulses reach their peak amplitudes, said pulse-shaping means including circuitry for subtractively combining said incoming signals with said compensating wave to produce a resulting pulse train with amplitudes close to zero at said instants t.sub.0 +T;
• an equalizer with a cascade of nonlinear decision stages and interleaved processing stages, for the correction of intersymbol interference, the first decision stage of said equalizer being connected to said pulse-shaping means for receiving said resulting pulse train therefrom;
• and
• cascaded delay means connected between said pulse-shaping means and said processing stages for supplying the latter with differently delayed samples of said pulse train taken at staggered periods corresponding to the operating times of the respective decision and processing stages.