Adaptive equalizer for ISDN U-interface transceiver

A communication system for receiving and sampling a stream of pulse code modulation (PCM) signals with previous signal distortions and post signal distortions including a data processing system for equalizing said PCM signals wherein said PCM signals r(n) being sampled at a baud period of T and being represented by:

• ##EQU8## Where n being a positive integer, Xj being a 2B1Q data and h(t.sub.o) being a channel response at time t.sub.o, said data processing system comprising:
• a feedforward filtering means being a linear equalizing means including an anti-causal finite impulse filter (FIR) and a causal FIR filter for receiving and for filtering said previous signal distortions and a portion of said post distortions in said PCM signals for generating an output signal containing a major component X.sub.n h(t.sub.0);
• said linear equalizing means includes M+L+1 stages for performing a filtering function of:
• ##EQU9## where M, L, are positive integers, f.sub.n is the output signal, Cj are the coefficients of said filtering means and the coefficient C.sub.0 is maintained at a constant value of one;
• a threshold detector for receiving said output signal containing a major component X.sub.n h(t.sub.0) generated by said feedforward filtering means for determining a threshold level for said PCM signals and generating corresponding equalized output signals;
• said threshold detector further including a threshold error generating means for generating a threshold error representing the difference between the input and the output signals of said threshold detector;
• an output means for receiving from said threshold detector and then outputting said corresponding equalized output signals;
• a feedback filtering means receiving and processing said equalized output signals from said output generating means for generating feedback signal;
• said feedforward filtering means further including a subtracting means for subtracting said feedback signal received from said feedback filtering means from said output signal containing a major component X.sub.n h(t.sub.0) generated by said feedforward filtering means to generate a post-feedback signal;
• a coefficient update means for receiving said threshold error from said threshold error generating means for generating coefficient update output signals;
• a gain controller for receiving said post-feedback signal from said subtracting means and said coefficient output signals from said coefficient update means for deleting said threshold error in performing a gain compensation on said post-feedback signal;
• and
• said feedforward filtering means further receives said feedback signal from said feedback filtering means to adaptively adjust said feedforward filtering means.

A data processing method for equalizing pulse code modulation (PCM) signals with previous signal distortions and post signal distortions said PCM signals wherein said PCM signals r(n) being sampled at a baud period of T and being represented by:

• ##EQU10## Where n being a positive integer, Xj being a 2B1Q data and h(t.sub.o) being a channel response at time t.sub.o, said method comprising the steps of:
• a) utilizing a feedforward filtering means for receiving said PCM signals and filtering said previous signal distortions and a portion of said post distortions for generating an output signal containing a major component X.sub.n h(t.sub.0) by performing a filtering function of:
• ##EQU11## where M, L, are positive integers, f.sub.n is the output signal, Cj are the coefficients of said filtering means and the coefficient C.sub.0 is maintained at a constant value of one;
• b) processing said output signal from said feedforward filtering means for generating an equalized signal;
• c) processing said equalized signal for generating a feedback signal and feeding back said feedback signal to said feedforward filtering means and
• d) utilizing said feedback signal to adaptively adjust said feedforward filtering means.