  In the transmission of digital data at a relatively high rate over a
particular band limited channel, it is normally necessary to employ an
equalizer at the receiver in order to correct the signal distortion introduced
by the channel .ISI (inter symbol interference) leads to large error
probability if it is not suppressed .The possible solutions for coping with ISI
such as equalization technique. Maximum Likelihood Sequence Estimation (MLSE)
implemented with Viterbi algorithm is the optimal equalizer for this ISI
problem sense it minimizes the sequence of error rate. This estimator involves
a very considerable amount of equipment complexity especially when detecting a
multilevel digital signal having large alphabet, and/or operating under a
channel with long impulse response, this arises a need to develop detection
algorithms with reduced complexity without losing the performance. The aim of
this work is to study the various ways to remove the ISI, concentrating on the
decision-based algorithms (DFE, MLSE, and near MLSE), analyzing the difference
between them from both performance and complexity point of view. An Improved
non linear equalizer with Perturbation algorithm has been suggested which
trying to enhance the performance and reduce the computational complexity by
comparing it with the other existing detection algorithms.
