The most important feature of the equalizer is it removes Intersymbol Interference. Equalizers essentially ensure that the probability of BER is reduced by using different techniques e.g. MMSE, GMM..etc. to get a good approximation to the originally transmitted data. There is a lot of info around Equalizer, Equalizers and Channel estimation + Equalization ..BEsides which some good books are there by sklar, proakis and mk simon...are to name a few popular ones.