الفهرس 
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Abstract
A linear equalizer is essentially an adaptive filter and its performance is crucial to the goal of maximizing the transmission rate throught the communication channels. Intersymbol interference ISI distortion is caused by time-dispersive channels, where the symbols transmitted before and after a given symbol corrupt the detection of that symbol. Adabtive equalizer is a key part of the receiver and is used to remove the ISI caused by the communication channel. Adaptive algorithms are used to adjust the coefficients of the equalizer such that the error signal is minimized according to some criteria. Blind adaptive equalizers can achieve adaption of their tap coeifficients without the use of a training sequence. Several blind equalization algorithms exist including, the constant modulus algorithm CMA, the multimodulus algorithms that combine existing cost functions to obtain enhance performance. DD methods helps decreasing the convergence time of blind adaptive algorithm. The step size parameters plays an important role in determining the performance characteristics of the adaptive algorithm in terms of the convergence rate and the amount of steady-state MSE. in general, a smaller step size results in a smaller state-state MSE but also a slower rate of convergence. On the other hand, a larger step size results in a faster rate in convergence but a large seady-state MSE. to eliminate the trade-off between the convergence rate and the steady-state MSF, one would use a variable step size VSS technique. the dicison feedback equalizer DFE is a nonlinear equalizer which is useful for channels with servere amplitude distortion.