REVIEW ON CHANNEL EQUALIZATION
Communication systems comprise three fundamental elements: transmitter, channel and
receiver. When signals are transmitted through a communications system, they are obstructed
by some distortions which are mainly intersymbol interference (ISI) and noise. The
transmitted signal is distorted by ISI which is caused by multipath effect in band limited
(frequency selective) time dispersive channels and is the cause of bit errors on the receiver
side. ISI is considered the main factor negatively affecting fast transmission of data over
wireless channels. In order to eliminate or minimize these distortions, equalizers are
employed in these systems. Equalization is the method of compensating for, eliminating or
reducing the amplitude and phase distortion introduced by the transmission medium in
communications systems. In a general meaning, the term equalization refers to any signal
processing operation which minimizes ISI. An equalizing filter overcomes the ISI caused by
individual received symbols of a transmitted data stream, as well as the crosstalk that for
example occurs due to coupling of a transmitted pulse or that results from the capacitive
coupling of the transmitted pulse on an outgoing pair interfering with the received pulse on an
incoming pair. The task of equalizers is to provide efficient and error free communications by
ensuring that signals transmitted through the channel are recovered as original at the end of
the receiver that communications system has.
Distortions may be linear or nonlinear depending on the channel characteristics of channel.
When transmitting information through a physical channel, various mechanisms distort the
transmitted signal significantly, causing degradation or even failure in the communications.
These mechanisms can be classified as additive thermal noise, man-made noise and
atmospheric noise. In practice, many of the physical channels are characterized by various
channel models. The