Channel equalization

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Introduction
In a communication system, the information is transmitted over a RF channel

The RF channel distorts the transmitted signal
Amplitude, frequency, phase are changed

A receiver should compensate the distortions to recover the transmitted signal
Channel equalization is the compensation process of the distortions in a RF transmission
In order to counter intersymbol interference effect, the observed signal is passed through equalizer whose characteristics are the inverse of the channel characteristics. If the equalizer is exactly matched to the channel, the combination of the channel and equalizer is just a gain so that there is no intersymbol interference present at the output of the equalizer

Channel Equalizer

An equalizer performs these important functions:
Filtering: Finding information about the data of interest at time t using data extracted upto time t
Prediction: finding information about future quantity of interest by using the data measured upto the present time.

Linear and Non linear Filters

A filter is said to be linear if the filtered and predicted quantity at the output is a linear function of the quantity applied at the input of the filter otherwise it is a non linear filter.