Equalization Techniques. By: Mohamed Osman Ahmed Mahgoub. Introduction.
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By: Mohamed Osman Ahmed Mahgoub
Wireless communication is the most interesting field of communication these days, because it supports mobility (mobile users). However, many applications of wireless comm. now require high-speed communications (high-data-rates).
Inter-symbol-interference, takes place when a given transmitted symbol is distorted by other transmitted symbols.
Cause of ISI
ISI is imposed due to band-limiting effect of practical channel, or also due to the multi-path effects (delay spread).
the equalizer is a digital filter that provides an approximate inverse of channel frequency response.
Need of equalization:
is to mitigate the effects of ISI to decrease the probability of error that occurs without suppression of ISI, but this reduction of ISI effects has to be balanced with prevention of noise power enhancement.
which is a digital filter with N-taps that have a tunable complex coefficients, and N-1 delay elements.
which uses a sophisticated recursive structure that has some advantages such as, better stability, flexibility to change length of equalizer.
Linear Equalization techniques
which are simple to implement, but greatly enhance noise power because they work by inverting channel frequency response.
Non-Linear Equalization techniques
which are more complex to implement, but have much less noise enhancement than linear equalizers.
It cancels all ISI effect by inverting the channel frequency response, andaccordingly leads to large noise enhancement.
In which the signal recovery is done by prior knowledge concerning channel, or by array calibration information (no need for training sequence).