Abstract
The recent digital transmission systems impose the application of channel equalizers with short training time and high tracking rate. Equalization techniques compensate for the time dispersion introduced by communication channels and combat the resulting inter-symbol interference (ISI) effect. Given a channel of unknown impulse response, the purpose of an adaptive equalizer is to operate on the channel output such that the cascade connection of the channel and the equalizer provides an approximation to an ideal transmission medium. Typically, adaptive equalizers used in digital communications require an initial training period, during which a known data sequence is transmitted. A replica of this sequence is made available at the receiver in proper synchronism with the transmitter, thereby making it possible for adjustments to be made to the equalizer coefficients in accordance with the adaptive filtering algorithm employed in the equalizer design. In this paper, an overview of the current state of the art in adaptive equalization techniques has been presented.
Highlights
One of the most important advantages of the digital transmission systems for voice, data and video communications is their higher reliability in noise environment in comparison with that of their analog counterparts
For a reliable digital transmission system it is crucial to reduce the effects of intersymbol interference (ISI) and it is where the equalizers come on the scene
Given a channel of unknown impulse response, the purpose of an adaptive equalizer is to operate on the channel output such that the cascade connection of the channel and the equalizer provides an approximation to an ideal transmission medium
Summary
One of the most important advantages of the digital transmission systems for voice, data and video communications is their higher reliability in noise environment in comparison with that of their analog counterparts. Most often the digital transmission of information is accompanied with a phenomenon known as intersymbol interference (ISI) [1]. This means that the transmitted pulses are smeared out so that pulses that correspond to different symbols are not separable. There are non stationary channels like wireless communications These channels’ transfer functions vary with time, so that it is not possible to use an optimum filter for these types of channels. The static equalizer is cheap in implementation but its noise performance is not very good [3]-[20] As it is told before, most of the time, the channels and, the transmission system’s transfer functions are not known.
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