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Adaptive Wireless Tranceivers P2

Introduction To Equalizers In most digital data transmission systems the dispersive linear channel encountered exhibits amplitude and phase distortion. As a result, the received signal is contaminatedby Intersymbo1 Interference (ISI). In a system, which transmits a sequenceof pulse-shaped information symbols, the time domain full response signalling pulses are smeared hostile dispersive by the channel, resulting in intersymbol interference. At the receiver, the linearly distorted signal has to be equalized in order torecover the information. The equalizers that are utilized to compensate for the IS1 can be classified according to their structure, the optimising criterion and the algorithms used to adapt the. | Adaptive Wireless Tranceivers L. Hanzo C.H. Wong M.S. Yee Copyright 2002 John Wiley Sons Ltd ISBNs 0-470-84689-5 Hardback 0-470-84776-X Electronic Chapter Introduction To Equalizers In most digital data transmission systems the dispersive linear channel encountered exhibits amplitude and phase distortion. As a result the received signal is contaminated by Intersymbol Interference ISI . In a system which transmits a sequence of pulse-shaped information symbols the time domain full response signalling pulses are smeared by the hostile dispersive channel resulting in intersymbol interference. At the receiver the linearly distorted signal has to be equalized in order to recover the information. The equalizers that are utilized to compensate for the ISI can be classified according to their structure the optimising criterion and the algorithms used to adapt the equalizer coefficients which are summarized in Figure 2.1. On the basis of their structures the equalizers can be classified as linear or decision feedback equalizers. Each of these structures will be discussed at a later stage with more emphasis on the Decision Feedback Equalizer DFE . Equalizers can also be distinguished on the basis of the criterion used to optimise their coefficients. The optimization is governed by the performance criteria used. For example when applying the mean square error criterion MSE the equalizer is optimised such that the mean squared error between the distorted signal and the actual transmitted signal is minimized. Various optimization criteria will be discussed in the following sections with more emphasis on the MSE criterion. A range of adaptive algorithms can be invoked in order to provide the equalizer the means of adapting its coefficients to the time-varying dispersive channels. We will not elaborate on the fine details of these algorithms until the next chapter where attention will be given to the well known Least Squares LS algorithms in particular to the Recursive Kalman .