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View File - University of Engineering and Technology, Taxila

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which can be written as89>=R xy ðtÞ ¼E xðtÞ½hðtÞxðt þ tÞŠ>: |fflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflffl} >;yðt þ tÞð3:40bÞNote that ‘’ denotes convolution. So the expectance can still be exp<strong>and</strong>ed asEfxðtÞ½hðtÞxðt þ tÞŠg ¼ hðtÞR x ðtÞ ¼hðtÞEfxðtÞxðt þ tÞgð3:41Þwhere R x is the autocorrelation <strong>of</strong> x. Using these results, the conditionsexpressed by (3.39) can be expressed as the autocorrelation function <strong>of</strong> theequalizer output in terms <strong>of</strong> the desired data autocorrelation function sinceonly the channel output z c ðtÞ is fed into the equalizer:½R zdŠ¼ ½hŠ ½R zcŠ|{z}½hðmÞŠð3:42Þwhere½hŠ ¼The desired coefficient matrix, the same as defined by (3.32b).23R zcð0Þ R zcðDÞ ... R zcð2NDÞR zcð DÞ R zcð0Þ ... R zc½2ðN 1ÞDŠ½R zcŠ¼ . . ... . 6745R zcð 2NDÞ R zc½ð 2N þ 1ÞDŠ ... R zcð0Þ<strong>and</strong>23R zdð NDÞR zd½ ðN 1ÞDŠ½R zdŠ¼6. 74 . 5R zdðNDÞð3:43aÞð3:43bÞThe conditions for obtaining the optimum tap weights using the MMSEcriterion are identical to the conditions for the zero forcing weights except thatcorrelation-function samples are used instead <strong>of</strong> pulse-response samples.Two questions readily come to mind regarding setting the tap weights:1. What should be used for the desired response, z d ðtÞ?2. What procedure should we follow if the sample values are notavailable?Copyright © 2002 by Marcel Dekker, Inc. All Rights Reserved.

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