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signal processing from power amplifier operation control point of view

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CHAPTER 3<br />

ZERO-FORCING DECISION FEEDBACK<br />

EQUALIZATION<br />

Decision feedback equalization (DFE) uses past symbol decisions (detected values)<br />

to remove ISI from previous symbols. In this chapter we will consider a zero-forcing<br />

strategy, in which ISI from future symbols is avoided. Assuming the detected<br />

values are correct, ISI from past symbols is also avoided. Thus, ISI is forced to<br />

zero. This is not necessarily the best strategy, but it is a useful starting point<br />

for understanding more sophisticated strategies. In Chapter 5, we will examine<br />

other strategies, including Minimum Mean-Square Estimation (MMSE) DFE and<br />

Maximum Likelihood (ML) DFE.<br />

3.1 THE IDEA<br />

Let's assume we have a detected or known value for s () . Next we want to determine<br />

si using ri, which can be modeled as<br />

ri =-10si+9so + ni. (3.1)<br />

Since we have an idea of what SQ is, we can subtract its influence on rj, giving<br />

0i = ri - 9So, (3-2)<br />

which, assuming So = so, can be modeled as<br />

i/i = —lOsi + rii- (3.3)<br />

Channel Equalization for Wireless Communications: From Concepts to Detailed 57<br />

Mathematics, First Edition. Gregory E. Bottomley.<br />

© 2011 Institute of Electrical and Electronics Engineers, Inc. Published 2011 by John Wiley & Sons, Inc.

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