A Short Introduction to Adaptive Equalization

21 pp, April 1998.

Preface:

The present text is intended to give a short introduction to adaptive equalization, appearing in cellular digital communications. This text, complemented with relevant material from the textbook Adaptive Signal Processing by B. Widrow and S. Stearns, provides the background material for one of the mini projects in the course "Adaptive Signal Processing" taught to undergraduate students at the Signals and Systems group, Uppsala University.

In this presentation, we consider discrete-time channel models and equalizers, having finite impulse response (FIR structure). We begin with a short discussion of digital communications and the mobile telephony environment. We then discuss the equalization problem. Two different types of equalizers will be presented: the transversal linear equalizer and the transversal decision feedback equalizer. Direct and indirect methods to adaptive equalization will be described. First presented is the traditional, direct way of adapting the coefficients of the filters in an equalizer directly from data. Then, it is discussed how these coefficients can be adapted indirectly by first estimating channel parameters and then based on those estimates calculate the equalizer.
 

Contents:

1. Introduction

1. The air interface of a digital communication system
2. The mobile telephony environment

2. The transmission model

3. Equalizer design

•  The linear transversal equalizer
• The transversal Decision Feedback Equalizer

4. Adaptive equalization structures

1. Direct adaption of the equalizer parameters
2. Indirect adaption of the equalizer parameters
3. Comparison

Appendix

1. A.1. Derivation of the MSE optimal transversal linear equalizer
2. A.2. Derivation of the MSE optimal transversal DFE

Source:

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