Adaptive equalization

S.U.H. Qureshi
1985 Proceedings of the IEEE  
Bandwidth-efficient data transmission over telephone and radio channels is made possible by the use of adaptive equalization to compensate for the time dispersion introduced by the channel. Spurred by practical applications, a steady research effort over the last two decades has produced a rich body of literature in adaptive equalization and the related more general fields of reception of digital signals, adaptive filtering, and system identification. This tutorial paper gives an overview of
more » ... current state of the art in adaptive equalization. In the first part of the paper, the problem of intersymbol interference ( 1 9 ) and the basic concept of transversal equalizers are introduced followed by a simplified description of some practical adaptive equalizer structures and their properties. Related applications of adaptive filters and implementation a p proaches are discussed. Linear and nonlinear receiver structures, their steadystate performance and sensitivity to timing phase are presented in some depth in the next part. It is shown that a fractionally spaced equalizer can serve as the optimum receive filter for any receiver. Decision-feedback equalization, decision-aided IS1 cancellation, and adaptive filtering for maximum-likelihood se quence estimation are presented in a common framework. The next two parts of the paper are devoted to a discussion of the convergence and steadystate properties of least mean-square (LMS) adap tation algorithms, including digital precision considerations, and three classes of rapidly converging adaptive equalization algorithms: namely, orthogonalized LMS, periodic or cyclic, and recursive least squares algorithms. An attempt is made throughout the paper to describe important principles and results in a heuristic manner, without formal proofs, using simple mathematical notation where possible.
doi:10.1109/proc.1985.13298 fatcat:csxa4sag4jes5poyujgwsiqj2e