Compound Precoding: A Pre-Equalization Technique for the Bandlimited Gaussian Channel

Compound precoding is a state-of-the-art technique for combining trellis coding and decisionfeedback equalization (DFE) prior to upstream transmission on the telephone-line channel, and is an option in the International Telecommunications Union (ITU)-T V.92 standard. In this paper, we provide a detailed overview of this technique. We demonstrate that compound precoding combines in a straightforward manner with most practical trellis codes. We show that compound precoding exhibits a signal-to-noise ratio (SNR) gain with respect to other schemes which combine decision-feedback equalization with trellis coding, and quantify this gain. We also show that, for stability of the compound precoder, the precoder feedforward filter must be decomposed into its constituent minimum phase (MP) and all pass (AP) components. Finally, a simulation study of V.92 upstream transmission demonstrates the shaping advantage of compound precoding over competitor techniques for pre-equalization in this setting. Index Terms Equalization, trellis coding, precoding, modems. This paper is a preprint of a paper accepted by IET Communications and is subject to Institution of Engineering and Technology Copyright (http://www.ietdl.org/journals/doc/IEEDRL-home/info/support/copyinf.jsp). When the final version is published, the copy of record will be available at IET Digital Library (http://www.ietdl.org/). M. F. Flanagan and A. D. Fagan are with the Department of Electronic and Electrical Engineering, University College Dublin, Belfield, Dublin 4, Ireland (e-mail: [email protected], [email protected]). M. McLaughlin is with DecaWave Ltd., Digital Depot, Thomas St., Dublin 8, Ireland (email:[email protected]). March 13, 2009 DRAFT