Analysis of Adaptive Interference Cancellation Using Common-Mode Information in Wireline Communications
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Research Article Analysis of Adaptive Interference Cancellation Using Common-Mode Information in Wireline Communications ¨ ¨ Thomas Magesacher, Per Odling, and Per Ola Borjesson Department of Information Technology, Lund University, P.O. Box 118, 22100 Lund, Sweden Received 4 September 2006; Accepted 1 June 2007 Recommended by Ricardo Merched Joint processing of common-mode (CM) and differential-mode (DM) signals in wireline transmission can yield significant improvements in terms of throughput compared to using only the DM signal. Recent work proposed the employment of an adaptive CM-reference-based interference canceller and reported performance improvements based on simulation results. This paper presents a thorough investigation of the cancellation approach. A subchannel model of the CM-aided wireline channel is presented and the Wiener solutions for different adaptation strategies are derived. It is shown that a canceller, whose coefficients are adapted while the far-end transmitter is silent, yields a signal-to-noise power ratio (SNR) that is higher than the SNR at the DM channel output for a large class of practically relevant cases. Adaptation while the useful far-end signal is present yields a front-end whose output SNR is considerably lower compared to the SNR of the DM channel output. The results are illustrated by simulations based on channel measurement data. Copyright © 2007 Thomas Magesacher et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1.
INTRODUCTION
Transmission of information over copper cables is conventionally carried out by differential signalling. On physicallayer level, this corresponds to the application of a voltage between the two wires of a pair. The signal at the receive side is derived from the voltage measured between the two wires. Differential-mode (DM) signalling over twisted-wire pairs, originally patented by Bell more than hundred years ago [1], exhibits a high degree of immunity against ingress of unwanted interference, caused, for example, by radio transmitters (radio frequency interference) or by data transmission in neighboring pairs (crosstalk) [2]. The inherent immunity of a cable against ingress decays with frequency. In fact, the performance of almost all high data-rate (and thus also highbandwidth consuming) digital subscriber line (DSL) systems is limited by crosstalk. The number of strong crosstalk sources is often very low—one, two or three dominant crosstalkers significantly raise the crosstalk level and thus reduce the performance on the pair under consideration. In such cases, it is beneficial to exploit the common-mode (CM) signal, which is the signal corresponding to the arithmetic mean of the two voltages measured between each wire and earth, at the receive side
[3–5]. The CM signal and the DM signal of a twisted-wire pair are strongly correlated. Exploiting the CM signal in addition to the
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