Performance of Crosstalk Cancellation in VDSL

Crosstalk in DSL leads to significant performance degradation and large losses in data-rate. Several crosstalk cancellation techniques have been proposed to address this problem, however, in the existing literature the analysis of these approaches is based on SNR calculations and the SNR-gap approximation. Furthermore, for crosstalk cancellation techniques based on decision-feedback, the effect of error propagation is completely ignored. This makes it hard to predict the performance of crosstalk cancellation in real life, and to see if the significant potential gains can actually be realized. To address this problem, this paper uses Monte- Carlo simulation to investigate the performance of the various crosstalk cancellation techniques that have been proposed. The effect of noise-enhancement in zeroforcing crosstalk cancellers and error-propagation in decision-feedback cancellers is examined. The results confirm that a very simple crosstalk cancellation structure can achieve near-optimal performanc

Adaptive NLMS Partial Crosstalk Cancellation in Digital Subscriber Lines

Crosstalk is a major limitation to achieving high data-rates in next generation VDSL systems. Whilst crosstalk cancellation can be applied to completely remove crosstalk, it is often too complex for application in typical VDSL binders, which can contain up to hundreds of lines. A practical alternative, known as partial cancellation limits the cancellation to crosstalkers that cause severe interference to the other lines within the binder. In real VDSL systems, the crosstalk environment changes rapidly as new lines come online; old lines go offline, and the crosstalk channels change with fluctuations in ambient temperature. Therefore, adaptive crosstalk cancellers are often required. In this paper, we propose a new detection guided adaptive NLMS method for Adaptive Partial Crosstalk Cancellation that detects significant crosstalkers and tracks variations in their crosstalk channels. This exploits the sparse and column-wise diagonal dominant properties of the crosstalk channel matrix and leads to fast convergence, accurate crosstalk channel tracking, with a lower update complexity. The end result is an adaptive Partial Crosstalk Cancellation algorithm that has lower run-time complexity than prior state-of-the-art whilst yielding comparatively high data-rates and reliable service