Adaptive NLMS Partial Crosstalk Cancellation in Digital Subscriber Lines

Abstract

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.