Low Complexity Training Methods for Common Mode Aided Cancellation of Intermittent Alien Noise in Downstream VDSL

Abstract

The adoption of precoding (vectoring) in VDSL2 at the central office has resulted in mitigation of the far-end crosstalk seen at the customer premises equipment (CPE). As a result, alien noise (including repetitive impulse noise) is the new dominant source of impairment for downstream VDSL. At the CPE, an additional common mode (CM) sensor can sense the electromagnetically coupled alien noise signal, which can then be used to cancel the alien noise coupling into the differential mode signal. The intermittent and repetitive nature of the noise sources necessitates that the CM sensor based noise cancellation algorithm be capable of training and adapting during data mode in the presence of the useful data signal, since the presence of alien noise cannot be guaranteed during the modem training phase. In this paper, we propose a novel two-stage frequency domain algorithm based on a per-tone cancellation model for this purpose. The proposed algorithm outperforms previously proposed time domain algorithms in terms of convergence speed in many practical scenarios due to the decision directed nature of the proposed algorithm. We also analyse the theoretical convergence of the algorithm, which is also validated by the simulation experiments.