On low complexity per-tone common mode sensor based alien noise cancellation for downstream VDSL

For VDSL systems, alien noise cancellation using an additional common mode sensor at the customer premises equipment (CPE) receiver can be done by combining the differential-mode (DM) signal with the common-mode (CM) signal passed through a long linear filter. Frequency domain per-tone cancellation offers a low complexity approach to the problem but suffers from loss in cancellation performance due to approximations in the per-tone model. We analyze this loss and show that it is possible to minimize it by a post-training “delay” adjustment. We also address the problem of training such a noise canceller during data mode in the presence of a much stronger useful data signal in DM since noise events may not occur during modem train-up. We propose an algorithm based on the per-tone approach which is capable of fast convergence during data mode for intermittent alien noise sources, analyze its convergence behaviour and demonstrate the usefulness of the pertone approach and the proposed training algorithm over existing time domain methods.