Per-Tone model for Common Mode sensor based alien noise cancellation for Downstream xDSL

TL;DR

This paper proposes a low-complexity, frequency domain per-tone approach for alien noise cancellation in xDSL systems using common mode sensors, analyzing and mitigating performance loss through delay adjustments.

Contribution

It introduces a per-tone cancellation method for common mode sensor-based alien noise reduction, with analysis and practical validation of performance trade-offs.

Findings

Per-tone cancellation reduces complexity and training time.

Delay adjustment can minimize cancellation performance loss.

Real measurements show acceptable performance loss in practical scenarios.

Abstract

For xDSL systems, alien noise cancellation using an additional common mode sensor at the downstream receiver can be thought of as interference cancellation in a Single Input Dual Output (SIDO) system. The coupling between the common mode and differential mode can be modelled as an LTI system with a long impulse response, resulting in high complexity for cancellation. Frequency domain per-tone cancellation offers a low complexity approach to the problem besides having other advantages like faster training, 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 convenient post-training "delay" adjustment. We also show via measurements that the loss of cancellation performance due to the per-tone model is not very large for real scenarios.