A Downstream Crosstalk Channel Estimation Method for Mix of Legacy and Vectoring-Enabled VDSL

TL;DR

This paper presents a practical downstream crosstalk channel estimation method for mixed legacy and vectoring-enabled VDSL lines, enabling effective multiuser MIMO cancellation during system upgrade phases.

Contribution

It introduces a novel channel estimation approach that works in mixed line environments, aligning with maximum-likelihood performance and practical deployment constraints.

Findings

Estimation method achieves performance comparable to maximum-likelihood estimators.

The approach effectively handles mixed legacy and vectoring-enabled line scenarios.

Practical implementation with error reporting capability for downstream vectoring.

Abstract

With the latest technology of vectoring, DSL data rates in the order of 100Mbps have become a reality that is under field deployment. The key is to cancel crosstalk from other lines, which is also known as multiuser MIMO cancellation for wireless communications. During the DSL system upgrade phase of field deployment, mix of legacy and vectoring-enabled VDSL lines is inevitable and a channel estimation solution for the entire mix is needed before vectoring can be enforced. This paper describes a practical method for crosstalk channel estimation for downstream vectoring, assuming that a vectoring-enabled DSLAM forces DMT symbol-level timing to be aligned for all of the lines, but also assuming that the location of synch symbols are aligned only among vectoring-enabled lines. Each vectoring-enabled receiver is capable of reporting error samples to vectoring-DSLAM. The estimation method is not only practical, but also matches the performance of Maximum-Likelihood estimator for the selected training sequences.