A Near-Optimal Linear Crosstalk Precoder for VDSL

Crosstalk is the major source of performance degradation in VDSL. In downstream transmission crosstalk precoding can be applied. The transmitted signal is predistorted, such that the predistortion annihilates with the crosstalk introduced in the binder. Several crosstalk precoders have been proposed. Unfortunately they either give poor performance or require non-linear operations, which results in a high complexity. In this paper we present a simple, linear diagonalizing crosstalk precoder with low run-time complexity. A lower bound on the performance of the DP is derived. This allows performance to be predicted without explicit knowledge of the crosstalk channels, which simplifies service provisioning considerably. This bound shows that the DP operates close to the single-user bound. So the DP is a low complexity design with predictable, near-optimal performance. The combination of spectra optimization and crosstalk precoding is also considered. Spectra optimization in a broadcast channel generally involves a highly complex optimization problem. Since the DP decouples transmission on each line, the spectrum on each modem can be optimized through a dual decomposition, leading to a significant reduction i