Linear and Nonlinear Precoding Based Dynamic Spectrum Management for Downstream Vectored G.fast Transmission
Abstract: In the G.fast digital subscriber line frequency range (up to 106 or 212 MHz), where crosstalk channels may even become larger than direct channels, linear zero-forcing forcing (ZF) precoding is no longer near near-optimal optimal for downstream (DS) vectored transmission. To improve perfor performance, mance, we develop a novel lowlow complexity algorithm for both linear and nonlinear precoding precoding-based based dynamic spectrum management that maximizes the weighted sum sum-rate rate under realistic perper line total power and per-tone tone spectral mask constraints. It applies to DS scenarios with a single copper line at each customer site [i.e., broadcast channel (BC) scenarios], as well as to DS scenarios with multiple copper lines at some or all customer sites (i.e., the so so-called multiple-input-multiple-output--BC scenarios). The algorithm lgorithm alternates between precoder and equalizer optimization, where the former relies on a Lagrange multiplier based transformation of the DS dual decomposition approach formulation into its dual upstream (US) formulation, together with a low-complexity complexity iterative fixed-point point formula to solve the resulting US problem. Simulations with measured G.fast channel data of a very high crosstalk cable binder are provided revealing a significantly improved performance of this algorithm over ZF techniques for vario various us scenarios, and in addition, a faster convergence rate compared with the state state-of-the the-art WMMSE algorithm.