Low-Complexity Nonlinear Zero-Forcing Precoding Based Dynamic Spectrum Management for Improving the G.fast Peak-Rate Performance

We consider nonlinear zero-forcing (ZF) precoding based dynamic spectrum management for improving the G.fast peak-rate performance when only a few users in the cable binder are active. In order to compute the optimal ZF precoder under complicated per-line power constraints (PLPCs), we present a novel low-complexity dual decomposition algorithm, in which the key is the use of Lagrange multiplier based virtual precoders to transform the per-line power constraints into an easier virtual sum-power constraint (SPC), such that the SPC-optimal QR decompostion-based precoder may be re-used. We show a reduced computational complexity of this algorithm over the state-of-the-art SVD-based dual decomposition algorithm. We present simulations of a 10-line cable binder that demonstrate powerful peak-rate gains over standard precoding, due to the increasingly stronger crosstalk channels in the G.fast frequency range (up to 212 MHz).