Zero-forcing and MMSE precoding for G.fast

Hybrid copper/fiber networks bridge the gap between the fiber link at the distribution point and the customer by using copper wires over the last meters. The G.fast transmission technology has been designed to be used in such a fiber to the distribution point (FTTdp) network. Crosstalk management using MIMO precoding in downlink and MIMO equalization in uplink is a key to the required performance of FTTdp. Currently, there are mostly linear and nonlinear zero-forcing (ZF) methods discussed for precoding in G.fast. This paper presents a spectrum optimization algorithm for both zero-forcing precoding methods. Minimum mean squared error (MMSE) precoding shows significant advantages under certain channel conditions. A performance comparison of MMSE precoding for G.fast with linear and nonlinear zero-forcing methods indicates that MMSE precoding outperforms standard linear and nonlinear ZF precoding. Applying the proposed spectrum optimization brings all three methods to a similar performance.