Weighted MMSE Tomlinson-Harashima Precoding for G.fast

Recently, ITU finished its standard for G.fast, utilized in so called fiber-to-the-distribution-point (FTTdp) networks, where only the last meters from the fiber link to the customer are bridged by existing copper wires. The target is to increase the data rate over the short copper link up to 1 Gbit/s, which is an increase by the factor of ten compared to VDSL2, by extending the frequency band up to 212 MHz. At higher frequencies, the crosstalk between the lines is amplified, which makes crosstalk management essential to obtain the targeted data rates. Tomlinson-Harashima Precoding (THP) is a non-linear precoding technique, which is considered for the 212 MHz G.fast systems. Up to now, linear zero-forcing (ZF) and weighted minimum mean-square-error (WMMSE) precoding, as well as ZF THP, have been investigated for G.fast. In this paper, we show how WMMSE THP can be utilized in this scenario. We show that WMMSE THP outperforms ZF THP in terms of achievable rate in large systems. However, we see that the rate gain is not significant, although the WMMSE THP solution almost achieves the channel capacity.