Sensitivity of nonlinear precoding to imperfect channel state information in G.fast

Nonlinear Tomlinson-Harashima precoding has been proposed as a near-optimal interference mitigation technique for downstream transmission in G.fast systems, particularly in the transmit spectrum above 106 MHz. We propose an alternative implementation of Tomlinson-Harashima precoding and examine performance of the common and alternative implementations with respect to quantization errors and imperfect channel state information. We show that Tomlinson-Harashima precoding is more sensitive than optimized linear precoding to varying channel state information due to fluctuations in ambient conditions and sudden changes in termination impedance. We also show that Tomlinson-Harashima precoding only outperforms optimized linear precoding when the channel state information is almost perfectly known.