Improved Loading Rule for FEXT Noise Impaired Users in Vectored VDSL Systems

The present paper proposes an original rule that aims at maximizing the number of bits loaded to each subcarrier of far-end crosstalk (FEXT) noise impaired VDSL systems while guaranteeing an error probability below a set target. This rule exploits the knowledge of the coupling between pairs in a cable bundle as well as the modulation scheme used by the FEXT noise source(s) and becomes particularly attractive in vectored VDSL systems with residual FEXT noise since such systems facilitate the coupling estimation. We show that this new rule may significantly improve spectral efficiency of VDSL systems compared to the traditional loading rule derived under pure Gaussian noise assumption and that, under particular FEXT noise conditions, the SNR loading threshold per subcarrier can be reduced by up to 14.3dB.