Optimum upstream power back-off and multiuser detection for VDSL

The problem of multiuser detection for upstream very-high-speed digital subscriber line (VDSL) transmission, where far-end crosstalk (FEXT) signals at the input of a VDSL receiver are viewed as interferers that share the same channel as the remote user signal, is addressed. Knowledge of the FEXT impulse responses at the central office, as well as upstream transmission based on multicarrier modulation by all remote users, are assumed. The joint application of upstream power back-off with a reduced-complexity decision-feedback (DFE) multiuser detector, where only the most significant crosstalk interferers are suppressed, is considered, and the coefficients of the minimum mean-square error structure are determined. Then a novel optimum power back-off algorithm is introduced, and its performance in terms of achievable rates evaluated. Finally, numerical results that illustrate the impact of power back-off on achievable performance of a VDSL system with multiuser detection are presented.