Optimal Spectrum Balancing in Multi-User xDSL Systems With On/Off Power Loading

Abstract

Optimal Spectrum Balancing (OSB) is a centralized algorithm that optimally allocates transmit power over frequencies in a multi-user DSL environment where crosstalk is a major factor limiting performance. By using a dual decomposition, OSB decouples the spectrum management problem over frequencies. This results in per-tone optimization problems that are solved with an exhaustive search. This exhaustive search, however, has an exponential complexity in the number of users. For scenarios with several users this often becomes computationally intractable. In this paper, this complexity is reduced by limiting the possible power loadings on each tone to ON/OFF loading with an adjustable ON-level. This leads to a simple OSB algorithm with manageable complexity, simple flat transmit spectra and only minor performance degradation.