Bit Loading for Precoded DSL Systems

Crosstalk is one of the main impairments of digital subscriber line (DSL) systems. To combat this impairment, several techniques were proposed in the literature that employ some form of precoding in the downstream. However, most existing bit allocation algorithms are not applicable to precoded DSL systems when the power in each transmission line is constrained. In this paper, we propose a bit allocation algorithm for this scenario. The proposed algorithm maximizes the bit rate given the available power. It somewhat extends single-user algorithms in that it sequentially allocates bit to the "best" user and tone. In the proposed algorithm we use a definition of "best" that is suitable for precoded systems. Simulation results show that the proposed algorithm achieves almost the same rates as those of power allocation algorithms, which do not take into account the discrete nature of the transmitted information.