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 de nition 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.

Crosstalk is one of the main limiting factors in the data rates achievable by digital subscriber line (DSL) systems, and several algorithms have been proposed to mitigate this impairment. In this paper, we compare the achievable rates of binders under different crosstalk-mitigating techniques. When computing these rates, we also compare two different power constraints: either on the total power in the binder or on the power in each twisted wire pair. We will see that, for the scenarios considered in this paper, the fact that the signals are jointly processed in one or both ends of the DSL link leads to roughly the same performance, which can be far superior to that of systems with no cooperation between the users. Both power constraints also lead to similar achievable rates.

Multiuser Processing refers to a set of fundamental techniques for improving the performance of the modern wireless communications systems. Most of these techniques have been proposed and studied for specific scenarios, according to the multiple access technology to be employed. The theory and methods of blind source separation (BSS) can provide a more general framework over which multiuser techniques may be investigated and analysed as a particular case. This is the main idea to be exploited along the present paper. We show how this point of view opens perspectives to deal with important problems of multiuser systems such as signal detection and collision resolution. For this task, an information-theoretic based criterion and algorithm, issued from BSS theory, is presented together with an algorithm for estimation of the number of active users in the system. Simulation results are carried out to illustrate the performance of the designed approach, compared to other blind and trained solutions.

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Resumo-Este artigo propõe o uso do software MATLAB R e seu Toolbox Data Acquisition (DAQ) como uma plataforma simples e acessível para a prática de processamento de sinais em tempo-real. Ilustramos a proposta através da análise da implementac ¸ão em software de um enlace digital de comunicac ¸ão, também conhecido como software-defined radio, com processamento em tempo-real e que utiliza sinais ac ústicos como forma de transmissão.Palavras-Chave-MATLAB, tempo-real, modem ac ústico, rádio definido por software, projetos, processamento digital de sinais.

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