There are many spectrum balancing algorithms to combat the deleterious impact of crosstalk interference in digital subscriber lines (DSL) networks. These algorithms aim to find a unique operating point by optimizing the power spectral densities (PSDs) of the modems. Typically, the figure of merit of this optimization is the bit rate, power consumption or margin. This work poses and solves a different problem: instead of providing the solution for one specific operation point, it finds a set of operating points, each one corresponding to a distinct matrix with PSDs. This solution is useful for planning DSL deployment, for example, helping operators to conveniently evaluate their network capabilities and better plan their usage. The proposed method is based on a multiobjective formulation and implemented as an evolutionary genetic algorithm. Simulation results show that this algorithm achieves a better diversity among the operating points with lower computational cost when compared to an alternative approach.
Resumo-A Linha Digital do Assinante (DSL) é uma tecnologia de transmissão de dados em banda larga que aproveita as redes telefônicas existentes. A linha telefônica possui varias limitações, sendo a principal o crosstalk, o qual limita a taxa de transmissão de dados do DSL. Novas técnicas de alocação de potência estão sendo desenvolvidas, as quais são conhecidas como Gerenciamento Dinâmico do Espectro (DSM -Dynamic Spectrum Management). Testes em uma linha real foram realizados e os resultados foram comparados com valores padronizados através de simulações. Por fim, o uso de técnicas de DSM foram testadas através de simulações para o ambiente real.
This article propose a technique of adaptive coding of images, implemented from the classification of the size blocks MxM, with the aid of the technique of segmentation of images for the detection of discontinuities in the image, generating K classes with different levels of discontinuities, containing, each one, a variable number of blocks by class. The bits allocation table in this method is determined by the log-variance rule, using only one block of size K of sub-blocks MxM, each one belonging to a class. The method is applied using the DCT, with the uniform, laplacian and gaussian quantization of Lloyd-Max, and with blocks of size 8x8. The proposed method was applied in several images, like Lena, Barbara, Baboon, Goldhill, presenting a medium gain of 4 dB in the SNR at rate 1 bpp, and a maximum gain of 9,04 dB at rate 5 bpp, when compared with the method of images coding using DCT without classification.
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