Valdemar Cardoso da Rocha

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This paper presents a new segmentation-based method for generating high-quality monochromatic images of historical documents. The proposed segmentation algorithm is based on the entropy of the histogram of the image. The algorithm eliminates back-to-front interference in documents written on both sides on translucent paper.
—Irregular low-density parity-check (LDPC) codes are particularly well-suited for transmission schemes that require unequal error protection (UEP) of the transmitted data due to the different connection degrees of its variable nodes. However, this UEP capability is strongly dependent on the connection profile among the protection classes. This paper applies(More)
This paper concerns the capacity of the discrete noiseless channel introduced by Shannon. A sufficient condition is given for the capacity to be well-defined. For a general discrete noiseless channel allowing non-integer valued symbol weights, it is shown that the capacity—if well-defined—can be determined from the radius of convergence of its generating(More)
This paper derives a simple closed form expression for computing the power spectral density of constrained sequences whose constraints are characterized by a function of an ergodic Markov process specified in terms of a Mealy machine. A suitable matrix description of the stochastic behavior of the constrained sequence is used to express its autocorrelation(More)
—A multi-edge framework for unequal error protecting (UEP) LT codes is derived by distinguishing between the edges connected to each protection class. Under the framework introduced, two existing techniques for the design of unequal error protecting LT codes can be evaluated and explained in a unified way. Furthermore, a simple and flexible design technique(More)
—In the first chapter of Shannon's A Mathematical Theory of Communication, it is shown that the maximum entropy rate of an input process of a constrained system is limited by the combinatorial capacity of the system. Shannon considers systems where the constraints define regular languages and uses results from matrix theory in his derivations. In this work,(More)
Iterative decoding of turbo convolutional codes for the noisy 2-user binary adder channel is investigated. It is shown that iterative BCJR decoding yields considerable gain after just a few iterations for low-complexity codes constructed from turbo convolutional codes. Introduction: The two-user binary adder channel (2-BAC) is one of the sim