This paper proposes the use of a similarity measure based on information theory called correntropy for the automatic classification of pathological voices. By using correntropy, it is possible to obtain descriptors that aggregate distinct spectral characteristics for healthy and pathological voices. Experiments using computational simulation demonstrate that such descriptors are very efficient in the characterization of vocal dysfunctions, leading to a success rate of 97% in the classification. With this new architecture, the classification process of vocal pathologies becomes much more simple and efficient.
We present an in-depth analysis of the fractal nature of 21 classical music pieces previously shown to have scale-free properties. The musical pieces are represented as networks where the nodes are musical notes and respective durations, and the edges are its chronological sequence. The node degree distribution of these networks is analyzed, looking for self-similarity. This analysis is done in the full network, in its fractal dimensions, and its skeletons. The assortativeness of the pieces is also studied as a fractal property. We show that two-thirds of these networks are scale-invariant, i.e. scale-free in some dimension or their skeleton. In particular, two pieces were given attention because of their exceptional tendency for fractality.
Resumo-Sistemas de rádio cognitivo devem ser capazes de perceber faixas de frequência desocupadas para transmissões oportunísticas, assim como detectar a presença de usuários primários quando estes ocupam seu espectro licenciado. Portanto, um elemento crucial para a operação desses sistemasé o sensoriamento espectral. Este trabalho apresenta uma arquitetura inteligente de sensoriamento, baseada no cálculo da função de densidade espectral cíclica do canal sensoriado e na utilização de um comitê de máquinas perceptron múltiplas camadas, para detectar sinais modulados na presença de ruído Gaussiano branco aditivo. A arquitetura proposta foi avaliada no sensoriamento de modulações QPSK e os resultados obtidos nos experimentos realizados comprovaram a eficiência desta arquitetura mesmo em cenários com baixa relação sinal-ruído.
This work presents a novel spectral sensing method for the detection of signals presenting nonlinear phase variation over time. The introduced method is based on the angle-time cyclostationarity theory, which applies transformations to the signal to be sensed in order to mitigate the effects of nonlinear phase variation. The architecture is employed for sensing binary phase shift keying (BPSK) signals, being also compared with time cyclostationarity. The obtained simulation results clearly demonstrate the efficiency of the proposed approach, while presenting improved performance in terms of the detection rate of primary users increased by about 8 dB.
Neste trabalho foi implementado um módulo gerador de sinais PWM (Modulação por largura de pulso -Pulse Width Modulation) em uma plataforma de hardware reconfigurável. Foi utilizado a linguagem de descrição Verilog em um FPGA (Field-Programmable Gate Array) Spartan 6 XC6SLX9 da Xilinx. Foram obtidos resultados experimentais que indicam que o módulo implementado é eficiente na geração de sinais de PWM, possuindo boa precisão no controle do ciclo de trabalho e frequência dos sinais Palavras chave: PWM gerados apresentando, com erros inferiores a 2% em comparação com os valores teóricos esperados.
Resumo-Em sistemas de rádio cognitivo é desejável que usuários não licenciados possam ter oportunidades de transmissão em porc ¸ões do espectro que não estejam sendo utilizadas em um determinado momento. Um dos principais desafios para a operac ¸ão destes sistemas é o desenvolvimento de técnicas de sensoriamento espectral confiáveis, que possibilitem uma alocac ¸ão eficiente de frequências a medida que estas ficam disponíveis. Este trabalho apresenta um método de sensoriamento que utiliza uma medida calculada a partir da densidade espectral cíclica do canal sensoriado, para detectar por limiar sinais modulados na presenc ¸a de ruído aditivo Gaussiano branco. O conjunto de modulac ¸ões utilizadas na avaliac ¸ão do método inclui as modulac ¸ões AM, BPSK e QPSK. Resultados numéricos de desempenho comprovam a eficiência do método proposto, mesmo em baixos valores de relac ¸ão sinal-ruído.
In mobile communication systems, the signals propagate through multipath over time-varying channels, which are subject to distortion caused by fading and Doppler shifts. In order to minimize such distortions, coding techniques and transmission diversity can be employed, e.g., wavelet coding. In this work, the wavelet coding is investigated in scenarios of cognitive radio systems with dynamic spectrum access. Cognitive radio systems with dynamic spectrum access should be able to sense unoccupied frequency bands for opportunistic transmissions, as well as detect the presence of primary users when they occupy their licensed spectrum. Therefore, an essential element for the accurate operation of cognitive radio systems encoded by wavelet coding is the ability to sense the signals encoded by this technique. It is effectively demonstrated that the possibility of sensing such signals is associated with a suitable design of the signal constellation used in the modulation of the coded symbols. The constellation design of these is performed via genetic algorithms using a multiobjective optimization approach. The developed system is evaluated according to the robustness to time-varying flat fading through a bit error probability (BER) versus Eb/N0 analysis. The spectral sensing ability is also addressed employing the cyclostationary analysis. The results denote the feasibility of using wavelet coding in radio scenarios with dynamic spectrum access, with good performance in terms of BER and signal detection rates.
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