Strategy for the Analysis of Lossy Bragg Fibers

Leonardo R. Marinho, Antonio R. Sapienza, José R. Souza

DOI: 10.14209/sbrt.2012.89

Keywords: Bragg fibers transfer matrix transversal modes TE 0n and TM 0n .

Abstract

This paper presents a mathematical model for the analysis of losses and dispersion in Bragg fibers with hollow core, based on the transfer matrix method. The paper introduces a strategy for the efficient numerical calculation of the dispersion characteristics of TE 0n , and TM 0n modes. The results are validated by comparison with other methods in the literature.

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Classificação de Voz versus Silêncio via Dicionários Redundantes

Raffaello Claser, Ivandro Sanches

DOI: 10.14209/sbrt.2012.107

Keywords: Matching Pursuit Histograms Voice Detection

Abstract

This paper presents a technique to solve the pro- blem of classifying portions of signal between voice and silence. Surprisingly, the proposed technique is not based on the variation of energy levels over the signal, but on the fundamental charac- teristics that determine the essence of each of these two classes of signals, namely voice and silence. To this end, a redundant dictionary of basis functions (atoms) is built and the signal is analyzed via Matching Pursuit. From this analysis, the technique training phase, the a priori discrete probability distribution of occurrence of a set of atoms for each class of interest is computed, allowing subsequent discrimination between the classes. The paper presents promising results for signals with high signal to noise ratio.

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Impacto de Erros de Canal na Percepção de Qualidade em Sequências de Videoconferência de Alta Definição

Cassius D. Estrada, Alexandre Ciancio, José F. L. de Oliveira, Felipe Ribeiro Lopes, Eduardo A. B. da Silva, Amir Said

DOI: 10.14209/sbrt.2012.111

Keywords: HDTV videoconference channel erros packet loss quality assessment

Abstract

In this work we assess the impact of channel errors on the perceived quality in high definition videoconference applications. A database containing 31 high definition sequences (1080i) without compression was generated. The set of generated sequences may present backgrounds of different complexities as well as other features, such as number of subjects, face occlusion, skin color, among others. 16 representative sequences were degraded with channel error simulating packet loss that ranged from 0 to 0.05% and post processed by error concealment techniques. Results suggest that the localized nature of channel errors (in contrast to encoding errors) may mask the perception of quality by the users in a way that are not associated to the error rate itself, but also to the nature of the video content.

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A Simple Approximation to the the κ - μ Phase Probability Density Function

Iury B. G. Porto, Michel D. Yacoub

DOI: 10.14209/sbrt.2012.112

Keywords: κ-μ model fading channels approximation phase probability density function

Abstract

In this article, a new random variable whose distribution closely follows that of the exact distribution of the κ-μ phase distribution is introduced. Whereas the exact statistics is given in an integral form, the approximate one is obtained in a simple formulation that can be computed in a very efficient manner. More interestingly, whereas the exact phase distribution of the κ-μ model comprises Rice and Nakagami-m as special cases, as designed, the special cases of the approximate phase solution are correspondingly Von Mises and, amazingly, Nakagami-m, obtained in an exact manner.

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Espectroscopia de Impedância e o Uso em Antenas Ressonadoras Dielétricas

Ronaldo Cristino Mariano, Bruno Sousa Araújo, Mairton Cavalcante Romeu, Antonio Jefferson Mangueira Sales, Antonio Sérgio Bezerra Sombra.

DOI: 10.14209/sbrt.2012.108

Keywords: impedance spectroscopy solid state reaction dielectric resonators

Abstract

This work aims at the discussion of dielectric antennas ressoadoras. Will be discussed to prepare the ceramic material used in the manufacture of dielectric resonators, which can be used as antennas. The characterization of interest for the transmission in the resonator is made primarily by impedance spectroscopy.

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Estudo das propriedades dielétricas em microondas da cerâmica BNO (BiNbO 4 ) com adição de ZnO

Antonio Jefferson Mangueira Sales, Ronaldo Cristino Mariano, Bruno Sousa Araújo, Mairton Cavalcante Romeu, Antonio Sérgio Bezerra Sombra

DOI: 10.14209/sbrt.2012.219

Keywords: BiNbO4 solid state reaction dielectric resonators

Abstract

The objective of this work is to study the microwave dielectric properties of the compound BiNbO4 (BNO) with addition of ZnO and discuss the influence of the additions in view of possible applications in dielectric resonators. The BNO ceramic has been produced by the standard method of solid state. The ZnO (3, 5 and 10% by weight) was added in order to analyze the changes in the dielectric properties of ceramic bulks produced. Polyvinyl alcohol (PVA) was also incorporated into the manufacturing process as organic binder. The samples were characterized by X-ray diffraction (XRD) and a study of dielectric properties using the technique of Hakki Coleman was done. The Rietveld refinement indicated that the pure BNO produced, has an orthorhombic type structure (space group: P nna 52). The dielectric properties: dielectric constant ( ε ’), dielectric loss factor (tg δ ) and quality factor (Qu), were measured ambient temperature. The presence of ZnO more melting PVA binder in all concentrations change the dielectric properties of the samples compared to the standard sample (BNO pure).

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Adjustments of Log-Distance Path Loss Model for Digital Television in Lima

J. R. Fernández, M. Quispe, G. Kemper, J. Samaniego, D. Díaz

DOI: 10.14209/sbrt.2012.109

Keywords: Log-distance path loss model field measurements digital television coverage estimation propagation exponent

Abstract

it is necessary to perform a proper planning for an efficient deployment of new infrastructure for transmission of digital television in countries that have adopted such technology. In that sense, the coverage prediction process, which makes use of path loss propagation models, plays an important role. The log-distance path loss model determines that the average power loss depends logarithmically on the distance and it has a parameter called propagation exponent which is required to be calculated for each studied environment. This paper describes the adjustments made to the log-distance path loss model using data from three sets of signal strength measurements in Lima, Peru. Through a series of iterations, two computationally simple models for estimating the average path loss were obtained. The performance of the models were evaluated comparing their results with those calculated using Okumura-Hata and the Rec. ITU-R P.1546 model, showing good results. The proposed strategy used here can be applied to any other environment of propagation to estimate the path loss.

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Mecanismo de detecção de ataques Wormhole em Redes Tolerantes a Atrasos e Desconexões

Henrique Zelak Leite Bastos, Luiz Carlos Pessoa Albini

DOI: 10.14209/sbrt.2012.113

Keywords: Delay tolerant networks Wormhole attack

Abstract

Delay Tolerant Networks (DTNs) do not have any infrastructure or centralized unit and they allow nodes to exchange messages without routes between them. These points are commonly explored by attackers. One of these attacks is the wormhole. It uses a pre-established infrastructure to force all routes to go through the attacker, forcing a large number of messages to go through such nodes. In this way, the attacker can intercept messages or even neutralize the network. This article presents a new method to detect wormhole attacks in DTNs, based on GPS equipped nodes. Thus, it is possible to precisely determine the integrity of the network nodes, improving the performance of previous methods.

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Probabilidade de Erro Sı́mbolo com Esquema θ -QAM sob Desvanecimento Nakagami- m Correlacionado

Wamberto J. L. Queiroz-UFCG, Marcelo S. Alencar-UFCG, Francisco Madeiro-UPE, Waslon T. A. Lopes-UFCG

DOI: 10.14209/sbrt.2012.114

Keywords: Symbol error probability Nakagami fading gene- ralized QAM

Abstract

This paper presents an evaluation of the sym- bol error probability-SEP of θ-QAM scheme under correlated Nakagami-m fading with MRC receiver using Gaussian and Von Mises distributions for modeling the direction of arrival. New mathematical expressions for the SEP are presented and is shown as the magnetic coupling between the elements of the antenna array associated with the receiver can influence SEP.

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Avaliação de Desempenho de um Protocolo de Segurança para Sistemas RFID

Matheus A. Cavalcante, Marcelo P. Sousa

DOI: 10.14209/sbrt.2012.115

Keywords:

Abstract

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