An Optimal Path Stability Achieved By a Cross-Layer Proposal for Wireless Networks

Marcos Tomio Kakitani, Anelise Munaretto, Mauro Fonseca

DOI: 10.14209/sbrt.2010.59

Keywords:

Abstract

This article presents an adaptive cross-layer solution for wireless networks. The main objective is to estimate the impact that different physical layer variations and approaches can have on the network layer. The data loss probability obtained directly from physical layer will provide the routing protocol enough information to choose routes with the highest successful transmission probabilities. This proposal was evaluated under simulations and the obtained results point to a more stable network with fewer route recalculations and smaller number of packets lost.

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Resonances of Modified Bowtie Nanoparticles with Higher Field Enhancements

Karlo Q. da Costa, Victor Dmitriev

DOI: 10.14209/sbrt.2010.47

Keywords: Surface plasmons subwavelength structures bowtie metal nanoparticles spectral response

Abstract

In this paper, we present an analysis of the resonant behavior of modified bowtie nanoparticles with polynomial sides. The method of moments is used to solve numerically the scattering problem. With this model, we investigate the variation of the spectral response and near field distribution in function of the length and polynomial order of the nanoparticles. The results show that these particles possess smaller number of resonances in the analyzed wavelength range and their resonant wavelength, near field enhancement and confinement are higher than those of the conventional bowtie particle with linear sides.

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A complex version of the LASSO algorithm and its application to beamforming

Jose F. de Andrade Jr., Marcello L. R. de Campos, Jose A. Apolinário Jr.

DOI: 10.14209/sbrt.2010.94

Keywords: Beamforming LASSO algorithm complex-valued version optimum constrained optimization

Abstract

Least Absolute Shrinkage and Selection Operator (LASSO) is a useful method to achieve coefficient shrinkage and data selection simultaneously. The central idea behind LASSO is to use the L1-norm constraint in the regularization step. In this paper, we propose an alternative complex version of the LASSO algorithm applied to beamforming aiming to decrease the overall computational complexity by zeroing some weights. The results are compared to those of the Constrained Least Squares and the Subset Selection Solution algorithms. The performance of nulling coefficients is compared to results from an existing complex version named the Gradient LASSO method. The results of simulations for various values of coefficient vector L1-norm are presented such that distinct amounts of null values appear in the coefficient vector. In this supervised beamforming simulation, the LASSO algorithm is initially fed with the optimum LS weight vector.

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Comparison of the Performance of Rain Attenuation Prediction Methods for Terrestrial Links

Luiz da Silva Mello, Marlene S. Pontes, Pantelis-Daniel Arapoglou

DOI: 10.14209/sbrt.2010.60

Keywords: Rain attenuation Terrestrial radio links Propagation prediction methods

Abstract

This paper presents the results of a comparative tests between rain attenuation prediction methods for terrestrial links. To perform the tests, experimental data from measurements available in the ITU-R data bank have been used. Results indicate that the method currently recommended by the ITU-R significantly underestimates the measured attenuation. Two other methods, proposed by Brazilian and Chinese administrations, provide more accurate results.

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Trust Management for Survivable Communication on Self-Organized Wireless Networks

Pedro Velloso, Guy Pujolle, Eduardo Silva, Michele Nogueira

DOI: 10.14209/sbrt.2010.119

Keywords:

Abstract

Self-organized wireless networks comprise different devices cooperating among themselves to provide network services. These networks support critical applications in different domains requesting simultaneously robustness, security and availability. Hence, it is essential to develop mechanisms for steering nodes’ cooperation in order to preserve essential network operations even in presence of intrusion, attacks or network failures. We propose a trust management framework whose goal is to guide node cooperation towards network survivability. Our framework evaluates node trustworthiness correlating adaptively criteria provided by node behavior, recommendations, security mechanisms and node attributes. Simulation results show improvements on network trustworthiness for different situations

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Nonlinear Binary Codes Derived from Constacyclic Codes

V. C. da Rocha Jr., J. S. de Lemos Neto

DOI: 10.14209/sbrt.2010.62

Keywords: Constacyclic codes constant-weight codes cyclically permutable codes maximum-distance-separable codes collision channel protocol sequences

Abstract

This paper presents theorems showing how to obtain a binary nonlinear code from a p-ary linear constacyclic maximum distance separable code, where p is a prime number, by using a representation of GF(p) as binary ptuples. Two asymptotically optimum classes of binary constantweight codes are constructed. Binary cyclic codes are derived for a representation of GF(p) as (p-1)-tuples. It is shown for Mersenne primes p greater than 3 that all p-ary codewords of these codes have full constacyclic order. An application of some of the cyclically permutable codes constructed is given as an example of the construction of protocol sequences for the M-active-out-of-T users collision channel without feedback introduced by Massey.

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OFDM Point-to-Multipoint Links at ISM 5 GHz Band: Experimental and Analytical Results

Rafael Tonin, Roger Pierre Fabris Hoefel

DOI: 10.14209/sbrt.2010.61

Keywords: 802.11a 802.16 link budget

Abstract

It is developed a case study, unifying theoretical and practical aspects, concerning planning and implementation of orthogonal frequency division multiplexing (OFDM) point-tomultipoint (PtMp) links at Industrial, Scientific and Medical (ISM) 5 GHz band. The proposed design methodology is validated using analytical results and field measurements.

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A Fingerprint-based Access Control using Principal Component Analysis and Edge Detection

Ernande F. Melo, H. M. de Oliveira

DOI: 10.14209/sbrt.2010.63

Keywords: Fingerprints PCA Edge Detection Euclidean and Mahalanobian distances ROC

Abstract

This paper presents a novel approach for deciding on the appropriateness or not of an acquired fingerprint image into a given database. The process begins with the assembly of a training base in an image space constructed by combining Principal Component Analysis (PCA) and edge detection. Then, the parameter value (H) – a new feature that helps in the decision making about the relevance of a fingerprint image in databases – is derived from a relationship between Euclidean and Mahalanobian distances. This procedure ends with the lifting of the curve of the Receiver Operating Characteristic (ROC), where the thresholds defined on the parameter H are chosen according to the acceptable rates of false positives and false negatives.

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Cross-Layer Interaction Between the Application, Routing and MAC Layers for Wireless Sensor Networks

Edsongley V. Almeida, Welliana B. Ramalho, Iguatemi E. Fonseca, Marcelo Sampaio de Alencar

DOI: 10.14209/sbrt.2010.64

Keywords:

Abstract

This paper proposes a network protocol that relies on cross-layer interaction between the Medium Access Control (MAC), Network and Application layers for wireless sensor networks (WSN). The protocol uses Time Division Multiple Access (TDMA) with varying time intervals, which, in conjunction with a routing protocol, defines the operation of network nodes and its relationship with the application layer. Simulation results indicate a reduction on the end-to-end delay and on the network average delay. The network power consumption is also reduced.

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A Comparative Analysis of Vocoders for Communications in Portuguese

Dirceu Leite Cavalcante, Rafael Dueire Lins

DOI: 10.14209/sbrt.2010.65

Keywords: vocoders G.722. G.723.1 G.726 G.728 G.729A iLBC Speex

Abstract

This paper analyzes the performance of voice encoders used for digital communications, especially in VoIP calls, for Brazilian Portuguese phonemes. The focus is the adaptation capacity of encoders to vocal tract changes in these intervals during the signal processing. Short sentences containing all the basic Portuguese phonemes were used. Information about fundamental frequency and the three first formants was extracted, for each interval, for a group formed by men and women of different ages. These intervals were created using the software Praat, which was also used to extract all the parameters. The results obtained showed a subtle difference in signal processing of the formant frequencies between sexes. It was observed a phenomenon of pitch correction in some intervals with a variant phoneme for both sexes. The encoders G.722, G.723.1, G.726, G.728, G.729A, iLBC and Speex were analyzed

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