Detecção Ótima por Grupos em Sistemas com Transmissão em Blocos

Byron Maza, Raimundo Sampaio Neto, César A. Medina

DOI: 10.14209/sbrt.2012.131

Keywords: OFDM single carrier systems groups detection ML detection

Abstract

Block transmission system, allows transmissions of N symbols simultaneously, with single carrier or multi-carrier modulation. Maximum likelihood optimal reception in multipath channels have a high computational cost of AN, where A is the constellation order (A = 2 for BPSK). To avoid this cost is usual to make symbol by symbol detection after equalization. In this work we propose a receiver with group detection having a good trade of between computation complexity and bit error rate performance

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Detecção e estimação em tempo real de direção de chegada de sinais impulsivos

Paulo C. Prandel, Izabela L. Freire, José A. Apolinário Jr.

DOI: 10.14209/sbrt.2012.134

Keywords: Detecção em tempo real estimação de direção de chegada sinais impulsivos arranjo de microfones

Abstract

O presente trabalho de inicação científica apresenta uma proposta de sistema em tempo real para detecção e a estimação da diração de chegada de sinais de áudio impulsivos. Utiliza-se um hardware específico para processamento em tempo real e um arranjo espacial de 7 microfones. Após detectado, o sinal é processado por um algortmo de estimação de direção de chegada (DoA, direction of arrival) que utiliza a correlação cruzada generalizada (GCC, Generalized Cross-Correlation) para medir as diferenças de tempo real. não ocorre perda de informação do ambiente pois os processos de detecção e a estimação de DoA ocorrem em paralelo. Este trabalho é a parte inicial (o sinal de teste é uma palma) da implementação de um sistema de localização de sniper, caso em que o sinal impulsivo é o disparo de uma arma de fogo.

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Um Método para Melhorar a QoE em Sistemas de Transmissão IPTV

Carlos Eduardo Maffini Santos, Carlos Marcelo Pedroso

DOI: 10.14209/sbrt.2012.135

Keywords: -,-,-

Abstract

A televisão transmitida através do protocolo IP(IPTV) está entre as mais promissoras tecnologias para entrega multimídia, permitindo um alto nível de interatividade com o usuario e integração com a internet. A transmissão de fluxos multimídia em tempo real requer garantia de recursos, como limitada perda de pacotes, largura de banda e baixo atraso e jitter para assegurar um bom nível de QoE (Quality of Experience). Este artigo propoe o uso de uma estratégia de descartes de pacotes prioritária, juntamente com um reconhecedor de carga útil, implementado com redes neurais artificiais, para evitar o descarte de pacotes transportando informações relevantes para a reconstrução da imagem. Mostra-se que o método proposto apresenta um melhor desempenho se comparado as abordagens existentes atualmente.

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Collaborative Spectrum Sensing under Spatially Correlated Shadowing Fading

Francisco Portelinha, Paulo Cardieri

DOI: 10.14209/sbrt.2012.136

Keywords: Spectrum sensing cognitive radio correlated shadowing fading

Abstract

Cognitive Radio is an innovative technology that allows unlicensed (secondary users) users to opportunistically access channels licensed to other users (primary users). A key procedure in the context of opportunistic access is the spectrum sensing, performed by secondary user to determine whether the channel is idle or busy. However, decisions regarding the channel state can be corrupted by fading conditions, leading to wrong decisions regarding the channel state. Collaborative spectrum sensing schemes have been proposed in the literature as a possible way to mitigate the effects of fading. In these schemes, local decisions or observations about the channel state are combined to reach a global decision. Even though collaborative spectrum sensing in general leads to a higher performance, correlated shadowing may reduce the benefits of collaboration. In this paper we investigate the performance of different combining rules in collaborative spectrum sensing in correlated shadowing environment. Our results show that the incremental performance gain achieved by adding more users in the collaboration scheme tends to reduce when the number of users in the collaboration grows, indication that there is a limit in the performance of collaborative spectrum sensing.

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Uma Arquitetura de Hardware e Software Livres para um Telefone VoIP

J. C. S. Américo Filho, D. F. M. Mota, R. C. Mendes, J. A. N. da Silveira, J. C. M. Mota

DOI: 10.14209/sbrt.2012.137

Keywords: VoIP BF518 SIP Liblinphone RTP DSP

Abstract

In this paper we propose a solution of hardware and software for a VoIP phone. The processor ADSP-BF518 makes up the core hardware. All software developed and used is free.

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Alocação Dinâmica de Recursos Bio-inspirada Aplicada a Redes de Cuidados Médicos

Marcelo P. Sousa, Waslon T. A. Lopes, Francisco Madeiro, Marcelo S. Alencar

DOI: 10.14209/sbrt.2012.138

Keywords: Wireless Sensor Networks Cognitive Radio Healthcare Modulation Diversity Resources

Abstract

In this paper, the authors present a protocol inspired by the natural behaviour of desert ants, to allocate resources in accordance with the emergency degree of patients, in healthcare networks. Simulation results show the decrease of the average delay as the probability of opportunistic access increases, which privileges the emergency reporting of patients with higher priority to access the resources. Furthermore, the packet loss rate is decreased by the use of cooperative modulation diversity with spectrum sensing.

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Arquiteturas e Aplicações de Rádio sobre Fibra

Thyago Monteiro S. Pinto, Ísis de A. Lima, Jose Ewerton P. de Farias

DOI: 10.14209/sbrt.2012.139

Keywords: RoF hybrid access networks OFDM

Abstract

This paper presents a discussion on radio over fiber systems (RoF). Some applications and architectures and numerical results for the physical layer performance of a 8- channel OFDM over fiber system are included

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Recurrent Source Separation Structures as Iterative Methods for Solving Nonlinear Equation Systems

R. A. Ando, L. T. Duarte, D. C. Soriano, R. Attux, R. Suyama, Y. Deville, C. Jutten

DOI: 10.14209/sbrt.2012.132

Keywords: Source Separation Nonlinear Mixtures Iterative Methods for Equation Solving Recurrent Networks

Abstract

Source Separation, Nonlinear Mixtures, Iterative Methods for Equation Solving, Recurrent Networks

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Um Esquema de Codificação AL-FEC para Recepção Móvel no Sistema Brasileiro de Televisão Digital

Roberto W. Krauss M., Evelio M. G. Fernández

DOI: 10.14209/sbrt.2012.133

Keywords: SBTVD Raptor Codes mobile reception AL-FEC

Abstract

An Application Layer - Forward Error Correction (AL-FEC) scheme for mobile reception for the Brazilian Digital Television System (SBTVD) is proposed. The mobile reception in the SBTVD is not as effective due to the Doppler effect that occurs when the user is moving. In order not to modify standards already established, it is proposed to implement an AL-FEC scheme based on Raptor codes as a software upgrade in the SBTVD. Simulation results show that proposed scheme provides coding gain with a relatively low cost implementation

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Outage Analysis of Cooperative OFDM Systems with Nonlinear Amplifiers and Relay Selection

C. Alexandre R. Fernandes, Daniel Benevides da Costa, Andre L. F. de Almeida

DOI: 10.14209/sbrt.2012.140

Keywords: Amplify-and-forward relay selection OFDM nonlinear power amplifier outage probability.

Abstract

Cooperative communications have emerged as a promising solution for wireless networks. In particular, currently there is a growing interest in amplify-and-forward (AF) cooperative systems with relay selection. On the other hand, orthogonal frequency division multiplexing (OFDM) has shown to be a key technology for future wireless communication systems. One of the main problems of OFDM systems is the high peak-to-average power ratio (PAPR) of the transmitted signals, which may cause the introduction of nonlinear distortions due to the presence of nonlinear power amplifiers (PAs). In this paper, a theoretical analysis of the outage probability of an AF OFDM system with relay selection is developed. Our analysis takes into consideration the nonlinear distortions introduced by a nonlinear PA and shows how its parameters affects the outage probability for different SNR levels. Numerical results are provided to validate the analytical results.

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