Implementação e Análise de Desempenho de umSistema OFDM com Hardware de Baixo Custo

Eder O. de Souza, João T Dias, Demerson Gonçalves

DOI: 10.14209/sbrt.2021.1570724232

Keywords: prototipagem OFDM SDR

Abstract

Resumo-Com o objetivo de analisar a viabilidade de implementação de elementos de novos sistemas de comunicação sob uma abordagem SDR, este trabalho apresenta a prototipagem de um enlace de comunicação OFDM usando a ferramenta de código aberto GNU Radio e interface de hardware de baixo custo com HackRF One e RTL-SDR. Resultados preliminares se mostraram promissores, permitindo a concepção e teste de sistemas de comunicação digital de uma forma prática e levando em consideração a real condição do canal e deficiências do front-end.

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Realce de Sinais em Ambiente com Variações Acústicas Subaquáticas

Antônio Walkir Sibanto Caldeira, Rosângela Coelho

DOI: 10.14209/sbrt.2021.1570724234

Keywords: Realce de Sinais acústica submarina índice de não-estacionariedade

Abstract

This paper presents a comparative study of acoustic signal enhancement methods in the presence of underwater noises. For this evaluation, the OMLSA, UMMSE and NNESE methods will be used, which are able to deal with nonstationary noises, for enhancing speech and chirp signals. Experiments are conducted considering three nonstationary acoustic noises, using two quality measures (PESQ and OQCM) and intelligibility measure (STOI) for speech signals and one quality measure (SegSNR) for chirp signal. The results show that NNESE presents higher improvements in both experimental scenarios.

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Uma Solução Exata Mais Eficiente para a Soma de Variáveis Aleatórias Nakagami-m e Aplicações

Fernando Darío Almeida García, Francisco Raimundo Albuquerque Parente, Nathaly Orozco, Henry Carvajal, José Cândido Silveira Santos Filho

DOI: 10.14209/sbrt.2021.1570724236

Keywords: Cumulative distribution function Equal-gain combining Nakagami-m distribution Probability density function

Abstract

Sums of random variables (RVs) play a key role in the performance analysis of communication systems. In particular, sums of Nakagami-m RVs allow the performance characterization and evaluation of equal-gain combining (EGC) receivers, a classical diversity technique that has been explored in fifth-generation mobile networks. As the statistical characterization of sums of variables --- in terms of the probability density function (PDF) or the cumulative distribution function (CDF) --- involves an intricate mathematical treatment, the exact solutions available for the sum of Nakagami-m RVs are time-consuming, limited, or even unfeasible as the number of RVs in the sum increases. In this work, we obtain novel exact expressions for the PDF and CDF of the sum of Nakagami-m variates, in terms of infinite series. Compared with the state of the art, the new expressions reduce the computational cost (or, equivalently, the computation time) by more than 95%. To show the applicability of these expressions, we analyze the outage probability in EGC receivers. Monte-Carlo simulations corroborate our analytical results.

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Aplicação de Reservoir Computing para Filtragem de Sinais Caóticos Imersos em Ruído

André Lucas O Duarte, Marcio Eisencraft

DOI: 10.14209/sbrt.2021.1570724246

Keywords: sistemas dinâmicos reservoir computing machine learning eliminação de ruído

Abstract

Resumo- Neste trabalho mostra-se a aplicação de umreservoircomputerpara mitigar ruído adicionado a uma componentecaótica gerada a partir do mapa de Hénon. Assume-se queamostras do sinal caótico livre de ruído estão disponíveis paratreinamento, permanecendo desconhecido o processo caótico quegerou o sinal.

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Performance Evaluation of GPSR and AODV Routing Protocols for High Vehicular Density VANETs

Álvaro T. Amaya, Alexandre Pohl, Ricardo Lüders

DOI: 10.14209/sbrt.2021.1570724253

Keywords: Vehicular ad-hoc network Routing protocols High traffic density Hello messages

Abstract

The vehicular Ad-hoc network (VANETs) is a challenging scenario for routing protocols. The high mobility of nodes is responsible for fast changes of topology and frequent interruptions of links. To cope with this challenge, Greedy Perimeter Stateless Routing (GPSR) and Ad-hoc On-demand Distance Vector (AODV) routing protocols have been devised and widely employed in VANETs. However, most approaches have not properly studied the impact of transmission rates and the effect of time intervals of beacons (Hello messages) in the performance of these protocols. In order to address this impact, this work presents an evaluation of GPSR and AODV protocols in an urban scenario of high vehicular density regarding transmission rates and Hello messages intervals. Results show better performance of GPSR for high transmission rate and high traffic density when compared with AODV. Likewise, GPSR achieves more benefits and fewer impacts from Hello messages than AODV.

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Algoritmo de Detecção de Mudanças Interativo Baseado em Pilhas de Imagens SAR Multitemporais

Pablo Kunz de Jesus, Ricardo Simão Diniz Dal Molin Jr., Marcello G. Costa, Dimas Irion Alves, Manish Sharma, Renato Machado

DOI: 10.14209/sbrt.2021.1570724307

Keywords: Change detection algorithm image stacks clutter suppression

Abstract

This paper presents a change detection (CD) technique for synthetic aperture radar (SAR) image stacks. The algorithm considers three SAR images as input. One image is a common reference for the other two. One image pair is used for detecting targets of interest, while the other assists in clutter suppression. The proposed method explores a control chart to limit the range of amplitudes possibly associate with changes of interest, removing the complexity of the constant false alarm rate (CFAR) filter considered in classical LRT algorithms. For the experimental tests, it was considered ultrawideband (UWB) very high frequency (VHF) SAR images. Due to their temporal stability, typical in this type of SAR image, clutter could be successfully suppressed, favoring reducing the false alarm rate and keeping a high probability of detection.

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Protótipo de um Sistema de Comunicação Acústico para Fins Didáticos

Lucas Bezerra Dantas Saraiva, Vicente A. de Sousa Jr., Daniel R. de Luna

DOI: 10.14209/sbrt.2021.1570725084

Keywords:

Abstract

The various stages of a communication system are often not well explored in the academic environment due to the cost of radiofrequency equipment to put into practice the knowledge discussed in the classroom. The purpose of this work is to present an acoustic communication system prototype using script programming language, which can serve as a simple platform for software-defined radio (SDR), bringing practical experience and interactivity to the student learning digital modulation. The experiment may spark the idea of using everyday devices to compose handmade communications systems, by using devices such as a headset (as a transmitter) and microphone (as a receiver). As a case study, an image is transmitted by mechanical waves in the audible range, visualizing the signal in time and frequency, and also discussing aspects of synchronization and response to the channel impulse.

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Cobertura de TV Digital: Avaliação Subjetiva e Medições Em um Cenário Real

Aureliano Neto, André Diniz, Marcio Rodrigues, Vicente A. de Sousa Jr., Hallyson Mendonça

DOI: 10.14209/sbrt.2021.1570725854

Keywords:

Abstract

Open and free Digital TV remains an importantand popular service in Latin America, specially in Brazil with the implantation of the Brazilian Digital Terrestrial TelevisionSystem (SBTVD-T). This paper presents a case study of power measurements obtained according to the ABNT 15604/2017 standard, aiming to compare the coverage area of the digital television service in the city of Natal with that projected with SIGAnatel, which runs the point-to-area prediction method ITU-R P.1546. As a main result, we intended to fill the gap with technical material related to the discussion of digital TV in Brazil by presenting measures of power from stations in operation as well as subjective signal quality evaluations provided by final users for comparison purposes.

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A Case Study on Forecasting New Daily Cases of COVID 19 at Different Scales in Brazil

Elloá Guedes, Cetherine Martins, Paulo Ribeiro Lins Júnior, Edmar Candeia Gurjão

DOI: 10.14209/sbrt.2021.1570726085

Keywords: COVID 19 Machine Learning Forecasting Model Selection

Abstract

Forecasting new COVID-19 daily cases is a task that favors actions that mitigate the damages caused by the virus. In this perspective, the present work evaluates different Machine Learning models for this purpose, considering different scales in Brazil (country, state, and city levels). After a grid search with 860 configurations, the results indicate an Artificial Neural Network well suited for national level forecasting. On the other hand, with a lower performance at the larger scale, Elastic Net was good at predicting smaller ones. This case study highlights the difficulties of model reusing for COVID 19 forecasting and also the necessity of model choice and adjustment depending on the data scale.

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Kalman Filter-Based Carrier Tracking with Ionospheric Scintillation Mitigation for GNSS

Rafael A. M. Lopes, Felix Antreich, Hélio Kuga

DOI: 10.14209/sbrt.2021.1570726233

Keywords:

Abstract

In this work we present two architectures of Kalman phase locked loop (PLL) to mitigate ionospheric scintillation induced effects on global navigation satellite systems (GNSS) receivers: a discriminator-based and an extended Kalman PLL using independent kinematic process models for the scintillation phase and amplitude to improve robustness in carrier synchronization. We show that the Kalman PLLs achieve advanced Doppler phase and scintillation amplitude estimation performance compared to an extended Kalman PLL with an autoregressive (AR) scintillation process model, with comparable scintillation phase estimation performance. The proposed Kalman PLLs have the additional benefits of not requiring parameter identification of AR models.

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