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- A 2D Ray-Tracing Based Model for Micro- and Millimeter-Wave Propagation Through VegetationPublication . Leonor, Nuno R.; Caldeirinha, Rafael F. S.; Fernandes, Telmo R.; Ferreira, David; Sánchez, Manuel GarcíaA novel two dimensional model to characterize the electromagnetic behavior of trees has been developed with the purpose of being used in ray-tracing based simulation platforms. This model uses various point scatterers with specific radiation characteristics to describe the effect of the trees present in the radiowave propagation path. The method to extract the parameters of the point scatterers from measurements is presented. The performance of this novel formulation is assessed in a tree formation scenario against measurements results obtained in a controlled environment, inside an anechoic chamber, at 20 and 62.4 GHz. Additionally, a comparison analysis with a discretized radiative energy transfer (dRET) approach is conducted, where a relatively good agreement has been found. The absence of readily plug-in models considering propagation through and/or around vegetation makes this new tool interesting for radio planning purposes.
- 360° Video Coding using Adaptive Tile PartitioningPublication . Carreira, J.; Faria, Sergio M. M. de; Tavora, Luis M. N.; Navarro, Antonio; Assuncao, Pedro A.Encoding 360° video with ultra high definition requires high bit rate to guarantee either immersive experiences and acceptable QoE in video delivery services, or high performance in machine vision applications. However, since in general the full Field-of-View (FoV), i.e., 360°, is not required at once, a great deal of bandwidth can be saved by allowing partial decoding of limited size FoVs. The conventional approach to accomplish such goal has been to encode several fixed-size independent tiles of each video frame. In this work a novel tile-based video coding scheme is proposed to achieve further reduction on the average maximum bit rate required for partial delivery of 360° video. The proposed method dynamically adapts the tile sizes to the omnidirectional video content in order to obtain uniform bit rate in each one. Therefore, more complex image regions, i.e., those requiring higher bit rates are partitioned in smaller tiles, allowing finer bit rate granularity when FoVs with higher spatiotemporal complexity are selected for transmission and decoding. The simulation results show that the proposed adaptive tile-based coding mechanism outperforms the conventional fixed-size tilling methods, achieving an average of 4.78% and 16.88% bit rate reduction for FoVs of 90° × 90° and 45° × 45°, respectively.
- 3D Indoor Radio Coverage for 5G Planning: a Framework of Combining BIM with Ray-tracingPublication . Louro, João; Fernandes, Telmo Rui; Rodrigues, Hugo; Caldeirinha, Rafael F. S.This paper presents a framework to predict indoor radio wave coverage in buildings. Such method includes the capability to import BIM (Building Information Modelling) files that contain structured physical geometry and dimension data, including the material types that are of uttermost importance in evaluating their dielectric properties. Appropriated extraction of physical and dielectric attributes of the building elements was used as input to a 3D radio wave propagation ray-tracing developed in MatLab that allows the prediction of the received radio signal level at any location within the computational volume. Results are presented for line-of-sight contributions and first and second order reflections. Despite the generic nature of the proposed framework, prediction results are presented at 3.6 GHz, envisaging emerging 5G indoor radio coverage.
- 3D PARTICLE SYSTEMS FOR AUDIO APPLICATIONSPublication . Fonseca, NunoAlthough particle systems are well know for their use in computer graphics, their application in sound is very rare or almost non-existent. This paper presents a conceptual model for the use of particle systems in audio applications, using a full rendering system with virtual microphones: several virtual particles are spread over a virtual 3D space, where each particle reproduces one of the available audio streams (or a modified version), and the overall sound is captured by virtual microphones. Such system can be used on several audio-related areas like sound design, 3D mixing, reverb/impulse response design, granular synthesis, audio up-mixing, and impulse response up-mixing.
- 4D Light Field Disparity Map estimation using Krawtchouk PolynomialsPublication . Lourenco, Rui; Rivero-Castillo, Daniel; Thomaz, Lucas A.; Assuncao, Pedro A. A.; Tavora, Luis M. N.; Faria, Sergio M. M. deThis work presents an improved method to estimate disparity maps obtained from light field cameras using a novel edge detection algorithm based on Krawtchouk polynomials. The proposed method takes advantage of these polynomials to determine gradient information and find the edges based on automatically estimated weak and strong thresholds. The calculated edges in the gray scale epipolar plane image representation of a light field are then used to improve the accuracy of object boundaries in the the disparity map. The proposed method achieves better results when compared to other edge detection algorithms, both in terms of objective and subjective quality, specifically by reducing the mean squared error and the artifacts in the object boundaries. Furthermore, on average, the proposed method outperforms the state-of-the-art depth estimation algorithms, in terms of the objective quality of the final disparity map, namely for the commonly used HCI dataset.
- 802.21-MPA-IMS ArchitecturePublication . Rodrigues, Carlos Miguel de Jesus; Rabadão, Carlos; Pereira, AntónioMobility has become a keyword nowadays with the evolution of mobile devices market and proliferation of realtime services. IP Multimedia Subsystem (IMS) is a single, standardized service framework that supports voice, video, data and messaging services, but does not provide seamless mobility for packet based sessions. This paper purposes an IMS architecture with IEEE 802.21 and media-independent pre-authentication (MPA) integrated. IEEE 802.21 can enable this seamless mobility in IMS and, additionally, MPA provides a secure handover optimization scheme, reducing, as a consequence, handover latency. The main goal of this architecture is to provide seamless and secure handovers between different access technologies in an IMS-based environment.
- Abordagem baseada em Algoritmos Genéticos para deteção de vulnerabilidades de SQL Injection em Aplicações Web PHPPublication . Baptista, Kevin; Bernardino, Anabela Moreira; Bernardino, Eugénia MoreiraHoje em dia, existe uma maior preocupação com a segurança no desenvolvimento de aplicações web. No entanto, ainda existem muitos ataques a este tipo de aplicações, perpetuados por hackers que se aproveitam das vulnerabilidades destas aplicações. Estas vulnerabilidades podem estar associadas a inúmeros fatores, desde configurações incorretas, falhas nas políticas de segurança, sistemas ou componentes desatualizados ou problemas diretamente associados ao código desenvolvido. Os ataques a aplicações web tem como resultado perda de informação privilegiada. Para mitigar este problema, existem varias ferramentas automatizadas que permitem auxiliar profissionais da área a identificar estas vulnerabilidades. No entanto, manter estas ferramentas atualizadas com a evolução tecnológica tem-se demonstrado um desafio. Neste artigo, propomos uma abordagem para detetar vulnerabilidades de SQL Injection no código-fonte de varias aplicações web PHP, usando Algoritmos Genéticos (AG). Os resultados obtidos mostram a eficiência do AG em relação a outras ferramentas existentes.
- Active reflection coefficients characterization system for multiple input multiple output antennasPublication . Jordão, Marina; Belo, Daniel; Caldeirinha, Rafael F. S.; Oliveira, Arnaldo S. R.; Carvalho, Nuno B.The main objective of this study is to present a characterization system that can be used to measure the active reflection coefficient of each port of the multiple input multiple output (MIMO) antennas, when the main beam is steered to an intended direction. Since MIMO systems are composed of antennas with several elements and each antenna element is connected to a power amplifier, an active component, the beamforming will contribute to the mismatch of each branch. To this extent, a calibrated measurement system has been implemented using off-the-shelf software defined radio and designed to effectively extract such coefficients, when all the ports are simultaneously excited. Results for linear and planar MIMO antenna arrays have been experimentally obtained for several beam directions and the impact of beamforming on each element of the antenna is presented and compared to simulated results. Additionally, their behaviour was also assessed when some of the radiation elements are deliberately disconnected, mimicking those not working properly.
- Adaptive Evolutionary Testing: An Adaptive Approach to Search-Based Test Case Generation for Object-Oriented SoftwarePublication . Ribeiro, José Carlos Bregieiro; Zenha-Rela, Mário Alberto; de Vega, Francisco FernándezAdaptive Evolutionary Algorithms are distinguished by their dynamic manipulation of selected parameters during the course of evolving a problem solution; they have an advantage over their static counterparts in that they are more reactive to the unanticipated particulars of the problem. This paper proposes an adaptive strategy for enhancing Genetic Programming-based approaches to automatic test case generation. The main contribution of this study is that of proposing an Adaptive Evolutionary Testing methodology for promoting the introduction of relevant instructions into the generated test cases by means of mutation; the instructions from which the algorithm can choose are ranked, with their rankings being updated every generation in accordance to the feedback obtained from the individuals evaluated in the preceding generation. The experimental studies developed show that the adaptive strategy proposed improves the test case generation algorithm's efficiency considerably, while introducing a negligible computational overhead.
- Álgebra Linear: uma abordagem intuitiva e práticaPublication . Silva Vicente, Leonel; Campos, Carlos; OPSA 2.0 – Observatório para o Sucesso AcadémicoEste livro nasceu da vontade de partilhar a experiência acumulada ao longo de vários anos de ensino de Álgebra Linear, procurando oferecer a estudantes e professores uma abordagem clara, prática e acessível. Este documento pretende ser um instrumento de apoio ao estudo da álgebra linear, contribuindo para que os leitores desenvolvam o seu raciocínio matemático e adquiram um conjunto de técnicas que lhes permitam resolver uma ampla variedade de problemas. Os autores esperam, com este livro, reforçar as competências dos leitores e facilitar a sua progressão nos respetivos cursos superiores, na investigação ou na vida profissional. Não se pretende, de forma alguma, substituir os inúmeros manuais de álgebra linear já existentes. O objetivo principal é apresentar uma abordagem intuitiva e prática dos tópicos essenciais - desde os conceitos fundamentais de vetores, matrizes, sistemas de equações lineares e determinantes, até aos temas mais avançados, como os espaços vetoriais reais, as transformações lineares e os valores e vetores próprios. Cada conceito é introduzido de forma clara e concisa, sendo acompanhado de exemplos ilustrativos que facilitam a compreensão e a aplicação prática. Este livro não tem como propósito explorar exaustivamente os conteúdos nem desenvolver demonstrações matemáticas formais, dado que tal já é amplamente tratado na bibliografia especializada. Ainda assim, reconhece-se a importância das demonstrações teóricas e da compreensão rigorosa dos fundamentos. Para os leitores que pretendam aprofundar a teoria de forma mais sistemática, são sugeridos, no final do documento, diversos livros de referência que apresentam um tratamento formal e aprofundado da álgebra linear. A estrutura do livro assenta na divisão dos conteúdos em atividades autónomas, cada uma das quais requer, em média, entre 3 e 5 horas de estudo ou trabalho, consoante os conhecimentos prévios, as competências do leitor e os objetivos a atingir. Sempre que possível, encoraja-se a consulta de bibliografia complementar, Índice de Conteúdos com o intuito de aprofundar e consolidar os conceitos apresentados.No último capítulo são incluídos testes que permitem ao leitor aplicar os conhecimentos adquiridos ao longo dos vários capítulos. Estes exercícios visam reforçar a aprendizagem, promover a autonomia e facilitar a identificação de eventuais lacunas conceptuais. A resolução dos testes, idealmente realizada num período de cerca de uma hora e sem recurso a apoio externo, constitui uma oportunidade para desenvolver competências na interpretação e aplicação prática dos conteúdos estudados.