Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-04-19T13:47:30Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Aleciano_Lobo_Junior_Dissertacao.pdf: 9925931 bytes, checksum: bcf8228c8e29cef0e7302ea7716436ec (MD5) / Made available in DSpace on 2017-04-19T13:47:31Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Aleciano_Lobo_Junior_Dissertacao.pdf: 9925931 bytes, checksum: bcf8228c8e29cef0e7302ea7716436ec (MD5) Previous issue date: 2016-08-24 / CNPQ / A implantação de sistemas de transportes inteligentes (Intelligent Transportation System (ITS)) representa um desafio para a comunidade científica e industrial. As melhorias na segurança e eficiência do tráfego de veículos são os principais objetivos de sistemas ITS. Em 2014, acidentes de trânsito foram responsáveis por 32.765 mortes e mais de dois milhões de feridos somente nos Estados Unidos. O Brasil teve resultados piores em 2014: foram 52.226 pessoas mortas em acidentes de trânsito. A Administração Nacional de Segurança em Tráfego de Autoestradas (National Highway Traffic Safety Administration (NHTSA)) estima que sistemas de comunicações veiculares possam reduzir a ocorrência e severidade de 22 de 37 tipos comuns de acidentes. Assim, comunicações Vehicle-to-Vehicle (V2V) e Vehicle-to-Infrastructure (V2I) podem melhorar a segurança por meio da complementação, ou em alguns casos, provendo alternativas aos equipamentos ativos tradicionais baseados no sensoriamento como radares, Light Detection And Ranging (LIDAR) ou por visão. Sobre a eficiência do tráfego de veículos, sistemas ITS implantados via Vehicular Ad-Hoc Networks (VANETs) irão também contribuir para as melhorias nestes índices por meio de ferramentas de monitoramento de tráfego, rotas dinâmicas e alertas sobre as condições da via. Em algumas localidades, estas características de tráfego variam ao longo de um mesmo dia, portanto, engenheiros ITS e pesquisadores devem estar preparados para este comportamento dinâmico de maneira efetiva enquanto analisam o desempenho do sistema. Por outro lado, uma vez que sistemas ITS dependem de serviços de rede, estudos específicos são necessários para considerar os parâmetros de comunicação e de mobilidade veicular. Este trabalho apresenta um modelo de desempenho que considera parâmetros de mobilidade e comunicação para guiar a tomada de decisões no planejamento e gerência de infraestruturas VANETs. As Redes de Petri Estocásticas (SPN) são o formalismo adotado. A dissertação também adota uma metodologia de avaliação. Para representar o comportamento das estações sem fio, foram empregadas distribuições expolinomiais. Os resultados mostram que o modelo proposto produz resultados que podem auxiliar engenheiros e projetistas a implantar e gerenciar infraestruturas VANETs. / The deployment of Intelligent Transportation System (ITS) is a challenge for industry and scientific community. Improvements on safety and vehicular traffic efficiency are the main ITS goals. In 2014, car accidents were responsible for 32,675 deaths and over two million injuries in the United States alone. Brazil had worse results: in 2014, 52,226 people died in car accidents. The National Highway Traffic Safety Administration (NHTSA) estimates that vehicular communications may reduce the severity of 22 of 37 common types of accidents. Thus, V2V and V2I wireless communications may enable improved safety system effectiveness by complementing or, in some instances, providing alternative approaches to the traditional active safety equipment based on autonomous sensing, such as radar, lidar, or vision. Regarding vehicular traffic efficiency, ITS deployed through Vehicular Ad-Hoc Networks (VANETs) will also contribute to improvements in these indices by traffic monitoring tools, dynamic routes, and road condition alerts. In some locations, those traffic characteristics change widely within a single day, therefore, ITS engineers and researchers must deal with that dynamic behavior in an effective manner while analyzing the system performance. On the other hand, once the ITS depends on networking services, specific studies are required to consider the communication parameters along with vehicle mobility. This work presents a performance model that considers both mobility and communication parameters to guide decision-making during the design and management of VANETs infrastructures. The Stochastic Petri Net (SPN) is the adopted formalism. This dissertation also adopts an evaluation methodology. We employed expolynomial distributions to represent the service rates of the wireless stations. Results show that the proposed model provides results that may assist engineers to design and manage VANETs infrastructures.

Safety analysis is critical when developing new engineering systems. Many systems have to function under randomly occurring events, making stochastic processes useful in a safety modelling context. However, a general stochastic process is very challenging to analyse mathematically. Therefore, model restrictions are necessary to simplify the mathematical analysis. A popular simplified stochastic model is the Semi-Markov process (SMP), which is a generalization of the "memoryless" continuous-time Markov chain. However, only a subclass of Semi-Markov models can be analysed with non-simulation based methods. In these models, the cumulative density function (cdf) of the random variables describing the system is in the form of expolynomials. This thesis investigates the possibility to extend the number of Semi-Markov models that can be analysed with non-simulation based methods by approximating the non-expolynomial random variables with expolynomials. This thesis focus on approximation of models partially described by LogNormal and Weibull distributed random variables. The result shows that it is possible to approximate some Semi-Markov models with non-expolynomial random variables. However, there is an increasing difficulty in approximating a non-expolynomial random variable when the variability in the distribution increases. / Säkerhetsanalys är avgörande när man utvecklar nya tekniska system. Många system måste fungera under slumpmässigt inträffande händelser, vilket gör stokastiska processer användbara i ett säkerhetsmodellerande sammanhang. En allmän stokastisk process är dock mycket utmanande att analysera matematiskt. Därför är begränsningar på modellen nödvändiga för att förenkla den matematiska analysen. En populär förenklad stokastisk modell är Semi-Markov-processen (SMP), vilket är en generalisering av den "minneslösa" tids-kontinuerliga Markov-kedjan. Dock är det endast en underklass av Semi-Markov-modeller som kan analyseras med icke-simuleringsbaserade metoder. I dessa modeller är den kumulativa densitetsfunktionen (cdf) för de slumpmässiga variablerna som beskriver systemet i form av expolynomials. Denna rapport undersöker möjligheten att utöka antalet Semi-Markov-modeller som kan analyseras med icke-simuleringsbaserade metoder genom att approximera de icke-expolynomial slumpvariablerna med expolynomials. Vi fokuserar på approximering av modeller som delvis beskrivs av LogNormal distribuerade och Weibull distribuerade slumpmässiga variabler. Resultatet visar att det är möjligt att approximera vissa stokastiska variabler som är icke-expolynomial i Semi-Markov-modeller. Resultatet visar dock att det är en ökande svårighet att approximera en icke-expolynomial slumpmässiga variabeln när variabiliteten i fördelningen ökar.