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Nuno Fábio Gomes Camacho Ferreira Controlo De Acesso Ao Meio Universidade de Aveiro Departamento de Eletrónica, Telecomunicações e Ano 2019 Informática Nuno Fábio Controlo de Acesso ao Meio em Comunicações Gomes Veiculares de Tempo-Real Camacho Ferreira Medium Access Control in Real-Time Vehicular Communications Universidade de Aveiro Departamento de Eletrónica, Telecomunicações e Ano 2019 Informática Nuno Fábio Controlo de Acesso ao Meio em Comunicações Gomes Veiculares de Tempo-Real Camacho Ferreira Medium Access Control in Real-Time Vehicular Communications Tese apresentada à Universidade de Aveiro para cumprimento dos requisitos necessários à obtenção do grau de Doutor em Engenharia Eletrotécnica. Apoio financeiro da FCT refª SFRH/BD/31212/2006 e do FSE no âmbito do III Quadro Comunitário de Apoio. Dedico este trabalho à minha esposa, Mónica, ao meu filho, Guilherme, à minha mãe, Paulina, e à minha sogra Filomena, que estará sempre comigo. o júri Presidente Doutor João Filipe Colardelle da Luz Mano, Professor Catedrático da Universidade de Aveiro Vogais Doutora Susana Isabel Barreto de Miranda Sargento, Professora Associada com Agregação da Universidade de Aveiro Doutor José Boaventura Ribeiro da Cunha, Professor Associado com Agregação da Universidade de Trás-os-Montes e Alto Douro Doutor Paulo José Lopes Machado Portugal, Professor Associado da Universidade do Porto Doutor José Alberto Gouveia Fonseca, Professor Associado da Universidade de Aveiro Doutor Mário Jorge de Andrade Ferreira Alves, Professor Coordenador do Instituto Superior de Engenharia do Porto agradecimentos Attaining a PhD degree may, sometimes, seem like an endless road, in which hard work and innovative ideas may not seem enough. However, that illusion may be suppressed with the support and encouragement of important people, which I did and owe gratitude to them. First of all, I would like to thank Professor José Alberto Gouveia Fonseca, for all the discussions and knowledgeable feedback, as well as his friendship and support. Special words also to Professor Joaquim Ferreira, whose help and support in this final stage were very important. I appreciate the financial and logistic support of the Portuguese Foundation for Science and Technology (FCT), the University of Aveiro (UA), and the Institute of Electronics and Telematics Engineering of Aveiro (IEETA), for the realization of this thesis. To my dear wife, Mónica, for her inexhaustible support and constant companionship and encouragement, to my beloved son, Guilherme, for being a source of motivation, and to my mother, Paulina, for always being there unconditionally in my entire life, I am truly grateful. To Filomena, I am sorry for not being able to show you this, I am sure you would be proud. A special thanks to my sister Mariana, to my true friend Pedro, and my entire family. I would also like to thank my colleagues. Thanks to the jury who kindly accepted to review my thesis. palavras-chave Controlo de Acesso ao Meio (MAC), Ambientes Veiculares, Comunicações Tempo-Real, IEEE 802.11p / WAVE, Infra-Estrutura. resumo Apesar de diversas medidas preventivas, o número de acidentes rodoviários continua a ser muito elevado, sendo mesmo considerado uma questão de saúde pública por algumas entidades. Esta tese tem como objetivo geral contribuir para a redução desse número de acidentes, e consequentes fatalidades, através da utilização de aplicações de segurança que envolvem comunicação entre veículos. Em particular, o objetivo principal é garantir que a comunicação entre utentes, em ambientes veiculares, seja efetuada com limites temporais apropriados à transferência de informações críticas. De forma mais detalhada, é estudada a gestão do escalonamento das transmissões (controlo de acesso ao meio – MAC) que irá definir quem vai comunicar e quando o pode fazer. São estudadas situações (desejadas) onde há uma infra-estrutura de comunicações com cobertura integral (RSUs), a partir da qual se faz a coordenação do acesso ao meio pelos veículos (OBUs), e situações (esporádicas, por ausência de RSU) em que a rede de comunicação é “ad hoc” e apenas constituída pelos veículos presentes. Utiliza-se a recente norma WAVE / IEEE 802.11p, específica para comunicações veiculares, e propõe-se uma solução baseada em TDMA, com coordenação apropriada entre RSUs para disseminação efetiva de um evento crítico de segurança. A escolha do instante para o broadcast inicial do evento de segurança também é tida em conta, e são comparados dois casos distintos. No caso da ausência de infraestrutura, derivam-se métodos para minimizar colisões no acesso ao meio de comunicação, e maximizar a largura de banda disponível. Os resultados refletem o atraso total end-to-end, mostrando tempos apropriados para os requisitos das aplicações em causa, e evidenciando melhorias aquando da escolha alternativa para o instante do broadcast inicial. keywords Medium Access Control (MAC), Vehicular Environments, Real-Time Communications, IEEE 802.11p / WAVE, Infrastructure. abstract Despite several preventive measures, the number of roadway accidents is still very high, being considered even a problem of public health by some entities. This thesis has as global purpose of contributing to the reduction of that number of accidents, and consequent fatalities, by using safety-related applications that use communication among vehicles. In particular, the primary goal is guaranteeing that communication between users in vehicular environments is done with appropriate time bounds to transfer safety-critical information. In detail, it is studied how to manage the scheduling of message’s transmissions (medium access control - MAC), in order to define precisely who will communicate and when is the appropriate instant. The preferable situation where a communication infrastructure is present with full coverage (RSUs) is also studied, from which medium access control is defined precisely, and vehicles (OBUs) become aware of medium utilization. Also, sporadic situations (e.g., absence of RSUs) are studied in which the communication network is “ad hoc” and solely formed by the current vehicles. It is used the recently WAVE / IEEE 802.11p standard, specific for vehicular communications, and it is proposed a TDMA based solution, with appropriate coordination between RSUs in order to effectively disseminate a critical safety event. It is taken into account two different ways of choosing the instant for the initial broadcast, and both cases are compared. In case there is no infrastructure available, methods are derived to minimize communication medium access collisions, and to maximize the available bandwidth. The results reflect the total end-to-end delay, and show that adequate times are attained, and meet with the requisites for the type of applications being considered. Also, enhancements are obtained when using the alternate choice for the initial broadcast instant. TABLE OF CONTENTS TABLE OF CONTENTS ................................................................................................................................. XV LIST OF FIGURES ....................................................................................................................................... XIX LIST OF TABLES ........................................................................................................................................ XXI LIST OF ABBREVIATIONS ........................................................................................................................ XXIII LIST OF VARIABLES ................................................................................................................................XXVII CHAPTER 1 .................................................................................................................................................. 1 INTRODUCTION .......................................................................................................................................... 1 1.1 CONTEXT SCENARIO .................................................................................................................................. 2 1.2 PROBLEM STATEMENT AND MOTIVATION ..................................................................................................... 4 1.3 THE THESIS ............................................................................................................................................. 5 1.4 CONTRIBUTIONS ...................................................................................................................................... 5 1.5 DOCUMENT ORGANIZATION ....................................................................................................................... 6 CHAPTER 2 .................................................................................................................................................. 9 OVERVIEW OF VEHICULAR COMMUNICATIONS .......................................................................................... 9 2.1 WIRELESS COMMUNICATIONS AND REAL-TIME REQUIREMENTS ...................................................................... 10 2.1.1 Wireless Communications ............................................................................................................. 10 2.1.2 Real-Time Requirements ............................................................................................................... 12 2.2 VEHICULAR NETWORKS AND STANDARDS .................................................................................................... 15 2.2.1 Accidents
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