Controlo de acesso ao meio em comunicações veiculares de tempo-real

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.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.Programa Doutoral em Engenharia Eletrotécnic

Evolution of NICNET as an incrementally intelligent network

The evolution of NICNET, the Computer-Communication network of the National Informatics Centre, is so oriented that integration and globalization are progessively implemented utilizing the latest cost-effective technologies available In the international market. With the choice of SSMA/CDMA based VSAT technology utilizing a C-band transponder, during the nucleating stage of NICNET, the top 500 cities and towns in India have been linked apart from more than 100 sites of mega projects and economically important locations. In the next step, high speed SCPC based VSATs with two-way as well as data broadcast capabilities utilizing a Ku-band transpoder is enabling the realisation of the NICNET InfoHighway linking metropolises and big cities as an overlay network over tile low speed NICNET. Dedicated high speed external gateways provide initial infrastructure for globalization of NICNET. In the next phase, it is planned to introduce software based information networking architecture on NICNET for which the concept of structure-function matrix based incrementally intelligent network design is proposed in this paper. As the demand for sophisticated services like CUGs, virtual private network Service, universal personal communications, mobile communication and multimedia services increase, NICNET will be required to respond with more flexible access, intelligent management and versatile charging regimes than what is possible currently, all within the frame-work of an open system architecture. Imperatives of globalization and service creation will be rendered incrementally intelligent utilising an approach based on intelligent hypermedia with imbedded expert system for realising intelligent navigation and integration. The same AI approach is determined to be advantageous for intelligent integration of traffic and facility with adaptive flexible routing. The design of NICNET as an intelligent global network providing a versatile local infrastructure with multiple gateway hooks to a global network employing low or medium earth orbiting satellite constellation, is identified as a desirable long term goal

The Impact of the Internet on Telecommunication Architectures

The ever-growing popularity of the Internet is dramatically changing the landscape of the communications market place. The two separate worlds of the Internet and Telecommunications are converging. The respective advantages of the two environments are being integrated to fulfill the promise of the information super-highways. In this paper, we examine the impact of the Internet on the main telecommunication architectures, namely the IN, the TMN and TINA. There are two new tendencies for implementing telephony services in combination with the Internet: running part of the control sys tem over the Internet, or conveying both the user data and the control information over the Internet. We examine these two trends, and elaborate on possible ways of salvaging the best parts of the work achieved by the TINA-Consortium in the Internet context

A Worldwide State-of-the-Art Analysis for Bus Rapid Transit: Looking for the Success Formula

This paper’s intended contribution, in terms of providing an additional angle in the existing Bus Rapid Transit (BRT) state-of-the-art knowledge spectrum, is a dual one. On the one hand, it provides a detailed description of the mode, re-defining BRT as an overall concept by identifying, discussing, and categorizing in a systematic way its strengths and its weaknesses in comparison with rail-based solutions and conventional bus services. On the other hand, it presents in detail a number of selected scheme-oriented applications from around the world, looking into some of the basic ingredients behind BRT’s success (or failure) stories. This is a scientific effort that could inform the reader about the current status of BRT internationally and about the challenges and opportunities that exist when trying to materialize BRT’s potential as an effective urban passenger solution that could challenge the merits of more conventional mass-transit options

Global Trade Impacts: Addressing the Health, Social and Environmental Consequences of Moving International Freight Through Our Communities

Examines freight transportation industry trends; the impact of global trade on workers, the environment, and health in both exporting and importing countries; and organizing strategies and policy innovations for minimizing the damage and ensuring health

Anything You Can Do I Can Do Better

We are about to witness one of those revolutionary shifts in technology that pass through similar stages of pathologic stress often chronicled for human behavior: first an imperceptible perturbation deemed a singularity or interesting curiosity; then the change grows into a faddish amusement or distraction; soon the amusement starts generating enough money or activity to become either, or both. a real business or a threat to other established enterprises or even to the social order; and finally the technological change takes hold, completely revamps its corner of the universe, economy, or society, and now enters the realm of permanent ?problem? or ?opportunity,? depending on your own particular history and demeanor. The much abused shift of ?paradigms? hardly suffices to describe such changes, for paradigms deal with models of behavior, business, and sociopolitical g?stalt. The Internet is more than a new and different model for communicating electrons. The Internet doesn?t even exist, yet it has passed through the several stages of stress, and is midway between becoming a real business and a threat to the established order of things, and likely to completely revamp telecom, if not some segment of the universe