Orientador: Paulo Cardieri / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-11T20:35:16Z (GMT). No. of bitstreams: 1 Nardelli_PedroHenriqueJuliano_M.pdf: 487443 bytes, checksum: d0645b76b7fd0f22601a42712d440da4 (MD5) Previous issue date: 2008 / Resumo: As características inerentes às redes ad hoc sem fio como, por exemplo, a ausência de uma infraestrutura pré-determinada e a possibilidade de enlaces de múltiplos saltos, exigem medidas de desempenho que capturem as inter-relações entre as camadas física, de acesso ao meio e de enlace. Com base na métrica eficiência de informação agregada e no atraso de pacote, as relações de compromisso entre diversas variáveis da rede são analisadas neste trabalho. É mostrado também que a possibilidade de retransmissão para pacotes recebidos em erro pode melhorar o desempenho da rede. Considerando sistemas em que uma parcela dos enlaces ativos estão em situação de outage, observa-se que os melhores resultados ocorrem para probabilidade de ocorrência de outage na rede entre 50% e 80%. Para enlaces de múltiplos saltos, os resultados mostram que é preferível ter transmissões formadas por um número maior de saltos, com receptores que exijam uma maior potência mínima para a recepção de um pacote. / Abstract: The inherent characteristics of ad hoc networks such as the lack of infrastructure and the possibility of multi-hop links require performance measures that capture the relationships between physical layer, medium access control and link layer. Based on aggregate information efficiency metric and packet delay, trade-offs involving several networks variables are analyzed. It is shown that the possibility of packet retransmission improves the network performance. In networks where part of the active links is in outage, the best results are found for outage probabilities between 50% and 80%. Concerning multi-hop links, the results show that it is preferable having transmissions with a greater number of hops formed by receptor terminals that require higher threshold powers for a packet reception. / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Road accidents represent a serious social problem and are one of the leading causes of human death and disability on a global scale. To reduce the risk and severity of a road accident, a variety of new safety applications can be realized through wireless communications among vehicles driving nearby each other, or among vehicles and especially deployed road side units (RSUs), a technology known as a vehicular ad hoc network (VANET). Most of the VANET-enabled safety applications are based on broadcasting of safety messages by vehicles or RSUs, either periodically or in case of an unexpected event, such as a hard brake or dangerous road condition detection. Each broadcast safety message should be successfully delivered to the surrounding vehicles and RSUs without any excess delay, which is one of the main functions of a medium access control (MAC) protocol proposed for VANETs. This thesis presents VeMAC, a new multichannel time division multiple access (TDMA) protocol specifically designed to support the high priority safety applications in a VANET scenario. The ability of the VeMAC protocol to deliver periodic and event-driven safety messages in VANETs is demonstrated by a detailed delivery delay analysis, including queueing and service delays, for both types of safety messages. As well, computer simulations are conducted by using MATLAB, the network simulator ns-2, and the microscopic vehicle traffic simulator VISSIM, in order to evaluate the performance of the VeMAC protocol, in comparison with the IEEE 802.11p standard and the ADHOC MAC protocol (another TDMA protocol proposed for ad hoc networks). A real city scenario is simulated and different performance metrics are evaluated, including the network goodput, protocol overhead, channel utilization, protocol fairness, probability of a transmission collision, and safety message delivery delay. It is shown that the VeMAC protocol considerably outperforms the existing MAC schemes, which have significant limitations in supporting VANET safety applications. In addition to enhancing road safety, in-vehicle Internet access is one of the main applications of VANETs, which aims at providing the vehicle passengers with a low-cost access to the Internet via on-road gateways. This thesis presents a new strategy for deploying Internet gateways on the roads, in order to minimize the total cost of gateway deployment, while ensuring that a vehicle can connect to an Internet gateway (using multihop communications) with a probability greater than a specified threshold. This cost minimization problem is formulated by using binary integer programming, and applied for optimal gateway placement in a real city scenario. To the best of our knowledge, no previous strategy for gateway deployment has considered the probability of multihop connectivity among the vehicles and the deployed gateways. In order to allow a vehicle to discover the existence of an Internet gateway and to communicate with the gateway via multihops, a novel data packet routing scheme is proposed based on the VeMAC protocol. The performance of this cross-layer design is evaluated for a multichannel VANET in a highway scenario, mainly in terms of the end-to-end packet delivery delay. The packet queueing at each relay vehicle is considered in the end-to-end delay analysis, and numerical results are presented to study the effect of various parameters, such as the vehicle density and the packet arrival rate, on the performance metrics. The proposed VeMAC protocol is a promising candidate for MAC in VANETs, which can realize many advanced safety applications to enhance the public safety standards and improve the safety level of drivers/passengers and pedestrians on roads. On the other hand, the proposed gateway placement strategy and packet routing scheme represent a strong step toward providing reliable and ubiquitous in-vehicle Internet connectivity.