Medium Access Control, Packet Routing, and Internet Gateway Placement in Vehicular Ad Hoc Networks
A vehicular ad hoc network (VANET) is an emerging technology which is expected to enhance the public safety standards and provide a safer environment for drivers/passengers and pedestrians on roads through a variety of advanced safety applications. Most of the safety applications proposed for VANETs are based on one-hop broadcasting of safety messages by vehicles and/or road side units (RSUs). Given that any inaccuracy in the broadcasted safety messages may result in serious consequences, such as vehicles damage or drivers injuries, the need of an efficient one-hop broadcast service is intolerable in VANETs. The thesis explains the severe limitations of the existing medium access control (MAC) protocols in supporting a reliable broadcast service, and introduces a new multichannel time division multiple access (TDMA) protocol, known as VeMAC, which can provide such a crucial service for VANETs. The ability of the VeMAC protocol to deliver periodic and event-driven safety messages in VANETs is investigated by presenting 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 VANETs). A real city scenario consisting of roads around the University of Waterloo (UW) campus is simulated and different performance metrics are considered, including the network goodput, protocol overhead, channel utilization, protocol fairness, probability of a transmission collision, and safety message delivery delay.
In addition to the road safety applications, 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. The thesis proposes a new strategy for deploying Internet gateways on the roads, together with a novel scheme for data packet routing, in order to allow a vehicle to access the Internet via multihop communications in a VANET. The gateway placement strategy is 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 deployment around the UW campus. On the other hand, the proposed packet routing scheme is based on the VeMAC protocol, and the performance of this cross layer design is evaluated for a multichannel VANETs, in terms of the end-to-end packet delay and the percentage of occupied time slots per frame in a highway scenario. The packet queueing at each relay vehicle is considered in the end-to-end packet delay analysis, and numerical results are presented to study the effect of different parameters, including the vehicle density and the packet arrival rate, on the performance metrics.