Packet Delivery Delay and Throughput Optimization for Vehicular Networks.

摘要

Vehicular networking is a new emerging wireless technology that supports the communication amongst vehicles and enables vehicles to connect with the Internet. This networking technology provides vehicles with endless possibility of applications, including safety, convenience, and entertainment applications. Examples for these applications are safety messaging, real-time traffic, route updates, and general purpose Internet access. The goal of vehicular networks is to provide an efficient, safe, and convenient environment for the vehicles.;In vehicular networking technology, vehicles connect either through other vehicles in an ad-hoc multi-hop fashion or through road side units (infrastructure) which connects them to the Internet. Each approach has its own advantages and disadvantages. However, one of the main objectives of vehicular networking is to achieve a minimal delay for message delivery, and encourage a continuous connectivity for vehicles.;This dissertation introduces a novel hybrid communication paradigm for achieving seamless connectivity in Vehicular Ad-hoc NETworks (VANET), wherein the connectivity is often affected by changes in the dynamic topology, vehicles' speed, as well as traffic density. Our proposed technique---named QoS-oriented Hybrid Vehicular Communications Protocol (QoSHVCP)---exploits both existing network infrastructure through a Vehicle-to-Infrastructure (V2I) protocol, as well as a traditional Vehicle-to-Vehicle (V2V), that satisfies Quality-of-Service requirements. We analyze time delay as a performance metric, and determine delay propagation rates when vehicles are transmitting high priority messages via QoSHVCP.;Focusing on V2V communication, we propose a novel reliable and low-collision packet-forwarding scheme, based on a probabilistic rebroadcasting. Our proposed scheme, called Collision-Aware REliable FORwarding (CAREFOR), works in a distributed fashion where each vehicle receiving a packet, rebroadcasts it based on a predefined probability. The success of rebroadcast is determined based on allowing the message to travel the furthest possible distance with the least amount of packet rebroadcast collision.;Moreover, we present a QoS-Aware node Selection Algorithm (QASA) for VANET routing protocols. Our algorithm is focused on selecting the vehicle to communicate with, and is achieved by exploiting the bridging approach for message forwarding i.e., vehicles on the east (west) select from west (east). The QoS metrics that are being optimized are the throughput in the network, as well as end-to-end delay for packets.;Finally, we exploit the use of autonomous vehicles in order to optimize the end-to-end packet delivery delay. Our protocol introduces a dynamic metric that depends on the vehicular density on the highway in order to control the inter-vehicle distance.;Our results show a great promise for their future use in vehicular technology.