Improving the Reliability and Efficiency of Data Transmission in Vehicular Ad-Hoc Network

Abstract

With the increment of population, vehicle transportation problems like traffic congestion and accidents are becoming more severe in our society. To enhance the transportation environment, Intelligent Transportation Systems (ITS) have been deployed to bring smart connectivity to transportation. As a core component of ITS, Vehicular Ad-Hoc Network (VANET) has received considerable attention in information sharing and data delivery services. It is able to offer direct communications between vehicles and between vehicles and roadside units (RSUs). Connected vehicles can send and receive hazard information on the current traffic situation and therefore alert drivers the potential dangerous conditions like icy road or impending collisions. A large number of applications have been proposed based on the advent of DSRC devices which is the defacto communication devices for VANET for both safety and non-safety purposes. In order to support a variety of applications, we aim at improving the reliability and efficiency of data transmission in VANET. A new two-tier BUS-VANET architecture is proposed which fully integrates traffic infrastructures with public transportation and private vehicles. In this new architecture, the communications of vehicles, not only benefit from the existence of buses, but also consider the effects of using RSUs and Traffic Control Center (TCC). RSUs are used to ensure service coverage while TCC is helpful for locating the destination vehicle quickly. We also investigate the benefits that can be obtained by taking advantage of traffic infrastructures. Comparing to traditional VANET, better performance can be achieved in BUS-VANET with less delivery delay and higher delivery rate. To overcome the high packet collision probability under high traffic density as the main weakness of IEEE 802.11p protocol, time division multiple access (TDMA) based MAC protocols have been proposed in VANET. However, considering the real two-way traffic, packet collisions still occur due to the contention or multiple vehicles using the same slot while approaching each other called encounter collisions. We proposed two TDMA based MAC protocols: MAT-MAC and PTMAC. MAT-MAC is designed for two-way traffic. It aims to reduce the number of both encounter and contention collisions while maintain high slot utilization even under unbalanced traffic scenario. PTMAC is a novel predication based MAC protocol. Most of the encounter collisions can be predicted and potentially eliminated before they really happen. It is not only suitable for two-way traffic but also for four-way intersections. Varieties of applications have been developed taking advantage of Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communications. Unlike wired communication, wireless communication is relatively unreliable, which significantly impacts the service quality. To further improve the transmission performance, it is necessary to investigate and deeply understand the performances of different types of applications over DSRC transmission. A real environment test-bed is developed using DSRC devices to investigate the performance of multi-hop multimedia streaming transmission. We also evaluate the performance of MapReduce applications over a Vehicular Cloud. Impacts of different parameters and appropriate parameter settings are discussed based on VANET transmission features.