A Multi-Layered Reliability Approach in Vehicular Ad-Hoc Networks

Introduction

Vehicular Ad-hoc Networks (VANETs) are a type of Mobile Ad-hoc Networks (MANETs) where each vehicle creates a spontaneous inter-connection with other neighboring vehicles for data and control packet exchange. VANETs contribute to the ideology of Intelligent Transport Systems (ITS), the future of smart commuting. VANETs can be designed to use for comfort applications as well as safety applications. Some components of VANETs include intelligent traffic signal intersections for relaying the information from one vehicle to the other or for assisting vehicles to be routed towards their destinations along the best route, emergency dispatch centers to respond in case of an accident, and road side units (RSUs) for relaying the information and assisting packet flow through the network and much more.

Some of the applications of VANETs include traffic signal violation warnings, curve speed warnings, pre-crash warnings, cooperative forward collision warnings, left-turn assistance, emergency vehicle approach warnings, etc. The US Department of Transportation, National Highway Traffic Safety Administration (NHTSA) (National Highway Traffic Safety Administration, 2005) has set application specific requirements for range of communication, allowable latency and frequency of operation for each application of VANETs. In the process of meeting these requirements, there is a need to ensure a reliable wireless communication network. Reliability of a network is the ability to operate under desired working conditions by meeting all the minimum requirements set by the network operators (Modarres et al., 2003). For example, in the event of alerting the approach of emergency vehicles, the drivers falling in the same route of the emergency vehicle have to be alerted in time to avoid any interruption to the emergency vehicle traversing through the route. In this scenario, reliability analysis plays an important role in choosing the best route for packets to be delivered across the network, choosing trusted neighbors for forwarding the information, confirming that the latency and packet loss requirements are met, etc.

Reliability of wireless communication systems has taken a giant leap in the wake of designing and engineering high-speed cellular technology (5G wireless network technology) which demands 99.9999% (six 9’s) availability. One of the key application areas for 5G is VANETs. VANETs, being one of the crucial applications of wireless cellular networks, should aim for meeting such reliability constraints. The objective of this paper is to create a reliability framework for Vehicular Ad-Hoc Networks with respect to various layers of network communications. Each layer in the VANET protocol stack has been taken into consideration and different reliability aspects have been discussed. Then a comprehensive understanding is available. The rest of the paper is organized as follows: Section II contains a literature survey of the previous work done in the area of reliable VANETs, Section III discusses Dedicated Short-Range Communications (DSRC) and 802.11p standards for the VANET protocol stack, Section IV lists the first three communication layers of VANETs along with some key parameters which effect the reliability in each layer, and Section V elaborates on the proposed framework of layered reliability and discusses techniques which can be implemented to increase the reliability of the VANET.