Journal of Computer Science 10 (9): 1617-1627, 2014 ISSN: 1549-3636 © 2014 Science Publications doi:10.3844/jcssp.2014.1617.1627 Published Online 10 (9) 2014 (http://www.thescipub.com/jcs.toc) Corresponding Author: Dahlia Sam, Department of CSE, Dr M.G.R Educational and Research Institute University, Chennai, India 1617 Science Publications JCS A TIME SYNCHRONIZED HYBRID VEHICULAR AD HOC NETWORK OF ROADSIDE SENSORS AND VEHICLES FOR SAFE DRIVING Dahlia Sam and V. Cyril Raj Department of CSE, Dr M.G.R Educational and Research Institute University, Chennai, India Recieved 2013-10-14; Recieved 2014-01-29; Accepted 2014-04-10 ABSTRACT VANET is a type of ad hoc network in which the moving vehicles act as nodes. There has been lot of research for using VANETs in many applications. One of the main applications is the use of VANETs to improve driving safety. In any safety related applications, the vehicular nodes have to constantly communicate with each other and the roadside equipments. For e.g., the roadside units sense real time information about road conditions, road blocks or animals straying on the road and passes the message to the approaching vehicles. The alert message enables the driver to take timely decisions in preventing accidents or delay. However there are two issues in the above system. One problem is that VANETs are subject to frequent network disconnections especially in low traffic areas. Due to this some events in the road may go undetected while the detected events may not be transmitted on time. The second issue it with maintaining a synchronized clock within the network. Only then the messages communicated between the nodes will be meaningful. To overcome the above issues and make the system more reliable we propose to include roadside wireless sensor nodes along with the vehicular nodes in the network. The roadside wireless sensor nodes can be deployed at fixed distances and communicate wirelessly with the vehicular nodes. They play an important role in keeping the network connected and guarantee message transmission. We also propose a Hybrid Clock Synchronization (HCS) algorithm to synchronize the clocks of all the nodes. This integrated network which is also time synchronized is called the Hybrid VANET (H-VANET). The proposed H-VANET was simulated and tested using GrooveNet. On comparing our system with the conventional VANET implementing RBS for synchronization, it was seen that our model has better performance and reliability. Keywords: Hybrid VANET, H-VANET, Hybrid VANET-WSN, Hybrid Clock Synchronization (HCS) 1. INTRODUCTION In today’s world driving is becoming an indispensible part of everyone’s life. The number of drivers on the road has been steadily increasing over the years. There are more vehicles on the road than ever before. This number is sure to keep increasing in future. With this, the need for a real time intelligent vehicle communication system has become very important. One promising technology of the future that focuses on this issue is the Vehicular Ad hoc Network (VANET). Researchers are working on using VANETs for applications like driving safety, intelligent speed control, lane changing, safe highway entry and exiting, timely warning during hard braking and accidents. All these aid to improve the safety of the highway system. 1.1. Background Vehicular communication has become an important area of research in the past decade. There has been lot of study going on to develop an Intelligent Transport