International Journal of Computer Theory and Engineering, Vol. 5, No. 4, August 2013 629 DOI: 10.7763/IJCTE.2013.V5.763 Abstract—Vehicular Ad hoc Network (VANET) is a subclass of mobile ad hoc networks (MANETs). VANETs provide a variety of interesting applications. Many of these applications rely on broadcasting of messages to other vehicles. The simplest broadcasting algorithm is flooding. Because of a large number of vehicles during peak hour, blindly flooding may lead to packet collision and high contention named broadcast storm problem. This paper presents a broadcasting approach for safety messages that dynamically adjust waiting time of a vehicle according to the number of neighbor vehicles and distance to source. We evaluate the performance of our proposed approach in terms of reachability, reliability. The simulation results show our protocol introduces better performance than flooding and random waiting time protocol. Index Terms—Vehicular Ad hoc Network, broadcast storm problem, network density I. INTRODUCTION Vehicular Ad hoc Network (VANET) is a new technology to build a wireless network between vehicles (V2V). VANETs are based on short-range wireless communication (e.g., IEEE 802.11) between vehicles. The Federal Communication Commission (FCC) has allocated 75 MHz in 5.9 GHz band for Dedicated Short Range Communication (DSRC). DSRC was conceived to provide the architecture for vehicles in Vehicular Network to communicate with each other and with infrastructure. In DSRC, subsequently specialized as Wireless Access in Vehicular Environment (WAVE), GPS-enabled vehicles that are equipped on-board units can communicate with each other. VANETs are a special class of Mobile Ad hoc Networks (MANETs). The major characteristics as compared to MANETs are following: components building the network are vehicles, dynamic topology, geographically constrained topology, vehicle mobility and time-varying vehicle density [1]. VANETs could play an important role in the future of vehicle communications. VANETs provide a variety of interesting applications from safety to comfort. Many of these applications rely on broadcasting. There are many proposed approaches for broadcasting in MANETs. The simplest one is flooding. In flooding each mobile host rebroadcast the packets when received for the first time. In this scheme the total number of broadcast is equal to N-1, where N is the total number of vehicles [2]. Flooding is simple but it consumes much network resources as it has a large number of redundant Manuscript received November 22, 2012; revised January 30, 2013. The authors are with the Universiti Teknologi Malaysia, Skudai 81310, Johor, Malaysia (e-mail: nsara3@ live.utm.my, afida@.utm.my, shukorar@ utm.my, kramin2@ live.utm.my). messages. It leads to serious redundancy, contention and collision in mobile wireless networks, which is referred to broadcast storm problem [1]. Due to lack of packet acknowledgements, packet retransmission and medium reservation, it is difficult to guarantee that a packet can reach all nodes in vehicular Ad Hoc Networks due to wireless contention. There are different solutions such as probabilistic, counter-based, distance-based, location-based [3]. Probabilistic scheme is designed to tackle the overhead problem by suggesting that each node re-forwards the packet with some fix probability p < 1. The counter-based scheme broadcast a packet when the number of received copies is less than a pre-determined threshold. In the distance-based scheme a node rebroadcast the message when the distance between sender and receiver is larger than a threshold. The location-based scheme rebroadcast the message if the additional coverage is larger than a bound A. The main problem in Vehicular Ad Hoc Networks is to reduce broadcast redundancy to prevent collision. In this paper, we propose a broadcasting approach that calculates waiting time of each node based on local density and distance that can reduce the number of unnecessary broadcasting messages in Vehicular Ad Hoc Networks. This algorithm is fully distributed means it needs only local information of each node in the network. The rest of this paper is organized as follow: Section II presents the related work of broadcasting in VANETs. Section III presents details of dynamic broadcasting algorithm in VANETs. In Section IV, performance evaluation and simulation study are shown, finally this paper is concluded in Section V. II. RELATED BACKGROUND The broadcast storm problem has been previously investigated in MANETs. Various techniques were proposed for mitigating this problem. We will review this method in this part. In probability based Method each vehicle calculate a probability to decrease redundancy and collision. In [4] a method has been proposed that is similar to simple flooding except that vehicles rebroadcast with a probability. A distributed gossip-based routing is designed to solve the overhead problem. In this scheme each node rebroadcast the packet with a probability p < 1 [5]. Zhang and Agrawal [6] have described an adjusted probabilistic scheme. This scheme uses probabilistic and counter-based schemes simultaneously. This scheme dynamically adjusts the rebroadcast probability p at each mobile node according to the value of the packet counter. The Sara Najafzadeh, Norafida Ithnin, Shukor Abd Razak, and Ramin Karimi Dynamic Broadcasting in Vehicular Ad hoc Networks