The Optimal Radio Propagation Model in VANET Khalid Abdel Hafeez, Lian Zhao, Zaiyi Liao, Bobby Ngok-Wah Ma Electrical and Computer Engineering Department Ryerson University, ON, Canada, M5B 2K3 kabdelha@ryerson.ca, lzhao@ee.ryerson.ca, zliao@ryerson.ca, bma@ee.ryerson.ca Abstract — There are many parameters that affect the per- formance of Vehicular Ad hoc Networks (VANETs) applica- tions and protocols. To test the new applications and proto- cols on a real setup is very difficult and very costly. Most re- searchers use simulation tools to study and analyze VANETs. The simulators usually use simple radio propagation models that did not take into account all the obstacles in the environ- ment. In this paper we analyze different radio propagation models that have been introduced in the most popular network simulator (ns2) and predict the radio propagation model that best characterize the vehicular environment. Keywords: Vehicular Ad hoc Networks (VANET), Propaga- tion models, DSRC (IEEE802.11p),ns2,OFDM. I. INTRODUCTION In the near future, vehicles will be equipped by Dedi- cated Short Range Communication (DSRC) devices (IEEE 802.11p) [1] to form mobile ad hoc networks on roads. This type of networks called Vehicular Ad hoc Networks (VANET) have different characteristics than the regular mo- bile ad hoc networks such as the high mobility of their nodes (vehicles) and the fast changing of their topology, etc. There are many applications and routing protocols that have been developed or under development for VANETs to help the drivers to travel more safely and to reduce the number of fatalities due to road accidents. In 2004 the World Health Organization (WHO) [2] reported more than one million deathes due to road accidents, most of these accidents are preventable if there is a deployed intelligent transportation system to extend the drivers’ awareness from what they can directly see to the maximum communication range. For example if one of the vehicles has an accident, it has to send a warning message to all vehicles behind it to in- form them about the traffic situation to avoid a chain col- lision. The safety information has to be propagated in a short time (usually less than 0.5 sec) [3]. The research and application development in VANETs are driven by the IEEE802.11p technology [1] which is intended to enhance the IEEE 802.11 to support the Intelligent Transportation System (ITS) applications where reliability and low latency are crucial. The IEEE 802.11p or Wireless Access in Vehic- ular Environment(WAVE) [4] will use CSMA/CA as the basic medium access scheme in the licensed ITS 5.9GHz (5.850-5.925GHz) band in North America (75MHz spec- trum) and will use Orthogonal Frequency Division Multi- plexing (OFDM) scheme to provide for both the Inter Ve- hicle Communication (IVC) and Vehicle to Infrastructure Communication wireless connection up to 1000m. The 75MHz spectrum is divided into seven 10MHz channels and a 5 MHz guard band. Each channel uses 10MHz fre- quency bandwidth in contrast to IEEE802.11a which uses 20MHz to increase its tolerance to the multi-path propa- gation and Doppler spread effects in vehicular networks. The physical layer of the IEEE 802.11p is a variation of the IEEE802.11a standard. It employs 64 OFDM subcarri- ers where 52 of them are used in actual data transmission. The short and long training symbols located at the begin- ning of every packet are used for signal detection, time syn- chronization and channel estimation while the guard inter- vals GI are used to eliminate the inter symbol interference (ISI) from the multipath propagation channel. Table 1 sum- marizes the parameters of the DSRC IEEE802.11p and the IEEE802.11a. The IEEE 802.11p technology is aimed to support up to 1000m communication range between vehicles or vehicles and infrastructure. A realistic study conducted by [5] shows that the maximum range this technology can reach in a high- way scenario is up to 880m for the line of sight (LOS) and 58 to 230 m in the none line of sight (NLOS). It seems that this technology did not take into account all the mobility effects and the characteristics of the radio environment on the roads. The nodes (vehicles) are in high mobility ei- ther in the same or in opposite direction which will result in Doppler shift causing frequency dispersion. The radio wave in vehicular environment will face many challenges like: absorption, reflection, refraction, diffraction and scat- tering due to obstacles on the road like trucks, buildings, trees, hills and bridges. The vehicular environment is very huge and to test the new applications and protocols designed for this environment on a real setup is very difficult and very costly. This is the reason that most researchers use simu- lation tools to study and analyze VANETs. The simulators usually use simple propagation models that did not take into account all the obstacles in the environment. The rest of this paper is structured as follows. In section II, we introduce the main radio propagation models. We analyze the vehicular environment in section III. In section IV we show the simulation results and conclude this paper in section V.