International Conference on Computer and Communication Engineering (ICCCE 2012), 3-5 July 2012, Kuala Lumpur, Malaysia 978-1-4673-0479-5/12/$31.00 ©2012 IEEE CLUSTER-BASED MULT-HOP VEHICULAR COMMUNICATION WITH MULTI-METRIC OPTIMIZATION Mahmoud A. Alawi, Rashid. A. Saeed, Aisha A. Hassan Department of Electrical and Computer Engineering, IIUM Jalan Gombak, 53100, Kuala Lumpur, MALAYSIA Abstract-Dead spot and out of coverage problem are serious problems especially in the rural and suburban areas where the network infrastructure is not deployed. In this paper, a new end to end multi hop relay scheme for vehicular communication is proposed to extend the coverage or/and relaxing frequent handoff process. The scheme allows vehicles to continue connected to infrastructure network i.e. UMTS. Relay discovery, relay selection and gateway selection are discussed and examined. The proposed scheme can be implemented on top of any VANET routing protocols. AODV and DSDV were used as underlying protocol to evaluate our scheme. An integrated simulation environment combined of VanetMobiSim and NS2 is used to simulate our proposed scheme. The simplified gateway selection shows the best performance on top of AODV compare to DSDV. Keywords: VANET, heterogeneous network, UMTS, multi hop relay scheme I. INTRODUCTION Heterogeneous wireless network is the one of the hot research topics in wireless domain. It supports the wireless devices with the capability to interoperate in more than one wireless technology seamlessly. A good example is the combination of Universal Mobile Telecommunication System (UMTS) network and IEEE802.11 based vehicular network (VANET) to form more robust network in terms of speed and coverage area [1]. VANET possesses many unsolved problems which hinder the promising of intelligent transportation system (ITS) to bring the safety and entertainment in transportation system. Firstly, frequency network disconnection caused by high speed of the vehicles makes the inter connection time between V2V and V2I to be very small due to the unpredictable motion of vehicles which is difficult to predict when the vehicles will change their speed and cause unexpected network disconnection. Secondly is the limitation of the network coverage especially in rural and suburban areas whereby the infrastructure network is not well deployed. Lastly, VANET signaling uses broadcast mechanism to disseminate the data and control signals, this easily causes flood to the network which results to extra overhead and create network scalability problems[2] [3]. In [2][4][6] problems of establishment and maintaining a connection to the Internet were discussed and new protocols were proposed. The protocols use the lifetime prediction of the link to select the best route to the gateway. The longer life time the better the route in the sense that, it reduce frequent link breakage which have high impact on Quality of Service (QoS). A multi hop relay mechanism to connect VANET to the Infrastructure network was studied in [4]. The work involves experimental evaluation of using relay vehicle when the source vehicle moves towards the base station (Node B) and when it moves away from the base station. In [1], Clustering- based Multi-metric adaptive mobile Gateway Management mechanism (CMGM) was proposed. CMGM allows minimum number of vehicles to connect to UMTS network by allowing normal vehicles to use the GWC to communicate with the UMTS network. Clustering mechanism was used to cluster the gateway candidates, which depends on direction of movement, UMTS-RSS (Received Signal Strength), and IEEE802.11p transmission ranges. GWCs closed to the cluster center are always selected as Cluster head. Normal vehicles use cluster heads to communicate to UMTS network. Three metrics are used for mobile gateway selection; mobility speed, UMTS RSS and link stability. However, this algorithm is complex in terms of cost of creating and maintaining the clusters for rapid environment as in VANET. In addition to that, the signaling traffic and time that is used for clustering formation and cluster head selection is larger than the time of data traffic exchange. In this paper we used hybrid metrics of the link life time to determine the stability of the link between the source vehicle and the relay vehicle along with best route capacity selection to avoid overload and hence bottleneck in one gateway. The remainder of this paper is organized as follows; section II reviews the related work. Section III introduces the simplified gateway selection through multi hop scheme, while section IV deals with the simulation and performance evaluation of the proposed scheme and section V concludes the paper. In our work we proposed a simplified mechanism to formulate a cluster and gateway selection by formulating clusters only at the UMTS cell edges. This done by using received signal strength (RSS) threshold as a cluster formation indicator, in addition to use the best available route capacity for gateway selection. 22