Clustering enhancement for VANETs in highway scenarios

The recent research on reliable data dissemination techniques vehicular ad hoc networks (VANETs) motivates for a stable VANET clustering algorithm. However, considering topology dynamics and the high mobility of vehicles, it's not easy to make the network connected in a restricted delay. In this paper, we develop an enhanced clustering algorithm to form stable clusters for delay-bounded applications (car crash alert, dangerous zone advertisement, etc.) on highway scenarios. Because these applications can't support long cluster formation process, our scheme aims to minimize both the cluster head election and the cluster member selection durations. To achieve this goal, the network partition is initially done by the slowest vehicle in order to accelerate the cluster formation. Then, a multi-metric waiting time function is implemented to select the cluster head. It takes as parameters speed difference and relative distance between neighboring nodes. Finally, we add a switching mechanism which allows for choosing a new substitute cluster head when the current cluster head risks leaving the cluster. This effectively enhances cluster lifetime and reduces frequent re-clustering in high speed scenarios. Simulation results confirm that our technique enables formation of long living and stable clusters in a reduced delay.

I. Introduction

Vehicular Ad Hoc Network (VANET) is an important field in Information Transportation System (ITS) [1]. The United State Federal Communication (FCC) has allocated a 75 MHz radio spectrum in the 5.9 band to be utilized by the Dedicated Short Range Communication (DSRC) standard [2]. It's dedicated to Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communication. It offers safety and non-safety services related to drivers' comfort. Many issues in VANET have been addressed to deal mainly with safety messages dissemination and to provide road security [3]. Examples of these applications: warning the vehicles behind of car crash, notification about traffic congestion or hazardous zones, etc. Despite of great resemblance between VANET and MANET structures [4], MANET models and protocols aren't applicable to VANET topologies. Mobile nodes move either slowly or rapidly, hence generating frequent network disconnections. As high speed nodes form quick dynamic topology, real-time data transmission is required. Recent researches have resorted to reliable realtime data dissemination schemes that ensure efficient broadcast of safety messages within a dynamic environment [5]. However, such techniques cause broadcast storm problems [6]. They consist in instability in resource allocation and bandwidth sharing. By the way, network performances are greatly affected.