Medium access control protocols for safety applications in Vehicular Ad-Hoc Network: A classification and comprehensive survey

Vehicular Ad-Hoc Network (VANET) is seen as an emerging solution to improve road safety, highway assistance and traveler comfort accounting to vivid applications including safety, non-safety and infotainment applications. Over the past few years, research paradigm has shifted towards areas such as multi-hop broadcasting, information security, clustering, etc. covering intra-vehicular and vehicle-to-infrastructure communication modes. Whereas these scenarios provide diversified information dissemination techniques through various applications of Intelligent Transportation Systems (ITS), data dissemination in VANET environment is still a challenging task, mainly due to rapid changes in network topology and frequent disruptions in connectivity. A distinguished area that still lacks significant research contributions is towards designing reliable and efficient Medium Access Control (MAC) protocols for vehicular communication in order to enhance travel safety. The main motivation behind such a survey is to integrate a wide range of research contributions that have been recently proposed to envisage the inherent characteristics of vehicular communication. Such a study serves as a reference for an in-depth research towards enhancements in the PHY/MAC layers. In this paper, we present state-of-the-art survey of the MAC protocols available for vehicular safety. We classify these protocols based on different applications and the techniques they adopt. We also review the performance metrics used for evaluating these protocols. In later sections, we qualitatively analyze the protocols based on different parameters along with related issues and the challenges they generate. We highlight the mechanisms involved, conceptual features, optimization techniques, strength and drawbacks of the available protocols as well as their applicability in future deployment. Finally, we discuss the open issues and future research directions.