# An Overview of Vehicular Communications
###### Abstract  
The transport sector is commonly subordinate to several issues, such as traffic congestion and accidents. Despite this, in recent years, it is also evolving with regard to cooperation between vehicles. The fundamental objective of this trend is to increase road safety, attempting to anticipate the circumstances of potential danger. Vehicle-to-Vehicle (V2V), Vehicle-to-Infrastructure (V2I) and Vehicle-to-Everything (V2X) technologies strive to give communication models that can be employed by vehicles in different application contexts. The resulting infrastructure is an ad-hoc mesh network whose nodes are not only vehicles but also all mobile devices equipped with wireless modules. The interaction between the multiple connected entities consists of information exchange through the adoption of suitable communication protocols. The main aim of the review carried out in this paper is to examine and assess the most relevant systems, applications, and communication protocols that will distinguish the future road infrastructures used by vehicles. The results of the investigation reveal the real benefits that technological cooperation can involve in road safety.  
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Other protocols that can be used in vehicular communications are Bluetooth [13] and IEEE 802.15.4/ZigBee [14], adequately revised [15]. The main aim of all the cited standards is to reduce the connection times and to extend the transmission range, allowing proper operation in conditions of high mobility and vehicular density. In the transport research field, the primary purpose of these technologies is the improvement of road safety, trying to prevent any dangerous situations. In this context, the V2V (Vehicle-to-Vehicle) [16; 17], V2I (Vehicle-to-Infrastructure) [18; 19], and V2X (Vehicle-to-Everything) [20; 21] technologies intends to provide communication models that can be used by vehicles in different application contexts. The resulting infrastructure is an ad-hoc mesh network whose nodes are not just vehicles, but all mobile devices equipped with a wireless module.  
The main intention of the review carried out in this paper is to prove that the introduction of these intelligent systems in transport engineering leads to authentic advantages for road safety. One of the significant areas of interest in today's vehicular industry is the development of technological solutions aimed at improving road safety. To this end, several solutions have been installed in the cars currently available on the market, such as anti-collision sensors [22], intelligent navigation systems [23], driver notification systems [24], assisted parking systems [25], and autonomous driving [26]. However, each company uses proprietary technologies that are unable to interact and cooperate with the equipment installed in vehicles fabricated by other manufacturers. Precisely for these reasons, it is essential to create a standardized system that can interoperate all over the world, providing an easy and effective integration between all these services and applications on the market [27; 28; 29; 30].  
It is necessary to note that the term V2X encompasses all types of communications involving vehicles, including V2V and V2I. However, in the review carried out in this paper, these three communication areas are analyzed separately to highlight in more detail the distinctiveness of each of them. This paper is organized as follows: Section 2 is focused on V2V, presenting the primary systems and applications that best meet the requirements necessary for the realization of effective technological cooperation among vehicles. Sections 3 and 4 introduces the main features of V2I and V2X, respectively. Finally, Section 5 gives conclusive remarks for the paper along with future directions.