# An Overview of Vehicular Communications
## 2 Vehicle-To-Vehicle
The central OEM systems today widespread are the following:  
* Blind Spot Monitoring (BSM) [37]: it is an assistance system that monitors the blind spots of the exterior rear-view mirrors, using radar sensors. This system informs the driver of a vehicle arrival with a visual signal integrated into the two left and right rear-view mirrors, based on the side where the vehicle in front passes. * Anti-Schlupf Regierung (ASR), also known as Traction Control System (TCS) or Automatic Stability Control (ASC) [38]: it is a system aimed at regulation and control of the sliding of the wheels during acceleration which, similarly to the homologous system for the braking control, allows to better control the traction in the starting phase (and during the cruise phase), according to the conditions of the road surface. * Electronic Stability Program (ESP) [39]: it is a device that acts when the vehicle shows signs of lateral heeling (yaw), i.e., in the event of oversteer or understeer movements. Therefore, it allows the vehicle to maintain the correct trajectory and to go not out of the way. * Forward Collision Warning (FCW) [40]: it is a system based on radar sensors that monitor the road. This system recognizes the objects and detects the distance between the vehicle and the likely obstacles on the road: if the speed of travel is a risk of imminent collision, the driver can be alerted through acoustic sensors or light signals on the onboard display. Figure 1: Mesh topologies. * Automatic Emergency Braking (AEB) [41]: it is an assisted emergency braking system that combines advanced driver assistance with electronic stability control to slow down the vehicle and potentially reduce the severity of the impact when the collision is unavoidable. If the driver brakes inadequately or does not brake at all (for instance, due to a sleep blow), the pre-crash system acts by arranging various components of the car to mitigate the impact. In this way, for instance, the belts are stretched to the maximum, air is pumped into the airbags, the windows and the sunroof are closed, to prevent damage to the occupants, in the event of the vehicle overturning, and the brake intervenes slightly to reduce impact violence, also attracting the driver's attention. If installed in the vehicle, the active head restraints are inclined forward to prevent whiplash injuries in the impact. * Brake Assist System (BAS) [42]: it is an active device mounted on the vehicle's braking system which only comes into operation in the event of sudden emergency braking, when the brake pedal is pressed very quickly but without the necessary pressure to activate the ABS (or anti-lock system). It is an electronic control unit that avoids the locking of the wheels of the vehicles ensuring the drivability during the braking. In this case, the BAS activates the automatic raising of the pressure on the pedal, until the correct functioning of the ABS on all the wheels, thus ensuring a better braking action. * Lane Departure Warning System (LDWS) [43]: it is a device that warns the distracted driver of exceeding the line that delimits its lane. It is activated through a switch on the center console and warns the driver with a slight acoustic signal if the vehicle passes one of the lane lines without an apparent reason, for instance, without using the direction indicator. The V2V technology, thanks to the cooperation with these already existing security systems, will yield efficient management of possible pitfalls in the roadways all over the world. The new Intelligent Transport Systems (ITSs) will employ data from V2V communication to enhance traffic management, allowing vehicles to also communicate with road infrastructures, such as traffic lights or signs. These technologies could become mandatory in the not too distant future and contribute to building more reliable self-driving cars on motorways.