Basic principles of V2X technology
What is V2X?
V2X technology is a standardized and widely accepted way of mid-range communication among traffic users and road infrastructure.
Imagine that your car activates brakes even before you realize that the car two vehicles ahead is braking. Or when driving in low visibility, you are warned that there is a car accident ahead. Or that emergency vehicles cross traffic lights safely and fast. This all (and many more) is what V2X provides.
V2X (Vehicle to everything) is also known by the acronym Car2X, C2X (Car to everything) or C2C (car to car). The “X” means that the vehicle can communicate not only to other vehicles, but also to traffic infrastructure devices (e.g., a traffic light controller) or even vulnerable road users (pedestrians, riders on scooters, bikes). In Europe, the communication is standardized and known by the name ITS-G5. It is a decentralized (hence very robust) communication, which operates at the frequency 5900 MHz.
The primal goal of introducing such communication technology is to increase the safety and efficiency of the traffic. Unlike traditional sensors used at vehicles or traffic infrastructure (radar, lidar, cameras), V2X as radio communication can “see” behind the corner, ahead of the several vehicles etc. It is a necessary step towards autonomous mobility.
However, before the technology gets that far and becomes so widespread, there is a clear benefit even now: priority at traffic lights.
Basic elements of V2X ecosystem
Roadside Unit (RSU)
Roadside unit creates a wireless interface between a road traffic technology device and vehicles in its surroundings. The traffic infrastructure device can be for instance a traffic light controller, weather metering station, traffic control center or a even a station information panel. The communication is bidirectional – the vehicle can receive important information about the traffic in its surroundings (warning messages, signal plan of the traffic controller), while the RSU can receive priority requests from the vehicles or just information about the vehicles’ movement. Often, the RSU is connected to a C-ITS Back Office server.
Onboard Unit (OBU)
To become part of the C-ITS ecosystem, a vehicle should be equipped with an On-board unit (Onboard Unit). Thanks to OBU, the vehicle will get access to all V2X messages sent by vehicles or RSUs in its surrounding and it can also inform others about its movement or a dangerous situation. Simply said, having the OBU on board means safer rides. The OBU is typically connected to a display, be it a tablet or a vehicle dashboard. For public transport or emergency vehicles the OBU ensures prioritization at intersections. Another example is that an autonomous shuttle receives information about the signal plan of the intersection.
OBUs in passenger car are no longer future, they are already installed standard vehicles, such as VW Golf.
C-ITS Back office (C-ITS BO)
For a road operator or a public transport provider, it is necessary to be able to inform drivers about a situation in the traffic. If a traffic monitoring center detect a traffic event (accident, traffic jam, …), the C-ITS BO will generate a warning message and send it to RSUs which distribute the message to vehicles. On the other hand, if an RSU receives a warning message from a vehicle (emergency braking, slippery road), it forwards the message to the C-ITS BO. Thus, C-ITS BO can be seen as a gateway between the traffic monitoring center and C-ITS world.
In addition, C-ITS BO usually offers RSU and OBU monitoring and configuration capability, including device updates. As an example, statistics about vehicle priority can be calculated.
