
C2X communications scheme takes shape

The hardware for Fraunhofer’s C2X system is based on a WiFi hub modified for fast-moving objects such as cars. The device also includes a GPS receiver. The device in the car transmits position and sensor data such as speed, acceleration or skidding conditions to a roadside unit (RSU). In turn, the in-car unit receives current data on road conditions ahead, any known accidents ahead, traffic congestions or the speed recommendations for optimum traffic flow.
The system differentiates between three types of messages: First, periodic standardized telegrams transmitted up to ten times per second to the RSU as well as to other cars. These messages include position, driving direction and speed. The roadside units process these data and generate an overall image of the current traffic situation.
The second message type contains event-based information such as accidents in which the transmitting station is involved or which has been detected by the RSU if many vehicles perform emergency brakes at the same time. Also traffic congestion is detected since many cars at the same time signal very low speed. Another relevant event in this category is if the ESP in one or more cars is activated: This hints at a slippery road.
The third category is application messages. This type includes traffic light signals, or traffic information in general. RSUs can also receive and process messages from sources such as traffic management centers.
The configuration of the C2X system is flexible; in addition to the minimum configuration, additional applications and the respective software can be activated. The ongoing research now gets granular on ways to protect the system from overload situations resulting from events happening to many cars at the same time. The Fraunhofer experts are currently looking at methods for what they call “context-sensitive message aggregation”. The goal is to aggregate multiple messages of the same type and filter them according to their relevance.
