How do they work?
Last updated
Last updated
Cooperative Awareness Messages (CAM).
Periodic.
Contain information about the station such as its position and speed.
Decentralized Environmental Notification Messages (DENM).
Asynchronous.
Contain information about the event and the station that generated the message.
Create and maintain awareness of vehicles using the road network or RSUs.
The content varies depending on the type of ITS-S:
Vehicles: time, position, motion state, activated systems (e.g., cruise control, pedals, and others), and the attribute information includes data about the dimensions, vehicle type, and role in the road traffic;
RSUs: station type and location.
HF (High-Frequency) container with fast-changing vehicle data (such as location, heading, or speed).
LF (Low-Frequency) container with static or slow-changing data (such as the status of the exterior lights or pedals).
CAMs have generation requirements, with the generation frequency between 1 Hz and 10 Hz.
The HF container must be in every CAM message, while the low-frequency container can be updated at a maximum of 5 Hz frequency.
The generation process must be effective since the difference between CAM generation time and the time at which the CAM is delivered to the networking transport layer shall be less than 50 ms.
Asynchronous messages create and maintain awareness about a road event - e.g. road hazard or an abnormal traffic condition - such as its type, position, validity, timestamp, and history of the event.
While the content varies depending on the type of event, it is expected that at least the detection time, the position of the event, the type of the related station, and a set of cause codes identifying the type of event are present.
Containers for certain types of events - such as the Road Works.
Stationary Vehicle Containers.
Unlike CAMs, DENMs are generated as events occur, and thus, they are not generated periodically.
They have a validity period, which after ending, means the DENM can no longer be considered up-to-date. When an event is no longer occurring, a particular type of DENM, a termination DENM, can be used to signal the end of the event - e.g. the end of the road hazard or of adverse weather conditions.
Periodic messages are exchanged in the ITS network between stations to create and maintain awareness of VRUs and support the risk assessment.
Basic status: time, position, speed, heading, yaw rate and acceleration, orientation, lane position, dimensions, and VRU type.
Advantages of a VAM standard message over the usage of a CAM.
Flexibility in terms of fully specifying the VRU type and situation, which is not possible without changing the CAM standard (therefore defeating the purpose of using a standard).
VAMs can distinguish between several types of VRU - pedestrian, cyclist, motorcyclist, and animal.
Within each category, they can distinguish several possible roles (e.g. for a cyclist VRU, between bicyclist, a wheelchair user, a horse rider, a roller skater, an e-scooter, and others).
This distinction is crucial: several different VRUs - for example, a child pedestrian or a disabled pedestrian - have different dynamics from a typical pedestrian. That information can be used, for example, by safety services to fine-tune an accident prediction algorithm.
Periodic messages between stations to broadcast information about the current environment perceived by 1 or more sensors.
Sensors from a vehicle, a VRU, and infrastructure can use CPMs to exchange the information obtained from their surroundings, improving the awareness of the situation.
Sensor Information Container: sensor type - e.g. Radar, Lidar, video cameras, or fusion algorithms, and the area the sensor covers.
Perceived Object Container: objected perceived by the sensor, the classification, the confidence of the classification, and several data about its dynamics, such as distance, speed, acceleration, and angle.
