A quantitative study of Cooperative Awareness Messages in production VANETs

In Vehicular Ad-hoc Networks (VANETs), vehicles gather Cooperative Awareness Messages (CAMs) sent from other vehicles via wireless broadcast. Each received message has to be processed by an in-vehicle system. In series implementations, such an in-vehicle system needs to cope with limited resources whose capacity is not yet defined. Therefore, information about the received CAM rate is a crucial input for the development of series VANET products. CAMs from distant vehicles are less likely to be received than those of nearby vehicles. Designers of applications leveraging CAM information are interested in the frequency of received CAMs originating from vehicles depending on their distance. In this paper, we study future CAM rates depending on various parameters. We set up a road traffic simulation for selected highway scenarios. We estimate the rates of generated CAMs and introduce the notion of relative channel load. We present a new approximative channel model to determine a vehicle's message reception probability. That model is used to simulate the rates of received CAMs for each vehicle. Moreover, we investigate the origin of received CAMs and times between consecutive CAMs received from the same sender (inter-reception times) depending on distance. Most results depend on the penetration rate of VANET technology that will increase in the near future. We derive approximative formulae and use them to validate our simulation results. They are quite accurate, and so they may also serve for simple forecasts. The results from our analysis show that the rates of generated and received CAMs lead to several challenges for the design of an efficient and robust VANET implementation.