How much overhead is required for stable group formation in VANETs?

On-road-communications are increasing in relevance, due to the variety of applications for traffic management systems (TMS) and road safety. This interest is enforcing relevant efforts from research community and standardization bodies to support V2V (vehicle to vehicle) and V2I (vehicle to infrastructure) communications. In this framework, an hybrid approach between IEEE 802.11p standard together with LTE is becoming the current state-of-the-art solution to provide the required QoS in vehicular communications. In this direction, several research efforts propose, as a fundamental basis, the formation of virtual groups of vehicles that communicate with 802.11p for V2V and use LTE for V2I transmissions. In this paper we focus on the feasibility and efficiency of forming these mobile groups. We provide simulation and analytical results that show that it is possible to maintain stable connected groups of vehicles at high speeds by increasing the periodicity of control message exchange. Interference in the control channel is the only limitation in this scenario. On the other hand, it is still possible to maintain connected groups of vehicles with low overheads if part of the vehicles, the less stable ones, are disconnected from the groups. These two results are obtained analytically and by simulations in ns-2. The paper also evaluates the effects of the obtained results on the energy efficiency of the system.