Safe and Efficient Communication Protocols for Platooning Control

Modern vehicles are becoming smarter and smarter thanks to the continuous development of new Advanced Driving Assistance Systems (ADAS). For example, some new commercial vehicles can detect pedestrians on the road and automatically come to a stop avoiding a collision. Some others can obtain information about traffic congestion through the cellular network and suggest the driver another route to save time. Nevertheless, drivers (and our society as well) are always striving for a safer, cleaner, and more efficient way of traveling and standard, non-cooperative ADAS might not be sufficient. For this reason the research community started to design a vehicular application called "platooning". Platooning simultaneously tackles safety and traffic congestion problems by cooperatively coordinating vehicles in an autonomous way. Traffic flow is optimized by using an advanced Adaptive Cruise Control (ACC), called Cooperative Adaptive Cruise Control (CACC), which drastically reduces inter-vehicle gaps. By being autonomously coordinated, platooning vehicles implicitly implement automated emergency braking, a fundamental application for freeway safety. The idea is to form optimized road trains of vehicles where the first drives the train, while the others autonomously follow at a close distance, without requiring the driver to steer, accelerate, or brake. Platooning can have an enormous impact on future transportation systems by increasing traffic flow (and thus reducing congestion), increasing safety, reducing CO2 emissions, and reducing the stress of driving. This application is extremely challenging due to its inter-disciplinary nature. Indeed, it involves control theory, vehicle dynamics, communication, and traffic engineering. In this thesis we are mostly concerned with the communication aspects of this application, which is fundamental for making the vehicles cooperate, improving the efficiency of the application with respect to a pure sensor-based solution. Application requirements are very tight and, given that the envisioned communication technology will be IEEE 802.11-based, there are concerns on whether these requirements can really be met. The focus of the thesis is in this direction. The first contribution is the design of PLEXE, an extension for the widely used vehicular simulation framework Veins that enables research studies on various platooning aspects, including design and evaluation of control algorithms, communication protocols, and applications. The tool is open source and free to download and use, and it realistically simulates both communication and vehicle dynamics. This makes PLEXE a valid testing platform before real world deployment. The second contribution is a set of undirected information broadcasting (beaconing) protocols that specifically take into account the requirements of the application. We initially develop four static (i.e., periodic) approaches and compare them against two state of the art dynamic protocols, showing that our approaches are capable of supporting the application even in heavily dense scenarios. Then, we propose a dynamic protocol that further improves the application (increasing safety) and the network layer (reducing resource usage) performance. The final contribution is a platooning control algorithm that, compared to state of the art approaches, is re-configurable at run-time and that can be adapted to network conditions. We thoroughly test the algorithm in highly challenging scenarios. These scenarios include a realistic network setup where the road is shared by human- and automated-driven vehicles. Human-driven vehicles interfere with automated-driven ones by sending data packets on the same channel. Moreover, we also consider a scenario with realistic vehicle dynamics, which takes into account vehicles' engine and braking characteristics. The algorithm is shown to be robust to network and external disturbances, to have a fast convergence, and to be very stable. The results in this work thus represent a big step towards the real world implementation of platooning systems.