Resumen de Adaptive communication protocols for cooperative vehicular systems
Cooperative vehicular systems are expected to play a significant role in future transportation systems by enabling vehicle-to-vehicle and vehicle-to-infrastructure wireless communications. Based on the real-time information exchange among vehicles, and among vehicles and infrastructure units, cooperative vehicular systems will improve traffic safety and efficiency by extending, in space and time, the drivers' awareness of the surrounding environment. However, the challenging vehicular environment, together with the strict requirements of cooperative vehicular applications, and the scarcity of the radio spectrum, require the development of advanced communication protocols, especially to support cooperative road safety applications. In this context, this thesis focuses on the design and evaluation of adaptive communication protocols that are able to satisfy the strict requirements of cooperative vehicular applications, and efficiently use the radio channel. To reach these goals, this thesis performs a dimensioning and sensitivity analysis of cooperative vehicular systems from the application's perspective, in which the system and application's performance are analysed under different operating conditions. This study shows the demanding communication requirements of cooperative applications, especially under adverse operating conditions, and the need of efficiently controlling the channel load. It also demonstrates the importance of using adequate models for the dimensioning and performance evaluation of cooperative vehicular systems, and in particular, accurate radio channel models. This thesis also addresses the design and evaluation of an opportunistic communication mechanism that is able to satisfy the application requirements of stringent cooperative traffic safety applications, while efficiently using the radio channel. The reliability and scalability of the proposed mechanism is demonstrated under simplified and realistic operating conditions. The conducted analysis shows that the proposed mechanism significantly reduces the channel load with respect to fixed transmission power policies, thus demonstrating the channel congestion control benefits of opportunistic cooperative vehicular communication protocols. The work reported in this thesis demonstrates the need of considering each vehicle's traffic context information to exploit the dependencies between different applications. Cooperative vehicular applications have been normally studied separately. However, the conducted research shows that the traffic context information could be employed to improve the joint application traffic safety performance. Finally, this thesis addresses the design and evaluation of different channel congestion control policies based on the individual application requirements of each vehicle to proactively control the channel load. The proposed congestion control policies are also able to exploit the local traffic context information of each vehicle to avoid unnecessary interferences and reduce the channel load without sacrificing the applications reliability. To summarise, this thesis has contributed towards a better understanding of the operation and performance of cooperative vehicular communication protocols and applications. The proposed protocols and policies push forward the consideration of cooperative application requirements in the design of cooperative systems for an improved system reliability and increased efficiency.
