Brief summary: Inter-vehicle communication has a potential to improve road traffic safety and efficiency. Technical feasibility of communication between vehicles has been extensively studied, but due to the scarcity of application-level research, communication's impact on the road traffic is still unclear. This thesis addresses this uncertainty by designing and evaluating two fail-safe applications, namely, Rear-End Collision Avoidance and Virtual Traffic Lights.
Abstract: The persistent increase of road traffic volume, resulting vehicle collisions and traffic congestion, have fueled the research on inter-vehicle communication networks for several decades. Vehicles equipped with communication devices are envisioned to exchange information on their own status as well as on their surroundings. The exchanged information is thought to serve as an input for various driver assistance applications that aim to improve traffic safety and traffic efficiency. After many years of research, a solid understanding of technical aspects has been achieved. This is reflected in the approval of IEEE 802.11p and IEEE 1609.x standards as well as in the decision to create a standard requiring communication capability in all passenger vehicles. However, it is still not clear whether inter-vehicle communication is “fit” for safety-critical applications and what its impact on the road traffic will be. This uncertainty motivated the work behind this thesis. In particular, we contribute by elaborating methodologies on how to design and evaluate safety-critical applications, on the example of Rear-End Collision Avoidance (RECA) and Virtual Traffic Lights (VTL). Our goal is to determine whether these applications can be supported by inter-vehicle communication, in particular IEEE 802.11p, and result in safe and efficient traffic.
The first part of this thesis addresses the challenge of application design. Due to the safety-critical nature of the chosen applications, we embrace the strict requirement of fail-safety and present how applications can be designed in a fail-safe manner. We define a fail-safe application as an application that integrates mechanisms to counteract the effect of possible failures. Fail-safe features to counteract the effect of the two most obvious and frequent failure sources are integrated in the design of RECA and VTL applications, namely, unreliability of vehicular communication and unpredictability of driver behavior. In addition, we perform a requirement analysis which not only determines the necessary functionality of applications but also provides indications for communication when information needs to be received. The resulting VTL protocol has been formally verified with the model checking method. The chosen verification approach and the defined application requirements allow us to consider not only application and communication aspects but also movement of vehicles in verification.
In the second part of this thesis we address the challenge of application evaluation. In particular, we establish a connection between network and application layers with the help of the awareness principle. The awareness principle allows to translate the RECA application requirements into the required transmission parameters. Consequently, we determine the scalability of IEEE 802.11p communication to reliably support RECA and VTL applications and compare resulting traffic efficiency to conditions with no communication-based applications in place. Although a tradeoff between degree of reliability and traffic efficiency is quantified, it is shown that safety-critical applications can be reliably supported by IEEE 802.11p communication and result in a reasonable traffic efficiency level.
In addition, we perform a sensitivity analysis to determine the impact of inaccurate network and radio channel condition information on the network performance, which is assumed to be known in typical evaluations. We quantify the possible errors in estimating network performance and we identify the conditions that lead to the largest errors. This information can be used by future application designers when limiting or avoidance of errors caused by inaccurate information is particularly important.
Although a lot of work still needs to be done before first driver assistance applications will be commercially available, based on the results presented in this thesis, IEEE 802.11p communication is shown to be capable of supporting strict safety-critical applications, such as Rear-End Collision Avoidance and Virtual Traffic Lights, resulting in a safe and efficient traffic. The utilized methods can further be elaborated and used for the design and evaluation of other driver assistance applications.