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An Evaluation Framework for Safe Cooperative Vehicle Platooning
Ref: CISTER-TR-230605       Publication Date: 29, May, 2023

Abstract:
The development of cooperative vehicle systems is one of the industry's choices to mitigate traffic and transportation problems in urban centers and roads. However, the development of these systems is increasingly complex due to their multiple facets encompassing control, communications, and safety. The high level of integration between communication networks, sensors, actuators, and the dynamic characteristics of individual and group vehicles demands coordinated systems capable of responding in real-time to environment variations.
This Thesis addresses the building of a design framework for validation of the safety and performance aspects of these cooperative Cyber-Physical Systems (Co-CPS). We choose the study of cooperative vehicular platoons (Co-VP), since such applications are of great interest, due their potential to reduce energy consumption, improve traffic flow and increase transportation capacity. However, the literature shows a gap space in the integrated study of Co-VP control dynamics regarding communication issues. These systems are prone to safety failures when threatened by communication errors and delays. Moreover, the difficulty in consolidating a validation tool capable of jointly analyzing these aspects, showing the impacts of communication on control systems, was also observed.
The efficient validation of Co-VP systems demands a deep understanding of multiple topics. We begin by presenting a review of Co-VP research in terms of control and compile the most important characteristics of ETSI ITS-G5, the chosen communication infrastructure. Next, we conduct a multidimensional survey on the advances related to this subject, evaluating the control models and the impacts that network constraints cause on these vehicles. Finally, we present strategies to minimize security problems involving these applications.
Seeking to mitigate the lack of a Co-VP simulation tool that meets the needs of safety validation, this Thesis describes the construction of an integrated framework for developing, testing, and evaluating these systems. Encompassing microscopic aspects of communication and control, CopaDrive uses ROS as an integrative tool, extending the framework from simulation to implementation on a robotic testbed through a hybrid environment, in a Hardware in the Loop (HIL). Using the 3D robot simulator and a communication network simulator, we evaluate how the use of Cooperative Awareness Messages (CAMs), defined by ETSI ITS-G5, impacts the ability of the platoon to perform a u-turn. Furthermore, this Thesis presents how the same control and communication model was used in HIL, to validate a Control Loss Warning (CLW) module. Finally, we also show how the control model can be validated using a robotic testbed, using real On-board Units (OBUs).
The vehicles participating in a cooperative platoon are subject to quick conditions changes. Thus, considering only their longitudinal motion is not a reasonable option since the cars will inevitably have to make turns and face obstacles on a usual path. Therefore, we propose a Look-Ahead controller capable of integrating the lateral and longitudinal controls of the vehicles in the platoon in a distributed way. By propagating the trajectory of the lead vehicle through predecessor-follower communication, we reduce heading and distance errors, increasing the system's safety. We also propose using a lateral adjustment to correct the effect of cutting corners caused by the distance between the leader and the follower when a turn is performed.
The evolution of Co-VP systems is intrinsically dependent on communications, which are responsible for ensuring message delivery. Regarding the ITS-G5, this Thesis restricts the CAMs triggering mechanism by proposing a Platoon Service Profile (PSP). We show how this restriction contributes to increased platoon performance by reducing lateral and longitudinal errors in realistic scenarios. We also compare other message firing models established by ETSI ITS-G5 and conclude that using PSP does not significantly increase network throughput. We also show its applicability for urban and freeway scenarios.
Since the scenarios and technologies surrounding CPS are highly dynamic, we also show how CopaDrive can be used to validate cooperative vehicular applications for different environments. In this Thesis, for convenience and without loss of generality, we apply the proposed framework to a learning academic system using an inter-vehicular sensor network based on the IEEE 802.15.4 communication protocol.

Enio Filho

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