Designing Network Motifs in Connected Vehicle Systems: Delay Effects and Stability

Arising technologies in vehicle-to-vehicle (V2V) communication allow vehicles to obtain information about the motion of distant vehicles. Such information can be presented to the driver or incorporated in advanced autonomous cruise control (ACC) systems. In this paper, we investigate the effects of multi-vehicle communication on the dynamics of connected vehicle platoons and propose a motif-based approach that allows systematical analysis and design of such systems. We investigate the dynamics of simple motifs in the presence of communication delays, and show that long-distance communication can stabilize the uniform flow when the flow cannot be stabilized by nearest neighbor interactions. The results can be used for designing driver assist systems and communication-based cruise control systems. INTRODUCTION Adaptive cruise control (ACC) is receiving increasing attention these days due to the demand for safety and driver comfort in modern automobiles [1]. In traditional radar-based ACC systems, the vehicle only has information available about the motion of the preceding vehicle [2, 3]. However, emerging wireless communication technologies enable vehicles to observe the motion of distant vehicles, which can potentially increase the efficiency and safety of vehicular networks. At the same time, the modeling, analysis and design of connected vehicle platoons present additional challenges due to increased connectivity and delays caused by intermittency and packet drops in vehicle-to-vehicle (V2V) communication [4]. These delays can impact the performance of the transportation system significantly [5, 6]. In this paper we address the following two challenges: (i) the ∗Address all correspondence to this author. controllers must be modular and function even when connections are lost or new connections are established; (ii) the controllers must be robust against the delays arising in the communication channels. We propose a modeling framework that allows the existence of uniform traffic flow independent of the communication structure and analyze the limitations of the controllers with different delay configurations. In order to make the arising connected systems tractable we use a motif-based approach inspired by recent results in systems biology [7]. Analyzing the dynamics of simple motifs allows one to evaluate the effects of communication delays on plant and string stability. By combining these motifs, one can build complicated networks of prescribed behavior in a systematic way. The results are summarized using linear stability diagrams and numerical simulations are used to demonstrate the nonlinear behavior. The proposed approach can be used to design cooperative adaptive cruise control (CACC) systems where information about the motion of the vehicle in front (sensed by a radar) is integrated with the information about the motion of distant vehicles (received through wireless communication). Moreover, the presented framework is also applicable when human drivers react to the motion of the preceding vehicle while they are assisted by controllers that act upon the data received from distant vehicles. We show that by appropriately selecting the control gains for the long-distance communication links, plant and string stability can be achieved even in cases when the reaction time of human drivers is too large to allow stabilization for any shortdistance gain combinations. 1 Copyright © 2013 by ASME Proceedings of the ASME 2013 Dynamic Systems and Control Conference DSCC2013 October 21-23, 2013, Palo Alto, California, USA DSCC2013-4081