Cooperative adaptive cruise control : tradeoffs between control and network specifications

In this study, we consider a Cooperative Adaptive Cruise Control (CACC) system which regulates inter-vehicle distances in a vehicle string. Improved performance can be achieved by utilizing information exchange between vehicles through wireless communication besides local sensor measurements. However, wireless communication introduces network-induced effects that may compromise the performance of the CACC system. Therefore, we approach the design of a CACC system from a Networked Control System (NCS) perspective. Network-induced imperfections in a NCS are mainly due to limited bandwidth of the network, multiple nodes sharing the same medium, and other limitations such as transmission delays and losses. Tradeoffs between CACC performance and network speci¿cations need to be made for achieving desired performance under these network-induced constraints. In this paper, we present a NCS modelling framework that incorporates the effect of sample-and-hold and network delays that occur due to wireless communication. Moreover, we employ this model to study the so-called string stability performance of the string in which vehicles are interconnected by a vehicle following control law and a constant time headway spacing policy. Speci¿cally, we study how string stability is affected by network-induced effects such as delays.