Scalability limitation of homogeneous vehicular platoon under undirected information flow topology and constant spacing policy

This paper studies the scalability limitation of vehicular platoons moving with constant spacing policy under undirected information flow topologies, and proposes one basic way to improve stability margin, i.e., using communication topologies with constant tree depth. A vehicular platoon is considered as a combination of four components: node dynamics, decentralized controller, information flow topology, and formation geometry. Tools, such as algebraic graph theory and matrix factorization technique, are employed to model and analyze the scalability limitation. The major findings include: (1) under linear identical decentralized controllers, the stability thresholds of control gains are explicitly established for platoons under undirected information flow topologies; (2) the stability margin decays to zero as the platoon size increases unless there is a large number of followers pinned to the leader.