  In this paper, we study the longitudinal control problem for a platoon of
vehicles with unknown nonlinear dynamics under both the predecessor-following
and the bidirectional control architectures. The proposed control protocols are
fully distributed in the sense that each vehicle utilizes feedback from its
relative position with respect to its preceding and following vehicles as well
as its own velocity, which can all be easily obtained by onboard sensors.
Moreover, no previous knowledge of model nonlinearities/disturbances is
incorporated in the control design, enhancing in that way the robustness of the
overall closed loop system against model imperfections. Additionally, certain
designer-specified performance functions determine the transient and
steady-state response, thus preventing connectivity breaks due to sensor
limitations as well as inter-vehicular collisions. Finally, extensive
simulation studies and a real-time experiment conducted with mobile robots
clarify the proposed control protocols and verify their effectiveness.
