String-Stable Cooperative Adaptive Cruise Control With Minimized Time Headway in the Face of Delayed Communication

The cooperative adaptive cruise control problem is considered in a one-vehicle lookahead configuration with first-order feedback and feedforward controllers. The feedback controller uses the spacing error defined with a constant time gap, while the feedforward controller filters the preceding vehicle input (as the desired acceleration) received through delayed communication. The communication delay is assumed to be constant and yet unknown. A lower bound is then derived for the legitimate time headway choices in terms of the maximum possible communication delay and the vehicle time constant. The delay margin of the feedback loop turns out to be quite large with the suboptimal controllers. On the other hand, a major drawback of approaching the infimum time headway is observed as the increased noise sensitivity of the feedback loop especially in the case of small maximum communication delays.