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In this paper, we investigate the benefits of Vehicleto-Vehicle (V2V) communication for autonomous vehicles and provide results on how V2V information helps reduce employable time headway in the presence of parasitic lags. For a string of vehicles adopting a Constant Time Headway Policy (CTHP) and availing the on-board information of predecessor's vehicle position and velocity, the minimum employable time headway (hmin) must be lower bounded by 2τ0 for string stability, where τ0 is the maximum parasitic actuation lag. In this paper, we quantify the benefits of using V2V communication in terms of a reduction in the employable time headway: (1) If the position and velocity information of r immediately preceding vehicles is used, then hmin can be reduced to 4τ0/(1 + r); (2) furthermore, if the acceleration of 'r' immediately preceding vehicles is used, then hmin can be reduced to 2τ0/(1 + r); and (3) if the position, velocity and acceleration of the immediate and the r-th predecessors are used, then hmin ≥ 2τ0/(1 + r). Note that cases (2) and (3) provide the same lower bound on the minimum employable time headway; however, case (3) requires much less communicated information.While AVs employing CTHP may not require communicated information for string stability, the use of V2V and I2V communications when employing CTHP may seem paradoxical and this point has not clearly been articulated in [4]. The necessity for using communication when employing CTHP in trucks was recently brought to the attention of the authors by Ploeg [5] who noticed string instability without V2V or I2V communication in a platoon of three trucks when employing a time headway of about 0.35 seconds. Other numerical simulations and experiments also seem to suggest that employing the acceleration or velocity information of immediately preceding vehicle(s) can help reduce the time headway [3], [6]- [8]. We must point out that the topic of communication and its benefit in reducing time headway was first considered for Semi-Autonomous Cooperative ACC in [6]; the points of departure of this work from [6] are many fold: (1) in this work, we consider architectures involving multiple predecessors, and (2) we do not feed back acceleration of controlled vehicle.In order to reduce the employable time headway, modern systems such as the Cooperative Adaptive Cruise Control (CACC) systems utilize vehicular communication to acquire additional information [7]. In this work, we quantify the benefits of V2V communication in terms of reduction in the employable time headway in the presence of parasitic lags while guaranteeing string stability. For this purpose, we consider a singular perturbation to model parasitic actuation dynamics.The advantage of using V2V communication in improving safety of the vehicles in the platoon has been explored in the literature. For example, the use and benefits of V2V for collision avoidance via emergency lane changing in AVs was discussed in [9]. In an emergency braking scenario, intervehicular communication aids coordination among v...

Adaptive estimation of time-varying parameters in linearly parametrized systems is considered. The estimation time is divided into small intervals; in each interval the time-varying parameter is approximated by a time polynomial with unknown coefficients. A condition for resetting of the parameter estimate at the beginning of each interval is derived; the condition guarantees that the estimate of the time-varying parameter is continuous and also allows for the coefficients of the polynomial to be different in various time intervals. A modified version of the least-squares algorithm is provided to estimate the time-varying parameters. Stability of the proposed algorithm is shown and discussed. Simulation results on an example are given to validate the proposed method.