Graceful Degradation of Cooperative Adaptive Cruise Control

Cooperative adaptive cruise control (CACC) employs wireless intervehicle communication, in addition to onboard sensors, to obtain string-stable vehicle-following behavior at small intervehicle distances. As a consequence, however, CACC is vulnerable to communication impairments such as latency and packet loss. In the latter case, it would effectively degrade to conventional adaptive cruise control (ACC), thereby increasing the minimal intervehicle distance needed for string-stable behavior. To partially maintain the favorable string stability properties of CACC, a control strategy for graceful degradation of one-vehicle look-ahead CACC is proposed, based on estimating the preceding vehicle's acceleration using onboard sensors, such that the CACC can switch to this strategy in case of persistent packet loss. In addition, a switching criterion is proposed in the case that the wireless link exhibits increased latency but does not (yet) suffer from persistent packet loss. It is shown through simulations and experiments that the proposed strategy results in a noticeable improvement of string stability characteristics, when compared with the ACC fallback scenario.