Graceful degradation of CACC performance subject to unreliable wireless communication

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 packet loss, in which case it would effectively degrade to conventional Adaptive Cruise Control (ACC), thereby increasing the minimal intervehicle distance needed for string-stable behavior. Therefore, a control strategy for graceful degradation of one-vehicle look-ahead CACC is proposed to partially maintain the string stability properties of CACC. This strategy is based on estimating the preceding vehicle´s information, here acceleration, using the onboard sensors. Whenever needed, this estimated acceleration can be used as an alternative to the desired acceleration transmitted through wireless communication for this type of CACC. It is shown through simulations and experiments that the proposed strategy results in a noticeable improvement of string stability characteristics, when compared to the situation in which ACC is used as a fallback scenario.