TCP-like congestion control for broadcast channel access in VANETs

Broadcasting of position and movement information in vehicular ad hoc networks is essential for achieving an awareness of connected vehicles about their environment. If a vehicle broadcasts its position several times per second, then other vehicles can use this information as input for advanced driver assistance systems. Vehicular communication based on the 802.11p standard in the 5GHz band provides a channel for disseminating such awareness information. However, the channel access is not coordinated among the participating vehicles and, thus, a congestion of the channel is possible, i.e. a situation where access delays rise and packet reception rates drop. An initial ETSI standard on congestion control tries to solve the problem by assigning transmit rate limits depending on channel load. We investigate here an alternative solution inspired by the congestion control mechanism of TCP. We describe necessary adaptions of the TCP congestion control to a single-hop broadcast communication and evaluate pros and cons in comparison to a fixed-state congestion control by extensive simulations. Our results exemplify typical differences in effective reception ranges and update intervals, and show performance advantages of adaptive DCC algorithms.