Improving Information Age in SAE J2945 Congestion-Controlled Beaconing

The Society of Automotive Engineers (SAE) J2945 standard prescribes a wireless channel congestion control algorithm for Basic Safety Messages (BSMs) in vehicular safety communication. The algorithm utilizes transmit (Tx) power and rate controls, but we find that the Tx power control hardly engages in most practical vehicular traffic densities. We explain the cause, and propose an alternative way to utilize both control mechanisms. Specifically, we suggest that the Tx power control be first exerted to its limit, followed by the Tx rate control coping with further congestion. We show that the proposed alternative not only addresses the inadequate power control issue, but also leads to better information age performance for vehicles in the most safety-critical distances.