Resolving the Unfairness of Distributed Rate Control in the IEEE WAVE Safety Messaging

In the IEEE Wireless Access in Vehicular Environment (WAVE), the periodic broadcast of the basic safety message (BSM) enables proximity awareness in the vehicle-to-vehicle (V2V) context. To maximize the level of awareness and consequently the driving safety, the BSM transmission at the highest allowed rate is desired in principle. A caveat, however, is controlling the BSM traffic within the given channel capacity because otherwise it can actually lower the delivery probability due to message collisions. To avoid such a congestion situation, a traditional mode of control is regulating the frequency of the BSM transmission based on the channel load. In this paper, we shed light on the pitfalls that lurk in exercising adaptive rate control based on an observed global state such as the channel load. Specifically, we show that straightforward threshold- or hysteresis-based controls can irrevocably render the rate assignments irrelevant to the given vehicle density pattern. As a solution, we show that distributed but coordinated control provably leads to stability and relevance to the given vehicle density pattern.