Vehicular wireless communications require both congestion control to guarantee the availability of a fraction of the bandwidth for safety-related event-driven messages in emergency cases, and awareness control to adapt the beaconing activity to the application needs and surrounding traffic situation. Most current approaches either ignore the traffic situation and only adapt the beaconing rate to the channel congestion state or override the congestion control limits, leading to questionable results in both cases. In this paper, we conceive and validate a novel approach, combining both aspects. Based on distributed Network Utility Maximization (NUM), our algorithm satisfies the constraints on channel availability, whereas the safety of the surrounding traffic situation is captured with a time-to-collision metric, used to assign priorities in the optimal allocation problem. The performance of the proposed approach is validated and compared to other popular algorithms. Results show that our proposal automatically anticipates a potential increase in rate due to a critical safety situation, but does not interfere with the reserved bandwidth for safety applications.

Introduction

Connected vehicles extend the capabilities of multiple advanced driver-assistance systems and automated vehicles by enabling the possibility of performing cooperative actions, such as Cooperative Automated Driving (CAD) or increasing the awareness of a vehicle’s sensor systems [1]. CAD can improve safety and efficiency by introducing Cooperative Adaptive Cruise Control (CACC) applications [2], including not only platoon driving, but also cooperative collision avoidance [3], among others. Cooperative inter-vehicular applications usually rely on the exchange of broadcast single-hop status messages (beacons) among vehicles on a single control channel, which provides detailed information about vehicle position, speed, heading, acceleration, curvature, and other data of interest [4]. Beacons, called Cooperative Awareness Messages (CAM) in European standards and Basic Safety Messages (BSM) in the US standard, are transmitted periodically at a certain beaconing rate. The aggregated load on the wireless channel due to periodic beacons can rise to a point where it can limit or prevent the transmission of other crucial messages, which is called channel congestion due to beaconing activity. Even though this problem has been previously analyzed by different related proposals [5]–[۱۰], some aspects deserve further consideration.