To Send or To Defer? Improving the IEEE 802.11p/1609.4 Transmission Scheme
Résumé
The IEEE 1609.4 protocol has been proposed to improve message delivery in Vehicular Ad Hoc Networks (VANETs) through its multi-channel usage. To ensure good performance for safety applications, during the first half of a synchronization interval, each vehicle tunes a dedicated Control CHannel (CCH) to exchange safety messages, and during the second half, either it stays on the CCH or switches to one of the six available Service CHannels (SCH). As demonstrated in the literature, such behavior leads safety messages to suffer from synchronous collisions at the start of the CCH interval, as well as from high end-to-end delays caused by the queue-up during the SCH intervals. To address these issues, we propose DMS, a Distributed MAC Scheduler that relies on the Optimal Stopping Theory to evenly balance the channel load by introducing tolerated deferring delays before sending a message. This ensures a higher reception probability and lower collision risks, while complying with Enhanced Distributed Channel Access (EDCA) access categories (ACs). Simulation study shows the ability of our approach to increase the reception rate of safety messages up to 25%, to decrease loses up to 47%, and to improve the load balancing during the CCH interval.