Joint Optimization of Emergency and Periodic Message Transmissions in Vehicular Networks

Abstract

There are two broad safety related message categories in vehicular networks: emergency and periodic messages that should share the scarce wireless resource simultaneously. Emergency messages deliver time-critical information with guaranteed reliability, e.g., road-safety information, whereas periodic ones convey normal status update information, e.g., vehicular positions, that is less time- and loss-critical. Recent studies on efficient Medium Access Controls (MACS) under these requirements propose to use the IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol with a strict priority. In this paper, we first model this protocol by a coupled embedded markov chain, and consider an optimization problem that requires to jointly characterize delivery probability and delay of those two types of messages. Our characterization of delivery probability and delay using the modeled embedded Markov chain enables one to easily find the right protocol parameters that satisfy given requirements of emergent and periodic messages, providing a useful engineering value in running the MAC protocol over vehicular networks. We conduct extensive simulations to validate our analytical findings, which we believe is of broad interest to an environment consisting of emergent and periodic message transmissions such as tactical networks with drones.