I. Introduction
Machine-to-machine (M2M) communications is one of the most important enabling technologies for the emerging Internet-of-Things paradigm that has found wide applications in various domains such as smart grid, intelligent transportation, and e-health. Aimed at providing pervasive connectivity for autonomous devices with minimum or no human intervention, M2M communications has garnered significant attention in recent years, and is expected to play an instrumental role in next-generation data communication networks [1], [2].