I. Introduction
Machine-to-machine (M2M) applications are rapidly growing, and will become an increasingly important source of traffic and revenue in cellular networks [1]. Unlike most human generated or consumed traffic, M2M is often characterized by a very large number of small transactions. The LTE air interface design for high-data-rate applications may not effectively support reliable and low-latency M2M communications with a vast number of devices. Emerging examples include Internet of Things (IoT) sensor [2] and time of arrival measurements [3], smart grids for power distribution automation, industrial manufacturing, control and automation applications [4], and traffic safety, and monitoring of materials and wireless control of industrial plants [5].