I. Introduction
Long Term Evolution-Advanced (LTE-Advanced), proposed by the Third Generation Partnership Project (3GPP), is the most promising fourth generation mobile network. In LTE-Advanced network, the 3GPP proposes Machine-type Communications (MTC) as a new paradigm where devices transfer data among themselves with limited human interaction. MTC is now widely used in many aspects, such as monitoring system and industrial automation. In most situations, devices keep silent until there are data delivered from/to them. However, if devices are active all the time, most of the power is wasted. In addition, many MTC devices are powered by battery. Certainly, power saving has already become an important issue in MTC.