I. Introduction
Internet of Things (IoT) is structurally divided into three parts: perception layer, network layer and application layer. The important component of perception layer is a variety of devices [1]. Massive Machine Communication Scenario (mMTC) is widely applied in environmental sensing, intelligent agriculture, event monitoring, etc. and a large number of devices are needed [2], [3]. For mMTC communication, at each given moment, only a few devices are active. Thus, device activity detection in the network is very important to ensure successful communication.