Physical layer security for massive access in cellular Internet of Things

The upcoming fifth generation (5G) cellular network is required to provide seamless access for a massive number of Internet of Things (IoT) devices over the limited radio spectrum. In the context of massive spectrum sharing among heterogeneous IoT devices, wireless security becomes a critical issue owing to the broadcast nature of wireless channels. According to the characteristics of the cellular IoT network, physical layer security (PHY-security) is a feasible and effective way of realizing secure massive access. This article reviews the security issues in the cellular IoT network with an emphasis on revealing the corresponding challenges and opportunities for the design of secure massive access. Furthermore, we provide a survey on PHY-security techniques to improve the secrecy performance. Especially, we propose a secure massive access framework for the cellular IoT network by exploiting the inherent co-channel interferences. Finally, we discuss several potential research directions to further enhance the security of massive IoT.