Joint Power and Sub-Channel Allocation for Secure Transmission in NOMA-Based mMTC Networks

In this paper, we consider the physical layer security for non-orthogonal multiple access (NOMA)-based uplink massive machine type communication (mMTC) networks. Aiming at the maximization of the system secrecy capacity, with the presence of eavesdroppers, we propose a joint power and sub-channel allocation for secrecy capacity (JPSASC) algorithm to obtain the suboptimal solution of the joint problem. Particularly, the power allocation problem is modeled as a non-cooperative game with a distributed perspective, where each MTC device selfishly optimizes its power allocation over multi-channels to maximize its own secrecy capacity. The existence of Nash equilibrium (NE) is proved and a sufficient condition to ensure the uniqueness of NE is given. Moreover, the distributed power allocation and preference secrecy capacity maximum (PSCM) algorithms are proposed for power allocation and sub-channel allocation problem, respectively. Simulation results verify that JPSASC algorithm outperforms other algorithms in maximizing secrecy capacity. Furthermore, the secrecy capacity in NOMA-based mMTC is improved compared with that in orthogonal multiple access schemes.