Optimal Secure NOMA Clustering and Power Allocation in Distributed Satellite-Enabled Internet of Things

The satellite-enabled Internet of Things (S-IoT) plays a crucial role by providing stable and global connectivity. However, its rapid growth brings many challenges in managing massive devices and addressing security threats. In this article, we propose a new distributed network architecture combined with nonorthogonal multiple access (NOMA) for S-IoT. We consider a secure NOMA transmission scenario, where an appropriate legitimate device in an NOMA cluster is chosen as a jammer. To maximize the system’s total secrecy rate, we formulate an optimal secure NOMA clustering and power allocation, which is nonconvex and difficult to solve directly. To solve the joint optimization problem, the original problem is transformed into two subproblems, and we propose staged algorithms to solve them efficiently. First, a distributed iterative NOMA clustering algorithm is proposed to iteratively group S-IoT devices into multiple NOMA clusters. Then, a particle swarm optimization (PSO)-based optimal secure power allocation (OSPA) algorithm and a soft actor critic (SAC)-based OSPA are proposed to allocate powers for intracluster devices. The PSO/SAC-based OSPA algorithm can be performed among different NOMA clusters in a parallel way, which greatly improves the efficiency of power allocation. Finally, an optimal dynamic jammer strategy is proposed to dynamically select an idle device to act as a jammer, greatly improving the security performance of the systems. The simulation results demonstrate the advantages of the proposed distributed algorithms and also show that the proposed scheme greatly outperforms the state-of-the-art schemes in terms of the secrecy rate.