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 paper, we propose a new distributed network architecture combined with non-orthogonal 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 non-convex 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. Firstly, 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 intra-cluster 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.