Secrecy Performance of a Multi-NOMA-MIMO System in the UEH Relaying Network Using the PSO Algorithm

In this paper, we investigate the secrecy performance of the nonorthogonal multiple access (NOMA) system in an untrusted relaying energy harvesting (UEH) network with the multiple-input multiple-output (MIMO) architecture using the maximum ratio transmission (MRT) and maximal ratio combining (MRC) techniques. In this network, a source communicates with users with the help of a relaying network composed of multiple untrusted components using the amplify-and-forward (AF) protocol. These untrusted relay nodes are equipped with a single antenna and employ the power-splitting (PS) protocol to harvest energy from received signals. Moreover, to improve the secrecy outage performance and protect the confidential information from the untrusted relaying network, the source acts as the jammer to generate artificial noise (AN). To evaluate the secrecy performance of each user and the overall system, we derive the closed-form expressions of the secrecy outage probability (SOP) over the Rayleigh fading channels and use a Monte Carlo simulation to verify the accuracy of these analytical results. Moreover, to analyze the secrecy data rate, the maximization problem of the sum secrecy rate (SSR) of the system is solved by applying the particle swarm optimization (PSO) algorithm based on power allocation (PA). These results are also validated with the optimal exhaustive search method. Furthermore, we compare the MIMO/NOMA and MIMO/OMA systems and examine the effects of various system parameters to characterize the secrecy effectiveness of both systems.