Maximizing physical layer security in relay-assisted multicarrier nonorthogonal multiple access transmission

This letter investigates the physical layer security of dual-hop nonorthogonal multiple access (NOMA) networks. We consider a multicarrier transmission scenario which consists of a single source, a relay, an eavesdropper, and multiple users. Our objective is to maximize the sum secure rate of the system with optimal power allocation over different sub-carriers at the source. Because of the rate expression and binary variable, the optimization problem is formulated as a nonconvex and mixed integer programming problem. Thus, the optimal solution is obtained through duality theory which is considered to be an efficient method for solving nonconvex optimization problems. We compare the performance of the proposed NOMA scheme with orthogonal frequency multiple access (OFDMA) scheme. Our simulation results show that the proposed NOMA scheme has good performance in convergence and significantly outperforms the traditional OFDMA scheme.