Sum Secrecy Rate Maximization in NOMA Downlink SWIPT Systems

Abstract

In this paper, we investigate physical layer security in non-orthogonal multiple access (NOMA) downlink simultaneous wireless information and power transfer (SWIPT) systems, which consist of one access point (AP), information receivers (IRs), and energy receivers (ERs) that are capable of eavesdropping the IR. In order to achieve the target, maximizing the secure sum rate (SSR) of IRs under the conditions of satisfying both the IR’s rate demand and the ER’s harvested energy demand, an algorithm about power allocation of the AP is proposed. Due to the non-convexity of the SSR problem we simplify the objective function at first and decompose it into a series of subproblems, which are easily transformed into convex problems. Thus, the solution of subproblems can be derived according to the Karush–Kuhn–Tucker (KKT) conditions. Then, on account of the relationship between subproblems and original problem, the optimal power allocation is easily obtained. Using the numerical results, we demonstrate that the proposed algorithm can achieve better performance in NOMA downlink SWIPT system than the orthogonal multiple access (OMA) scheme respecting the SSR.