Sum Rate Maximization of Secure NOMA Transmission with Imperfect CSI

In multiple access systems, physical layer security is degraded since more attacking targets are available for the eavesdropper. Fortunately, it has been recently demonstrated that non-orthogonal multiple access (NOMA) could improve secure transmission performance. However, it is still unknown how to design a transmission scheme for maximizing the sum rate when the channel state information is imperfectly known at the transmitter. To fill this gap, we formulate a maximization problem of sum rate while incorporating versatile metrics such as outage probability, quality of service, and transmit power. By leveraging the first-order and log-concavity properties of the Marcum Q-function, the maximum sum rate of the secure NOMA transmission scheme is efficiently obtained. Simulation results validate the strength of this newly established scheme when compared with conventional orthogonal multiple access scheme.