Secrecy Outage Probability and Fairness of Packet Transmission Time in a NOMA System

In this paper, we analyze the secrecy outage probability (SOP) and the fairness of average packet transmission time for a non-orthogonal multiple access (NOMA) system which consists of a base station (BS) and two legal NOMA users in the presence of an eavesdropper (Eve). In order to extract the superimposed signal, the Eve is considered in two modes, i.e., successive interference cancellation (SIC) mode and parallel interference cancellation (PIC) mode. Accordingly, we analyze the secrecy performance of the considered system by deriving a new exact expression for SOP. Furthermore, the optimal power allocation between two legal users is determined such that the average transmission time from BS to two legitimate users are approximately equal to achieve the fairness of average packet transmission time. Monte Carlo simulations are provided to verify our analytical results.