Secrecy Performance of Uplink MIMO-NOMA with Antenna Selection in a Mixed RF-FSO System

In this paper, we investigate the physical layer security of a two-user multiple-input-multiple-output (MIMO) non-orthogonal multiple access (NOMA) with transmit antenna selection (TAS) in mixed radio frequency (RF) and free-space optical (FSO) communications. Specifically, the uplink RF transmissions between the users and a relay node undergo a Nakagami-m fading while the FSO link between the relay node and the destination node experiences a gamma-gamma fading. Considering this model, the statistical features constituted of the probability density function (PDF) and cumulative distribution function (CDF) are obtained in closed form. The derived expressions are subsequently used to obtain the analytical expressions of the secrecy outage probability (SOP) and the probability of the strictly positive secrecy capacity (SPSC). Monte Carlo simulations are provided to verify the accuracy of the proposed analytical framework.