Physical layer security in a downlink-NOMA network with hardware impairment

In this paper, we investigate the secrecy outage performance of a non-orthogonal multiple access (NOMA) energy harvesting (EH) untrusted relaying network in the presence of the residual transmit RF impairments with imperfect successive interference cancellation (SIC). The source node communicates with users via the multiple amplify-and-forward (AF) untrusted relay nodes which use the time-switching (TS) protocol to harvest energy from the source's signal. To improve the secrecy performance of the proposed system the source node also works as the jammer to generate the artificial noise (AN). For evaluating the secrecy performance of system, the expressions for secrecy outage probability (SOP) are derived, and the Monte Carlo simulation is used to verify the accuracy of these theoretical analyses. Moreover, the effects of various parameters, such as power allocation levels, position of untrusted relay, performance of SIC and transmit hardware impairment levels on the SOP of the proposed system in comparison with the orthogonal multiple access (OMA) are investigated.