Active RIS-NOMA-Aided Covert Communication with Hardware Impairments

In this letter, we investigate an active reconfigurable intelligent surface (RIS) and non-orthogonal multiple access (NOMA)-aided covert communication system with hardware impairments, where a base station conducts NOMA downlink transmissions to a covert user and a public user. More specifically, we derive the analytic expressions for the outage probability (OP), the detection error probability (DEP), and optimal detection thresholds. Then, we study the influence of detection threshold, RIS deployment location, and power distribution factor on the covert performance. Compared to the passive RIS system with the same total power budget, numerical results show that the active RIS system achieves better covert performance and effectively overcomes the double path-loss attenuation.