Mixed FSO/Active IRS-Aided MISO NOMA Communication With Imperfect CSI and SIC

This article characterizes the performance of mixed free-space optical (FSO)/active intelligent reflecting surface (IRS)-aided nonorthogonal multiple access (NOMA) communication in the presence of imperfect channel state information (CSI) and imperfect successive interference cancelation (SIC). The detrimental effects of atmospheric turbulence on the FSO communication link, which affects end-to-end communication, are also presented. Considering practical implementation, we illustrate the impact of phase quantization error, imperfect SIC, and imperfect CSI on the outage performance. Our numerical analysis indicates that the outage performance can be significantly improved by utilizing multiple transmit apertures through transmit aperture selection at the base station and employing multiple transmit antennas via maximum ratio transmission at the relay. In addition, the numerical results demonstrate that performance improvements are achieved by mitigating double path loss through an active IRS compared to a passive IRS. The closed-form expression for the outage probability is derived using methods of moments and then verified through Monte Carlo simulations. To gain more valuable insights, asymptotic expressions are also provided for high RF transmit power and high FSO transmit power scenarios. Consequently, diversity orders are derived for an asymptotic study of the outage performance of the considered NOMA network.