Secrecy Performance of SWIPT-NOMA Network With TAS/OSTBC-MRC Scheme in the Presence of Practical Impairments

This article analyzes the secrecy performance of a power domain downlink multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA) system capable of simultaneous wireless information and power transfer (SWIPT). In this system, a base station (BS) with multiple antennas communicates simultaneously with$L$legitimate mobile users, each also equipped with multiple antennas. The BS employs orthogonal space-time block coding (OSTBC) which does not require channel state information (CSI). Meanwhile, mobile users utilize maximum ratio combining (MRC) to benefit from the advantages of receive diversity in addition to the transmit diversity offered by OSTBC. Then, to enhance the secrecy, a second scenario, the transmit antenna selection (TAS) based scheme is also studied where the transmit antennas at the BS are selected for the desired user, is implemented at the price of partial CSI. The article derives closed-form expressions for the secrecy outage probability (SOP), harvested power outage probability and overall SOP of the system for both the OSTBC-MRC scheme and the OSTBC-MRC scheme with TAS. The analysis is performed over Nakagami-$m$fading channels, considering practical impairments such as channel estimation error (CEE), feedback delay (FBD) and imperfect successive interference cancellation (ipSIC). Additionally, asymptotic analyses illustrate the effects of CEE and FBD on diversity order and array gain. The results demonstrate that the proposed system with antenna selection significantly outperforms configurations without antenna selection across various user scenarios. Moreover, enhancing both the number of transmit and receive antennas simultaneously yields a greater improvement in secrecy performance than increasing either one of them alone and ipSIC degrades the performance of the low-power allocated users (near users) due to residual interference in the cancellation process. This trend holds with an increase in the number of transmit antennas that provide superior resilience to FBD and CEE compared to increasing receive antennas exclusively. Monte Carlo simulations confirm the validity of the analytical results.