Robust Secure Transmission Design for RIS-Aided MISO-NOMA System with Hardware Impairments and Imperfect CSI.

Hardware impairments (HWI) and the channel state information (CSI) estimation errors inevitably degrade the security performance of the communication system. In this work, we explore a robust beamforming solution for a reconfigurable intelligence surface (RIS)-assisted multiple-input single-output (MISO) multi-user secure network under HWI and imperfect CSI. Artificial noise (AN) is designed to jam eavesdroppers while non-orthogonal multiple access (NOMA) is employed to suppress the interference between legitimate users. Aimed at maximizing secrecy sum rate, the active beamforming with AN at the BS and the passive beamforming at the RIS are jointly optimized. The nonconvex optimization problem is handled using the semi-definite relaxation (SDR), where the eavesdropper's channel uncertainty is tackled by the S-procedure. Then the multi-variable coupling problem is decomposed into two sub-problems and three blocks of variables are alternately optimized using the block coordinate descent (BCD) method. The results suggest that the developed scheme outperforms the benchmark ones in terms of security and resistance to HWI.