Secure Beamforming for IRS-Enhanced NOMA Networks

—Owing to the increasing demand of higher spectrum efﬁciency and large-scale connectivity, non-orthogonal multiple access (NOMA) has become a highly competitive candidate for the upcoming sixth-generation (6G) systems. Nevertheless, the instable wireless propagation environment and potential wireless security risk become bottlenecks in applications of NOMA. Fortunately, intelligent reﬂecting surface (IRS) that can construct the three-dimensional beamforming and reconﬁgure the channels emerges as a highly efﬁcient technology to break through the limitations of NOMA. Thus, in this article, we ﬁrst present an overview of NOMA, and particularly illustrate its main shortcomings and security risks. Then, we introduce the IRS technology and provide further enhancement by applying IRS to NOMA networks. In addition, typical security threats in IRS-NOMA networks are shown, followed by two countermeasures based on the joint transmit beamforming and IRS reﬂecting beamforming towards external and internal eavesdropping, re- spectively. Simulation results are carried out to demonstrate the feasibility and effectiveness of these two schemes. Several challenges and future directions are also discussed.