Securing NOMA by an Active RIS: Joint Reflection and Jamming Design

This paper proposes a new active reconfigurable intelligent surface (A-RIS) assisted joint reflection and jamming (JRJ) scheme to enhance the physical layer security of non-orthogonal multiple access, provide higher degrees of freedom, and overcome the effect of double fading. Specifically, the elements on the A-RIS are exploited for simultaneous signal reflection and jamming generation. The transmit beamforming, amplification factor, working mode, and phase shift of each A-RIS element are jointly optimized to maximize the system sum rate by considering imperfect channel state information of an eavesdropper. A penalty based alternating optimization algorithm is then devised to solve the above resource allocation problem. Numerical results are provided to demonstrate the security advantage of the proposed JRJ scheme over the existing baselines.