Secure Communication of Active RIS Assisted NOMA Networks

Abstract

As a revolutionary technology, reconfigurable intelligent surface (RIS) has\nbeen deemed as an indispensable part of the 6th generation communications due\nto its inherent ability to regulate the wireless channels. However, passive RIS\n(PRIS) still suffers from some pressing issues, one of which is that the fading\nof the entire reflection link is proportional to the product of the distances\nfrom the base station to the PRIS and from the PRIS to the users, i.e., the\nproductive attenuation. To tackle this problem, active RIS (ARIS) has been\nproposed to reconfigure the wireless propagation condition and alleviate the\nproductive attenuation. In this paper, we investigate the physical layer\nsecurity of the ARIS assisted non-orthogonal multiple access (NOMA) networks\nwith the attendance of external and internal eavesdroppers. To be specific, the\nclosed-form expressions of secrecy outage probability (SOP) and secrecy system\nthroughput are derived by invoking both imperfect successive interference\ncancellation (ipSIC) and perfect SIC. The secrecy diversity orders of\nlegitimate users are obtained at high signal-to-noise ratios. Numerical results\nare presented to verify the accuracy of the theoretical expressions and\nindicate that: i) The SOP of ARIS assisted NOMA networks exceeds that of\nPRIS-NOMA, ARIS/PRIS-assisted orthogonal multiple access (OMA); ii) Due to the\nbalance between the thermal noise and residual interference, introducing excess\nreconfigurable elements at ARIS is not helpful to reduce the SOP; and iii) The\nsecrecy throughput performance of ARIS-NOMA networks outperforms that of\nPRIS-NOMA and ARIS/PRIS-OMA networks.\n