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

翻译：作为一种革命性技术，可重构智能表面因其固有的无线信道调控能力，已被视为第六代通信不可或缺的组成部分。然而，无源RIS仍面临一些紧迫问题，其中整个反射链路的衰落与基站到无源RIS距离及无源RIS到用户距离的乘积成正比，即乘积衰减。为解决该问题，研究者提出了有源RIS以重构无线传播条件并缓解乘积衰减。本文研究了存在外部与内部窃听者时，有源RIS辅助的非正交多址接入网络的物理层安全。具体而言，通过引入不完美串行干扰消除与完美SIC，推导了安全中断概率和安全系统吞吐量的闭合表达式。在高信噪比条件下，获得了合法用户的保密分集阶数。数值结果验证了理论表达式的准确性，并表明：i) 有源RIS辅助NOMA网络的安全中断概率优于无源RIS-NOMA、有源RIS/无源RIS辅助的正交多址接入；ii) 由于热噪声与残余干扰间的权衡，在有源RIS上增加过多可重构元件无助于降低SOP；iii) 有源RIS-NOMA网络的保密吞吐量性能优于无源RIS-NOMA及有源RIS/无源RIS-OMA网络。