Although reconfigurable intelligent surface (RIS) can improve the secrecy communication performance of wireless users, it still faces challenges such as limited coverage and double-fading effect. To address these issues, in this paper, we utilize a novel multi-functional RIS (MF-RIS) to enhance the secrecy performance of wireless users, and investigate the physical layer secrecy problem in non-orthogonal multiple access (NOMA) networks. Specifically, we derive the secrecy outage probability (SOP) and secrecy throughput expressions of users in MF-RIS-assisted NOMA networks with external and internal eavesdroppers. The asymptotic expressions for SOP and secrecy diversity order are also analyzed under high signal-to-noise ratio (SNR) conditions. Additionally, we examine the impact of receiver hardware limitations and error transmission-induced imperfect successive interference cancellation (SIC) on the secrecy performance. Numerical results indicate that: i) under the same power budget, the secrecy performance achieved by MF-RIS significantly outperforms active RIS and simultaneously transmitting and reflecting RIS; ii) with increasing power budget, residual interference caused by imperfect SIC surpasses thermal noise as the primary factor affecting secrecy capacity; and iii) deploying additional elements at the MF-RIS brings significant secrecy enhancements for the external eavesdropping scenario, in contrast to the internal eavesdropping case.

翻译：尽管可重构智能表面（RIS）能够提升无线用户的保密通信性能，但其仍面临覆盖范围有限与双衰落效应等挑战。为解决这些问题，本文采用一种新型多功能RIS（MF-RIS）来增强无线用户的保密性能，并研究非正交多址接入（NOMA）网络中的物理层保密问题。具体而言，我们推导了存在外部与内部窃听者时，MF-RIS辅助NOMA网络中用户的保密中断概率（SOP）与保密吞吐量表达式。同时在高信噪比（SNR）条件下分析了SOP与保密分集阶数的渐近表达式。此外，我们还考察了接收机硬件限制及传输误差导致的不完美连续干扰消除（SIC）对保密性能的影响。数值结果表明：i) 在相同功率预算下，MF-RIS实现的保密性能显著优于有源RIS及同时透射反射型RIS；ii) 随着功率预算增加，不完美SIC导致的残余干扰将超越热噪声成为影响保密容量的主要因素；iii) 与内部窃听场景相比，在MF-RIS上部署更多单元能为外部窃听场景带来显著的保密性能提升。