Reconfigurable intelligent surface (RIS) has been regarded as a promising technology since it has ability to create the favorable channel conditions. This paper investigates the secure communications of RIS assisted non-orthogonal multiple access (NOMA) networks, where both external and internal eavesdropping scenarios are taken into consideration. More specifically, novel approximate and asymptotic expressions of secrecy outage probability (SOP) for the k-th legitimate user (LU) are derived by invoking imperfect successive interference cancellation (ipSIC) and perfect successive interference cancellation (pSIC). To characterize the secrecy performance of RIS-NOMA networks, the diversity order of the k-th LU with ipSIC/pSIC is obtained in the high signal-to-noise ratio region. The secrecy system throughput of RIS-NOMA networks is discussed in delay-limited transmission mode. Numerical results are presented to verify theoretical analysis that: i) The SOP of RIS-NOMA networks is superior to that of RIS assisted orthogonal multiple access (OMA) and conventional cooperative communication schemes; ii) As the number of reflecting elements increases, the RIS-NOMA networks are capable of achieving the enhanced secrecy performance; and iii) The RIS-NOMA networks have better secrecy system throughput than that of RIS-OMA networks and conventional cooperative communication schemes.

翻译：可重构智能表面（RIS）因其具有构建有利信道条件的能力而被视为一项前景广阔的技术。本文研究了RIS辅助非正交多址接入（NOMA）网络的安全通信问题，其中同时考虑了外部和内部窃听场景。具体而言，通过引入非完美连续干扰消除（ipSIC）和完美连续干扰消除（pSIC），推导了第k个合法用户（LU）保密中断概率（SOP）的新颖近似和渐近表达式。为表征RIS-NOMA网络的保密性能，在高信噪比区域获得了采用ipSIC/pSIC的第k个LU的分集阶数。在时延受限传输模式下讨论了RIS-NOMA网络的保密系统吞吐量。数值结果验证了理论分析：i）RIS-NOMA网络的SOP优于RIS辅助正交多址接入（OMA）及传统协作通信方案；ii）随着反射单元数量增加，RIS-NOMA网络能够实现增强的保密性能；iii）RIS-NOMA网络相比RIS-OMA网络和传统协作通信方案具有更好的保密系统吞吐量。