In this paper, an analytical framework for secure simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted non-orthogonal multiple access (NOMA) transmissions in large-scale networks is proposed, where users and eavesdroppers are randomly distributed. Both the time-switching protocol (TS) and energy splitting (ES) protocol are considered for the STAR-RIS. To characterize system performance, the channel statistics are first provided, and the Gamma approximation is adopted for general cascaded $\kappa$-$\mu$ fading. Afterward, the closed-form expressions for both the secrecy outage probability and secrecy ergodic rate are derived. To obtain further insights, the asymptotic performance for the secrecy diversity order and the secrecy slope are deduced. The theoretical results show that 1) the secrecy diversity orders of the strong user and the weak user depend on the path loss exponent and the distribution of the received signal-to-noise ratio, respectively; 2) the secrecy slope of the ES protocol achieves the value of one, higher than the slope of the TS protocol which is the mode operation parameter of TS. The numerical results demonstrate that: 1) there is an optimal STAR-RIS mode operation parameter to maximize the system performance; 2) the STAR-RIS-NOMA significantly outperforms the STAR-RIS-orthogonal multiple access.
翻译:Translated abstract:
本文提出了一种分析框架,用于在随机分布的用户和窃听者中,对大规模网络中的用户进行物理层安全的同时传输和反射重构智能面 (STAR-RIS) 辅助的非正交多址传输 (NOMA)。该文同时考虑了时间分换协议 (TS) 和能量分割 (ES) 协议下的 STAR-RIS。为了表征系统性能,首先提供了通道统计信息,并采用 Gamma 近似来描述通用级联的 $\kappa$-$\mu$ 衰落。然后,推导了安全中断概率和安全平均速率的闭式表达式。为了进一步深入了解,推导了安全多样性阶数和安全斜率的渐近性能。理论结果表明:1) 强用户和弱用户的安全多样性阶数分别取决于路径损耗指数和接收信噪比分布;2) ES 协议的隐秘斜率达到了 1,高于 TS 协议的斜率,其余操作参数是 TS 的模型操作参数。数值结果表明:1) 存在最优的 STAR-RIS 模式操作参数,以最大化系统性能;2) STAR-RIS-NOMA 明显优于 STAR-RIS-正交多址传输。