非理想SIC下全双工NOMA系统的安全性能分析

针对存在多个非共谋窃听者，研究了一种基于全双工中继和两阶段中继选择（TSRS）的非正交多址接入（NOMA）物理层安全通信方案。每个通信过程包含一个传输时隙，系统在每个时隙开始由TSRS策略选择最优中继，所选中继在从源节点接收NOMA叠加信号的同时，向两个目的节点转发上一时隙的再编码叠加信号，两个目的节点采用串行干扰消除（SIC）技术从中继叠加信号中解码获取各自的期望信号。推导了非理想SIC下系统安全中断概率的近似表达式，进行了蒙特卡洛（Monte-Carlo）仿真验证，同时分析了各仿真参数（SIC残余干扰系数、目标安全速率、中继规模等）与系统安全中断概率的关系。理论分析与模拟仿真的结果表明，全双工技术与TSRS的结合方案能有效提升系统的安全中断性能。将该方案应用于实际通信系统设计时，选择合适传输信噪比（SNR）、提高串行干扰消除能力或适当增加中继数量均可实现更好的保密性能。

Secrecy Performance Analysis of Full-Duplex NOMA Systems with Imperfect SIC

? ?In the presence of multiple non-colluding eavesdroppers， a non-orthogonal multiple access （NOMA） scheme is proposed for physical layer secure communications based on full-duplex relay and two-stage relay selection （TSRS）. Each communication process contains a transmission time slot. At the beginning of each time slot， the system selects the optimal relay by the TSRS strategy. While receiving the NOMA superimposed signal from the source node， the selected relay forwards the re-encoded superimposed signal of the previous time slot to two destination nodes. The two destination nodes decode their respective desired signals from the relayed superimposed signal by using successive interference cancellation （SIC）. The approximated expression for the secrecy outage probability of the system under imperfect SIC is derived and validated by Monte-Carlo simulations. Meanwhile， the relationship between some simulation parameters （SIC residual interference coefficient， target secrecy rate， number of relays， etc） and the secrecy outage probability of the system is analyzed. Theoretical analysis and simulation results show that the combined FD-TSRS scheme can effectively improve the secrecy outage performance of the system. When the scheme is applied to the design of practical communication system， some measures， such as selecting appropriate transmit signal-to-noise ratio （SNR）， enhancing the capability of successive interference cancellation or appropriately increasing the number of relays， can help to achieve better secrecy performance.