We investigate physical layer security of an uplink NOMA system consisting of one base station, multiple users and one eavesdropper. During each uplink transmission, two users are paired to perform NOMA and another user is opportunistically selected from the remaining idle users to act as a friendly jammer to emit artificial noise for confusing the eavesdropper. To enhance the transmission security for the system, we propose two friendly jammer selection aided uplink NOMA transmission schemes, namely random jammer selection aided uplink NOMA transmission (RJS-UNT) scheme without knowing the eavesdropper’s channel state information (CSI), and optimal jammer selection aided uplink NOMA transmission (OJS-UNT) scheme where the eavesdropper’s CSI is available. For comparison purpose, a non-jammer selection aided uplink NOMA transmission (NJS-UNT) scheme is also considered. Analytical closed-form expressions for the secrecy outage probability (SOP) are derived to evaluate the secrecy performance achieved by the proposed schemes. Also, the asymptotic SOPs are provided to obtain further insights. The analysis and simulation results indicate that the schemes converge to SOP floors with the increasing SNR, while the floors achieved by the RJS-UNT and OJS-UNT schemes are significantly lower than that achieved by the NJS-UNT scheme, showing the security advantage of the proposed schemes.

中文翻译：

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基于干扰选择的上行NOMA系统安全增强

我们研究了由一个基站、多个用户和一个窃听者组成的上行链路 NOMA 系统的物理层安全性。在每次上行传输过程中，两个用户配对执行 NOMA，并从剩余的空闲用户中机会性地选择另一个用户作为友好干扰器，发出人造噪声以迷惑窃听者。为了提高系统的传输安全性，我们提出了两种友好的干扰选择辅助上行 NOMA 传输方案，即不知道窃听者信道状态信息（CSI）的随机干扰选择辅助上行 NOMA 传输（RJS-UNT）方案和最优干扰选择辅助上行 NOMA 传输 (OJS-UNT) 方案，其中窃听者的 CSI 可用。为了比较，还考虑了无干扰选择辅助上行链路 NOMA 传输 (NJS-UNT) 方案。导出了保密中断概率 (SOP) 的解析闭式表达式，以评估所提出的方案所实现的保密性能。此外，提供渐近 SOP 以获得进一步的见解。分析和仿真结果表明，随着 SNR 的增加，方案收敛到 SOP 层，而 RJS-UNT 和 OJS-UNT 方案实现的层显着低于 NJS-UNT 方案实现的层，显示了安全优势拟议的计划。