Non-orthogonal multiple access (NOMA) and massive multiple-input multiple-output (MIMO) systems are highly efficient. Massive MIMO systems are inherently resistant to passive attackers (eavesdroppers), thanks to transmissions directed to the desired users. However, active attackers can transmit a combination of legitimate user pilot signals during the channel estimation phase. This way they can mislead the base station (BS) to rotate the transmission in their direction, and allow them to eavesdrop during the downlink data transmission phase. In this paper, we analyse this vulnerability in an improved system model and stronger adversary assumptions, and investigate how physical layer security can mitigate such attacks and ensure secure (confidential) communication. We derive the secrecy outage probability (SOP) and a lower bound on the ergodic secrecy capacity, using stochastic geometry tools when the number of antennas in the BSs tends to infinity. We adapt the result to evaluate the secrecy performance in massive orthogonal multiple access (OMA). We find that appropriate power allocation allows NOMA to outperform OMA in terms of ergodic secrecy rate and SOP.

中文翻译：

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主动窃听者存在下的大规模MIMO-NOMA系统保密

非正交多址（NOMA）和大规模多输入多输出（MIMO）系统非常高效。由于定向到所需用户的传输，因此大规模MIMO系统具有固有的抵抗被动攻击者（窃听者）的能力。但是，主动攻击者可以在信道估计阶段发送合法用户导频信号的组合。这样，它们可能会误导基站（BS）在其方向上旋转传输，并允许它们在下行链路数据传输阶段进行窃听。在本文中，我们以改进的系统模型和更强的对手假设分析此漏洞，并研究物理层安全性如何减轻此类攻击并确保安全（机密）通信。当基站中的天线数量趋于无穷大时，我们使用随机几何工具得出了保密中断概率（SOP）和遍历保密容量的下限。我们调整结果以评估大规模正交多路访问（OMA）中的保密性能。我们发现，在遍历保密率和SOP方面，适当的功率分配可使NOMA胜过OMA。