An information-theoretic confidential communication is achievable if the eavesdropper has a degraded channel compared to the legitimate receiver. In wireless channels, beamforming and artificial noise can enable such confidentiality. However, only distribution knowledge of the eavesdropper channels can be assumed. Moreover, the transmission of artificial noise can lead to an increased electromagnetic field (EMF) exposure, which depends on the considered location and can thus also be seen as a random variable. Hence, we optimize the $\varepsilon$-outage secrecy rate under a $\delta$-outage exposure constraint in a setup, where the base station (BS) is communicating to a user equipment (UE), while a single-antenna eavesdropper with Rayleigh distributed channels is present. Therefore, we calculate the secrecy outage probability (SOP) in closed-form. Based on this, we convexify the optimization problem and optimize the $\varepsilon$-outage secrecy rate iteratively. Numerical results show that for a moderate exposure constraint, artificial noise from the BS has a relatively large impact due to beamforming, while for a strict exposure constraint artificial noise from the UE is more important.

翻译：从信息论角度出发，当窃听者信道劣于合法接收者信道时，可实现信息论意义上的保密通信。在无线信道中，波束成形与人工噪声技术可达成此类保密需求。然而实际中通常仅能获知窃听信道的分布特性，且人工噪声的发射会增强电磁场暴露水平——该暴露水平具有位置依赖性，同样可视作随机变量。为此，本文在基站与用户设备通信、存在瑞利分布单天线窃听者的场景中，以δ-暴露约束下的ε-中断保密速率优化为目标：首先推导出保密中断概率的闭式表达式，据此将优化问题凸化处理，并迭代求解最优ε-中断保密速率。数值结果表明：在中等暴露约束下，基站发射的人工噪声因波束成形增益影响显著；而在严格暴露约束下，用户终端发射的人工噪声则更为关键。