Unmanned aerial vehicles (UAVs) have the potential for time-sensitive applications. Due to wireless channel variation, received data may have an expiration time, particularly in critical situations such as rescue operations, natural disasters, or the military. Age of Information (AoI) is a metric that measures the freshness of received packets to specify the validity period of information. In addition, it is necessary to guarantee the privacy of confidential information transmission through air-to-ground links against eavesdroppers. This paper investigates UAV-assisted covert communication to minimize AoI in the presence of an aerial eavesdropper for the first time. However, to ensure the eavesdropper's error detection rate, UAV-enabled beamforming employs the power-domain non-orthogonal multiple access (PD-NOMA) technique to cover the covert user by a public user. PD-NOMA technique significantly improves the user's AoI, too. The joint optimization problem contains non-convex constraints and coupled optimization variables, including UAV trajectory, beamforming design, and the user's AoI which is challenging to derive a direct solution. We have developed an efficient alternating optimization technique to address the formulated optimization problem. Numerical results demonstrate the impact of the main parameters on the performance of the proposed communication system.

翻译：无人机在时间敏感型应用中展现出巨大潜力。由于无线信道的时变性，接收数据可能存在时效性，这在救援行动、自然灾害或军事行动等关键场景中尤为突出。信息年龄是衡量接收数据包新鲜度的指标，用于界定信息的有效期限。此外，必须确保通过空对地链路传输的机密信息能够抵御窃听者的攻击，保障通信隐私。本文首次研究了存在空中窃听者场景下，以最小化信息年龄为目标的无人机辅助隐蔽通信系统。为确保窃听者的误检率，无人机采用功率域非正交多址接入技术，通过公共用户的信号覆盖隐蔽用户。该技术同时显著改善了用户的信息年龄性能。该联合优化问题包含非凸约束与耦合的优化变量，涉及无人机轨迹、波束成形设计以及用户信息年龄，难以直接求解。我们开发了一种高效的交替优化算法来处理所构建的优化问题。数值仿真结果验证了关键参数对所提通信系统性能的影响。