Millimeter wave (mmWave)-based unmanned aerial vehicle (UAV) communication is a promising candidate for future communications due to its flexibility and sufficient bandwidth. However, random fluctuations in the position of hovering UAVs will lead to random variations in the blockage and signal-to-noise ratio (SNR) of the UAV-user link, thus affecting the quality of service (QoS) of the system. To assess the impact of UAV position fluctuations on the QoS of air-to-ground mmWave UAV communications, this paper develops a tractable analytical model that jointly captures the features of three-dimensional (3D) position fluctuations of hovering UAVs and blockages of mmWave (including static, dynamic, and self-blockages). With this model, we derive the closed-form expressions for reliable service probability respective to blockage probability of UAV-user links,and coverage probability respective to SNR, respectively. The results indicate that the greater the position fluctuations of UAVs, the lower the reliable service probability and coverage probability. The degradation of these two evaluation metrics confirms that the performance of air-to-ground mmWave UAV systems largely depends on the UAV position fluctuations, and the stronger the fluctuation, the worse the QoS. Finally, Monte Carlo simulations demonstrate the above results and show UAVs' optimal location to maximize the reliable service and coverage probability, respectively.

翻译：基于毫米波（mmWave）的无人机（UAV）通信因其灵活性和充足的带宽而成为未来通信的有力候选方案。然而，悬停无人机位置的随机波动会导致无人机-用户链路中阻塞和信噪比（SNR）的随机变化，从而影响系统的服务质量（QoS）。为评估无人机位置波动对空对地毫米波无人机通信QoS的影响，本文建立了一个易处理的解析模型，该模型同时捕捉了悬停无人机三维（3D）位置波动和毫米波阻塞（包括静态、动态和自阻塞）的特征。利用该模型，我们分别推导了可靠服务概率（与无人机-用户链路的阻塞概率相关）和覆盖概率（与信噪比相关）的闭式表达式。结果表明，无人机位置波动越大，可靠服务概率和覆盖概率越低。这两个评估指标的退化证实了空对地毫米波无人机系统的性能在很大程度上取决于无人机的位置波动，波动越强，QoS越差。最后，蒙特卡洛模拟验证了上述结果，并分别展示了最大化可靠服务和覆盖概率的无人机最优位置。