Effects of Vertical Fluctuations on Air-to-Ground mmWave UAV Communications

Unmanned aerial vehicle (UAV)-based millimeter wave (mmWave) communications have unique mobility and data rate advantages. However, the position of the UAV may fluctuate randomly in the horizontal and vertical directions due to wind, system stability error, or attitude control system fault, which may affect the mmWave channel blockage characteristic and system quality of service (QoS) performance. In this letter, we study the impact of UAV fluctuations in the vertical direction on the blockage and QoS of air-to-ground mmWave UAV communications for the first time. By deriving the closed-form expressions of blockage probability, we find that although the blockage probability is proportional to the variance of the vertical fluctuation, the vertical fluctuation has little effect on the blockage probability due to the small weight of the variance. In contrast, vertical fluctuations significantly impact the reliable service probability. The stronger the vertical fluctuation is, the smaller the reliable service probability and the worse the QoS. Finally, Monte Carlo simulations verify the above conclusions.