A general empirical path loss (PL) model for air-to-ground (A2G) millimeter-wave (mmWave) channels is proposed in this paper. Different from existing PL models, the new model takes the height factor of unmanned aerial vehicles (UAVs) into account, and divides the propagation conditions into three cases (i.e., line-of-sight, reflection, and diffraction). A map-based deterministic PL prediction algorithm based on the ray-tracing (RT) technique is developed, and is used to generate numerous PL data for different cases. By fitting and analyzing the PL data under different scenarios and UAV heights, altitude-dependent model parameters are provided. Simulation results show that the proposed model can be effectively used to predict PL values for both low- and high-altitude cases. The prediction results of the proposed model better match the RT-based calculation results than those of the Third Generation Partnership Project (3GPP) model and the close-in model. The standard deviation of the PL is also much smaller. Moreover, the new model is flexible and can be extended to other A2G scenarios (not included in this paper) by adjusting the parameters according to the simulation or measurement data.

本文提出了空对地 (A2G) 毫米波 (mmWave) 信道的通用经验路径损耗 (PL) 模型。与现有PL模型不同，新模型考虑了无人机（UAV）的高度因素，将传播条件分为三种情况（即视线、反射和绕射）。开发了一种基于光线追踪 (RT) 技术的基于地图的确定性 PL 预测算法，用于为不同情况生成大量 PL 数据。通过对不同场景和无人机高度下的PL数据进行拟合和分析，提供与高度相关的模型参数。仿真结果表明，所提出的模型可以有效地用于预测低海拔和高海拔情况下的 PL 值。与第三代合作伙伴计划（3GPP）模型和近距离模型相比，所提出模型的预测结果更符合基于RT的计算结果。PL 的标准偏差也小得多。此外，新模型具有灵活性，可以通过根据仿真或测量数据调整参数，扩展到其他 A2G 场景（本文未包含）。