Millimeter-wave UAV channel model with height-dependent path loss and shadowing in urban scenarios

Abstract Uncrewed aerial vehicles (UAVs) serving as aerial base stations (ABSs) are expected to extend 6G millimeter-Wave (mmWave) coverage and improve link reliability in urban areas. However, UAV-based air-to-ground channels are highly dependent on height and urban geometry. This paper proposes an ABS height-dependent mmWave channel model and investigates whether urban geometry, beyond the standard built-up parameters, significantly affects line-of-sight (LoS) probability ( PLoS $P_{\\text{LoS}}$ P LoS ) and large-scale fading (LSF). Using MATLAB ray tracing (RT) at 26 GHz, we simulate approximately 10K city realizations for four urban layouts that share identical built-up parameters but differ in their spatial organization. We extract elevation-based PLoS $P_{\\text{LoS}}$ P LoS using a sigmoid model and derive height-dependent path-loss exponents (PLEs) and shadow-fading trends using exponential fits. Results show that PLE for non-LoS decreases toward 2.5 $2.5$ 2.5 – 3 $3$ 3 at high altitudes, LoS PLE remains near 2 $2$ 2 , and shadow fading reduces with height. We also find that geometric layout introduces a modest but consistent change in PLE ( almost equals plus or minus 0.2 $\\approx \\pm 0.2$ ≈ ± 0.2 ), even when built-up parameters are fixed. The proposed model matches RT results and provides a practical, height-dependent LSF model for ABS planning in urban scenarios.