Millimeter-Wave UAV Channel Model with Height-Dependent Path Loss and Shadowing in Urban Scenarios

TL;DR

The paper addresses height-dependent A2G mmWave propagation for UAV-based ABSs in urban areas, proposing a unified height-dependent LSF model and evaluating geometry effects beyond built-up statistics. It leverages large-scale MATLAB ray tracing at 26 GHz across four urban layouts with identical built-up parameters, extracting elevation-based LoS probabilities via a sigmoid and fitting height-dependent PLE and shadow fading. The study introduces three random urban layouts (SRU, FUU, HEU) to isolate geometric effects and validates the model against ray-tracing data using KL divergence, finding good statistical agreement. The results show LoS PLE near 2, NLoS PLE decreasing with height to about 2.5–3, and decreasing shadow fading at higher altitudes, with geometry contributing a small +/-0.2 PLE shift, providing a practical planning tool for ABS deployments in complex urban areas.

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 (A2G) 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 LoS probability (PLoS) and Large-Scale Fading (LSF). Using MATLAB ray tracing 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 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-Line-of-Sight (NLoS) decreases toward 2.5-3 at high altitudes, Line-of-Sight (LoS) PLE remains near 2, and shadow fading reduces with height. We also find that geometric layout introduces a modest but consistent change in PLE (+/- 0.2), even when built-up parameters are fixed. The proposed unified model aligns well with ray-tracing statistics and offers a practical, height-dependent LSF model suitable for ABS planning in complex urban scenarios.

Figures (6)

• Figure 1: Manhattan and proposed urban layouts for high-rise urban environment ($\alpha = 0.5, \beta = 300, \gamma = 50$).
• Figure 2: Combined Layouts PLE across ABS altitude and environment.
• Figure 3: NLOS PLE as a function of ABS deployment altitude for the four urban environments, the combined data, and the fitted height-dependent model for the combined data.
• Figure 4: Empirical $P_{\text{LoS}}$ as a function of elevation angle for four standard environments, comparing individual layouts, combined RT data, and the unified combined model.
• Figure 5: Comparison of modeled channel against RT data in the combined layouts case.