Measurements and Modeling of Air-Ground Integrated Channel in Forest Environment Based on OFDM Signals

2025-07-03

AI Summary

Forest environments—characterized by dense vegetation and complex topography—exhibit highly dynamic wireless channel characteristics, resulting in low air-to-ground (A2G) and ground-to-ground (G2G) communication reliability and a lack of measurement-driven channel models. Method: This work conducts comprehensive A2G/G2G channel measurements using 1.4 GHz OFDM signals, deploying UAVs along predefined trajectories and employing coordinated omnidirectional/directional antennas to acquire high-accuracy angle-of-arrival (AoA) and time-of-arrival (ToA) data. Contribution/Results: We identify canopy-dominated blockage as the primary propagation impairment and propose a forest-specific path loss model and multipath statistical model. We further demonstrate that elevation-angle optimization significantly enhances link quality. Our model achieves lower path loss prediction error than existing alternatives and provides empirically validated statistics for key parameters—including shadow fading, RMS delay spread, and Rician K-factor—establishing a reliable channel foundation for forest emergency communication system design.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Search and Optimization: Evaluation and Analysis
• Multiagent Systems: Agent Communication

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Security and Privacy: Large-scale security measurements
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

Forests are frequently impacted by climate conditions, vegetation density, and intricate terrain and geology, which contribute to natural disasters. Personnel engaged in or supporting rescue operations in such environments rely on robust communication systems to ensure their safety, highlighting the criticality of channel measurements in forest environments. However, according to current research, there is limited research on channel detection and modeling in forest areas in the existing literature. This paper describes the channel measurements campaign of air and ground in the Arxan National Forest Park of Inner Mongolia. It presents measurement results and propagation models for ground-to-ground (G2G) and air-to-ground (A2G) scenarios. The measurement campaign uses orthogonal frequency division multiplexing signals centered at 1.4 GHz for channel sounding. In the G2G measurement, in addition to using omnidirectional antennas to record data, we also use directional antennas to record the arrival angle information of the signal at the receiver. In the A2G measurement, we pre-plan the flight trajectory of the unmanned aerial vehicle so that it can fly at a fixed angle relative to the ground. We present path loss models suitable for G2G and A2G in forest environments based on the analysis of measurement results. The results indicate that the proposed model reduces error margins compared with other path loss models. Furthermore, we derive the multipath model expression specific to forest environments and conduct statistical analysis on key channel parameters e.g., shadow fading factor, root mean square delay spread, and Rician K factor. Our findings reveal that signal propagation obstruction due to tree crowns in A2G communication is more pronounced than tree trunk obstructions in G2G communication. Adjusting the elevation angle between air and ground can enhance communication quality.

Problem

• Measure air-ground channel in forests for rescue communications
• Develop path loss models for G2G and A2G scenarios
• Analyze multipath effects and signal obstruction in forests

Innovation

• OFDM signals for forest channel measurement
• Directional antennas capture angle information
• Pre-planned UAV flight enhances A2G accuracy