Low Altitude Air-to-Ground Channel Modelling Based on Measurements in a Suburban Environment

In this paper, a recently conducted measurement campaign for researching Unmanned-Aerial-Vehicle (UAV) air-to-ground propagation channels is introduced. Horizontal flights at multiple UAV flying heights above the ground were considered. The channels were sounded at carrier frequency 850 MHz with the bandwidth of 25MHz. Time-evaluating Channel impulse responses (CIRs) were extracted for complete flight route from the received signals. The high-resolution estimation algorithm space-alternating generalized expectation-maximization (SAGE) was applied to estimate the delays and Doppler frequencies of multi-path-components (MPCs). Based on the SAGE estimation results, channel characteristics including the path-loss, shadow fading and delay spread are thoroughly analyzed for different flying heights. Different from conventional models, the path-loss models and delay spread models established here are all functions of horizontal and vertical distances between the ground station and the UAV jointly. These results bring more insights of the air-to-ground channel characteristic, which are helpful for designing UAV communication techniques and performance evaluation.