5G-Based Measurements and Characterizations of Low-Altitude Tethered Balloon Multipath Channel

In this paper, a recently conducted measurement campaign for characterizing the low-altitude air-to-ground (A2G) channel and air-to-water(A2W) channel in a typical 5G network is introduced. In the experiment, the scenarios of a helium tethered balloon with different heights covering ground and fresh water were considered. Channel impulse responses (CIRs) are extracted from the synchronization signal and PBCH block (SSB) in the recorded 5G downlink data. The multipath statistics at different altitudes are estimated and analyzed based on CIRs. It is observed that about 88.61% (99.39%) of the A2G(A2W) measured channel responses can be represented by the 3-ray multipath model. There is a higher probability for the appearance of multipath components, When the tethered balloon altitude decreases. Moreover, the first reflected propagation path is determined by the geometry defined by the balloon platform transmitter, the ground-based(water-based) receiver, and the ground surface (water surface). For A2G channel, the delay of this path is between 40 and 120ns; for A2W channel, the delay of this path is between 40 and 80ns. The second reflected path is a more diffuse, random reflection whose amplitude is significantly smaller than the amplitude of the first reflection and whose mean delay is 252.76ns (274.52ns) for A2G(A2W) channel. Finally, we derived the Ricean K-factor to compare the relationship between LOS component and multipath component.