Ultra-Wideband Air-to-Ground Channel Measurements and Modeling in Hilly Environment

Unmanned aerial vehicles (UAVs) have aroused great attention for future wireless communications since the drone can be used as an aerial base station and also as a cellular user to perform on-demand tasks. Because the reliable and robust connection between UAV and ground station (GS) plays an essential role in the UAV-based air-to-ground (AG) communications, the accurate radio channel model is needed. In this paper, we conducted AG wideband radio channel measurements in a hilly environment at 6.5 GHz with a bandwidth of 500 MHz, which is one of the high bands for ultra-wideband (UWB) communications in IEEE standards. The large-scale characteristics, including path loss and shadow fading, are represented by the close-in (CI) model. The small-scale characteristics that illustrate the fading and the multipath effect are analyzed with three critical parameters, including the small-scale fading, Rician K-factor and root-mean-square (RMS) delay spread. Afterward, the tapped delay line (TDL) model is built according to the detected multipath in the power delay profile (PDP), and the channel impulse response (CIR) is discussed for wideband channel modeling. The results can be used for the design and analysis of the AG systems.