Air-to-ground (AG) communications have attracted much attention for future advanced wireless communications. Unmanned aerial vehicle, as a critical enabler in AG communications, can be operated in various environments, such as over-water, hilly, and built-up environments. A better understanding of radio channels in various scenarios can immensely facilitate the deployment and design of wireless systems. Thus, in this letter, wideband characterizations of AG channels are performed based on the multienvironment channel measurements, where the center frequency is set to 6.5 GHz with the bandwidth of 500 MHz, which provides high delay resolution to capture significant multipath. Two key channel parameters, Rician K-factor and root-mean-square (rms) delay spread, are used as metrics to characterize AG channels. The positive Rician K-factor indicates the line-of-sight (LOS)-dominated characteristic of the AG channel. The discrepancy of the rms delay spread shows the obvious influence of multipaths from building on channel delay characteristics.

中文翻译：

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适用于多种传播环境的宽带空对地信道表征

空对地 (AG) 通信在未来的高级无线通信中备受关注。无人机作为 AG 通信的关键推动因素，可以在各种环境中运行，例如水上、丘陵和建筑环境。更好地了解各种场景中的无线电信道可以极大地促进无线系统的部署和设计。因此，在这封信中，AG 信道的宽带特征是基于多环境信道测量来执行的，其中中心频率设置为 6.5 GHz，带宽为 500 MHz，这提供了高延迟分辨率以捕获重要的多径。两个关键的信道参数，赖斯 K 因子和均方根 (rms) 延迟扩展，被用作表征 AG 信道的指标。正的 Rician K 因子表示 AG 信道的视线 (LOS) 主导特性。均方根延迟扩展的差异显示了多径对信道延迟特性的明显影响。