Unmanned Aerial Vehicles (UAVs) are a disruptive technology that is transforming a range of industries. Because they operate in the sky, UAVs are able to take advantage of strong Line-of-Sight (LoS) channels for radio propagation, allowing them to communicate over much larger distances than equivalent hardware located at ground level. This has attracted the attention of organisations such as the Irish Defence Forces (DF), with whom we are developing a UAV-based radio relay system as part of the MISTRAL project. This relay system will support digital Very High Frequency (VHF) band communication between ground personnel, while they are deployed on missions. In this paper we report on the initial set of experimental measurements which were carried out to verify the feasibility of VHF signal relaying via UAV. In our experiments, a UAV carrying a lightweight Software-Defined Radio (SDR) receiver is positioned at a height of 500 meters above ground, while two 5W transmitters travel in vehicles on the ground. The SDR receiver measures the received signal power, while the Global Positioning System (GPS) coordinates of the vehicles are logged. This is combined to measure the signal pathloss over distance. Our results show that the signal is received successfully at distances of over 50 kilometers away. While the signals still appear to suffer from a degree of obstacle blockage and multipath effects, these communication ranges are a substantial improvement over the ground communication baseline, and validate the use of UAVs to support wide area emergency communication.

翻译：无人机（UAV）是一种颠覆性技术，正在改变多个行业。由于在天空运行，无人机能够利用强视距（LoS）无线电传播信道，从而与地面等硬件设备相比实现更远距离的通信。这吸引了包括爱尔兰国防军（DF）在内的组织关注——我们正与其合作开发基于无人机的无线电中继系统，作为MISTRAL项目的一部分。该中继系统将支持部署任务中的地面人员之间进行数字甚高频（VHF）频段通信。本文报告了为验证无人机中继VHF信号可行性而开展的首批实验测量结果。实验中，一架搭载轻量级软件定义无线电（SDR）接收器的无人机被置于距地面500米高度，同时两台5W发射器随车辆在地面移动。SDR接收器测量接收信号功率，并记录车辆的全球定位系统（GPS）坐标。通过结合这些数据，测量了信号路径损耗随距离的变化。结果表明，在超过50公里的距离上仍能成功接收信号。尽管信号仍存在一定程度的障碍物遮挡和多径效应影响，但该通信距离相比地面通信基线已有显著提升，验证了利用无人机支持广域应急通信的可行性。