Unmanned aerial vehicle (UAV)-based communications is a promising new technology that can add a wide range of new capabilities to the current network infrastructure. Given the flexibility, cost-efficiency, and convenient use of UAVs, they can be deployed as temporary base stations (BSs) for on-demand situations like BS overloading or natural disasters. In this work, a UAV-based communication system with radio frequency (RF) access links to the mobile users (MUs) and a free-space optical (FSO) backhaul link to the ground station (GS) is considered. In particular, the RF and FSO channels in this network depend on the UAV's positioning and (in)stability. The relative position of the UAV with respect to the MUs impacts the likelihood of a line-of-sight (LOS) connection in the RF link and the instability of the hovering UAV affects the quality of the FSO channel. Thus, taking these effects into account, we analyze the end-to-end system performance of networks employing UAVs as buffer-aided (BA) and non-buffer-aided (non-BA) relays in terms of the ergodic sum rate. Simulation results validate the accuracy of the proposed analytical derivations and reveal the benefits of buffering for compensation of the random fluctuations caused by the UAV's instability. Our simulations also show that the ergodic sum rate of both BA and non-BA UAV-based relays can be enhanced considerably by optimizing the positioning of the UAV. We further study the impact of the MU density and the weather conditions on the end-to-end system performance.

中文翻译：

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具有混合RF-FSO通道的基于无人机的中继网络的遍历总速率分析

基于无人机（UAV）的通信是一种有前途的新技术，可以为当前的网络基础架构增加各种新功能。鉴于无人机的灵活性，成本效益和方便使用，它们可以作为临时基站（BS）部署，以应对BS超载或自然灾害等按需情况。在这项工作中，考虑了基于UAV的通信系统，该系统具有到移动用户（MU）的射频（RF）接入链路和到地面站（GS）的自由空间光（FSO）回程链路。特别是，该网络中的RF和FSO通道取决于UAV的位置和（不稳定）状态。无人机相对于MU的相对位置影响RF链路中视线（LOS）连接的可能性，并且悬停的无人机的不稳定性影响FSO通道的质量。因此，考虑到这些影响，我们从遍历总速率的角度分析了使用无人机作为缓冲辅助（BA）和非缓冲辅助（non-BA）中继的网络的端到端系统性能。仿真结果验证了所提出的分析推导的准确性，并揭示了缓冲的好处，可补偿无人机的不稳定性引起的随机波动。我们的仿真还表明，通过优化无人机的定位，可以大大提高BA和非BA基于UAV的继电器的遍历总和率。