Unmanned aerial vehicles (UAVs) have recently received a significant interest to assist terrestrial wireless networks thanks to their strong line-of-sight links and flexible/instant deployment. However, UAVs’ assistance is limited by their battery lifetime and wireless backhaul link capacity. At the expense of limited mobility, tethered UAVs (T-UAVs) can be a viable alternative to provide seamless service over a cable that simultaneously supplies power and data from a ground station (GS). Accordingly, this paper presents a comparative performance analysis of T-UAV and regular/untethered UAV (U-UAV)-assisted cellular traffic offloading from a geographical area that undergoes heavy traffic conditions. By using stochastic geometry tools, we first derive joint distance distributions between the hot-spot users, the terrestrial base station (TBS), and the UAV. To maximize the end-to-end signal-to-noise ratio, a user association policy is developed, and corresponding association regions are analytically identified. Then, the overall coverage probability of the U-UAV/T-UAV-assisted system is derived for given locations of the TBS and the U-UAV/T-UAV. Moreover, we analytically prove that optimal UAV location falls within a partial surface of the spherical cone centered at the GS. Numerical results show that T-UAV outperforms U-UAV given that sufficient GS locations accessibility and tether length are provided.

中文翻译：

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优化束缚无人机的部署，最大程度地覆盖用户群中的蜂窝

由于其强大的视线链路和灵活/即时的部署，无人飞行器（UAV）最近引起了极大的兴趣来协助地面无线网络。但是，无人机的协助受到电池寿命和无线回传链路容量的限制。以有限的移动性为代价，系留式无人飞行器（T-UAV）可以作为可行的替代方案，通过电缆同时提供来自地面站（GS）的电源和数据来提供无缝服务。因此，本文提出了对T-UAV和常规/不受限制的UAV（U-UAV）辅助的蜂窝通信业务从交通繁忙的地理区域进行卸载的比较性能分析。通过使用随机几何工具，我们首先得出热点用户与地面基站（TBS）之间的联合距离分布，和无人机。为了最大化端到端的信噪比，开发了用户关联策略，并分析地标识了相应的关联区域。然后，针对TBS和U-UAV / T-UAV的给定位置，得出U-UAV / T-UAV辅助系统的总体覆盖率。此外，我们通过分析证明，最佳无人机位置位于以GS为中心的球形圆锥的局部表面内。数值结果表明，在提供足够的GS位置可及性和系链长度的情况下，T-UAV优于U-UAV。对于TBS和U-UAV / T-UAV的给定位置，得出U-UAV / T-UAV辅助系统的总覆盖概率。此外，我们通过分析证明，最佳无人机位置位于以GS为中心的球形圆锥的局部表面内。数值结果表明，在提供足够的GS位置可及性和系链长度的情况下，T-UAV优于U-UAV。对于TBS和U-UAV / T-UAV的给定位置，得出U-UAV / T-UAV辅助系统的总覆盖概率。此外，我们通过分析证明，最佳无人机位置位于以GS为中心的球形圆锥的局部表面内。数值结果表明，在提供足够的GS位置可及性和系链长度的情况下，T-UAV优于U-UAV。