This study considers a downlink power consumption problem for unmanned aerial vehicles (UAVs)-assisted wireless communications, in which UAVs are used as aerial base stations to provide service for the ground users and equipped with a directional antenna of fixed beamwidth. Moreover, the on-board circuit power of UAV is taking into consideration. The authors derive a closed-form expression for the optimal flying altitude and number of UAVs by minimising the total power consumption under the users' rate requirements in the given coverage area. The numerical simulation and theoretical results show that the optimal flying altitude of UAVs depends on the beamwidth of the directional antenna at UAVs, the on-board circuit power of UAVs, and the rate constraint of each user.

中文翻译：

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启用无人机的无线通信的高度和数量优化

这项研究考虑了无人飞行器（UAV）辅助无线通信的下行链路功耗问题，其中无人飞行器用作空中基站，为地面用户提供服务，并配备了固定波束宽度的定向天线。而且，正在考虑无人机的车载电路功率。作者通过在给定覆盖区域内根据用户速率要求将总功耗降至最低来得出最佳飞行高度和无人机数量的闭式表达式。数值仿真和理论结果表明，无人机的最佳飞行高度取决于无人机定向天线的波束宽度，无人机的电路功率以及每个用户的速率约束。