The millimeter-wave (mm-wave) bands enable very large antenna arrays that can generate narrow beams for beamforming and spatial multiplexing. However, directionality introduces beam misalignment and leads to reduced energy efficiency. Thus, employing the narrowest possible beam in a cell may not necessarily imply maximum coverage. The objective of this work is to determine the optimal sector beamwidth for a cellular architecture served by an unmanned aerial vehicle (UAV) acting as a base station (BS). The users in a cell are assumed to be distributed according to a Poisson Point Process (PPP) with a given user density. We consider hybrid beamforming at the UAV, such that multiple concurrent beams serve all the sectors simultaneously. An optimization problem is formulated to maximize the sum rate over a given area while limiting the total power available to each sector. We observe that, for a given transmit power, the optimal sector beamwidth increases as the user density in a cell decreases, and varies based on the height of the UAV. Thus, we provide guidelines towards the optimal beamforming configurations for users in rural areas.

翻译：毫米波频段支持超大天线阵列，可生成窄波束以实现波束赋形和空分复用。然而，方向性会引发波束失准并降低能效。因此，在小区中使用最窄波束不一定能实现最大覆盖。本文旨在确定以无人机作为基站的蜂窝架构中的最优扇区波束宽度。假设小区内用户服从给定密度的泊松点过程分布，我们考虑无人机采用混合波束赋形方案，使多路并行波束同时覆盖所有扇区。通过构建优化问题，在限制各扇区总功率的前提下最大化指定区域的总速率。研究发现，在给定发射功率条件下，最优扇区波束宽度随小区用户密度降低而增大，且与无人机飞行高度相关。由此，我们为农村地区用户的波束赋形配置优化提供了指导准则。