In this paper, we propose a cell-free scheme for unmanned aerial vehicle (UAV) base stations (BSs) to manage the severe intercell interference between terrestrial users and UAV-BSs of neighboring cells. Since the cell-free scheme requires enormous bandwidth for backhauling, we propose to use the sub-terahertz (sub-THz) band for the backhaul links between UAV-BSs and central processing unit (CPU). Also, because the sub-THz band requires a reliable line-of-sight link, we propose to use a high altitude platform station (HAPS) as a CPU. At the first time-slot of the proposed scheme, users send their messages to UAVs at the sub-6 GHz band. The UAVs then apply match-filtering and power allocation. At the second time-slot, at each UAV, orthogonal resource blocks are allocated for each user at the sub-THz band, and the signals are sent to the HAPS after analog beamforming. In the HAPS receiver, after analog beamforming, the message of each user is decoded. We formulate an optimization problem that maximizes the minimum signal-to-interference-plus-noise ratio of users by finding the optimum allocated power as well as the optimum locations of UAVs. Simulation results demonstrate the superiority of the proposed scheme compared with aerial cellular and terrestrial cell-free baseline schemes.

翻译：本文提出了一种面向无人机基站的无蜂窝方案，以管理地面用户与相邻小区无人机基站间的严重小区间干扰。由于无蜂窝方案需要巨大带宽用于回传，我们提出利用亚太赫兹频段实现无人机基站与中央处理单元之间的回传链路。此外，考虑到亚太赫兹频段需要可靠的视距链路，我们提出采用高空平台站作为中央处理单元。在所提方案的第一时隙，用户通过sub-6 GHz频段向无人机发送消息，无人机随后执行匹配滤波和功率分配。在第二时隙，各无人机为每个用户在亚太赫兹频段分配正交资源块，经模拟波束赋形后发送至高空平台站。高空平台站接收端在完成模拟波束赋形后，对每个用户的消息进行解码。我们构建了一个优化问题，通过求解最优功率分配与无人机最优部署位置，最大化用户的最小信干噪比。仿真结果表明，所提方案相较于空中蜂窝方案与地面无蜂窝基线方案具有显著优势。