In this paper, we propose a novel wireless architecture, mounted on a high-altitude aerial platform, which is enabled by reconfigurable intelligent surface (RIS). By installing RIS on the aerial platform, rich line-of-sight and full-area coverage can be achieved, thereby, overcoming the limitations of the conventional terrestrial RIS. We consider a scenario where a sudden increase in traffic in an urban area triggers authorities to rapidly deploy unmanned-aerial vehicle base stations (UAV-BSs) to serve the ground users. In this scenario, since the direct backhaul link from the ground source can be blocked due to several obstacles from the urban area, we propose reflecting the backhaul signal using aerial-RIS so that it successfully reaches the UAV-BSs. We jointly optimize the placement and array-partition strategies of aerial-RIS and the phases of RIS elements, which leads to an increase in energy-efficiency of every UAV-BS. We show that the complexity of our algorithm can be bounded by the quadratic order, thus implying high computational efficiency. We verify the performance of the proposed algorithm via extensive numerical evaluations and show that our method achieves an outstanding performance in terms of energy-efficiency compared to benchmark schemes.

中文翻译：

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具有可重构智能表面的节能空中回程系统


在本文中，我们提出了一种新型无线架构，安装在高空空中平台上，由可重构智能表面（RIS）实现。通过在空中平台安装RIS，可以实现丰富的视距和全区域覆盖，从而克服传统地面RIS的局限性。我们考虑这样一种场景：城市地区的交通量突然增加，促使当局快速部署无人机基站（UAV-BS）来为地面用户提供服务。在这种情况下，由于来自地面源的直接回程链路可能由于来自市区的多个障碍物而被阻挡，因此我们建议使用空中RIS反射回程信号，以便其成功到达无人机基站。我们共同优化航空 RIS 的布局和阵列分区策略以及 RIS 元件的相位，从而提高每个 UAV-BS 的能源效率。我们证明了我们的算法的复杂性可以被二次阶限制，因此意味着高计算效率。我们通过广泛的数值评估验证了所提出算法的性能，并表明与基准方案相比，我们的方法在能源效率方面实现了出色的性能。