This paper proposes a new three dimensional (3D) networking architecture enabled by aerial intelligent reflecting surface (AIRS) to achieve panoramic signal reflection from the sky. Compared to the conventional terrestrial IRS, AIRS not only enjoys higher deployment flexibility, but also is able to achieve 360$^\circ$ panoramic full-angle reflection and requires fewer reflections in general due to its higher likelihood of having line of sight (LoS) links with the ground nodes. We focus on the problem to maximize the worst-case signal-to-noise ratio (SNR) in a given coverage area by jointly optimizing the transmit beamforming, AIRS placement and phase shifts. The formulated problem is non-convex and the optimization variables are coupled with each other in an intricate manner. To tackle this problem, we first consider the special case of single-location SNR maximization to gain useful insights, for which the optimal solution is obtained in closed-form. Then for the general case of area coverage, an efficient suboptimal solution is proposed by exploiting the similarity between phase shifts optimization for IRS and analog beamforming for the conventional phase array. Numerical results show that the proposed design can achieve significant performance gain than heuristic AIRS deployment schemes.

中文翻译：

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通过空中智能反射面实现全景全角度反射

本文提出了一种新的三维（3D）网络架构，通过空中智能反射面（AIRS）实现从天空反射全景信号。与传统的地面IRS相比，AIRS不仅具有更高的部署灵活性，而且能够实现360$^\circ$全景全角反射，并且由于其具有更高的视线（LoS）可能性，一般需要更少的反射) 与地面节点的链接。我们专注于通过联合优化发射波束成形、AIRS 位置和相移来最大化给定覆盖区域内的最坏情况信噪比 (SNR) 的问题。公式化的问题是非凸的，优化变量以复杂的方式相互耦合。为了解决这个问题，我们首先考虑单位置 SNR 最大化的特殊情况以获得有用的见解，对于这种情况以封闭形式获得最佳解决方案。然后对于区域覆盖的一般情况，通过利用IRS相移优化与传统相控阵模拟波束形成之间的相似性，提出了一种有效的次优解决方案。数值结果表明，与启发式 AIRS 部署方案相比，所提出的设计可以实现显着的性能提升。