Aerial Intelligent Reflecting Surface: Joint Placement and Passive Beamforming Design With 3D Beam Flattening

Intelligent reflecting surface (IRS) is a promising technology to reconfigure wireless channels, which brings new degree of freedom for the design future networks. This article proposes three-dimensional (3D) system architecture enabled by aerial IRS (AIRS). Compared conventional terrestrial IRS, AIRS enjoys more deployment flexibility as well wider-view signal reflection, thanks its high altitude and thus likelihood establishing line-of-sight (LoS) links with ground source/destination nodes. We aim maximize worst-case signal-to-noise ratio (SNR) over all locations in target area jointly optimizing transmit beamforming source node, placement 3D passive AIRS. The formulated problem non-convex difficult solve. To gain useful insights, we first consider special case maximizing SNR at given location, optimal solution obtained closed-form. result shows that horizontal only depends on between source-destination distance altitude. Then general AIRS-enabled coverage, propose an efficient decoupling array gain, from optimization balancing resulting angular span cascaded channel path loss. Our proposed based novel beam broadening flattening technique, where divided into sub-arrays appropriate size, their phase shifts are designed form flattened pattern adjustable beamwidth catering size coverage area. Both uniform linear (ULA)-based planar (UPA)-based AIRSs considered our design, enable two-dimensional (2D) beamforming, respectively. Numerical results show designs achieve significant performance gains benchmark schemes.