In this letter, we study the passive beamforming design for optimizing the three-dimensional (3-D) coverage performance in an intelligent reflecting surface (IRS)-assisted communication system. In particular, we maximize the minimum (i.e., max-min) beamforming gain over all locations in the target area by jointly optimizing the passive reflection of all IRS elements. The resulting problem has a non-convex and semi-infinite beamforming gain constraint and a non-convex constant-modulus constraint. Both of them are reformulated to be finite and convex in the lifted matrix space with an additional rank-one constraint, and a difference-of-convex technique is developed to solve the reformulated problem efficiently. Finally, we demonstrate that the proposed passive beamforming solution outperforms the existing methods and can approach the upper bound on the max-min beamforming gain.

中文翻译：

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IRS 辅助通信中用于 3D 覆盖的无源波束成形


在这封信中，我们研究了无源波束成形设计，以优化智能反射面（IRS）辅助通信系统中的三维（3-D）覆盖性能。特别是，我们通过联合优化所有 IRS 元件的无源反射，最大化目标区域中所有位置的最小（即最大-最小）波束成形增益。由此产生的问题具有非凸半无限波束形成增益约束和非凸恒模约束。它们都被重新表述为在提升矩阵空间中是有限凸的，并具有附加的一阶约束，并且开发了凸差技术来有效地解决重新表述的问题。最后，我们证明所提出的无源波束形成解决方案优于现有方法，并且可以接近最大最小波束形成增益的上限。