In reconfigurable intelligent surfaces (RISs) aided communications, the existing passive beamforming (PB) design involves polynomial complexity in the number of reflecting elements, and thus is difficult to implement due to a massive number of reflecting elements. To overcome this difficulty, we propose a reflection-angle-based cascaded channel model by adopting the generalized Snell’s law, in which the dimension of the variable space involved in optimization is significantly reduced, resulting in a simplified hierarchical passive beamforming (HPB) design. We develop an efficient two-stage HPB algorithm, which exploits the angular domain property of the channel, to maximize the achievable rate of the target user. Simulation results demonstrate the appealing performance and low complexity of the proposed HPB design.

中文翻译：

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用于可重构智能表面辅助通信的分层无源波束形成


在可重构智能表面（RIS）辅助通信中，现有的无源波束形成（PB）设计涉及反射元件数量的多项式复杂性，因此由于反射元件数量庞大而难以实现。为了克服这个困难，我们采用广义斯涅尔定律提出了一种基于反射角的级联信道模型，其中优化涉及的变量空间的维数显着减小，从而简化了分层无源波束形成（HPB）设计。我们开发了一种高效的两阶段 HPB 算法，该算法利用信道的角域特性来最大化目标用户的可实现速率。仿真结果证明了所提出的 HPB 设计具有吸引人的性能和低复杂性。