Hierarchical Passive Beamforming for Reconfigurable Intelligent Surface Aided Communications

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