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arXiv · 2507.20113

Rotatable RIS Assisted Physical Layer Multicasting

Ji Wang·Jiayu Tian·Lijuan Qin·Kunrui Cao·Hongbo Xu·Xingwang Li·Tony. Q. S. Quek
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Abstract

Reconfigurable Intelligent Surfaces (RIS) dynamically control signal propagation to enhance wireless communications. This paper presents a novel framework for rotatable RIS assisted physical-layer multicast systems, aiming to maximize the sum of minimum multicast rates via joint optimization of base station beamforming, RIS phase shifts, and orientation. Unlike unicast or non-rotatable setups, the rotatable RIS adapts orientation to align signals with user groups, improving fairness and rates for weak users. An alternating optimization approach combines convex optimization for beamforming/phase shifts with exhaustive search and particle swarm optimization (PSO) for orientation. Majorization-Minimization-based algorithms solve subproblems iteratively. Simulation results show the framework achieves 24.1% rate improvement via exhaustive search and 20.0% via PSO over the non-rotatable RIS baseline, with PSO performance close to the exhaustive search upper bound, highlighting the benefits of physical-layer multicast and orientation optimization.

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Ji Wang, Jiayu Tian, Lijuan Qin, Kunrui Cao, Hongbo Xu, Xingwang Li, Tony. Q. S. Quek. 2025-07-27. Rotatable RIS Assisted Physical Layer Multicasting. https://arxiv.org/abs/2507.20113

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