Broad Beam Design for RIS-Assisted Massive MIMO Systems

doi:10.1109/TWC.2026.3709029

Broad Beam Design for RIS-Assisted Massive MIMO Systems

2026-07-09

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DOI：10.1109/TWC.2026.3709029

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In reconfigurable intelligent surface (RIS)-assisted massive multiple-input multiple-output (MIMO) broadcast systems, conventional narrow-beam designs fail when user locations are unknown and line-of-sight (LoS) links are blocked. This paper investigates the design of spatially uniform broad beams for both uni-polarized and dual-polarized RISs. Based on classical array theory, we model the RIS power-domain array factor (PDAF) as the power spectrum of its configuration information, which motivates us to propose an alternating direction method of multipliers (ADMM)-based optimization framework. For active uni-polarized RIS, we minimize the mean square error (MSE) between the actual and ideal omnidirectional PDAF under a tunable peak-to-average power ratio (PAPR) constraint, considering both uniform linear array (ULA)- and uniform rectangular array (URA)-type RIS configurations. For passive dual-polarized URA-type RIS, we minimize the complementary integrated sidelobe level (CISL) in the frequency domain to synthesize phase-only configurations that achieve spatially uniform coverage without amplitude control. All proposed algorithms can be efficiently implemented using one-dimensional or two-dimensional fast Fourier transform (FFT) and inverse FFT (IFFT) operations. Numerical experiments demonstrate that both proposed algorithms exhibit excellent convergence and stability, and outperform state-of-the-art methods across multiple evaluation metrics.

Keywords:

Reconfigurable intelligent surface (RIS)

broad beamforming

dual-polarized communication

uni-polarized communication

ADMM

Broad Beam Design for RIS-Assisted Massive MIMO Systems

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