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arXiv · 2512.01542

Spectral-Energy Efficiency Tradeoff of Nearly-Passive RIS in MIMO URLLC Downlink: Diagonal vs. Beyond Diagonal

Mohammad Soleymani·Alessio Zappone·Eduard Jorswieck·Marco Di Renzo·Ignacio Santamaria
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Abstract

This paper investigates the spectral and energy efficiency (EE) tradeoff of nearly-passive (NP), both locally and globally NP (GNP), reconfigurable intelligent surface (RIS), considering diagonal and beyond-diagonal (BD) implementations in multi-user multiple-input multiple-output (MU-MIMO) broadcast channels designed for ultra-reliable low-latency communication (URLLC). We demonstrate that while all RIS architectures enhance the spectral efficiency, GNP BD-RIS achieves the highest gains. However, its EE is highly sensitive to the static circuit power consumption since BD-RIS has many more circuit elements than diagonal architectures. Furthermore, we demonstrate that the benefits of BD-RIS over diagonal RIS diminish as the number of data streams per user increases due to enhanced channel diversity in MIMO systems.

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Mohammad Soleymani, Alessio Zappone, Eduard Jorswieck, Marco Di Renzo, Ignacio Santamaria. 2025-12-01. Spectral-Energy Efficiency Tradeoff of Nearly-Passive RIS in MIMO URLLC Downlink: Diagonal vs. Beyond Diagonal. https://arxiv.org/abs/2512.01542

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