{"ID":2834452,"CreatedAt":"2026-06-01T04:54:23.091178241Z","UpdatedAt":"2026-06-01T04:54:23.091178241Z","DeletedAt":null,"paper_url":"https://arxiv.org/abs/2512.01542","arxiv_id":"2512.01542","title":"Spectral-Energy Efficiency Tradeoff of Nearly-Passive RIS in MIMO URLLC Downlink: Diagonal vs. Beyond Diagonal","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.","short_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...","url_abs":"https://arxiv.org/abs/2512.01542","url_pdf":"https://arxiv.org/pdf/2512.01542v1","authors":"[\"Mohammad Soleymani\",\"Alessio Zappone\",\"Eduard Jorswieck\",\"Marco Di Renzo\",\"Ignacio Santamaria\"]","published":"2025-12-01T11:15:54Z","proceeding":"eess.SP","tasks":"[\"eess.SP\"]","methods":"[]","has_code":false}