Active-RIS Enhances the Multi-User Rate of Multi-Carrier Communications

This paper explores a multi-user multi-carrier system leveraging an active reconfigurable intelligent surface (RIS), where the joint design of the RIS's programmable reflecting elements and the subcarrier-wise beamformers at the base station is investigated. To overcome the limitation of the co...

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Bibliographic Details
Published in:IEEE transactions on vehicular technology 2024-11, Vol.73 (11), p.16948-16963
Main Authors: Tuan, Hoang Duong, Nasir, Ali Arshad, Dutkiewicz, Eryk, Poor, H. Vincent, Hanzo, Lajos
Format: Article
Language:English
Subjects:
Active reconfigurable intelligent surface
Beamforming
Closed-form solutions
Indexes
large-scale computation
Maximization
multi-carrier communication
multi-user rate enhancement
OFDM
Optimization
Reconfigurable intelligent surfaces
subcarrier-wise beamforming
Subcarriers
Symmetric matrices
Vectors
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Summary:This paper explores a multi-user multi-carrier system leveraging an active reconfigurable intelligent surface (RIS), where the joint design of the RIS's programmable reflecting elements and the subcarrier-wise beamformers at the base station is investigated. To overcome the limitation of the conventional design, which aims solely at sum-rate maximization resulting in zero rates for some users across all sub-carriers and thus failing to boost all users rates, we propose the two alternative designs: one maximizing the geometric mean of the users' rates (GM-rate maximization) and the other maximizing the soft users' minimum rate (soft max-min rate optimization). However, they pose challenges as large-scale nonconvex problems, rendering convex-solver computational approaches impractical. To tackle this, we develop iterative computational procedures based on closed-form expressions of scalable complexity. Extensive simulations demonstrate the substantial benefits of these novel designs in significantly enhancing multi-user rates. Notably, under the same power budget, the active-RIS-assisted multi-carrier system achieves approximately twice the minimum user-rate or sum rate compared to RIS-less or passive-RIS-assisted counterparts.
ISSN:0018-9545
1939-9359
DOI:10.1109/TVT.2024.3423433