Beyond Diagonal Reconfigurable Intelligent Surfaces Utilizing Graph Theory: Modeling, Architecture Design, and Optimization

Recently, beyond diagonal reconfigurable intelligent surface (BD-RIS) has been proposed to generalize conventional RIS. BD-RIS has a scattering matrix that is not restricted to being diagonal and thus brings a performance improvement over conventional RIS. While different BD-RIS architectures have b...

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Bibliographic Details
Published in:IEEE transactions on wireless communications Vol. 23; no. 8; pp. 9972 - 9985
Main Authors: Nerini, Matteo, Shen, Shanpu, Li, Hongyu, Clerckx, Bruno
Format: Journal Article
Language:English
Published: New York IEEE 01.08.2024
The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subjects:
Admittance
Beyond diagonal reconfigurable intelligent surface (BD-RIS)
Complexity
Complexity theory
Design optimization
forest-connected
Forestry
Forests
graph theoretical modeling
Graph theory
Impedance
Integrated circuit modeling
Iterative algorithms
Reconfigurable intelligent surfaces
S matrix theory
Scattering
tree-connected
Upper bounds
ISSN:1536-1276, 1558-2248
Online Access:Get full text
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Summary:Recently, beyond diagonal reconfigurable intelligent surface (BD-RIS) has been proposed to generalize conventional RIS. BD-RIS has a scattering matrix that is not restricted to being diagonal and thus brings a performance improvement over conventional RIS. While different BD-RIS architectures have been proposed, it still remains an open problem to develop a systematic approach to design BD-RIS architectures achieving the optimal trade-off between performance and circuit complexity. In this work, we propose novel modeling, architecture design, and optimization for BD-RIS based on graph theory. This graph theoretical modeling allows us to develop two new efficient BD-RIS architectures, denoted as tree-connected and forest-connected RIS. Tree-connected RIS, whose corresponding graph is a tree, is proven to be the least complex BD-RIS architecture able to achieve the performance upper bound in multiple-input singleoutput (MISO) systems. Besides, forest-connected RIS allows us to strike a balance between performance and complexity, further decreasing the complexity over tree-connected RIS. To optimize tree-connected RIS, we derive a closed-form global optimal solution, while forest-connected RIS is optimized through a low-complexity iterative algorithm. Numerical results confirm that tree-connected (resp. forest-connected) RIS achieves the same performance as fully-connected (resp. group-connected) RIS, while reducing the complexity by up to 16.4 times.
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ISSN:1536-1276
1558-2248
DOI:10.1109/TWC.2024.3367631