Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Active Beyond-Diagonal Reconfigurable Intelligent Surfaces: Modeling, Architecture Design, and Optimization

Shanpu Shen, Hongyu Li, Matteo Nerini, Qingqing Wu, Bruno Clerckx

Abstract

Beyond-diagonal reconfigurable intelligent surfaces (BD-RISs) are an emerging RIS 2.0 technology for future wireless communication. However, BD-RISs are primarily passive without active amplification, suffering from severe multiplicative path loss. To address the concern of multiplicative path loss, in this work we investigate the active BD-RIS including the modeling, architecture design, and optimization. We first analyze the active BD-RIS using multiport network theory with scattering parameters and derive a physical and electromagnetic compliant active BD-RIS aided communication model. We also design two new active BD-RIS architectures, namely fully- and group-connected active BD-RISs. Based on the proposed model and architecture, we investigate the active BD-RIS aided single-input single-output system and derive the closed-form optimal solution and scaling law of the signal-to-noise ratio. We further investigate the active BD-RIS aided multiple-input multiple-output system and propose an iterative algorithm based on quadratically constrained quadratic programming to maximize the spectral efficiency. Numerical results are provided and show that the active BD-RIS can achieve higher spectral efficiency than the active/passive diagonal RIS and passive BD-RIS. For example, to achieve the same spectral efficiency, the number of elements required by active BD-RIS is less than half of that required by active diagonal RIS, showing the advantages of active BD-RIS.

Active Beyond-Diagonal Reconfigurable Intelligent Surfaces: Modeling, Architecture Design, and Optimization

Abstract

Beyond-diagonal reconfigurable intelligent surfaces (BD-RISs) are an emerging RIS 2.0 technology for future wireless communication. However, BD-RISs are primarily passive without active amplification, suffering from severe multiplicative path loss. To address the concern of multiplicative path loss, in this work we investigate the active BD-RIS including the modeling, architecture design, and optimization. We first analyze the active BD-RIS using multiport network theory with scattering parameters and derive a physical and electromagnetic compliant active BD-RIS aided communication model. We also design two new active BD-RIS architectures, namely fully- and group-connected active BD-RISs. Based on the proposed model and architecture, we investigate the active BD-RIS aided single-input single-output system and derive the closed-form optimal solution and scaling law of the signal-to-noise ratio. We further investigate the active BD-RIS aided multiple-input multiple-output system and propose an iterative algorithm based on quadratically constrained quadratic programming to maximize the spectral efficiency. Numerical results are provided and show that the active BD-RIS can achieve higher spectral efficiency than the active/passive diagonal RIS and passive BD-RIS. For example, to achieve the same spectral efficiency, the number of elements required by active BD-RIS is less than half of that required by active diagonal RIS, showing the advantages of active BD-RIS.
Paper Structure (25 sections, 68 equations, 7 figures)

This paper contains 25 sections, 68 equations, 7 figures.

Table of Contents

  1. Introduction
  2. Multiport Network Analysis
  3. Transmitter and Receiver
  4. Active Beyond-Diagonal Reconfigurable Intelligent Surface
  5. Architecture Design of Active BD-RIS
  6. Single-Connected Active BD-RIS
  7. Fully-Connected Active BD-RIS
  8. Group-Connected Active BD-RIS
  9. Relationship to Passive BD-RIS
  10. Active BD-RIS Aided Communication Model
  11. General Active BD-RIS Aided Communication Model
  12. Simplified Active BD-RIS Aided Communication Model
  13. Active BD-RIS Aided SISO System
  14. Simplified Case with $A_{1}=\ldots=A_{N_{\mathrm{I}}}=A$ and $h_{\mathrm{RT}}=0$
  15. SNR Scaling Law
  16. ...and 10 more sections

Figures (7)

  • Figure 1: Diagram of active BD-RIS aided wireless communication system.
  • Figure 2: (a) 2-element single-connected active BD-RIS (that is essentially the 2-element active D-RIS) and (b) 2-element fully-connected active BD-RIS.
  • Figure 3: 4-element group-connected active BD-RIS having 2 groups and group size of 2.
  • Figure 4: SNR versus the number of elements $N_{\mathrm{I}}$. For the group-connected active/passive BD-RIS, the group size is fixed to $N_{\mathrm{G}}=4$.
  • Figure 5: Asymptotic SNR versus the number of elements $N_{\mathrm{I}}$.
  • ...and 2 more figures

Theorems & Definitions (2)

  • Remark 1
  • Remark 2