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Design and Optimization on Successive RIS-assisted Multi-hop Wireless Communications

Rujing Xiong, Jialong Lu, Jianan Zhang, Minggang Liu, Xuehui Dong, Tiebin Mi, Robert Caiming Qiu

TL;DR

The paper tackles energy-efficient, CSI-free optimization for successive RIS-assisted multi-hop wireless links by developing a generalized cascaded signal model that captures input–output electric-field relations across RISs and deriving a closed-form HPBW as a function of RIS size and beam direction. It then couples these insights into deployment and beam-design strategies that maximize aperture efficiency and directional gain, including a multi-beam MA-based approach for uniform illumination. The key contributions include the generalized multi-hop RIS model, explicit HPBW expressions, and deployment/beam-optimization formulations with semi-analytical solutions, all validated by simulations and a real 3.4 GHz two-hop RIS prototype demonstrating substantial gains over single-beam configurations. The work highlights practical significance for challenging environments (e.g., tunnels, dense urban areas) by enabling high-efficiency RIS-enabled coverage without requiring channel-state information estimation, with potential impact on next-generation wireless networks and open-RAN deployments.

Abstract

As an emerging wireless communication technology, reconfigurable intelligent surface (RIS) has become a basic choice for providing signal coverage services in scenarios with dense obstacles or long tunnels through multi-hop configurations. Conventional works of literature mainly focus on alternating optimization or single-beam calculation in RIS phase configuration, which is limited in considering energy efficiency, and often suffers from inaccurate channel state information (CSI), poor convergence, and high computational complexity. This paper addresses the design and optimization challenges for successive RIS-assisted multi-hop systems. Specifically, we establish a general model for multi-hop communication based on the relationship between the input and output electric fields within each RIS. Meanwhile, we derive the half-power beamwidth of the RIS-reflected beams, considering the beam direction. Leveraging these models and derivations, we propose deployment optimization and beam optimization strategies for multi-hop systems, which feature high aperture efficiency and significant gains in signal power. Simulation and prototype experiment results validate the effectiveness and superiority of the proposed systems and methods.

Design and Optimization on Successive RIS-assisted Multi-hop Wireless Communications

TL;DR

The paper tackles energy-efficient, CSI-free optimization for successive RIS-assisted multi-hop wireless links by developing a generalized cascaded signal model that captures input–output electric-field relations across RISs and deriving a closed-form HPBW as a function of RIS size and beam direction. It then couples these insights into deployment and beam-design strategies that maximize aperture efficiency and directional gain, including a multi-beam MA-based approach for uniform illumination. The key contributions include the generalized multi-hop RIS model, explicit HPBW expressions, and deployment/beam-optimization formulations with semi-analytical solutions, all validated by simulations and a real 3.4 GHz two-hop RIS prototype demonstrating substantial gains over single-beam configurations. The work highlights practical significance for challenging environments (e.g., tunnels, dense urban areas) by enabling high-efficiency RIS-enabled coverage without requiring channel-state information estimation, with potential impact on next-generation wireless networks and open-RAN deployments.

Abstract

As an emerging wireless communication technology, reconfigurable intelligent surface (RIS) has become a basic choice for providing signal coverage services in scenarios with dense obstacles or long tunnels through multi-hop configurations. Conventional works of literature mainly focus on alternating optimization or single-beam calculation in RIS phase configuration, which is limited in considering energy efficiency, and often suffers from inaccurate channel state information (CSI), poor convergence, and high computational complexity. This paper addresses the design and optimization challenges for successive RIS-assisted multi-hop systems. Specifically, we establish a general model for multi-hop communication based on the relationship between the input and output electric fields within each RIS. Meanwhile, we derive the half-power beamwidth of the RIS-reflected beams, considering the beam direction. Leveraging these models and derivations, we propose deployment optimization and beam optimization strategies for multi-hop systems, which feature high aperture efficiency and significant gains in signal power. Simulation and prototype experiment results validate the effectiveness and superiority of the proposed systems and methods.
Paper Structure (26 sections, 1 theorem, 47 equations, 18 figures, 2 tables, 1 algorithm)

This paper contains 26 sections, 1 theorem, 47 equations, 18 figures, 2 tables, 1 algorithm.

Table of Contents

  1. Introduction
  2. Contributions
  3. Outline
  4. Notations
  5. System Model
  6. BS-RIS-UE
  7. RIS-RIS-UE
  8. General Model
  9. Radiation Analysis of the RIS
  10. Aperture Efficiency
  11. The Half-Power Beamwidth
  12. Optimization Strategy
  13. Deployment Optimization
  14. RIS position optimization
  15. RIS aperture optimization
  16. ...and 11 more sections

Key Result

Theorem 1

Given a reflecting angle $\theta_2$ of RIS, the half-power beamwidth can be obtained through $\mathrm{HP} = |\theta^{*}_1-\theta^{*}_{2}|$, where $\theta^{*}_1=\sin ^{-1}\left( 1.391 \times \frac{2}{B kd}+\sin \theta_{2}\right)$, and $\theta^{*}_2=\sin ^{-1}\left( -1.391 \times \frac{2}{B kd}+\sin

Figures (18)

  • Figure 1: RIS-assistanted multi-hop wireless communications.
  • Figure 2: The RIS is illuminated by a single incident EM wave from ($r^\text{i}, \theta^\text{i}, \phi^\text{i}$).
  • Figure 3: Two-Hop RIS-assisted wireless communications.
  • Figure 4: Aperture efficiency and directional gains as a function of the distance between the feed source and the RIS.
  • Figure 5: The irradiation of the transmitting/reflecting beam. (a) Partial illumination. (b) Over illumination. (c) Exact illumination.
  • ...and 13 more figures

Theorems & Definitions (2)

  • Theorem 1
  • proof