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Beyond Diagonal RIS: A New Frontier for 6G Internet of Things Networks

Wali Ullah Khan, Chandan Kumar Sheemar, Eva Lagunas, Symeon Chatzinotas

TL;DR

This paper introduces Beyond-Diagonal RIS (BD-RIS) as a powerful evolution of conventional RIS, enabling non-diagonal scattering to jointly control amplitude and phase for finer wavefront manipulation. It catalogs BD-RIS architectures (single-, fully-, and group-connected) and operating modes (reflective, transmissive, hybrid, multi-sector), and highlights benefits in enhanced beamforming, adaptability, interference mitigation, and coverage for 6G IoT. A BD-RIS-enabled V2V case study demonstrates spectral-efficiency gains over D-RIS and baseline systems, validating practical advantages in underlay networks. The work also discusses hardware, channel-estimation, and non-idealities as major challenges, and outlines AI/ML optimization, JCAS, and physical-layer security as promising directions to realize BD-RIS’s full potential in 6G IoT and NTNs.

Abstract

Reconfigurable intelligent surface (RIS) technology has emerged as a promising enabler for next-generation wireless networks, offering a paradigm shift from passive environments to programmable radio wave propagation. Despite the potential of diagonal RIS (D-RIS), its limited wave manipulation capability restricts performance gains. In this paper, we investigate the burgeoning concept of beyond-diagonal RIS (BD-RIS), which incorporates non-diagonal elements in its scattering matrix to deliver more fine-grained control of electromagnetic wavefronts. We begin by discussing the limitations of traditional D-RIS and introduce key BD-RIS architectures with different operating modes. We then highlight the features that make BD-RIS particularly advantageous for 6G IoT applications, including advanced beamforming, enhanced interference mitigation, and flexible coverage. A case study on BD-RIS-assisted vehicle-to-vehicle (V2V) communication in an underlay cellular network demonstrates considerable improvements in spectral efficiency when compared to D-RIS and conventional systems. Lastly, we present current challenges such as hardware design complexity, channel estimation, and non-ideal hardware effects, and propose future research directions involving AI-driven optimization, joint communication and sensing, and physical layer security. Our findings illustrate the transformative potential of BD-RIS in shaping high-performance, scalable, and reliable 6G IoT networks.

Beyond Diagonal RIS: A New Frontier for 6G Internet of Things Networks

TL;DR

This paper introduces Beyond-Diagonal RIS (BD-RIS) as a powerful evolution of conventional RIS, enabling non-diagonal scattering to jointly control amplitude and phase for finer wavefront manipulation. It catalogs BD-RIS architectures (single-, fully-, and group-connected) and operating modes (reflective, transmissive, hybrid, multi-sector), and highlights benefits in enhanced beamforming, adaptability, interference mitigation, and coverage for 6G IoT. A BD-RIS-enabled V2V case study demonstrates spectral-efficiency gains over D-RIS and baseline systems, validating practical advantages in underlay networks. The work also discusses hardware, channel-estimation, and non-idealities as major challenges, and outlines AI/ML optimization, JCAS, and physical-layer security as promising directions to realize BD-RIS’s full potential in 6G IoT and NTNs.

Abstract

Reconfigurable intelligent surface (RIS) technology has emerged as a promising enabler for next-generation wireless networks, offering a paradigm shift from passive environments to programmable radio wave propagation. Despite the potential of diagonal RIS (D-RIS), its limited wave manipulation capability restricts performance gains. In this paper, we investigate the burgeoning concept of beyond-diagonal RIS (BD-RIS), which incorporates non-diagonal elements in its scattering matrix to deliver more fine-grained control of electromagnetic wavefronts. We begin by discussing the limitations of traditional D-RIS and introduce key BD-RIS architectures with different operating modes. We then highlight the features that make BD-RIS particularly advantageous for 6G IoT applications, including advanced beamforming, enhanced interference mitigation, and flexible coverage. A case study on BD-RIS-assisted vehicle-to-vehicle (V2V) communication in an underlay cellular network demonstrates considerable improvements in spectral efficiency when compared to D-RIS and conventional systems. Lastly, we present current challenges such as hardware design complexity, channel estimation, and non-ideal hardware effects, and propose future research directions involving AI-driven optimization, joint communication and sensing, and physical layer security. Our findings illustrate the transformative potential of BD-RIS in shaping high-performance, scalable, and reliable 6G IoT networks.

Paper Structure

This paper contains 30 sections, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Preliminaries of RIS Technology
  3. Overview of RIS
  4. BD-RIS: The Next Frontier
  5. Classification of BD-RIS
  6. BD-RIS Architecture
  7. BD-RIS Operating Modes
  8. Features of BD-RIS in 6G IoT Networks
  9. Enhanced Beamforming and Flexibility
  10. Adaptability to Dynamic IoT Environments
  11. Superior Interference Management
  12. Extended Coverage and Connectivity
  13. Versatile Applications
  14. Use Cases of BD-RIS in 6G IoT Networks
  15. BD-RIS in Smart Agriculture
  16. ...and 15 more sections

Figures (4)

  • Figure 1: Architectures of BD-RIS: (a) cell-wise single-connected BD-RIS with four cells, (b) cell-wise fully-connected BD-RIS with two cells, and (c) element-wise group-connected BD-RIS with two groups.
  • Figure 2: Use cases of BD-RIS in 6G IoT networks.
  • Figure 3: BD-RIS assisted V2V communication underlay cellular network.
  • Figure 4: Achievable spectral efficiency of V2V communication versus varying number of reconfigurable elements, considering V2V transmit power is 1W and cellular RSU power is 10W.