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Evaluating Beam Sweeping for AoA Estimation with an RIS Prototype: Indoor/Outdoor Field Trials

Dimitris Vordonis, Dimitris Kompostiotis, Vassilis Paliouras, George C. Alexandropoulos, Florin Grec

TL;DR

The paper addresses practical AoA estimation and positioning using a 1-bit RIS prototype in indoor/outdoor field trials. It develops a tractable end-to-end RIS model with a diagonal phase matrix Θ and a codebook-based beam-sweeping approach, validated by measurements that align with theory and reveal ground-bounce and frequency-selectivity effects. A low-complexity column-row scanning optimization is proposed to configure the RIS under 1-bit constraints, and beam sweeping is demonstrated to provide meaningful AoA estimates, with outdoor gains and indoor refinements achieving about $10^\circ$ residual error. The study indicates that RIS-aided beam sweeping can support initial access and localization in real environments, while highlighting bandwidth and multipath challenges that inform practical deployment and controller design.

Abstract

Reconfigurable Intelligent Surfaces (RISs) have emerged as a promising technology to enhance wireless communication systems by enabling dynamic control over the propagation environment. However, practical experiments are crucial towards the validation of the theoretical potential of RISs while establishing their real-world applicability, especially since most studies rely on simplified models and lack comprehensive field trials. In this paper, we present an efficient method for configuring a $1$-bit RIS prototype at sub-$6$ GHz, resulting in a codebook oriented for beam sweeping; an essential protocol for initial access and Angle of Arrival (AoA) estimation. The measured radiation patterns of the RIS validate the theoretical model, demonstrating consistency between the experimental results and the predicted beamforming behavior. Furthermore, we experimentally prove that RIS can alter channel properties and by harnessing the diversity it provides, we evaluate beam sweeping as an AoA estimation technique. Finally, we investigate the frequency selectivity of the RIS and propose an approach to address indoor challenges by leveraging the geometry of environment.

Evaluating Beam Sweeping for AoA Estimation with an RIS Prototype: Indoor/Outdoor Field Trials

TL;DR

The paper addresses practical AoA estimation and positioning using a 1-bit RIS prototype in indoor/outdoor field trials. It develops a tractable end-to-end RIS model with a diagonal phase matrix Θ and a codebook-based beam-sweeping approach, validated by measurements that align with theory and reveal ground-bounce and frequency-selectivity effects. A low-complexity column-row scanning optimization is proposed to configure the RIS under 1-bit constraints, and beam sweeping is demonstrated to provide meaningful AoA estimates, with outdoor gains and indoor refinements achieving about residual error. The study indicates that RIS-aided beam sweeping can support initial access and localization in real environments, while highlighting bandwidth and multipath challenges that inform practical deployment and controller design.

Abstract

Reconfigurable Intelligent Surfaces (RISs) have emerged as a promising technology to enhance wireless communication systems by enabling dynamic control over the propagation environment. However, practical experiments are crucial towards the validation of the theoretical potential of RISs while establishing their real-world applicability, especially since most studies rely on simplified models and lack comprehensive field trials. In this paper, we present an efficient method for configuring a -bit RIS prototype at sub- GHz, resulting in a codebook oriented for beam sweeping; an essential protocol for initial access and Angle of Arrival (AoA) estimation. The measured radiation patterns of the RIS validate the theoretical model, demonstrating consistency between the experimental results and the predicted beamforming behavior. Furthermore, we experimentally prove that RIS can alter channel properties and by harnessing the diversity it provides, we evaluate beam sweeping as an AoA estimation technique. Finally, we investigate the frequency selectivity of the RIS and propose an approach to address indoor challenges by leveraging the geometry of environment.

Paper Structure

This paper contains 12 sections, 6 equations, 31 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. Radiation Pattern of RIS: Theoretical model
  3. Practical Phase Optimization Method
  4. Indoor and Outdoor Measurement Setups
  5. Experimental Results and Discussion
  6. Radiation Pattern of RIS: Codebook-based Beamforming
  7. Impact of Frequency Selectivity on RIS Beamforming
  8. Proposed Beam Sweeping Methodology for AoA estimation
  9. Beam Sweeping in Outdoor Setup
  10. Beam Sweeping in Indoor Setup
  11. Conclusion
  12. Acknowledgement

Figures (31)

  • Figure 1: Outdoor setup: The Tx-RIS distance is 8.5 m, and the RIS-Rx distance is 8.5 m for all Rx positions, with all nodes positioned at a height of 1.3 m. Rx positions range from $0^\circ$ to $60^\circ$, with a step size of $5^\circ$, and the Tx is fixed at $-15^\circ$. RIS configurations are optimized to steer the beam toward each Rx position.
  • Figure 2: Indoor setup: The Tx-RIS distance is 5.5 m, and the RIS-Rx distance is 8.5 m for all Rx positions, with all nodes positioned at a height of 1.3 m. Rx positions range from $0^\circ$ to $45^\circ$, with a step size of $15^\circ$ and the Tx if fixed at $-15^\circ$. RIS configurations are optimized to steer the beam toward each Rx position.
  • Figure 4: RIS Configuration, $0^\circ$
  • Figure 5: RIS Configuration, $15^\circ$
  • Figure 6: RIS Configuration, $30^\circ$
  • ...and 26 more figures