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Optimal Operation of Active RIS-Aided Wireless Powered Communications in IoT Networks

Waqas Khalid, A. -A. A. Boulogeorgos, Trinh Van Chien, Junse Lee, Howon Lee, Heejung Yu

TL;DR

This work addresses IoT networks powered by wireless power transfer and aided by active RIS to overcome double fading that hampers passive RIS. It develops a complete analytical framework for the ergodic rate and outage probability, incorporating active amplification, RIS noise, phase quantization, and RIS power consumption, and derives closed-form-like expressions using moment-based approximations and Gamma-distribution fitting. The authors optimize the time-switching factor $\alpha$ for both ergodic and effective rate criteria, under and without RIS-power constraints, using KKT conditions and numerical methods, and demonstrate the superiority of active RIS over passive RIS with realistic phase quantization. The results indicate substantial performance gains in energy transfer efficiency and reliable data transmission, enabling more scalable WPC-enabled IoT deployments; the study also provides practical guidelines on choosing $\alpha$, RIS amplification, and element count under energy constraints. These insights have direct implications for designing energy-efficient, robust IoT networks in next-generation wireless systems, especially where device longevity and link reliability are critical.

Abstract

Wireless-powered communications (WPCs) are increasingly crucial for extending the lifespan of low-power Internet of Things (IoT) devices. Furthermore, reconfigurable intelligent surfaces (RISs) can create favorable electromagnetic environments by providing alternative signal paths to counteract blockages. The strategic integration of WPC and RIS technologies can significantly enhance energy transfer and data transmission efficiency. However, passive RISs suffer from double-fading attenuation over RIS-aided cascaded links. In this article, we propose the application of an active RIS within WPC-enabled IoT networks. The enhanced flexibility of the active RIS in terms of energy transfer and information transmission is investigated using adjustable parameters. We derive novel closed-form expressions for the ergodic rate and outage probability by incorporating key parameters, including signal amplification, active noise, power consumption, and phase quantization errors. Additionally, we explore the optimization of WPC scenarios, focusing on the time-switching factor and power consumption of the active RIS. The results validate our analysis, demonstrating that an active RIS significantly enhances WPC performance compared to a passive RIS.

Optimal Operation of Active RIS-Aided Wireless Powered Communications in IoT Networks

TL;DR

This work addresses IoT networks powered by wireless power transfer and aided by active RIS to overcome double fading that hampers passive RIS. It develops a complete analytical framework for the ergodic rate and outage probability, incorporating active amplification, RIS noise, phase quantization, and RIS power consumption, and derives closed-form-like expressions using moment-based approximations and Gamma-distribution fitting. The authors optimize the time-switching factor for both ergodic and effective rate criteria, under and without RIS-power constraints, using KKT conditions and numerical methods, and demonstrate the superiority of active RIS over passive RIS with realistic phase quantization. The results indicate substantial performance gains in energy transfer efficiency and reliable data transmission, enabling more scalable WPC-enabled IoT deployments; the study also provides practical guidelines on choosing , RIS amplification, and element count under energy constraints. These insights have direct implications for designing energy-efficient, robust IoT networks in next-generation wireless systems, especially where device longevity and link reliability are critical.

Abstract

Wireless-powered communications (WPCs) are increasingly crucial for extending the lifespan of low-power Internet of Things (IoT) devices. Furthermore, reconfigurable intelligent surfaces (RISs) can create favorable electromagnetic environments by providing alternative signal paths to counteract blockages. The strategic integration of WPC and RIS technologies can significantly enhance energy transfer and data transmission efficiency. However, passive RISs suffer from double-fading attenuation over RIS-aided cascaded links. In this article, we propose the application of an active RIS within WPC-enabled IoT networks. The enhanced flexibility of the active RIS in terms of energy transfer and information transmission is investigated using adjustable parameters. We derive novel closed-form expressions for the ergodic rate and outage probability by incorporating key parameters, including signal amplification, active noise, power consumption, and phase quantization errors. Additionally, we explore the optimization of WPC scenarios, focusing on the time-switching factor and power consumption of the active RIS. The results validate our analysis, demonstrating that an active RIS significantly enhances WPC performance compared to a passive RIS.
Paper Structure (20 sections, 5 theorems, 32 equations, 6 figures)

This paper contains 20 sections, 5 theorems, 32 equations, 6 figures.

Table of Contents

  1. Introduction
  2. Motivation
  3. Contribution and Organization
  4. System Model
  5. Network Description
  6. Channel Modeling
  7. Active RIS Model
  8. Phase Error
  9. Energy Transfer and Information Transmission
  10. Performance Analysis
  11. Ergodic Rate
  12. Outage Probability
  13. Power Consumption of an Active RIS
  14. Optimizing Ergodic and Effective Rates
  15. Optimizing Ergodic Rate ($\hat{R_{v}}$) with $\alpha$
  16. ...and 5 more sections

Key Result

Lemma 1

Given the random variables $x$ and $y$, we have when $\frac{\mathbb{V} \{x+y\}}{ \mathbb{E}^3\{x+y\}} < \delta_1$ and $\frac{\mathbb{V} \{y\}}{ \mathbb{E}^3\{y\}} < \delta_2$ for positive $c_1$, $c_2$, $\delta_1$ and $\delta_2$.

Figures (6)

  • Figure 1: System model diagram of active RIS-aided WPC in IoT networks, including the circuit configuration of active elements.
  • Figure 2: Ergodic Rate ($\hat{R_{v}}$) vs. transmission power of a wireless RF power hub $P$ ($P_p$).
  • Figure 3: Outage Probability ($P_O$) vs. transmission power of a wireless RF power hub $P$ ($P_p$).
  • Figure 4: Ergodic rate ($\hat{R_{v}}$) and effective rate ($R_{eff}$) vs. time switching factor $\alpha$.
  • Figure 5: Power consumption of an active RIS ($P_{c}$) vs. amplification gain ($\rho_{m}$) and transmission power of $P$ ($P_{p}$).
  • ...and 1 more figures

Theorems & Definitions (10)

  • Lemma 1
  • Proof
  • Theorem 1
  • Proof
  • Theorem 2
  • Proof
  • Theorem 3
  • Proof
  • Theorem 4
  • Proof