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Exploiting Self-Sustainable Information-Bearing RIS in Underlay CR-NOMA Networks

Zeyang Sun, Shuai Han, Chenyu Wu, Sai Xu, Yuanwei Liu

Abstract

Information-bearing reconfigurable intelligent surfaces (IB-RIS) provide a promising solution to self-sustainable and green communications by harvesting ambient radio frequency energy while embedding information via passive reflection. This paper investigates a self-sustainable IB-RIS (SIB-RIS)-assisted non-orthogonal multiple access (NOMA) network operating in an underlay cognitive radio (CR) system. Specifically, a multi-antenna primary transmitter (PT) serves a primary user (PU) and concurrently illuminates the secondary nodes, which enables each SIB-RIS to perform simultaneous energy harvesting and backscatter-based information embedding at each RIS. Based on this model, a weighted sum spectral efficiency (WSSE) maximization problem is formulated for the secondary network by jointly optimizing the PT transmit beamforming vector, the SIB-RIS reflection coefficients, and the power-splitting ratios. To tackle the intricately-coupled non-convex problem, an efficient block coordinate descent (BCD) optimization framework is developed, which leverages fractional programming via Lagrangian dual and quadratic transforms together with a difference-of-convex programming approach. Numerical results demonstrate that the proposed SIB-RIS-assisted NOMA CR system yields substantial WSSE gains over both orthogonal multiple access (OMA)-based and active antenna schemes. Moreover, a 2-bit discrete-phase SIB-RIS implementation achieves competitive to which WSSE performance, confirming the practicality of the low-resolution architecture.

Exploiting Self-Sustainable Information-Bearing RIS in Underlay CR-NOMA Networks

Abstract

Information-bearing reconfigurable intelligent surfaces (IB-RIS) provide a promising solution to self-sustainable and green communications by harvesting ambient radio frequency energy while embedding information via passive reflection. This paper investigates a self-sustainable IB-RIS (SIB-RIS)-assisted non-orthogonal multiple access (NOMA) network operating in an underlay cognitive radio (CR) system. Specifically, a multi-antenna primary transmitter (PT) serves a primary user (PU) and concurrently illuminates the secondary nodes, which enables each SIB-RIS to perform simultaneous energy harvesting and backscatter-based information embedding at each RIS. Based on this model, a weighted sum spectral efficiency (WSSE) maximization problem is formulated for the secondary network by jointly optimizing the PT transmit beamforming vector, the SIB-RIS reflection coefficients, and the power-splitting ratios. To tackle the intricately-coupled non-convex problem, an efficient block coordinate descent (BCD) optimization framework is developed, which leverages fractional programming via Lagrangian dual and quadratic transforms together with a difference-of-convex programming approach. Numerical results demonstrate that the proposed SIB-RIS-assisted NOMA CR system yields substantial WSSE gains over both orthogonal multiple access (OMA)-based and active antenna schemes. Moreover, a 2-bit discrete-phase SIB-RIS implementation achieves competitive to which WSSE performance, confirming the practicality of the low-resolution architecture.
Paper Structure (17 sections, 55 equations, 7 figures, 1 algorithm)

This paper contains 17 sections, 55 equations, 7 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. Organization and Notation
  3. System Architecture and Problem Formulation
  4. System Architecture
  5. Self-Sustainable Power-Splitting Energy Harvesting
  6. Information-Bearing via Backscatter Modulation
  7. Signal Transmission and NOMA Decoding Model
  8. Problem Formulation
  9. Proposed Joint Optimization Algorithm
  10. Equivalent Transformation of Objective Function
  11. BCD-based Joint Optimization Scheme
  12. Computational Complexity Analysis
  13. Simulation Results
  14. Simulation Setup
  15. Results and Analyses
  16. ...and 2 more sections

Figures (7)

  • Figure 1: The proposed SIB-RIS-assisted NOMA CR system.
  • Figure 2: WSSE versus the number of iterations.
  • Figure 3: WSSE versus the number of reflection elements for each SIB-RIS.
  • Figure 4: WSSE versus the transmit power of the PT.
  • Figure 5: WSSE versus the number of antennas at the PT.
  • ...and 2 more figures