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User Clustering for STAR-RIS Assisted Full-Duplex NOMA Communication Systems

Abdelhamid Salem, Kai-Kit Wong, Chan-Byoung Chae, Yangyang Zhang

TL;DR

The paper addresses spectrum efficiency in STAR-RIS aided FD-NOMA networks by introducing simple yet effective DL/UL user clustering schemes and deriving closed-form ergodic-rate expressions under realistic fading and impairment models. It develops a two-stage optimization framework: first clustering, then joint STAR-RIS amplitude/phase design and power allocation, using PGAM and sub-optimal phase alignments to manage non-convexity. Key contributions include new clustering strategies, tractable ergodic-rate formulas that account for self-interference and imperfect SIC, and practical design methods that enhance cell-edge performance while managing interference. The findings demonstrate that larger STAR-RIS arrays and optimized clustering substantially improve edge-user rates and overall sum-rate, with clear guidance on when clustering outperforms pairing under various SIC and interference conditions.

Abstract

In contrast to conventional reconfigurable intelligent surface (RIS), simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) has been proposed recently to enlarge the serving area from 180o to 360o coverage. This work considers the performance of a STAR-RIS aided full-duplex (FD) non-orthogonal multiple access (NOMA) communication systems. The STAR-RIS is implemented at the cell-edge to assist the cell-edge users, while the cell-center users can communicate directly with a FD base station (BS). We first introduce new user clustering schemes for the downlink and uplink transmissions. Then, based on the proposed transmission schemes closed-form expressions of the ergodic rates in the downlink and uplink modes are derived taking into account the system impairments caused by the self interference at the FD-BS and the imperfect successive interference cancellation (SIC). Moreover, an optimization problem to maximize the total sum-rate is formulated and solved by optimizing the amplitudes and the phase-shifts of the STAR-RIS elements and allocating the transmit power efficiently. The performance of the proposed user clustering schemes and the optimal STAR-RIS design are investigated through numerical results

User Clustering for STAR-RIS Assisted Full-Duplex NOMA Communication Systems

TL;DR

The paper addresses spectrum efficiency in STAR-RIS aided FD-NOMA networks by introducing simple yet effective DL/UL user clustering schemes and deriving closed-form ergodic-rate expressions under realistic fading and impairment models. It develops a two-stage optimization framework: first clustering, then joint STAR-RIS amplitude/phase design and power allocation, using PGAM and sub-optimal phase alignments to manage non-convexity. Key contributions include new clustering strategies, tractable ergodic-rate formulas that account for self-interference and imperfect SIC, and practical design methods that enhance cell-edge performance while managing interference. The findings demonstrate that larger STAR-RIS arrays and optimized clustering substantially improve edge-user rates and overall sum-rate, with clear guidance on when clustering outperforms pairing under various SIC and interference conditions.

Abstract

In contrast to conventional reconfigurable intelligent surface (RIS), simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) has been proposed recently to enlarge the serving area from 180o to 360o coverage. This work considers the performance of a STAR-RIS aided full-duplex (FD) non-orthogonal multiple access (NOMA) communication systems. The STAR-RIS is implemented at the cell-edge to assist the cell-edge users, while the cell-center users can communicate directly with a FD base station (BS). We first introduce new user clustering schemes for the downlink and uplink transmissions. Then, based on the proposed transmission schemes closed-form expressions of the ergodic rates in the downlink and uplink modes are derived taking into account the system impairments caused by the self interference at the FD-BS and the imperfect successive interference cancellation (SIC). Moreover, an optimization problem to maximize the total sum-rate is formulated and solved by optimizing the amplitudes and the phase-shifts of the STAR-RIS elements and allocating the transmit power efficiently. The performance of the proposed user clustering schemes and the optimal STAR-RIS design are investigated through numerical results
Paper Structure (21 sections, 6 theorems, 166 equations, 6 figures, 2 algorithms)

This paper contains 21 sections, 6 theorems, 166 equations, 6 figures, 2 algorithms.

Table of Contents

  1. Introduction
  2. System Model
  3. Data Transmission and Problem Formulation
  4. User Clustering Scheme
  5. Key Principles
  6. User Clustering Algorithm
  7. Ergodic Rate Analysis
  8. DL
  9. Cell-center, Group $\mathcal{G}_{1}$
  10. Cell-center, Group $\mathcal{G}_{2}$
  11. Cell-edge, Group $\mathcal{G}_{3}$
  12. UL
  13. Cell-center, Group $\mathcal{G}_{1}$
  14. Cell-center, Group $\mathcal{G}_{2}$
  15. Cell-edge, Group $\mathcal{G}_{3}$
  16. ...and 6 more sections

Key Result

Theorem 1

The ergodic rate of the DL strongest user in a cluster can be evaluated by where $x_{1_{u_{1d}}},y_{1_{u_{1d}}},\textrm{ and }y_{2_{u_{1d}}}$ are defined as

Figures (6)

  • Figure 1: A STAR-RIS assisted FD communication system.
  • Figure 2: Illustration of user clustering scheme to serve 6 cell-center users and 3 cell-edge users in DL and UL modes.
  • Figure 3: Ergodic rates versus transmit SNR,$\bar{\gamma}$, for different phase shifts.
  • Figure 4: Ergodic rates versus transmit SNR,$\bar{\gamma}$, with different values of the SIC error factor and self interference.
  • Figure 5: Sum-rates of user-clustering and user-paring schemes versus the transmit SNR, $\bar{\gamma}$, for perfect and imperfect SIC.
  • ...and 1 more figures

Theorems & Definitions (6)

  • Theorem 1
  • Theorem 2
  • Theorem 3
  • Theorem 4
  • Theorem 5
  • Theorem 6