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Robust Beamforming for Practical RIS-Aided RSMA Systems with Imperfect SIC under Transceiver Hardware Impairments

Xuejun Cheng, Qian Zhang, Yunnuo Xu, Zheng Dong, Ju Liu, Bruno Clerckx

Abstract

Reconfigurable intelligent surface (RIS)-aided rate-splitting multiple access (RSMA) systems have demonstrated remarkable potential in enhancing spectral efficiency. However, most existing works rely on ideal hardware, which is unrealistic.In practical deployments, RIS elements suffer from amplitude-phase coupling, where transceivers are subject to hardware impairments (HWI), and successive interference cancellation (SIC) in RSMA networks cannot achieve perfect interference elimination for decoded signals.To address these limitations, we investigate a robust beamforming design for RIS-aided RSMA systems under practical hardware imperfections. We first characterize the asymptotic signal-to-noise ratio (SNR) of practical RIS systems when the beamformer is designed based on ideal RIS model, thereby theoretically quantifying the resulting performance degradation. We then derive a closed-form expression for the distortion noise power induced by transceiver HWI, while also accounting for residual interference due to imperfect SIC. Building on these insights, we establish a comprehensive system model that jointly incorporates all hardware-induced impairments and formulate a multiuser sum rate maximization problem. To solve the resulting non-convex optimization problem, we develop an efficient block variable relaxation algorithm. Simulation results verify that the proposed scheme significantly outperforms conventional non-orthogonal multiple access (NOMA) approaches, and achieves superior robustness compared with benchmark schemes neglecting HWI, imperfect SIC, or amplitude-phase coupling.

Robust Beamforming for Practical RIS-Aided RSMA Systems with Imperfect SIC under Transceiver Hardware Impairments

Abstract

Reconfigurable intelligent surface (RIS)-aided rate-splitting multiple access (RSMA) systems have demonstrated remarkable potential in enhancing spectral efficiency. However, most existing works rely on ideal hardware, which is unrealistic.In practical deployments, RIS elements suffer from amplitude-phase coupling, where transceivers are subject to hardware impairments (HWI), and successive interference cancellation (SIC) in RSMA networks cannot achieve perfect interference elimination for decoded signals.To address these limitations, we investigate a robust beamforming design for RIS-aided RSMA systems under practical hardware imperfections. We first characterize the asymptotic signal-to-noise ratio (SNR) of practical RIS systems when the beamformer is designed based on ideal RIS model, thereby theoretically quantifying the resulting performance degradation. We then derive a closed-form expression for the distortion noise power induced by transceiver HWI, while also accounting for residual interference due to imperfect SIC. Building on these insights, we establish a comprehensive system model that jointly incorporates all hardware-induced impairments and formulate a multiuser sum rate maximization problem. To solve the resulting non-convex optimization problem, we develop an efficient block variable relaxation algorithm. Simulation results verify that the proposed scheme significantly outperforms conventional non-orthogonal multiple access (NOMA) approaches, and achieves superior robustness compared with benchmark schemes neglecting HWI, imperfect SIC, or amplitude-phase coupling.
Paper Structure (12 sections, 2 theorems, 28 equations, 6 figures)

This paper contains 12 sections, 2 theorems, 28 equations, 6 figures.

Table of Contents

  1. Introduction
  2. Systems Model
  3. Practical Amplitude Model
  4. Signal Model
  5. RSMA
  6. NOMA
  7. asymptotic SNR
  8. Problem Formulation and Beamforming Optimization
  9. Optimize Precoding Vector
  10. Optimize Phase-Shift Matrix
  11. Simulation Results
  12. conclusion

Key Result

Proposition 1

The ratio of the asymptotic SNR under practical RIS model and ideal RIS model is given as follows where $S$ is the truncation order of the Taylor expansion, $t \geq 1$ is a positive integer, and $k!$ is the factorial of $k$.

Figures (6)

  • Figure 1: A Practical RIS-aided RSMA system.
  • Figure 2: Asymptotic SNR versus number of the RIS elements.
  • Figure 3: Convergence of the proposed AO algorithm.
  • Figure 4: The sum rate versus transmitted power under different multiple access systems with $m_t=m_r=0.01$.
  • Figure 5: The sum rate versus $m_t, m_r, \delta_{\text{SIC}}$ or $\beta_{\min}$ for different designs and RSMA convergence characteristics.
  • ...and 1 more figures

Theorems & Definitions (2)

  • Proposition 1
  • Proposition 2