EL-RIS Empowered Multicast-Unicast Covert Communication

LÜ Lu; LIANG Qi-hui; FENG Yun-peng; YANG Long; GUAN Xin-rong

doi:10.12263/DZXB.20250532

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EL-RIS Empowered Multicast-Unicast Covert Communication

PAPERS | 更新时间：2026-02-10

- EL-RIS Empowered Multicast-Unicast Covert Communication
- ACTA ELECTRONICA SINICA Vol. 53, Issue 11, Pages: 3932-3942(2025)
- 作者机构：
  
  1.西安电子科技大学通信工程学院，陕西西安 710071
  2.西安电子科技大学广州研究院，广东广州 510555
  3.中国人民解放军陆军工程大学通信工程学院，江苏南京 210007
- 作者简介：
- 基金信息：
  
  National Natural Science Foundation of China(62271368;62171461);Fundamental Research Funds for the Central Universities(QTZX23066);Shaanxi Innovation Capability Support Program(2024RS-CXTD-01);Key Research and Development Program of Shaanxi Province(2023-ZDLGY-50)
- DOI：10.12263/DZXB.20250532
  CLC： TN92;
- Received：21 June 2025，
  
  Accepted：17 November 2025，
  
  Published：25 November 2025
- 稿件说明：
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吕璐, 梁啟辉, 冯云鹏, 等. EL-RIS赋能的混合多播-单播隐蔽通信[J]. 电子学报, 2025, 53(11): 3932-3942.

LÜ Lu, LIANG Qi-hui, FENG Yun-peng, et al. EL-RIS Empowered Multicast-Unicast Covert Communication[J]. Acta Electronica Sinica, 2025, 53(11): 3932-3942.
吕璐, 梁啟辉, 冯云鹏, 等. EL-RIS赋能的混合多播-单播隐蔽通信[J]. 电子学报, 2025, 53(11): 3932-3942. DOI：10.12263/DZXB.20250532

LÜ Lu, LIANG Qi-hui, FENG Yun-peng, et al. EL-RIS Empowered Multicast-Unicast Covert Communication[J]. Acta Electronica Sinica, 2025, 53(11): 3932-3942. DOI：10.12263/DZXB.20250532

摘要

为了克服智能超表面（Reconfigurable Intelligent Surface，RIS）辅助的隐蔽通信系统中信号的“双重衰落”和能量泄露问题，本文提出了超大规模RIS（Extremely Large-scale RIS，EL-RIS）赋能的混合多播-单播隐蔽通信系统.EL-RIS凭借其巨大的阵列规模，显著扩展了通信的近场区域，有效提升了用户的信道增益，并为隐蔽通信引入了距离自由度，显著减少了泄露在窃听者处的信号能量.多播信号用于向多个用户广播公共信息，其发射功率服从均匀分布，形成功率不确定性，单播信号承载着用户的隐蔽信息，多播信号可以为单播信号的隐蔽传输提供“掩体”，混淆窃听者的检测，有效提高隐蔽通信速率.通过EL-RIS在用户位置处实现能量聚焦，同时抑制在窃听者处的能量泄露.为了最大化该隐蔽通信系统的性能，构建了一个联合优化基站波束成形和EL-RIS反射系数的非凸优化问题，在确保隐蔽性和多播信号成功解码的前提下，最大化用户隐蔽和速率，提出一种高效的交替优化（Alternating Optimization，AO）算法框架，将原问题解耦为基站波束成形设计和EL-RIS反射系数设计两个子问题，采用加权最小均方误差算法（Weight Minimum Mean Square Error，WMMSE）对目标函数进行重构，将非凸约束转化为二阶锥（Second-Order Cone，SOC）的形式，并进一步表示为线性矩阵不等式（Linear Matrix Inequality，LMI），降低优化问题的复杂度.在EL-RIS反射系数设计中，其单元模值约束导致问题非凸且难以求解.为此，本文提出了基于交替方向乘子法（Alternating Direction Method of Multipliers，ADMM）的低复杂度算法，通过引入辅助变量，将原问题解耦，进而构建增广拉格朗日函数，将问题分解为多个易于求解的子问题，提升算法效率.仿真结果表明，所提方案的隐蔽通信速率显著优于基准方案，单播信号能量可在用户位置处实现能量聚焦，在近场信道模型下，通过EL-RIS实现的波束聚焦可使隐蔽和速率比远场模型提高57%，增加EL-RIS单元数量可进一步扩展近场区域，增强波束聚焦效果，提升通信系统对于窃听者位置变化的稳健性，在极端窃听场景下，系统仍能维持较高的隐蔽通信速率.

Abstract

This paper proposes an extremely large-scale reconfigurable intelligent surface (EL-RIS)-empowered hybrid multicast-unicast covert communication system to overcome the “double-fading” effect and energy leakage issues in conventional RIS-assisted systems. By leveraging its massive array scale

the EL-RIS significantly expands the near-field region. This expansion not only enhances the user channel gain but also introduces a distance-degree of freedom for covert communication

thereby substantially reducing the signal energy leakage to the eavesdropper. The multicast signal is used to broadcast public information to multiple users

with its transmit power following a uniform distribution

creating power uncertainty

while the unicast signal carries the users’ covert information. The multicast signal can provide a “cover” for the covert transmission of the unicast signal

confusing the eavesdropper’s detection and effectively improving the covert rate. Energy focusing is achieved at the user locations via EL-RIS

while energy leakage at the eavesdropper is suppressed. To maximize the system’s performance

we formulate a non-convex optimization problem that jointly designs the base station beamforming and the EL-RIS reflection coefficients. Aiming to maximize the users’ covert sum rate under the constraints of covertness and successful multicast signal decoding. An efficient alternating optimization (AO) algorithm is proposed

which decouples the original problem into two subproblems base station beamforming optimization and EL-RIS reflection coefficient optimization. The weighted minimum mean square error (WMMSE) algorithm is employed to reformulate the objective function

transforming the non-convex constraints into second-order cone (SOC) forms

and further representing them as linear matrix inequalities (LMI)

thereby reducing the complexity of the optimization problem. For the design of EL-RIS reflection coefficients

the unit-modulus constraints render the problem non-convex and computationally challenging. To address this

a low-complexity algorithm based on the alternating direction method of multipliers (ADMM) is proposed. By introducing auxiliary variables

the original problem is decoupled. Subsequently

an augmented Lagrangian function is constructed to decompose the problem into multiple tractable subproblems

thereby enhancing the algorithm’s computational efficiency. Simulation results demonstrate that the proposed scheme significantly outperforms benchmark schemes in terms of covert communication rate

unicast signal energy can achieve focusing at the user locations. Under the near-field channel model

the beam focusing realized by EL-RIS improves the covert sum rate by 57% compared to the far-field model. Increasing the number of EL-RIS units can further extend the near-field region

enhance the beam focusing effect

and improve the communication system’s robustness against changes in the eavesdropper’s location. Even in extreme eavesdropping scenarios

the system can maintain a high covert communication rate.

关键词

Keywords

references

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