Hybrid Beamfocusing Design for RSMA-Enhanced Near-Field Secure Communications

2025-11-30

AI Summary

To address the limited physical-layer security caused by insufficient beam focusing accuracy under near-field spherical wavefronts in hybrid analog-digital (HAD) antenna architectures, this paper proposes a joint optimization framework integrating rate-splitting multiple access (RSMA) with hybrid beam focusing. Innovatively, the RSMA common stream is jointly leveraged for both information transmission and artificial noise generation to enhance near-field secrecy. A penalty-based alternating optimization algorithm is designed to jointly optimize analog/digital beamforming and common-stream power allocation. The theoretical model rigorously incorporates near-field spherical wavefronts, full-connection and sub-connection HAD architectures, and employs closed-form solutions to improve computational efficiency. Simulation results demonstrate that the proposed scheme achieves performance close to fully digital systems while significantly reducing the number of radio-frequency chains; it attains up to a 42.7% improvement in minimum secrecy rate over conventional far-field and pure beam-focusing baselines, without compromising high communication rates.

Technology Category

• Search and Optimization: Mixed Discrete/Continuous Search
• Machine Learning: Hardware-aware ML
• Constraint Satisfaction and Optimization: Mixed Discrete/Continuous Optimization

Application Category

• Security and Privacy: Large-scale security measurements
• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications
• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines

Abstract

Near-field spherical wavefronts enable spotlight-like beam focusing to mitigate unintended energy leakage, creating new opportunities for physical-layer security (PLS). However, under hybrid analog-digital (HAD) antenna architectures, beamfocusing alone may not provide foolproof privacy protection due to reduced focusing precision. To address this issue, this paper proposes a rate-splitting multiple access (RSMA)-enhanced secure transmit scheme for near-field communications with fully-connected or sub-connected HAD architectures. In the proposed scheme, the common stream is designed for dual purposes, delivering the desired message for legitimate users while acting as artificial noise to disrupt eavesdropping. The primary objective is to maximize the minimum secrecy rate by jointly optimizing the analog beamfocuser, digital beamfocuser, and common secrecy rate allocation. To solve the formulated non-convex problem, we develop a penalty-based alternating optimization algorithm. Specifically, the variables are partitioned into three blocks, where one block is solved via a surrogate optimization method, while the others are updated in closed form. Simulation results reveal that our transmit scheme: (1) approaches fully digital beamfocusing with substantially fewer radio frequency chains, (2) outperforms conventional beamfocusing-only and far-field security schemes, and (3) preserves secrecy without significantly compromising communication rates.

Problem

• Enhances near-field secure communications using RSMA and hybrid beamfocusing
• Maximizes secrecy rates by optimizing analog and digital beamfocusers jointly
• Reduces RF chains while maintaining performance and preventing eavesdropping

Innovation

• RSMA-enhanced secure transmit scheme for near-field communications
• Penalty-based alternating optimization algorithm for non-convex problem
• Common stream acts as dual-purpose message and artificial noise