Rate-Splitting Multiple Access for Secure Near-Field Integrated Sensing and Communication

2025-11-30

AI Summary

In near-field integrated sensing and communication (ISAC) systems, fully digital architectures incur prohibitive hardware costs, while hybrid analog-digital (HAD) architectures reduce cost at the expense of beam focusing accuracy—exacerbating multi-user interference and eavesdropping vulnerability. To address this, this paper pioneers the integration of rate-splitting multiple access (RSMA) into near-field ISAC, proposing a common-stream-based co-design: a single shared stream simultaneously enables interference management, artificial-noise-assisted physical-layer security, and sensing signal generation. The optimization problem is decomposed via block coordinate descent, and digital and analog beamformers are solved in closed form per stage using weighted minimum mean-square error (WMMSE), quadratic transformation, and Taylor series expansion. Experiments demonstrate that, with a 16× reduction in RF chains, the proposed scheme achieves performance close to the fully digital benchmark; secrecy rate improves significantly, sensing accuracy reaches millimeter-level precision, and security guarantees remain intact.

Technology Category

• Search and Optimization: Mixed Discrete/Continuous Search
• Intelligent Robots: Multimodal Perception & Sensor Fusion
• Machine Learning: Hardware-aware ML

Application Category

• Security and Privacy: Large-scale security measurements
• Systems and Infrastructure for Web, Mobile and WoT: Web applications in cross-disciplinary domains and verticals such as mixed reality, smart cities, and digital health
• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG

Abstract

Near-field integrated sensing and communication (ISAC) leverages distance-dependent channel variations for joint distance and angle estimation. However, full-digital architectures have prohibitive hardware costs, making hybrid analog-digital (HAD) designs the primary alternative. Nevertheless, such architectures compromise beamfocusing precision and lead to energy leakage, which exacerbates inter-user interference and increases eavesdropping risks. To address these challenges, this paper proposes a rate-splitting multiple access (RSMA)-enhanced secure transmit scheme for near-field ISAC. For the first time, it exploits the common stream in RSMA to concurrently (i) flexibly manage interference, (ii) act as artificial noise to suppress eavesdropping, and (iii) serve as sensing sequences. The objective is to maximize the minimum secrecy rate while satisfying the angle and distance Cramer-Rao Bound (CRB) constraints. This results in a hard, non-convex optimization problem, and we employ block coordinate descent to decompose it into three sub-problems with lower computational complexity. In the first stage of optimizing fully digital beamfocusers, we develop an iterative solution using weighted minimum mean-squared error (WMMSE), quadratic transform, and Taylor expansion methods, thus avoiding conventional semidefinite relaxation. In the second and third stages, the analog and digital beamfocusers are optimized in closed form. Simulation results show that the proposed scheme (1) achieves near full-digital beamfocusing performance with a 16-fold reduction in RF chains, (2) provides superior secrecy performance compared to conventional beamfocusing-only and far-field security schemes, and (3) enables high-accuracy sensing with negligible loss in secrecy performance.

Problem

• Addresses hardware cost and security issues in near-field ISAC systems
• Manages interference and eavesdropping using RSMA's common stream
• Maximizes secrecy rate under sensing accuracy constraints efficiently

Innovation

• RSMA common stream manages interference, noise, sensing
• Block coordinate descent with WMMSE, quadratic, Taylor methods
• Hybrid analog-digital achieves near full-digital performance with fewer RF chains