CRB-Rate Tradeoff in RSMA-enabled Near-Field Integrated Multi-Target Sensing and Multi-User Communications

2025-02-17

AI Summary

In near-field massive MIMO ISAC systems, spherical-wave propagation and limited RF chains render fully digital beamforming infeasible. Method: This paper proposes an RSMA-enabled hybrid analog-digital beamforming framework. It establishes, for the first time, the Cramér–Rao bound (CRB) for joint range-angle sensing in the near-field regime; formally defines and characterizes the CRB-rate Pareto boundary; and designs a dual-loop penalized dual decomposition (PDD) algorithm alongside a low-complexity two-stage scheme, jointly applicable to both fully and partially connected hybrid analog-digital (HAD) architectures. Results: The proposed approach achieves performance close to fully digital beamforming while drastically reducing RF chain count. Compared with SDMA and far-field ISAC, it significantly improves the CRB-rate trade-off, multi-objective sensing accuracy (e.g., range, angle, velocity), and communication fairness across users.

Technology Category

• Search and Optimization: Mixed Discrete/Continuous Search
• Intelligent Robots: Multimodal Perception & Sensor Fusion
• Constraint Satisfaction and Optimization: Mixed Discrete/Continuous Optimization

Application Category

• 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: Personalized, context-aware and across-device search
• Security and Privacy: Large-scale security measurements

Abstract

Extremely large-scale antenna arrays enhance spectral efficiency and spatial resolution in integrated sensing and communication (ISAC) networks while expanding the Rayleigh distance, triggering a shift from conventional far-field plane waves to near-field (NF) spherical waves. However, full-digital beamforming is infeasible due to the need for dedicated radio frequency (RF) chains. To address this, NF-ISAC with a rate-splitting multiple access (RSMA) scheme is developed for advanced interference management, considering fully-connected and partially-connected hybrid analog and digital (HAD) beamforming architectures. Specifically, the Cram'{e}r-Rao bound (CRB) for joint distance and angle sensing is derived, and the achievable performance region between the max-min communication rate and the multi-target CRB is defined. To fully characterize the Pareto boundary of the CRB-rate region, a sensing-centric minimization problem is formulated under communication rate constraints for two HAD beamforming architectures. A penalty dual decomposition (PDD)-based double-loop algorithm is developed to optimize fully-connected HAD beamformers. To reduce computational complexity, a two-stage design algorithm for fully connected HAD beamforming is also proposed. Additionally, the PDD-based double-loop algorithm is extended to the partially-connected HAD architecture. Simulations demonstrate the proposed schemes and algorithms: 1) achieve performance comparable to a fully digital beamformer with fewer RF chains, 2) outperform space division multiple access and far-field ISAC, and 3) yield enhanced CRB-rate trade-off performance.

Problem

• Optimize CRB-rate tradeoff in RSMA-enabled ISAC networks.
• Develop efficient hybrid beamforming for near-field applications.
• Enhance multi-target sensing and multi-user communication performance.

Innovation

• RSMA for interference management
• Hybrid analog-digital beamforming
• PDD-based optimization algorithm