Hybrid Beamfocusing Design for RSMA-Enabled Near-Field Wideband Communications

2025-12-04

AI Summary

Near-field broadband communication for extremely large-scale antenna arrays (ELAA) operating at high frequencies suffers from channel frequency-selective mismatch caused by spherical wavefronts and spatial-wideband effects. To address this, we propose a transmit scheme integrating rate-splitting multiple access (RSMA) with true-time-delay (TTD)-assisted hybrid beam focusing. The scheme jointly optimizes frequency-dependent and frequency-independent analog beams, digital beams, and common-rate allocation to maximize the minimum user rate. Our key contributions are: (i) the first application of RSMA to near-field broadband scenarios; (ii) the design of a TTD-based hybrid architecture supporting sub-connected RF topologies; and (iii) an efficient optimization framework leveraging block coordinate descent combined with penalty-based iterative methods. Simulation results demonstrate that the proposed scheme effectively mitigates spatial-wideband distortion, achieves performance comparable to fully digital solutions, significantly outperforms existing benchmarks, and substantially reduces RF chain complexity.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Search and Optimization: Mixed Discrete/Continuous Search
• Multiagent Systems: Agent Communication

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines
• Responsible Web: Data and user privacy-enhancing technologies for the Web

Abstract

Future wireless networks will utilize extremely large-scale antenna arrays (ELAAs) over high-frequency bands, which, however, produce near-field spherical wavefronts and spatial wideband effects. To exploit and mitigate these, this paper proposes a rate-splitting multiple access (RSMA)-enabled transmit scheme for wideband near-field communications (NFC). Our solution leverages true-time-delay (TTD)-based hybrid beamfocusing architectures to mitigate spatial wideband effect and reduce radio frequency chain requirements. The objective is to maximize the minimum rate by jointly optimizing frequency-dependent analog beamfocusing, frequency-independent analog beamfocusing, digital beamfocusing, and common rate allocation. To solve this complicated non-convex problem, we develop a penalty-based iterative algorithm that partitions the variables into three blocks and then employs block coordinate descent (BCD) to optimize each block alternately. This algorithm is further extended to support the sub-connected TTD-based analog beamfocusing architectures. Comprehensive simulation results indicate that our transmit scheme: 1) effectively compensates for spatial wideband effect, addressing a critical challenge in wideband operation; 2) achieves performance comparable to full digital beamfocusing while maintaining lower hardware complexity; 3) achieves substantial performance gains over the other two benchmarks.

Problem

• Mitigates near-field spatial wideband effects in large antenna arrays
• Reduces hardware complexity while maintaining high performance
• Optimizes beamfocusing and rate allocation for wideband near-field communications

Innovation

• Hybrid beamfocusing with TTD for spatial wideband mitigation
• Penalty-based iterative BCD algorithm for joint optimization
• Sub-connected TTD analog architecture for reduced hardware complexity