Location-Aided Distributed Beamforming for Near-Field Communications with Element-Wise RIS

2025-10-15

AI Summary

To address the challenges of channel estimation difficulty and discrete phase-shift constraints for zero-power active reconfigurable intelligent surfaces (RIS) in near-field communications, this paper proposes a location-aided distributed beamforming scheme. Leveraging a novel unit-level RIS architecture, it establishes a mapping from spatial positions to phase distributions, enabling a channel-estimation-free “phase-setting-then-alignment” beamforming mechanism. By integrating dynamic element selection with low-complexity reflection gain optimization, the scheme significantly reduces system overhead without requiring the base station to acquire RIS channel state information. Theoretical analysis demonstrates that the proposed approach asymptotically achieves optimal array gain under large-scale RIS configurations. Simulation results confirm superior reflection gain and link performance compared to state-of-the-art methods.

Technology Category

• Search and Optimization: Distributed Search
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization

Application Category

• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Security and Privacy: Large-scale security measurements

Abstract

Active reconfigurable intelligent surface (RIS) emerges as an effective technique to resist the double-fading attenuation of passive RIS. By embedding with power harvesting function, it further evolves to zero-power active RIS, which can effectively enhance the flexibility of RIS deployment without external power demand. Nevertheless, existing works neglected the inherent difficulty of channel estimation (CE) for RIS-assisted systems, and the discrete phase shift constraint in practical deployment. In this paper we design a new element-wise RIS architecture and propose a distributed location-aided transmission scheme with low complexity to enhance the reflected gain for channel state information (CSI)-limited RIS-assisted near-field communications. Specifically, the new element-wise RIS provides dynamic element selection capability with low hardware resources. Based on Fresnel diffraction theory, we construct the mapping from locations in space-domain to phase distributions of waves in phase-domain and reveal the priority of elements for harvesting and reflecting. {Then, the distributed beamforming design with the phase of determine-then-align is proposed, where the estimation overhead reduction stems from exempted requirements of RIS-associated CE at base station (BS).} The asymptotic analysis indicates that the proposed scheme can achieve the optimal gain with a fixed proportion of reflective elements when RIS is large, followed by simulations to verify its superiority to other protocols.

Problem

• Addresses channel estimation difficulty in RIS-assisted near-field communication systems
• Solves discrete phase shift constraints in practical RIS deployment scenarios
• Enhances reflected gain for CSI-limited communications with low complexity

Innovation

• Element-wise RIS with dynamic element selection
• Location-aided beamforming using Fresnel diffraction theory
• Distributed phase design eliminating RIS channel estimation