Cylindrical RIS-Assisted Low-Complexity Transmission with Differentiated Visible Regions Exploiting Statistical CSI

2025-08-17

AI Summary

To address the high-dimensional optimization challenge and persistent signal coupling caused by shared reflection in multi-user Reconfigurable Intelligent Surface (RIS)-assisted low-altitude communications for 6G, this paper proposes a line-of-sight (LoS) region differentiation mechanism based on a uniform cylindrical RIS array. The RIS is partitioned into user-dedicated and shared subunits, enabling decoupled beamforming via closed-form phase solutions for dedicated units and lightweight iterative optimization for shared units. Our key innovation lies in the first exploitation of cylindrical geometry to achieve spatial LoS-region partitioning, coupled with a hybrid control strategy designed using statistical channel state information (CSI), thereby significantly reducing optimization dimensionality without compromising performance. Simulation results demonstrate that, under comparable sum-rate performance, the proposed method reduces computational overhead by over 60% relative to conventional planar RIS schemes, offering both high efficiency and scalability.

Technology Category

• Search and Optimization: Mixed Discrete/Continuous Search
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Intelligent Robots: Learning & Optimization for ROB

Application Category

• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• 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: Vertical and domain-specific search

Abstract

Reconfigurable intelligent surfaces (RIS), recognized as a critical enabler for 6G networks, exhibit unprecedented capabilities in electromagnetic wave manipulation and wireless channel reconfiguration. By leveraging existing network infrastructure, RIS can cost-effectively create signal hotspots in low-altitude environments, ensuring robust connectivity to support the sustainable development of the low-altitude economy. However, achieving optimal phase shift design in multi-user scenarios faces two major challenges: the high-dimensional optimization introduced by massive RIS elements, and the persistent coupling of multi-user signals caused by shared RIS reflections. This paper utilize the visible region of an RIS arranged as the uniform cylindrical array (UCA) to reduce the complexity of phase shift design. Under the UCA architecture, RIS elements are categorized into two types: user-specific units and multi-user shared units. We then determine the optimal phase shifts by iteratively optimizing the phase shifts of multi-user shared units while directly configuring those of user-specific units based on a derived closed-form solution. The proposed approach significantly reduces optimization complexity, which is further corroborated by numerical simulation results demonstrating its substantial impact on both system performance and computational efficiency compared to the conventional RIS with uniform planar array.

Problem

• Reducing phase shift design complexity in RIS
• Decoupling multi-user signals in RIS-assisted networks
• Optimizing RIS elements for differentiated visible regions

Innovation

• Cylindrical RIS reduces phase shift complexity
• Iterative optimization for multi-user shared units
• Closed-form solution for user-specific units