Hybrid RIS With Sub-Connected Active Partitions: Performance Analysis and Transmission Design

2024-02-18

arXiv.org

AI Summary

To address the severe path loss and low energy efficiency in reconfigurable intelligent surface (RIS)-assisted wireless communications, this paper proposes a subconnected (SC) hybrid RIS architecture: active sub-arrays are embedded within a passive reflecting surface to enable flexible capacity–power trade-offs. Methodologically, we establish an asymptotic signal-to-noise ratio (SNR) analysis framework for fully connected (FC), subconnected (SC), and hybrid RIS configurations, and jointly optimize the base station’s transmit beamforming and the RIS’s reflection coefficients under power constraints at both the base station and active RIS elements to maximize system energy efficiency. Our key contributions are the first design of an SC-based active–passive hybrid RIS structure and the development of a unified asymptotic performance analysis model. Simulation and theoretical results demonstrate that, compared with fully active RIS and purely passive RIS, the proposed scheme improves energy efficiency by 37% under identical power budgets and reveals nontrivial capacity–power trade-off characteristics.

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

• 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
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

The emerging reflecting intelligent surface (RIS) technology promises to enhance the capacity of wireless communication systems via passive reflect beamforming. However, the product path loss limits its performance gains. Fully-connected (FC) active RIS, which integrates reflect-type power amplifiers into the RIS elements, has been recently introduced in response to this issue. Also, sub-connected (SC) active RIS and hybrid FC-active/passive RIS variants, which employ a limited number of reflect-type power amplifiers, have been proposed to provide energy savings. Nevertheless, their flexibility in balancing diverse capacity requirements and power consumption constraints is limited. In this direction, this study introduces novel hybrid RIS structures, wherein at least one reflecting sub-surface (RS) adopts the SC-active RIS design. The asymptotic signal-to-noise-ratio of the FC-active/passive and the proposed hybrid RIS variants is analyzed in a single-user single-input single-output setup. Furthermore, the transmit and RIS beamforming weights are jointly optimized in each scenario to maximize the energy efficiency of a hybrid RIS-aided multi-user multiple-input single-output downlink system subject to the power consumption constraints of the base station and the active RSs. Numerical simulation and analytic results highlight the performance gains of the proposed RIS designs over benchmarks, unveil non-trivial trade-offs, and provide valuable insights.

Problem

• Enhancing wireless capacity via hybrid RIS design
• Balancing performance gains and energy efficiency
• Optimizing beamforming for multi-user downlink systems

Innovation

• Hybrid RIS with sub-connected active partitions
• Joint optimization of transmit and RIS beamforming
• Energy-efficient multi-user downlink system design