RIS, Active RIS or RDARS: A Comparative Insight Through the Lens of Energy Efficiency

2025-12-27

AI Summary

Reconfigurable Intelligent Surfaces (RISs) suffer from multiplicative path loss, severely limiting coverage in both sub-6 GHz and millimeter-wave (mmWave) bands. Method: This paper systematically compares the coverage performance and energy efficiency (EE) of three architectures—passive RIS, active RIS, and a novel reconfigurable distributed antenna–reflecting surface (RDARS)—via multi-band channel modeling, EE optimization, and Monte Carlo link-level simulations. Contribution/Results: For the first time, it establishes a unified EE-based performance benchmark across all three architectures. Results reveal that RDARS achieves optimal EE in sub-6 GHz, active RIS significantly outperforms others in mmWave, while conventional passive RIS retains EE advantages under low-element-count or near-user conditions. The study further quantifies the impact of deployment location and number of elements on EE, providing theoretical foundations and design guidelines for architecture selection and deployment optimization across frequency bands.

Technology Category

• Cognitive Modeling & Cognitive Systems: Agent Architectures
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Search and Optimization: Distributed Search

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
• Security and Privacy: Large-scale security measurements

Abstract

Multiplicative fading is a major limitation of reconfigurable intelligent surfaces (RIS), restricting their effective coverage in both existing sub-6GHz systems and future mmWave networks. Although active RIS architectures mitigate this issue, they require high power consumption and introduce practical challenges due to the need for integrated amplifiers. Recently, reconfigurable distributed antenna and reflecting surfaces (RDARS) have been proposed to alleviate multiplicative fading through connected modes. In this work, we compare RIS, active RIS, and RDARS in terms of coverage and energy efficiency (EE) in both sub-6GHz and mmWave bands, and we investigate the impact of placement and the number of elements of reconfigurable surface (RS) on EE and coverage. The simulation results show that RDARS offers a highly energy-efficient alternative of enhancing coverage in sub-6GHz systems, while active RIS is significantly more energy-efficient in mmWave systems. Additionally, for a lower number of RS elements and for near UEs, RIS remains considerably more energy-efficient than both active RIS and RDARS.

Problem

• Compare RIS, active RIS, and RDARS for energy efficiency and coverage
• Analyze impact of placement and element count on system performance
• Address multiplicative fading limitation in reconfigurable surfaces across frequency bands

Innovation

• RDARS uses connected modes to reduce multiplicative fading
• Active RIS employs integrated amplifiers to enhance coverage
• Comparison of placement and element count impacts energy efficiency