NCR vs. Passive/Active RIS: How Much NCR Amplification is Required to Beat RIS?

2026-03-20

AI Summary

This study investigates the performance limits of network-controlled repeaters (NCRs) and passive/active reconfigurable intelligent surfaces (RISs) in enhancing uplink signal-to-noise ratio (SNR). Under line-of-sight propagation assumptions, closed-form SNR expressions are derived for narrowband and broadband scenarios, with and without direct links, across three assistance schemes. Theoretical analysis reveals that RIS-assisted SNR grows unboundedly with the number of reflecting elements, whereas NCR performance is fundamentally limited by noise amplification along the user–relay link. When the NCR is deployed near the user, it outperforms RIS only if its gain exceeds a specific threshold. System-level modeling and simulations quantify the required NCR gain to surpass both passive and active RIS under varying deployment geometries and system scales, offering practical design guidelines for the synergistic deployment of RIS and NCR technologies.

Technology Category

• Intelligent Robots: Multi-Robot Systems
• Planning, Routing, and Scheduling: Replanning and Plan Repair
• Cognitive Modeling & Cognitive Systems: Applications

Application Category

• Search and Retrieval-Augmented AI: Assisted, interactive, and conversational search
• 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

This paper investigates the fundamental tradeoff between reconfigurable intelligent surfaces (RISs) and network-controlled repeaters (NCRs) in terms of achievable signal-to-noise ratio (SNR). Considering an uplink system with a multi-antenna base station (BS) and a single-antenna user equipment (UE), we derive closed-form SNR expressions for passive RIS-, active RIS-, and NCR-assisted communication under line-of-sight propagation between the BS-RIS/NCR and RIS/NCR-UE. Both narrowband and wideband transmissions are analyzed, with and without the presence of a direct BS--UE link. Our analysis reveals a key structural difference: while the SNR achieved with RISs grows unboundedly with the number of RIS elements, the SNR provided by an NCR is fundamentally limited by the UE--repeater channel due to noise amplification. Nevertheless, we show that NCRs can outperform both passive and active RISs when deployed close to the UE, provided that sufficient amplification is available. Numerical results based on realistic path loss models quantify the amplification levels required for NCRs to outperform RISs across different deployment geometries and system dimensions. These findings provide clear design guidelines for the practical integration of RISs and NCRs in future wireless networks.

Problem

• Reconfigurable Intelligent Surface
• Network-Controlled Repeater
• Signal-to-Noise Ratio
• Amplification Gain
• Wireless Communication

Innovation

• Reconfigurable Intelligent Surface
• Network-Controlled Repeater
• Signal-to-Noise Ratio
• Amplification Gain
• Wireless Communication