[Paper Review] Multi-RIS-aided Wireless Communications in Real-world: Prototyping and Field Trials

Rujing Xiong, Jianan Zhang+7 more|arXiv (Cornell University)|Mar 6, 2023

Advanced Wireless Communication Technologies4 citations

TL;DR

This paper presents a scalable sandwich architecture for one-bit RIS unit cells and a cloud-based, remotely controlled system for multi-RIS deployment. Field trials in Wi-Fi and 5G networks demonstrate up to 20 dBm signal gain and 14 dB improvement in average RSRP using two-hop RIS relaying, with power gains diminishing in later nodes of multi-hop chains.

ABSTRACT

The performance of multiple reconfigurable intelligent surfaces (RISs) receives limited attention in previous studies. This article fills this research gap by investigating the capabilities of multiple RISs in real-world networks. We propose a simplified yet highly scalable sandwich architecture for implementing one-bit unit cells, with the flexibility to accommodate multi-bit unit cells. To effectively control multiple RISs, we present a cost-effective remote-controlling scheme and develop a cloud-based RIS management system. Through a series of four field trials, we demonstrate the effectiveness of multi-hop routing schemes in establishing reliable links. Our experiments reveal significant improvements in signal strength and data transmission in multi-RIS-aided Wi-Fi and commercial 5G networks. Furthermore, we investigate the power scaling law of RIS-aided beamforming and provide insights into the roles of the later nodes in multi-hop relay chains.

Motivation & Objective

• Address the lack of real-world evaluation for multiple RISs in commercial networks.
• Design a low-power, scalable RIS architecture suitable for multi-bit and one-bit unit cells.
• Develop a cost-effective, cloud-based remote control system for managing multiple RISs.
• Demonstrate the feasibility and performance gains of multi-hop RIS relaying in real-world environments.
• Investigate the power scaling behavior and performance limitations of multi-hop RIS chains.

Proposed method

• Propose a simplified three-layer sandwich architecture with a top radiating patch, middle substrate, and bottom control layer for one-bit RIS unit cells.
• Implement tunable phase shifts using PIN diodes connected to microstrip stubs, enabling 1-bit phase control at 5.8 GHz and 3.4 GHz.
• Integrate Wi-Fi-enabled microcontrollers for remote, network-based control of multiple RISs via LAN or Internet.
• Develop a cloud-based RIS management system to centralize configuration, monitoring, and scalability.
• Conduct four field trials: two in real-world 5G networks (including a parking garage with two-hop RISs) and two in an anechoic chamber for multi-hop testing.
• Use smartphones and professional tools (Cellular-Pro, Pilot Pioneer) to collect real-time RSRP, data rates, and signal strength measurements.

Experimental results

Research questions

• RQ1 Can a scalable, low-cost RIS architecture support effective multi-RIS deployment in real-world networks?
• RQ2 How effective is remote, cloud-based control for managing multiple RISs in practical scenarios?
• RQ3 To what extent can multi-hop RIS relaying improve signal coverage and data rates in challenging environments like tunnels and parking garages?
• RQ4 What is the power scaling behavior of RIS-aided beamforming across multi-hop relay chains?
• RQ5 Why do later RIS nodes in a multi-hop chain exhibit reduced power gains compared to earlier ones?

Key findings

• The two-hop RIS deployment in a 120-meter underground parking garage improved average RSRP from -105.84 dBm to -91.87 dBm, a gain of approximately 14 dB.
• In the two-hop setup, downlink speed increased from 79.63 Mbps to 110.58 Mbps, and uplink speed from 9.99 Mbps to 17.54 Mbps.
• Along a 120-meter pathway, a single RIS boosted average signal strength from -100 dBm to -80 dBm, achieving a 20 dBm gain.
• The RIS prototype consumed only 0.2 W at peak, demonstrating low power consumption for a 10×16 one-bit unit cell array.
• Power gains in multi-hop RIS chains diminish for later nodes, indicating practical limitations in signal amplification across successive relays.
• The study confirms a direct proportionality between RIS beamforming gain and the number of unit cells, supporting a power scaling law in RIS-aided systems.