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A Path to Smart Radio Environments: An Industrial Viewpoint on Reconfigurable Intelligent Surfaces
Ruiqi Liu, Qingqing Wu, Marco Di Renzo, Yifei Yuan
TL;DR
Existing wireless deployments face cost, energy, propagation, and complexity challenges, while RIS offers a low-cost passive approach to reconfiguring wireless channels. This paper surveys RIS industrial progress, use cases, challenges, and standardization, reporting prototype gains and outlining a path toward commercial integration. It identifies channel modeling, control, manufacturing, and standardization as central requirements for industrial feasibility.
Problem
Existing 5G approaches can require many active components, high energy and hardware costs, and greater complexity, while limited work addresses RIS commercialization and standardization challenges.
Method
The paper reviews RIS research, industrial development, use cases, practical challenges, and regional and international standardization activities from an industrial viewpoint.
Results
RIS prototypes and trials demonstrate measurable gains, including 14 dB gain at 500 meters with 1 W consumption, while standardization activities are beginning to coordinate future integration.
Takeaways & Limitations
Industrial RIS deployment depends on advances in channel modeling, estimation and feedback, real-time control, manufacturing, and standardized models, waveforms, signaling, and requirements.
Abstract
from arXiv · showhide
With both the standardization and commercialization completed in an unforeseen pace for the 5th generation (5G) wireless network, researchers, engineers and executives from the academia and the industry have turned their sights on candidate technologies to support the next generation wireless networks. Reconfigurable intelligent surfaces (RIS), sometimes referred to as intelligent reflecting surfaces (IRS), have been identified to be potential components of the future wireless networks because they can reconfigure the propagation environment for wireless signals with low-cost passive devices. In doing so, the coverage of a cell can be expected to increase significantly as well as the overall throughput of the network. RIS has not only become an attractive research area but also triggered a couple of projects to develop appropriate solutions to enable the set-up of hardware demonstrations and prototypes. In parallel, technical discussions and activities towards standardization already took off in some regions. Promoting RIS to be integrated into future commercial networks and become a commercial success requires significant standardization work taken place both at regional level standards developing organizations (SDO) and international SDOs such as the 3rd Generation Partnership Project (3GPP). While many research papers study how RIS can be used and optimized, few effort is devoted to analyzing the challenges to commercialize RIS and how RIS can be standardized. This paper intends to shed some light on RIS from an industrial viewpoint and provide a clear roadmap to make RIS industrially feasible.
I. INTRODUCTION
Existing 5G approaches face high hardware, energy, deployment, and processing costs, motivating cost-effective alternatives. RIS offers a low-cost way to reconfigure wireless propagation while remaining compatible with existing systems.
- Massive MIMO relies on many active RF chains, increasing hardware cost and energy consumption.
- Smaller cells require more active base stations and access points, further increasing operators’ expenditure.
- mmWave and THz deployments require additional active components and antennas to offset propagation loss, increasing signal-processing complexity.
- RIS uses many low-cost, nearly passive elements and a controller to shape impinging signals’ amplitudes and phases.
- Coordinated RIS scattering can reconfigure end-to-end channels into smart, programmable wireless propagation environments.
- RISs can operate as energy-efficient auxiliary devices without modifying user equipment, supporting flexibility and compatibility with legacy systems.
- The paper surveys RIS research, development, and standardization while analyzing industrial challenges and possible integration into commercial networks.
II. INDUSTRIAL PROGRESS, PROJECTS AND STANDARDIZATION
RIS industrial progress spans prototypes, research projects, white papers, collaborative initiatives, and regional standardization. Demonstrations show measurable gains, while standardization activities are beginning to coordinate future integration.
- RIS industrial development includes prototypes, white papers, funded projects, and ongoing standardization activities.
- A 28 GHz metasurface reflect-array increased downlink data rate from 60 Mbps without a reflector to 560 Mbps with one.
- RIS prototypes have demonstrated amplitude-and-phase modulation, OTA operation, and hardware-aware MIMO transmission.
- A 1,100-element RIS achieved 26 dB indoor gain, 27 dB short-range outdoor gain, and 14 dB gain at 500 meters with 1 W consumption.
- Seventeen white papers identify RIS as a candidate technology, including 11 with comprehensive RIS-focused analysis.
- Funded projects since 2012 have contributed to RIS theory and engineering, producing papers and prototypes while generating further concepts.
- IEEE ComSoc groups bring together researchers and industrial participants to discuss RIS costs and potential applications.
- Regional standardization addresses RIS channel modeling, estimation, feedback, beamforming, AI, networking protocols, use cases, and key technologies.
III. KEY USE CASES OF RIS
RISs can reconfigure wireless channels and support diverse applications by introducing additional control over propagation. Proposed use cases span coverage, capacity, reliability, sensing-related environments, and energy transfer.
- RISs adjust reflection amplitudes and phase shifts to reconfigure end-to-end channels and add degrees of freedom for network performance.
- Applications include UAV communications, mmWave coverage extension, wireless information and power transfer, and physical-layer security.
- RISs can support eMBB, URLLC, and mMTC, including high-capacity hotspots and improved coverage in stadiums, factories, shopping centers, and airports.
IV. CHALLENGES FROM THE INDUSTRIAL VIEWPOINT
RISs have substantial potential to improve cellular capacity and coverage, but practical deployment requires resolving several technical challenges.
- Wide deployment of RISs requires solving technical challenges before their potential can be realized in practical networks.
- The industrial challenge concerns translating RIS capacity and coverage potential into deployable next-generation cellular systems.
- RIS deployment readiness remains distinct from its demonstrated potential for improving system capacity and coverage.
A. Electromagnetic-Consistent Channel Models
RIS channel modeling must capture electromagnetic behavior at the element level and near-field effects caused by large surfaces. Simplified free-space models may be inadequate for many RIS-terminal links.
- A. Electromagnetic-Consistent Channel Models: RIS channel models must represent each element’s electromagnetic characteristics, because RIS performance depends on reconfiguring the propagation environment.Large RIS dimensions also create near-field effects that are uncommon in traditional transmitter-to-receiver systems.
- A. Electromagnetic-Consistent Channel Models: Free-space models using the Friis formula and independent element radiation patterns may be adequate for some line-of-sight links but ignore inter-element coupling.These simplifications are less suitable for RIS-terminal links with non-line-of-sight reflections, diffractions, or building penetration losses.
- A. Electromagnetic-Consistent Channel Models: Accurate RIS modeling requires more sophisticated element models and extensive channel measurements across sub-6GHz and millimeter-wave bands.The measurements are needed to characterize electromagnetic properties, coupling, and propagation conditions.
B. Comparison with Relays
RISs and relays can both shape wireless propagation, but they differ in hardware, processing, control, and achievable-rate tradeoffs. The paper frames their comparison around active-component cost, element gain, digital control, and RIS beamforming overhead.
- B. Comparison with Relays: Repeaters amplify and forward received RF signals, whereas L3 relays decode and regenerate them using physical- and MAC-layer processing.RISs are compared most directly with repeaters because both forward signals without digital processing.
- B. Comparison with Relays: The RIS–repeater tradeoff depends on repeater active-component cost and RIS unit gain, together with repeater digital control and RIS control overhead.These factors determine the hardware and coordination costs associated with obtaining beamforming gain.
- B. Comparison with Relays: RIS applications include UAV communication, millimeter-wave communication, simultaneous wireless information and power transfer, physical-layer security, mobile edge computing, and device-to-device systems.These use cases are illustrated as representative applications of RIS-assisted wireless networks.
- B. Comparison with Relays: A preliminary study compares achievable rates versus distance for an RIS and a half-duplex repeater using joint optimization of transmit beamforming and RIS reflection coefficients.The comparison uses an alternating optimization algorithm and an ITU Urban Micro path-loss model.
C. Practical Issues at the Physical Layer
RIS deployment introduces physical-layer challenges in channel estimation, scheduling, control signaling, and infrastructure. These challenges arise from nearly-passive operation, large element counts, and flexible deployment requirements.
- C. Practical Issues at the Physical Layer: Nearly-passive RISs expose only the cascaded transmitter-to-RIS-to-receiver channel, making efficient channel-estimation algorithms and protocols necessary to limit overhead.Their phase control range and quantization levels may also be limited compared with active RF devices.
- C. Practical Issues at the Physical Layer: RIS-aware scheduling requires base stations to know RIS presence and may require terminals to receive additional control signaling when RISs are not transparent.The large number of RIS elements also increases the complexity of resource-scheduling algorithms.
- C. Practical Issues at the Physical Layer: Flexible RIS deployment is constrained by wired and power-line limitations, so control signaling must operate with low power consumption and low complexity.This requirement complements algorithmic work on channel estimation and signal processing.
D. Control of the Frequency Bands
RISs generally lack digital or RF chains for fine frequency discrimination, creating interference risks between adjacent operator bands and limiting frequency-selective scheduling.
- D. Control of the Frequency Bands: Without digital or RF chains, an RIS cannot discriminate incident signals finely according to frequency band.Passive beamforming may therefore affect signals beyond the intended operator’s allocation.
- D. Control of the Frequency Bands: An RIS serving one operator can inadvertently disrupt another operator when their allocated frequency bands are adjacent.The interference results from passive beamforming across insufficiently selective frequency bands.
- D. Control of the Frequency Bands: RIS frequency selection may be less granular than the several-hundred-kilohertz resolution available from active RF filters, limiting frequency-selective scheduling.This constrains the performance potential of RIS-based frequency control.
E. Manufacturing of Metasurface-based RISs
Manufacturing metasurface-based RISs must balance large-scale, low-cost construction with consistent electromagnetic performance and long-term outdoor durability.
- RISs generally need hundreds of low-cost elements to compensate for link-budget deficits caused by their nearly-passive implementation.The absence of power amplifiers creates the deficit that the large element count must offset.
- Reflecting elements need consistent electrical properties across wide incidence and reflection angles to serve terminals in different cell locations.
- Outdoor RIS deployments must withstand sunlight, temperature changes, wind, rain, ice, snow, and pollution for months or years without significant electromagnetic deterioration.
V. STANDARDIZATION OF RISS: FORECASTED ROADMAP
RIS standardization is progressing from research and prototypes through regional activities toward possible 3GPP integration. The roadmap presents earlier 5G-Advanced adoption versus later 6G standardization, with timing constrained by technical maturity.
- Standardization typically progresses from academic and industrial research through prototypes, regional study items, international work items, and released technical specifications.The released specifications mark the technology’s official inclusion in global standards.
- Industry prototypes expected from 2020 provide firsthand cellular-network performance data for researchers and engineers.
- Regional RIS studies are already underway, while an ITU 6G-trends report was expected in June 2022 to describe RISs as a critical physical-layer component.
- 3GPP discussions on 6G systems were reasonably expected to begin after 2026, given the approximately decade-long duration of wireless generations and the 2016 start of 5G working groups.
- One pathway would study RIS scenarios and channel models in Release 18 and define a work item in Release 19, enabling possible 5G-Advanced deployment; another would defer RIS to 6G.
- RIS timing depends on unresolved technical problems and technology maturity, although a first 3GPP proposal in March 2021 made late 2021 the earliest possible start for a study item.
- ETSI approved an RIS industry specification group in June 2021, with activities scheduled to begin in September 2021 to coordinate pre-standardization research.
VI. CONCLUSIONS
RISs can create smart radio environments with lower power consumption and cost, but broader deployment still requires technical advances and standardization of key interfaces and performance requirements.
- RISs can manipulate propagation channels and enable smart radio environments at reduced power consumption and cost.
- Research challenges include channel modeling, channel estimation and feedback, and real-time RIS control.
- Standardization needs to address channel models, waveforms, control signaling, and performance requirements using available spectrum, technology, and test solutions.