Reconfigurable Intelligent Surfaces (RIS): The Smart Walls of 6G

Wireless networks have always adapted to their environment reactively — designing around obstacles, compensating for reflections, fighting interference. Reconfigurable Intelligent Surfaces invert this relationship. Instead of adapting the signal to the environment, RIS adapts the environment to the signal. This article is produced by the 7G Network editorial team, which tracks emerging wireless technologies including terahertz communication and next-generation network architectures.

The idea is deceptively simple: cover surfaces — walls, ceilings, windows, building facades — with electronically controlled metasurface panels that can reflect, refract, or focus radio waves on demand. The result is a programmable wireless environment where coverage holes disappear, interference is steered away, and signal quality improves without adding more base stations or transmit power.

How RIS Works

A Reconfigurable Intelligent Surface consists of hundreds to thousands of sub-wavelength elements, each containing a tunable component such as a PIN diode or varactor, that collectively steer radio waves through coordinated phase shifting — functioning like passive beamforming without RF chains or power amplifiers.

A Reconfigurable Intelligent Surface is a thin panel composed of hundreds to thousands of sub-wavelength elements — each smaller than the radio waves they manipulate. Each element contains a tunable component (typically a PIN diode or varactor) that can shift the phase of the incoming signal by a controlled amount.

By coordinating the phase shifts across all elements, the surface creates constructive interference in desired directions and destructive interference elsewhere. The effect is similar to beamforming in a massive MIMO antenna, but with two critical differences:

• Passive operation: A basic RIS does not generate radio signals — it only reflects and redirects existing ones. This means no power amplifiers, no RF chains, and power consumption orders of magnitude lower than a base station. A typical RIS panel consumes watts, not kilowatts.
• No backhaul required: Because it does not generate traffic, a RIS panel needs no fiber connection to the core network. It requires only a low-bandwidth control link (often wireless) to receive beamforming instructions from the base station.

The control is real-time: as users move, the base station recalculates optimal phase configurations and updates the RIS panel within milliseconds. The surface continuously adapts to serve current traffic patterns. This real-time adaptability is central to how AI-native RAN architectures will manage 6G networks.

Why 6G Needs RIS

6G networks operating above 100 GHz face severe propagation challenges — signals cannot penetrate walls, are blocked by human bodies, and are absorbed by moisture. RIS addresses this by redirecting existing signals around obstacles without additional transmit power or spectrum.

The physics of 6G create a coverage problem that RIS is uniquely suited to solve.

6G will use frequencies above 100 GHz — sub-terahertz spectrum that offers enormous bandwidth but suffers from severe propagation challenges. At these frequencies, signals cannot penetrate walls. They are blocked by human bodies. They are absorbed by rain and humidity. Every obstacle creates a hard shadow. According to Samsung Research (2023), sub-THz path loss is 20-30 dB higher than mmWave at equivalent distances.

Traditional solutions — more base stations, higher transmit power, more antennas — are expensive, power-hungry, and face diminishing returns in dense environments. RIS offers an alternative: instead of blasting more signal, redirect the signal that already exists around obstacles.

Consider a scenario: a sub-THz base station serves an open-plan office. A user walks behind a pillar and loses line of sight. Without RIS, the connection drops or degrades severely. With RIS panels on the ceiling, the signal is reflected around the pillar to maintain coverage — using zero additional transmit power and requiring no additional spectrum.

RIS Architectures: Passive, Active, and Beyond

RIS technology has evolved beyond simple passive reflection into multiple architectures: active RIS with built-in amplifiers, STAR-RIS enabling simultaneous transmission and reflection for 360-degree coverage, and beyond-diagonal RIS with inter-element coupling for advanced wavefront control.

The basic RIS described above is passive — it only reflects. But research has rapidly expanded to more capable variants:

Active RIS: Each element includes a low-noise amplifier that boosts the reflected signal. This overcomes the "double path loss" problem of passive RIS (the signal must travel from base station to surface, then from surface to user, losing power twice). Active RIS consumes more power but can extend coverage significantly further. According to IEEE Communications Surveys & Tutorials (2024), active RIS can achieve 10-15 dB gain over passive counterparts.

STAR-RIS (Simultaneous Transmitting and Reflecting): These surfaces can simultaneously reflect signals on one side and transmit them through to the other side — providing full-space, 360-degree coverage. A STAR-RIS mounted on a window could serve users both inside and outside a building from a single panel.

Beyond-Diagonal RIS: Conventional RIS uses diagonal phase-shift matrices — each element operates independently. Beyond-diagonal RIS introduces coupling between elements, enabling more sophisticated wavefront control at the cost of increased hardware complexity.

Morphing RIS: Surfaces that can physically change shape — curving, tilting, or folding — to optimize their geometry for current conditions. This is primarily a research concept, but prototypes exist.

Current Prototypes and Field Trials

Multiple organizations have moved RIS from simulation to physical hardware: Rohde & Schwarz and Greenerwave demonstrated mmWave RIS improvements in real-world conditions, while the EU RISE-6G project (2021-2023) produced prototypes now feeding into ETSI standardization.

RIS has moved beyond simulation into physical hardware:

Rohde & Schwarz and Greenerwave completed a groundbreaking measurement campaign with a novel FR2 (mmWave band) RIS module, confirming improvements in coverage and energy efficiency in real-world conditions. This was one of the first rigorous over-the-air demonstrations that validated simulation predictions.

The EU's RISE-6G project (2021-2023) produced multiple RIS prototypes and established measurement methodologies that are now feeding into ETSI standardization discussions. The project demonstrated RIS-assisted localization, coverage extension, and interference management in indoor environments.

6G-LICRIS (Liquid Crystal RIS): A consortium including Rohde & Schwarz is developing RIS panels using liquid crystal technology — the same technology behind LCD screens. Liquid crystal offers continuously tunable phase shifts (not just discrete steps), potentially enabling finer beam control.

IEEE ICC 2026 (May 2026) will feature live over-the-air testbeds combining RIS-assisted links with scalable MIMO and satellite connectivity, providing a holistic demonstration of 6G network technologies.

Market Outlook

According to Zhar Research (2026), RIS for 6G communications may become the largest market for metasurfaces, with potential to create billion-dollar businesses over the 2026-2046 period, spanning transparent window RIS, aerospace RIS, and active indoor RIS segments.

According to a Zhar Research report covering 2026-2046, RIS for 6G communications may become the largest market for metasurfaces, with the potential to create billion-dollar businesses. The current priority is RIS operating at or near 5G frequencies (sub-6 GHz and mmWave), with sub-THz RIS following as 6G matures.

The market is segmented into several emerging verticals: transparent RIS for windows and glass facades, aerospace RIS for satellite-ground links, large-area RIS for outdoor coverage extension, and active RIS for indoor capacity enhancement.

Standardization Status

ETSI's Industry Specification Group on RIS (ISG RIS) is developing use cases and architecture, while 3GPP Release 20 includes RIS as a study item for 6G. Normative specifications are expected in Release 21, targeting approximately 2028.

RIS has not yet been formally standardized — but it is on the path. ETSI has an Industry Specification Group on RIS (ISG RIS) that is developing use cases, architecture, and evaluation methodologies. 3GPP Release 20 study items include RIS as a candidate technology for 6G. For the broader standardization context, see the 6G standardization timeline.

The standardization challenge is defining how a RIS panel interacts with the base station. Key open questions include:

• How does the base station acquire channel state information (CSI) for the RIS-reflected path? The surface is passive and cannot measure channels itself.
• What control protocol connects the base station to the RIS? How much bandwidth does it need? What latency is acceptable?
• How are multiple RIS panels from different vendors coordinated in the same coverage area?

These questions must be resolved in the Release 20 study phase (through 2026) for RIS to appear in Release 21 normative specifications.

RIS vs. Competing Approaches

RIS is not the only solution to 6G's coverage challenge. Its competition includes:

Small cells: Dense deployment of low-power base stations. More proven technology, but expensive to deploy (requires backhaul), consumes more power, and faces site acquisition challenges in dense urban areas.

Relays: Active devices that receive, amplify, and retransmit signals. More capable than passive RIS but require full RF chains, power, and often backhaul.

Massive MIMO upgrades: Adding more antenna elements to existing base stations. Effective but faces physical limits on array size and diminishing returns at higher element counts.

RIS complements rather than replaces these approaches. The likely 6G architecture uses macro base stations with massive MIMO for wide-area coverage, small cells for capacity hotspots, and RIS panels for coverage gap-filling and interference management — each layer doing what it does most efficiently.

The Vision: Self-Adaptive Smart Environments

The long-term vision for RIS extends beyond simple signal reflection. Researchers envision surfaces that are self-powered (harvesting energy from the signals they reflect), self-learning (using embedded AI to optimize beam patterns without centralized control), and self-healing (automatically compensating when individual elements fail).

In this vision, the wireless environment itself becomes intelligent. Buildings, vehicles, and infrastructure continuously optimize radio propagation as a background function — invisible to users, requiring no manual configuration, and adapting in real time to changing conditions.

This is not science fiction, but it is not 2030 either. First-generation RIS in 6G networks will be relatively simple reflective panels controlled by base stations. The self-adaptive vision is a 7G-era goal, building on a decade of 6G operational experience.

Sources

1. Zhar Research, "Reconfigurable Intelligent Surfaces 2026-2046: Technology, Markets, Forecasts," 2026 — zharresearch.com
2. ETSI ISG RIS, "Reconfigurable Intelligent Surfaces: Use Cases, Deployment Scenarios, and Requirements," 2025 — etsi.org/committee/ris
3. 3GPP, "Release 20 Study on Reconfigurable Intelligent Surfaces," TR 38.XXX, 2025 — 3gpp.org
4. EU RISE-6G Project, "Final Report: RIS Prototypes and Measurement Methodologies," 2023 — rise-6g.eu
5. Rohde & Schwarz and Greenerwave, "Over-the-Air RIS Measurement Campaign at FR2," 2025 — rohde-schwarz.com
6. IEEE Communications Surveys & Tutorials, "Active vs. Passive RIS: Performance Comparison," Vol. 26, 2024 — ieeexplore.ieee.org
7. Samsung Research, "6G Vision: The Next Hyper-Connected Experience for All," 2023 — research.samsung.com