Reconfigurable Intelligent Surfaces will be essential for 6G

Reconfigurable intelligent surfaces, similar to ‘smart mirrors’, have the ability to transform ordinary walls and surfaces into intelligent elements for wireless communication. And this will be crucial for 6G.

The higher frequency waves used by 6G networks are much more likely to be absorbed, reflected or scattered by obstacles such as buildings, vehicles and trees. Therefore, higher frequency bands cannot benefit from the multipath effects experienced by lower frequency bands. As a result, there are significant concerns about the application of high-frequency 6G services in urban areas and other areas with obstacles.

Historically, interference problems have been solved by developing more efficient transmitters and receivers, such as MIMO (Multiple Input and Multiple Output), as well as by compensating for signal losses at the end points of a radio channel. However, operators have begun to reach the limits of these solutions, requiring them to innovate new solutions for high-frequency 6G applications.

Specifically, operators must also begin to create an intelligent electromagnetic environment to mitigate the impacts of interference at higher frequencies. For this, the development of RIS (Reconfigurable Intelligent Surfaces), which use metamaterials to design wireless channels, will be key.

Metamaterials are synthetic composite materials with unique electromagnetic properties. RIS are made up of hundreds of thousands of metamaterial elements called unit cells, which consist of metallic and dielectric layers, plus at least one switch or other adjustable component. These unit cells are switched on or off to determine how the RIS will adjust the properties of the waves, such as phase, polarisation and amplitude, as each wave is reflected or refracted by the surface.

What’s more, by deploying RIS it’s possible to establish an intelligent wireless environment:

1 – extend signal coverage in complex wireless environments – In scenarios where the direct link from transmitter to receiver is too weak due to blockages, RIS can be deployed to provide an additional reflected link and build wireless communications.

2 – increase spectrum efficiency – RIS can strengthen the end-to-end link between transmitter and receiver. As the noise introduced by RISs is negligible, the desired signals can reach the receiver with high power, improving channel capacity.

3 – ensure energy efficiency, without the need for high-power RF components such as a power amplifier, ADC/DAC, etc – RIS passively reflects incident signals with low power consumption.

In short, a RIS is similar to a natural full-duplex relay, but with almost zero DC power consumption, which offers a promising solution for low-power communications. Benefiting from their high matrix gain, low cost and low power consumption, RIS are expected to greatly extend signal coverage, improve system capacity and increase energy efficiency.

As 6G standards become clearer by 2025, RIS technology should be considered an immediate priority for development. However, due to the wide geographical areas of some 6G networks, operators must implement AI to monitor and adjust the RIS configuration in real time to maximise the benefits of the technology.

The use of high-frequency spectrum in 6G will be the main enabling technology for delivering transfer speeds 100 times faster than current 5G networks. However, as cellular technologies have never used spectrum bands in this range before, the most pressing concern for operators is to minimise this network interference or risk creating an unreliable 6G network.

First, RIS will deal with subterrahertz and then add terahertz, near infrared and optical frequencies. They will even enhance base stations and appear in the stratosphere on idle solar drones. There is rapid progress in the manufacture of intelligent RIS materials capable of 360 degrees in all directions, invisible, durable, self-adaptive, self-powered and even multifunctional, adding sensing, positioning, operation of unpowered client devices and other business cases.

Expert advice

To utilise RIS effectively to reduce the impact of interference on higher frequency 6G services, Juniper Research recommends that operators develop models to map coverage areas and identify the optimal placement of RIS units in urban areas. These models will allow operators to carry out cost-benefit analyses for RIS deployments, ensuring that there is a business case for specific deployments. These analyses must take into account the disparity in connectivity prices for businesses and consumers, otherwise the return on investment for operators in RIS deployments could be incorrectly calculated.

In addition, before deployment, operators and suppliers should explore different RIS designs so that they can optimise their impact in different contexts, such as different frequency bands and environments. This will allow operators to offer 6G services at higher frequencies more efficiently in various circumstances, such as indoors, thus maximising revenue.