What are Reconfigurable Intelligent Surfaces?

Understanding the latest industry technology to get its own ETSI ISG.

ETSI has formed a new Group to look at developing standards for an emerging type of radio antenna node.

Next generation antennas knowns as Reconfigurable Intelligent Surfaces (RIS) are being proposed as a new way to deliver radio network coverage.

So what is RIS, and what could they be used for? Arman Shojaeifard, from Interdigital, has been selected as Chair of the new RIS ISG (Industry Specifications Group). He told TMN that the antennas are in an early stage of development, but there is considerable R&D activity already looking at the technology.

Shojaeifard said, “A RIS is a new network node that makes use of smart radio surface technology: planar structures that are engineered with certain properties to allow a controller to dynamically able the adjust overall phase response, and control EMW properties such as reflection, refraction and absorption.”

“In a broader sense these elements typically have certain configurations that can play around with the properties of the cell, adjusting the phase of the waves that arrive at the RIS surface to make them reflect in a certain direction,” Shojaeifard added. That means the nodes can be controlled in real time to adapt to the environment or a specific use case.

The nodes consist of a number of layers, with an external layer of a number of passive metallic antenna elements, then a thin layer of copper, with an interior of circuitry used for controlling the antenna elements. Importantly, the proposal is for a link back to a controller in the network that provides the configuration signalling. The location of this controller and the signalling protocols are yet to  be fixed and will form part of the work of the ISG, as well as the specifications for the nodes themselves. As you’d expect, there is talk of ML and AI-based controllers providing the necessary output to the radio node.

A RIS will probably look much like existing nodes, your classic thin rectangle, although there is talk of being able to design them in more flexible shapes and forms, and in terms of their usage Shojaeifard placed them alongside massive MIMO, small cells, fully stacked cells and repeaters in the network toolkit.

“The intention for RIS is to fill in gaps for key challenges – one being around coverage enhancements. Essentially operators will face an ongoing challenge of congestion in Sub 6GHz bands, and then as they move up the frequencies they face more challenging propagation issues. So the challenge is to find cost efficient solutions to improve coverage;  RIS is on the radar in terms of providing improvements to existing systems and ensuring coverage of future systems. 

We are indeed  likely to see RIS a a key for higher frequency bands but they will be equally important for sub 6GHz

“One of its main characteristic is that is can be configured to operate at any part of radio spectrum. There’s a lot of mention of these surfaces being enabled for use higher bands like sub THz and THz, but importantly our feedback from MNOs is that they are looking at RIS in the short to midterm as a way to achieve further efficiencies over sub 6 GHz deployments. We are indeed  likely to see RIS a a key for higher frequency bands but they will be equally important for sub 6GHz.”

Going forward, there could be further uses for the reconfigurable surfaces, such as sensing.

“There are already a lot of R&D designs for these surfaces with various flavours of meta surface elements and components. So although it is early days for RIS as a candidate technology for future wireless systems, they have already attracted a lot of attention in the research community, with several collaborations and innovation happening. But we are still very much asking those questions such as; what are candidate use cases, how will they be manufactured, are they going to be cost effective and passive? These are all remaining challenges that need be addressed before the technology goes into the standardisation phase.”

Shojaeifard said that the ISG would “focus on identifying the relevant use cases and deployment scenarios.” It will also identify “where the technology is at, what are the gaps in terms of the electronics, signal processing and signalling” and then document all these requirements, identifying standardisation gaps that must be filled and created in order for RIS to work in way that is intended to do.

You can see the page for the RIS ISG here. Alongside Interdigital’s Shojaeifard, Richie Leo from ZTE and Professor Marco Di Renzo from CNRS were elected as Vice Chairs to the group.