6G and The Advent of Intelligent Surfaces
Metamaterials Will Turn Cities Into Big, Adaptive Antennas
As mobile networks evolve and the density of users only increases, there is a continuous push towards utilizing higher frequency bands to accommodate the increasing demand for higher data throughout, which requires more complex antenna designs and access techniques combined with higher radio access technology sophistication.
After years of designing increasingly efficient transmitters and receivers, and compensating for the signal losses at the endpoints of a radio channel with error-tolerant and bandwidth-efficient modulation techniques, engineers are beginning to realize that they are approaching the practical limits of communication efficiency. To get high performance as we go to higher frequencies, we will need to engineer the wireless channel itself. But how can we possibly engineer and control a wireless environment, which is determined by a breadth of factors, many of them random and therefore unpredictable?
Operating at elevated radio frequencies, such as those proposed for 6G, introduces significant challenges in radio signal propagation. Succinctly: higher frequency signals have shorter wavelengths, making them more susceptible to interacting with weather conditions but also with obstacles like buildings. What is more, they also interact with moving objects such as vehicles.
Unlike lower-frequency waves that can diffract (i.e., bend) around obstacles, high-frequency signals are more likely to be absorbed, reflected, or scattered, leading to a reliance on line-of-sight communication. This limitation poses a substantial problem for maintaining reliable radio communication in complex urban environments.
To address these challenges, the research trend in next-generation mobile comms is to develop and apply reconfigurable intelligent surfaces (RIS), which are advanced materials capable of dynamically controlling and guiding electromagnetic waves.
RIS are planar structures typically ranging in size from about 100 square centimeters to about 5 square meters or more, depending on the frequency and other factors. These surfaces use advanced substances called metamaterials to reflect and refract electromagnetic waves. Thin two-dimensional metamaterials, known as metasurfaces, can be designed to sense the local electromagnetic environment and tune the wave’s key properties as the wave is reflected or refracted by the surface. As the waves reach such a surface, it can alter the incident waves’ direction to strengthen the channel. These metamaterials can be programmed to make these changes dynamically, reconfiguring the signal in real time in response to changes in the wireless channel. Think of reconfigurable intelligent surfaces as the next evolution of the radio repeater concept.
Metamaterials are artificially engineered structures designed to have properties not found in naturally occurring materials, allowing them to manipulate electromagnetic waves in novel ways.
RIS technology leverages these material properties to actively manage the propagation of wireless signals, effectively mitigating issues related to signal blockage and reflection. The concept of RIS has gained significant attention in recent years, with research and development accelerating rapidly.
The integration of RIS into wireless communication systems offers several advantages.
By intelligently redirecting signals, RIS can create favorable propagation paths, effectively turning obstacles into reflective surfaces that aid in signal transmission. Imagine buildings equipped with outer walls coated with RIS surfaces. The building is not an obstacle anymore, but part of the radio channel.
This capability not only enhances coverage in challenging environments but also reduces the need for additional infrastructure, such as base stations or repeaters, leading to cost savings and improved network complexity.
Moreover, RIS can be dynamically reconfigured in real time, allowing the network to adapt to changing conditions and user demands. This adaptability is particularly beneficial in urban areas with high user density and complex architectural landscapes, where traditional line-of-sight communication is often impractical.
Conclusion
As mobile networks progress toward their next generation, addressing the inherent challenges of millimeter wave signal propagation will create interesting investment opportunities and an interesting technology stack to keep an eye on. Reconfigurable intelligent surfaces could play a big role in the coming generations of wireless and satellite networks1.