6G Metasurfaces: Signal Processing and Wireless Communications by Coding on Metamaterials

The forecast by International Telecommunication Union (ITU) predicts that by 2030, the overall mobile data traffic will reach 5 zettabytes (ZB) per month. Multiple-input multiple-output (MIMO) is the most celebrated mobile technology that provides the needed upgrade from 2G to 3G, from 3G to 4G and most recently from 4G to 5G in the form of massive MIMO. In 5G, the number of antennas at the base station (BS) has been increased to 64 and more are expected in future generation to cope with the rising demands. A major limitation of massive MIMO is however the cost of incorporating the large number of RF chains and linear power amplifiers (PAs) in the system. Massive MIMO at a user equipment (UE) remains unthinkable.

Recently, software-controlled metamaterial or programmable metasurface has emerged as a novel technology to enhance wireless communications system performance. Software-controlled metamaterials (or "meta-atoms" in short) can alter their electromagnetic (EM) properties to suit the purpose of various communication applications. On the one hand, they can be deployed on large surfaces to provide a smart radio environment by optimising the meta-atoms for reducing interference, enhancing security, extending the range of communication, and many more. On the other hand, they can also be used to mimic the signal processing for MIMO without the need for the increase in the number of RF chains and PAs. This metasurface-based MIMO is much more scalable in terms of costs and may make ultra-massive MIMO feasible in the future. Despite the early successes, there are critical challenges that greatly limit the impact of metasurface in mobile communications. From severe pathloss (poor propagation efficiency) to the difficulty for interference control, narrow bandwidth of meta-atom, and the bulkiness of metasurface MIMO, many fundamental challenges need to be overcome to truly unleash the potential of metasurfaces.

In this project, our aim is to tackle the challenges. In particular, we propose to utilise SWC (surface wave communications) in addition to the usual space wave communications in a novel way for both the smart radio environment and ultra-massive MIMO applications. The proposed research exploits the unique features of SWC and is the first in the world to introduce SWC in the design of mobile communications networks which is anticipated to revolutionise mobile communications by making possible the following characteristics:

-> Favourable propagation characteristics - The use of SWC provides pathways in the radio environment to have much less propagation loss for a smart radio environment.
-> Ease of interference management - Surface waves are made to be confined to the surface and radio waves appear only where they should be.
-> SWC-aided metasurface MIMO - SWC provides a novel architecture that miniaturises the design of metasurface MIMO and improves its energy efficiency greatly, which will make massive MIMO possible even at the side of UE.
- Wideband meta-atom - This project will also design a new meta-atom technology that has a wider bandwidth and the capability to switch between being a radiating element, a reflector, a diffractor or a propagation medium.

This project will benefit from the strong support from BT, Toshiba and City University of Hong Kong for testbed implementation and ensuring industrial impact.