The radio communication division of the international telecommunication union (ITU-R) has recently drafted new recommendations for the international mobile telecommunication 2030 (IMT-2030) framework, which is referred to as the sixth generation (6G) of telecommunication standards. In the past decade, several advanced wireless technologies, including small cells, millimeter-wave communications, and massive multiple-input multiple-output (MIMO) systems, have been proposed to enhance the network capacity and to enable ubiquitous wireless connectivity. The practical implementation and deployment of these technologies is, however, often limited by the associated prohibitive energy consumption and expensive hardware equipment. As a result, it has become apparent that 6G communication networks need to undergo a fundamental shift of design paradigm, which requires to include aspects of (energy) sustainability, besides those of network capacity and connectivity, at the design stage. This change of design paradigm requires radically new physical layer technologies.
In this context, we are assisting to the upsurge in brand-new technologies for the physical layer, which rely on encoding, processing, and decoding information in the wave domain, i.e. at the electromagnetic level, as opposed to conventional physical layer technologies that rely on digital information processing. The advantages of wave domain information processing include improved computational efficiency, simplified hardware architectures, and reduced energy consumption. This emerging trend has been facilitated by recent results in the field of configurable antennas and, especially, metasurfaces, which are engineered materials capable of processing the electromagnetic waves in the wave domain without the need of analog-to-digital and digital-to-analog conversions.
Examples of emerging technologies include (i) spatial, index, media-based, metasurface modulation, which encode information onto physical characteristics of antennas and metasurfaces; (ii) reconfigurable intelligent surfaces (RISs), which improve the transmission of data by appropriately shaping the propagation of electromagnetic waves at the electromagnetic level, turning radio propagation environments into smart radio propagation environments; (iii) holographic surfaces (HoloSs), which are continuous-aperture hybrid MIMO systems, where the data encoding and decoding is performed in the wave domain; (iv) stacked intelligent surfaces (SIMs), which are multi-layer metasurface-based devices, which resemble deep neural networks, where the data encoding and encoding is realized through signal processing operations in the wave domain; (v) fluid antenna systems; and (vi) surface wave communications (SWC), which are aimed to capitalize on the properties of surface waves (evanescent waves) for realizing efficient wave transformations.
Despite the potential performance gains and applications that these technologies may provide in future wireless networks, the major limiting factor preventing information, communication, and signal processing theorists from realizing their full potential and unveiling their ultimate performance limits lies in understanding the electromagnetic and physical properties and limitations underpinning them. Key open problems include how to appropriately model the physics of signal propagation and the processing of signals performed by these emerging devices in the wave domain. To overcome this status quo, it is necessary to cut across the current and established disciplinary boundaries between information, signal, and electromagnetic theories.
The objective of the SURFER project lies in developing a framework for modeling and optimizing wireless systems that use free-space waves and surface waves in order to enhance the performance of future networks and making them sustainable by design thanks to wave domain processing.
