Intelligent Reflective-Transmissive Metasurfaces for Full-Dimensional Communications: Principles, Technologies, and Implementation.

The recent development of metasurfaces has shown the potential to significantly improve the performance of wireless communication networks by manipulating the propagation environment with nearly-passive sub-wavelength scattering elements arranged on a surface. However, most studies of this technology focus on the reflective implementation of metasurfaces, i.e., the surface reflects the impinged signals towards receivers located at the same side of the transmitter, which restricts the coverage to one side of the surface. In this article, we introduce the concept of intelligent omni-surfaces (IOSs), which is able to serve mobile users on both sides of the surface to achieve full-dimensional communications by its reflective and transmissive properties. The working principle of the IOS is introduced and a novel hybrid beamforming scheme is proposed for IOS-based wireless communications. Moreover, we present a prototype of IOS-based wireless communications and report experimental results. Furthermore, potential applications of the IOS to wireless communications together with relevant research challenges are discussed.