Spectrum Efficiency Enhancement for Wireless Communications with Reconfigurable Metasurfaces

Reconfigurable metasurfaces are gaining more and more interests in both academia and industry in recent years. They are constructed by numerous elements, each element can reflect or refract signals from transmitters, thereby enhancing or suppressing the signals at receivers. The energy cost of reconfigurable metasurfaces is negligible since the elements are passive and the main consumption is from controllers, in addition, they are portable because of the compact sizes. With the aforementioned benefits, in this work, reconfigurable metasurfaces are explored in various communication scenarios such as unmanned aerial vehicle (UAV) communication, dual-function radar communication (DFRC), full-duplex (FD) communication to boost spectrum efficiency. Firstly, UAV communication which enjoys the unique advantages such as high agility and energy-green is prone to interception from eavesdroppers due to line-of-sight channels. Therefore, the potentials of reconfigurable metasurfaces are exploited in UAV-assisted communication networks in the perspective of physical layer security. Importantly, a closedform solution is originally obtained for such networks. In addition, this is the first work that considers the secrecy issues for DFRC systems in the presence of reconfigurable metasurfaces. One of the main contributions is that low computational complexity algorithms for such systems are developed to boost both detection and communication abilities, effectively addressing the spectrum scarcity problem. Finally, dual-side reconfigurable metasurfaces have been investigated in FD communication to tackle the main challenge for implementation, namely self-interference, as devices send and receive signals simultaneously. Specifically, the self-interference is mitigated by the reflection feature of the reconfigurable metasurfaces and the refraction feature helps to enhance transmission, which proposes a novel self-interference cancellation scheme to facilitate FD communication.