"Transmission, multiplexing and security in 5G and 6G telecommunications systems and networks"

This Ph.D. thesis focuses on the development of efficient techniques in various subsystems and overall technologies in broadband modulations, multiplexing, and multiple access technologies in telecommunication systems and 5th and 6th generation networks. The development of such techniques is a continuous research issue that concerns the scientific community. In addition, the subject of the thesis extends to the research and development of techniques to improve the security of 5G and 6G telecommunication networks exploiting features of the physical layer. The aim of the thesis is to address, answer and obtain a clear view for a set of challenging problems and questions. How and which techniques can exploit the features of the physical layer to enhance the already existing higher-layer security systems. How additional physical layer security can be achieved. Which are the most efficient techniques and in which cases. Finally, if there is any cost to other requirements that the physical layer must deliver, e.g. transmission rates and multiplexing.