Abstract: I welcome you to the fourth issue of the IEEE Communications Surveys and Tutorials in 2021. This issue includes 23 papers covering different aspects of communication networks. In particular, ...
Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal, REQUIMTE-CQFB and Faculty of Sciences and Technology of the New University of Lisbon, Campus da Caparica, Portugal, and ...