Software-defined reconfigurable intelligent surfaces: from theory to end-to-end implementationSoftware-defined reconfigurable intelligent surfaces: from theory to end-to-end implementation Peer-Reviewed Journal Publication Δημοσίευση σε Περιοδικό με Κριτές 2023-12-152022enProgrammable wireless environments (PWEs) utilize internetworked intelligent metasurfaces to transform wireless propagation into a software-controlled resource. In this article, the interplay is explored between the user devices, the metasurfaces, and the PWE control system from the theory to the end-to-end implementation. This article first discusses the metasurface hardware and software, covering the complete workflow from the user device initialization to its final service via the PWE. Furthermore, to be compatible with the 5G and 6G wireless systems, the software-defined networking (SDN) paradigm is extended to achieve scalable internetworking and central control in PWE deployments with multiple metasurfaces and multihop communication. Subsequently, the set of SDN foundations is exploited in order to abstract the physics behind PWEs and a theoretical framework is established to describe and manipulate them in an algorithmic form. This can lead to smart radio environments that are readily accessible from various engineering disciplines, facilitating their integration into existing networks, wireless systems, and applications. This article is concluded by outlining strategies for the optimal placement of metasurfaces within a PWE-controlled space, open challenges in PWE security, specialized SDN integration issues, and theoretical problems toward the graph-driven modeling of PWEs.This work was supported in part by the European Union’s Horizon 2020 Research and Innovation Programme-Project C4IIoT under Grant EU833828 and in part by the European Research Council (ERC) under Grant Agreement 864228 (AdjustNet) (2020–2025).http://creativecommons.org/licenses/by/4.0/Proceedings of the IEEE11091466-1493 Liaskos Christos Mamatas, Lefteris Pourdamghani Arash Tsioliaridou Ageliki Ioannidis Sotirios Ιωαννιδης Σωτηριος Pitsillides, Andreas Schmid Stefan Akyildiz, Ian Fuat Institute of Electrical and Electronics Engineers 6G Deployment optimization HyperSurfaces Intelligent metasurfaces Internetworking Multihop Programmable wireless environments (PWEs) Protocol stack Reconfigurable intelligent surfaces (RISs) Security Smart radio environments (SREs) Software-defined networking (SDN) Theoretical foundations