Intelligently wireless batteryless RF-powered reconfigurable surface: theory, implementation & limitationsIntelligently wireless batteryless RF-powered reconfigurable surface: theory, implementation & limitations Peer-Reviewed Journal Publication Δημοσίευση σε Περιοδικό με Κριτές 2025-04-152023enThis work exploits ultra-low cost, commodity, radio frequency identification (RFID) tags as elements of a reconfigurable intelligent surface (RIS). Such batteryless tags are powered and controlled by a software-defined radio reader, with properly modified software, so that a source-destination link is assisted, operating at a different band. Signal model includes small-scale and large-scale fading, direct link, as well as specific parameters relevant to reflection (i.e., backscatter) radio, such as antenna structural mode and reflection efficiency, typically overlooked in the literature. An algorithm is offered that computes the optimal RIS configuration with complexity of O(MlogM) in number of elements M , instead of intractable exponential complexity of exhaustive search, while accommodating any number K≥2 of loads. With the proposed algorithm, it is shown that performance gains reach a plateau for constant element spacing and increasing number of elements, suggesting that the weak, passive nature of backscattered links limits the performance gains, even with perfect channel estimation. Channel estimation with linear minimum mean squared error (LMMSE) estimator is shown to be effective, provided that there are sufficient number of pilot symbols. A concrete way is offered to design and prototype a wireless, batteryless, RF-powered, reconfigurable surface and a proof-of-concept is experimentally demonstrated.This work was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “First Call for H.F.R.I. Research Projects through the Faculty Members and Researchers and the Procurement of High-Cost Research Equipment” under Project 2846. An earlier version of this paper was presented at the IEEE GLOBECOM, Madrid, Spain, December 2021 [DOI: 10.1109/GLOBECOM46510.2021.9685256].http://creativecommons.org/licenses/by/4.0/IEEE Transactions on Wireless Communications2263942-3954 Vardakis Iosif Βαρδακης Ιωσηφ Kotridis Georgios Κοτριδης Γεωργιος Peppas Spyridon Πεππας Σπυριδων Skyvalakis Konstantinos Σκυβαλακης Κωνσταντινος Vougioukas Georgios Βουγιουκας Γεωργιος Bletsas Aggelos Μπλετσας Αγγελος Institute of Electrical and Electronics Engineers Backscatter radio RFID Gen2 Reconfigurable surface