Reconfigurable, Intelligent, and Sustainable Wireless Environments for 6G Smart Connectivity. - Strinati, Emilio Calvanese; Alexandropoulos, George C.; Wymeersch, Henk; Denis, Benoit; Sciancalepore, Vincenzo; D'Errico, Raffaele; Clemente, Antonio; Phan-Huy, Dinh-Thuy; De Carvalho, Elisabeth; Popovski, Petar (IEEE Communications Magazine, 2021)