“…In addition, harvesting power and green energy-powered CRNs have recently gained considerable attention [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. Specifically, the architecture, technical challenges, performance and applications of green energy-powered CRNs have been analyzed in [ 12 , 19 , 20 , 21 ] and the references therein.…”