Editorial: Resource Allocation in Cloud-Radio Access Networks and Fog-Radio Access Networks for B5G Systems - Dahrouj, Hayssam; Douik, Ahmed; El-Hajjar, Mohammed; Kaneko, Megumi; Li, Yonghui; Ngo, Duy T.; Saad, Mohamed; Shen, Kaiming; Zhang, Jun (Frontiers in Communications and Networks, 2021)