Fig. 1From: Femtocaching assisted multi-source D2D content delivery in cellular networksTwo main cache perspectives of D2D communication considering different placement devices. This figure shows the existing D2D communication schemes, which can be classified into two categories by taking into account different devices to implement local-storage, i.e., the mode of UTs or SBSs to carry out offloading. a Example of SBS offload, b Example of UT offloadBack to article page