Fog-Aided Device to Device Networks with Opportunistic Content Delivery
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In this paper, we investigate the caching placement and content delivery strategy in large-scale fog-aided device to device (F-D2D) networks by exploring the idea of opportunistic spectrum access (OSA) which is originally introduced in cognitive radio (CR). Let Φ_n denote the point process formed by the conventional user equipments (C-UEs) which request other files except the n-th file. Then, to resolve the contentions among the file requests and constrain the `inter-file' interference received at the C-UEs, an opportunistic content delivery strategy is proposed, under which a fog user equipment (F-UE) with the n-th file selected as the candidate file based on the random file selection (RFS) scheme or the most requested file selection (MRFS) scheme is designed to detect and exploit the spatial spectrum hole of Φ_n for the multicast of the n-th file to its associated C-UEs. Assuming decentralized probabilistic caching, the activation probability of F-UEs under the proposed opportunistic content delivery strategy is derived. Further, by adopting appropriate approximation, the successful content delivery probability (SCDP) of the F-D2D network is evaluated. We also investigate the caching placement optimization of F-UEs for the maximization of SCDP. It is shown through both the numerical and simulation results that the proposed opportunistic content delivery strategy can enhance the network SCDP performance.
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