In cache-enabled device-to-device (D2D) -aided cellular networks, the technique of caching\ncontents in the cooperative crossing between base stations (BSs) and devices can significantly reduce\ncore traffic and enhance network capacity. In this paper, we propose a scheme that establishes\ndevice availability, which indicates whether a cache-enabled device can handle the transmission\nof the desired content within the required sending time, called the delay, while achieving optimal\nprobabilistic caching. We also investigate the impact of transmission device availability on the\neffectiveness of a scenario of cooperative crossing cache placement, where content delivery traffic can\nbe offloaded from the local cache, a D2D transmitterâ??s cache via a D2D link, or else directly from a BS\nvia a cellular link, in order to maximize the offloading probability. Further, we derive the cooperation\ncontent offloading strategy while considering successful content transmission by D2D transmitters or\nBSs to guarantee the delay, even though reducing the delay is not the focus of this study. Finally, the\nproposed problem is formulated. Owing to the non-convexity of the optimization problem, it can be\nrewritten as a minimization of the difference between the convex functions; thus, it can be solved\nby difference of convex (DC) programming using a low-complexity algorithm. Simulation results\nshow that the proposed cache placement scheme improves the offloading probability by 13.5% and\n23% compared to Most Popular Content (MPC) scheme, in which both BSs and devices cache the\nmost popular content and Coop. BS/D2D caching scheme, in which each BS tier and user tier applies\ncooperative content caching separately.
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