A Delay-Driven Early Caching and Sharing Strategy for D2D Transmission Network

As device-to-device (D2D) caching technology allows a number of devices to cache some particular contents, requesters can obtain these contents directly from these neighbor devices rather than the base station (BS) and thus the burden can be efficiently reduced. However, the required time consumptions for caching contents, which may significantly affect the network delay performance, are ignored in the existing schemes. Consequently, a delay-driven caching and sharing strategy is proposed in this paper. Specifically, in the proposed strategy, each D2D device can obtain contents from BS and play as the cache device (CD). Moreover, the consumed time for CDs is integrated into the strategy design. Then, three kinds of delay, which are the delay for CDs to cache contents and the delay for requesters to get the required files from BS and CDs, respectively, are considered simultaneously. We formulate an optimization problem, which aims at minimizing the overall average network delay subject to the successful transmission probability as well as the content cache and request constraints. To solve the formulated complex non-convex problem, the original problem is divided into three subproblems and efficiently solved in an iterative manner. Moreover, as the convergence for solving the three subproblems are proved, the convergence of the developed iterative algorithm can be guaranteed. Simulation results demonstrate that the proposed strategy can efficiently reduce the overall average network delay as compared to the existing schemes.