Joint User Association and Content Placement for D2D-Enabled Heterogeneous Cellular Networks

The explosive increase of the multimedia traffic poses challenges on mobile communication systems. To stress this problem, caching technology can be exploited to reduce backhaul transmissions latency and improve content fetching efficiency. In this paper, we study the user association and content placement problem of device-to-device-enabled (D2D-enabled) heterogeneous cellular networks (HCNs). To stress the importance of the service delay of all the users, we formulate the joint user association and content placement problem as an integer-nonlinear programming problem. As the formulated NP-hardness of the problem, we apply the McCormick envelopes and the Lagrangian partial relaxation method to decompose the optimization problem into three subproblems and solved it by using Hungarian method and unidimensional knapsack algorithm. Simulation results validate the effectiveness of the proposed algorithm.