Utility Function Optimization Based Joint User Association and Content Placement in Heterogeneous Networks

The rapid growth of traffic demands has posed challenges and difficulties on both the radio access networks (RANs) and the backhaul links. To stress these problems, caching technology, more specifically, caching user contents at the infrastructures of different RANs is proposed as an effective approach. In this paper, we consider the joint user association and cache content placement problem in cache-enabled heterogeneous networks (HetNets). Stressing the tradeoff between user download delay and caching cost, we define a utility function which characterizes the joint network performance as the weighted sum of user download delay and the caching cost and formulate the joint user association and cache content placement problem as a network utility optimization problem. As the formulated optimization problem is a nonlinear integer optimization problem which cannot be solved conveniently using traditional optimization tools, we transform the original optimization problem equivalently into three convex subproblems by applying McCormick envelopes and Lagrange partial relaxation, and then solve the subproblems by means of Kuhn-Munkres (K-M) algorithm. Simulation results demonstrate the effectiveness of the proposed algorithm.