Cache Assignment for a Flexible Mobile User in Wireless Heterogeneous Networks

With the proliferation of smart mobile devices, there is an ever-increasing demand for multimedia content. To avoid congestion in backhaul links, mobile edge caching is a promising solution that can reduce delivery delays and improve users' quality of experience. In this regard, the requested content can be downloaded from a nearby small cell access point (also called helper) instead of a base station with a lower delay. In this paper, we address the problem of finding the optimal cache data placement to minimize the total delivery delay. We suppose the users are flexible in the sense that they request a set of multiple files from the library with a unique feature and are satisfied if any file within the requested set is received. Moreover, in the system model, the interference and the mobility of users are considered. More precisely, the effect of interference from other helpers is incorporated in calculating the delivery delay, and a random waypoint model is exploited to address the mobility of users within the network. Because of the complexity of the problem, finding the optimal solution is NP-hard. We prove that the problem is in the form of maximizing a monotone submodular function subject to matroid constraints. We exploit this property to provide an efficient approximate solution (i.e., a greedy algorithm) that is guaranteed to perform within a constant of as well as the optimal solution. Simulation results validate the efficiency of our proposed algorithm.