A near-optimal content placement in D2D underlaid cellular networks

The rapid growth of mobile data traffic, especially video streaming traffic, places a serious burden on cellular networks. D2D caching has emerged as a promising paradigm to alleviate network congestions, in which contents are cached at user terminals proactively and then shared among neighbor requesting users via D2D communications. In this paper, we study the content placement problem to maximize cache hit probability (i.e., the probability that contents requested by users are successfully served by neighbor helpers through D2D communications) in D2D underlaid cellular networks. To decide where to cache and which contents to be pushed, we formulate our problem considering D2D communication probability of helpers and preference probability of requesting users. Then our problem is proved to be a submodular function maximization problem under a matroid constraint. To solve this problem, we present an improved greedy algorithm which can achieve an approximation guarantee of \({\min \limits } (1, \linebreak \frac {1}{v_{0}+\frac {1}{t_{min}}} )\), based on the classic \(\frac {1}{2}\)-approximation algorithm. Simulation results show that our proposed scheme achieves higher cache hit probability and lower energy consumption compared with existing caching schemes.