Reducing download delay for cooperative caching in small cell network

As mobile devices become more and more popular, mobile traffic demands are increasing exponentially. To deal with such challenge, caching at small cell base stations (SBSs) is one of the most effective techniques for reducing the transmission delay of mobile applications. However, due to the limitation of the SBS storages, the improvement of reducing transmission delay is limited in small cell networks. In this paper, we propose a novel cooperative caching framework in a small cell network in which SBSs are grouped into disjoint clusters and cooperate through backhaul links to make use of SBS storages. A backhaul-based cooperative caching (BCC) scheme is introduced, and the problem for content placement is formulated to minimize the average download delay in small cell networks. Then, we show that the problem is equivalent to the maximization of a monotone submodular function subject to matroid constraints and propose a low-complexity greedy strategy with 1/2 performance guarantee. Simulation results demonstrate that the proposed scheme achieves lower download delay and better cache hit rate than other schemes.