Proactive content caching at base stations can efficiently reduce the traffic of backhaul links. In heterogeneous networks, small base station (SBSs) sleeping is usually adopted when the cell load is low to reduce the energy consumption, which, however, will make the cached contents unavailable and thus, bring new technical challenges to designing caching strategy. In this paper, we construct the framework of caching at sleeping-enabled SBSs with considering the interaction between caching and sleeping. We adopt the average hit rate as the system performance metric with the energy saving constraint induced by SBS sleeping. Due to the NP-hard property of the joint caching-sleeping problem, we decompose this problem into two subproblems to calculate the caching and SBS sleeping strategies separately, where these two subproblems are convex and submodular, respectively. We develop a greedy initialization followed by the iterative 1-interchange algorithm to obtain a caching-sleeping strategy whose performance is very close to the optimal one. The simulation results show that our algorithm leads to a significant increase of the system performance compared to the separate caching and sleeping optimization.
['Ruhui Li', 'Wei Wang', 'Aiping Huang', 'Zhaoyang Zhang']
Content caching at sleeping-enabled base stations in heterogeneous networks