Abstract
In this letter, we formulate a multi-tier caching and resource sharing (CRS) optimization problem for a high video streaming performance in 5G ultra-dense networks. Particularly, in user tier, the optimal sets of spectrum owning users (SUs) with available downlink resources, caching users (CUs) with cached video versions, and normal users (NUs) requesting the video versions are tripartite for video streaming over device-to-device (D2D) communications. In femto tier, the optimal caching strategy is found to indicate which video versions and where to cache them in the femtocell base station (FBSs). By cooperating with the video versions cached in macro tier, i.e., macro base station (MBS), the mobile users (MUs) can receive the video versions from D2D communications, FBSs, and MBS flexibly. The objective of the CRS solution is to maximize the video playback quality, while saving the caching storage of FBSs and satisfying a given throughput required by MUs and a given target signal to interference plus noise ratio of SUs.