Cluster-centric cache utilization design in cooperative small cell networks

In this paper, we propose an adaptive cluster-centric small cell network with cooperative caching and transmission design, in which small base stations (SBSs) are grouped into disjoint clusters and in-cluster cache space is utilized as an entity. We design a combined caching scheme where part of the available cache space is reserved for caching the most popular content in every SBS, while the remaining is used to increase the content diversity. Depending on the availability of the requested content, either joint transmission (JT) or parallel transmission (PT) is used to deliver the content to the served user. We provide analytical results on the successful content delivery probability of both schemes for a user located at the cluster center. The optimal cache utilization strategy to maximize the cache service probability is determined as a function of network parameters, revealing an interesting tradeoff between transmission diversity and content diversity. Simulation results show that our proposed cooperative design finely combines the benefits of cache-level and signal-level cooperation schemes.