Order-optimal caching in hierarchical networks
Lin Zhang, Zhao Wang, Ming Bo Xiao, Gang Wu · 2016
The decentralized caching is studied in hierarchical networks, where users request contents through intermediate nodes (helpers) from a file server. By placing contents randomly and independently in each node and carefully designing the data delivery, the correlations of the pre-stored contents across layers can be utilized to reduce the transmission rate in each layer. A hybrid caching scheme is developed by exploiting the cross-layer storage correlations as well as the single-layer and cross-layer multicast opportunities. It is observed that the achievable rate region of the hybrid caching scheme is strictly better than the caching scheme in [1]. Furthermore, the order-optimality of the hybrid caching scheme is demonstrated by achieving the performance within constant multiplicative and additive factors of the information-theoretic optimum. In particular, the multiplicative and additive factors are carefully quantified to be 48 and 4, respectively.