Joint content caching and fetching scheme with cooperative transmission in hierarchical networks

Concerned with the surge of content-centric applications, it is challenging to balance network traffic and cater to low-delay requirements. Hierarchical caching architecture of both edge network (EN) and core network (CN) emerges and leverages caching resources to reduce the delivery delay of contents. Most previous work takes an impractical assumption to treat the CN as a content provider, which neglects the collaboration by intermediate CN caches. Most importantly, it is still necessary to thoroughly study the tradeoff between CN delay and edge delay for files delivery so as to minimize the overall delivery delay across the network. In this paper, we consider a hierarchical caching network with distributed CN nodes and edge nodes, where cooperative transmission is enabled for edge nodes to transmit multi-files simultaneously. This poses a joint optimization problem of hierarchical file caching and fetching to minimize the overall delivery delay of requests. Since the problem is NP-hard, we decompose the original problem and design an iterative algorithm to address it. Numerical results validate that the proposed scheme can find a balanced solution between lowering edge delay by utilizing coordinated CN caching and lowering CN delay by solely relying on edge caching.