Edge Caching in Wireless Infostation Networks: Deployment and Cache Content Placement

Abstract

This paper studies the popularity-based content caching at the edge of the network. We consider a special edge caching network consisting of a set of infostations that are colocated with a cellular network. These infostations, equipped with large storage and high-speed wireless disseminators, are randomly and uniformly distributed within the coverage of a central base station. Then certain popular content files can be cached at the infostations and provisioned to the requesting user through dedicated short-range communications, upon a cache hit. Subject to a sum storage constraint over the infostations, the problem of maximizing the edge cache-hit-ratio is formulated, which requires a joint design on the number of infostations and the cache content placement at each infostation and is NP-hard in general. To provide insights on these two issues, we characterize a performance tradeoff regarding the number of infostations under maximal-popularity caching (MPC). Furthermore, a hybrid content placement (HCP), as a combination of MPC and the maximal-diversity caching (MDC), is proposed by employing a storage splitting factor. Simulation results demonstrate that there always exists an optimal number of infostations under different caching strategies except the MDC, and the proposed HCP can effectively improve the performance compared to MPC and MDC.