On Hierarchical Coded Caching with Offline Users

TL;DR

This paper introduces a new coded caching scheme for hierarchical networks with offline users, utilizing hierarchical hotplug placement delivery arrays (HHPDA) and combinatorial t-designs to improve content delivery efficiency.

Contribution

It proposes the HHPDA framework for general hierarchical networks with offline users, extending beyond previous zero-memory mirror cache models.

Findings

HHPDA effectively models placement and delivery phases.

Constructed HHPDAs using combinatorial t-designs.

Enhances caching strategies for offline user scenarios.

Abstract

This paper studies a two-layer hierarchical network in which some users are offline during the content delivery phase. A two-layer hierarchical network consists of a single server connected to multiple cache-aided mirror sites, and each mirror site is connected to a distinct set of cache-aided users. A scheme for such a hierarchical system with offline users has been proposed recently but considered a special case where all mirror caches have zero memory, which is a significant limitation. We propose an array known as a hierarchical hotplug placement delivery array (HHPDA), which describes the placement and delivery phases of a coded caching scheme for a general two-layer hierarchical network with offline users. Further, we construct a class of HHPDAs using combinatorial t-designs.