On Hierarchical Coded Caching with Offline Users

2025-07-01

AI Summary

This work addresses the coded caching problem in two-tier hierarchical networks under user offline scenarios, overcoming the limitation of prior works that assume zero-cache capacity at mirror nodes. We propose the Hierarchical Hot-Pluggable Delivery Array (HHPDA) framework, which integrates coded caching, hierarchical network modeling, and combinatorial $t$-design theory to support general settings where mirror nodes possess non-zero cache capacity—a first in the literature. Constructed via $t$-designs, HHPDA flexibly adapts to heterogeneous network topologies and dynamic user online/offline states, jointly optimizing content prefetching and delivery. Experiments demonstrate that the proposed scheme maintains high distribution efficiency under user offline conditions, achieving significant improvements in bandwidth utilization and system robustness compared to state-of-the-art approaches.

Technology Category

• Machine Learning: Hardware-aware ML
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization

Application Category

• Economics, Online Markets and Human Computation: Incentives in network design for Web infrastructures and ecosystems
• Systems and Infrastructure for Web, Mobile and WoT: Cloud, edge and content delivery systems for the Web
• Graph Algorithms and Modeling for the Web: Algorithms and analysis for incomplete, noisy, or partially observed Web-related graphs

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.

Problem

• Studies hierarchical networks with offline users
• Proposes HHPDA for general two-layer caching
• Uses t-designs to construct HHPDAs

Innovation

• Hierarchical hotplug placement delivery array
• Two-layer hierarchical network optimization
• Combinatorial t-designs for HHPDAs