On the Fundamental Limits of Coded Caching Systems with Restricted Demand Types

TL;DR

This paper investigates the fundamental limits of coded caching systems with demand restrictions, revealing new insights and proposing a novel coding scheme for systems where each file is requested by at least one user.

Contribution

It introduces a new understanding of demand type restrictions in coded caching and proposes a novel coding scheme for such constrained systems.

Findings

The worst demand type is not always the one with all files requested.

A new coding scheme offers additional operating points beyond existing schemes.

Demand restrictions can significantly influence caching strategies and limits.

Abstract

Caching is a technique to reduce the communication load in peak hours by prefetching contents during off-peak hours. An information-theoretic framework for coded caching was introduced by Maddah-Ali and Niesen in a recent work, where it was shown that significant improvement can be obtained compared to uncoded caching. Considerable efforts have been devoted to identify the precise information-theoretic fundamental limits of the coded caching systems, however the difficulty of this task has also become clear. One of the reasons for this difficulty is that the original coded caching setting allows all possible multiple demand types during delivery, which in fact introduces tension in the coding strategy. In this paper, we seek to develop a better understanding of the fundamental limits of coded caching by investigating systems with certain demand type restrictions. We first consider the canonical three-user three-file system, and show that, contrary to popular beliefs, the worst demand type is not the one in which all three files are requested. Motivated by these findings, we focus on coded caching systems where every file must be requested by at least one user. A novel coding scheme is proposed, which can provide new operating points that are not covered by any previously known schemes.