On the Fundamental Limit of Coded Caching Systems with a Single Demand Type

Abstract

Caching is a technique to reduce the communication load in peak hours by prefetching contents during off-peak hours. Recently Maddah-Ali and Niesen introduced an information theoretic framework for coded caching, and showed that significant improvement can be obtained compared to uncoded caching. Considerable efforts have been devoted to identify the precise information theoretic fundamental limit of such 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 multiple demand types during delivery, which in fact introduces tension in the coding strategy to accommodate all of them. In this paper, we seek to develop a better understanding of the fundamental limit of coded caching by investigating single demand type systems. We first show that in the canonical three-user three-file systems, such single demand type systems already provide important insights. Motivated by these findings, we focus on systems where the number of users and the number of files are the same, and the demand type is when all files are being requested. A novel coding scheme is proposed, which provides several optimal memory-transmission operating points. Outer bounds for this class of systems are also considered, and their relation with existing bounds is discussed.