Fundamental Limits of Caching: Improved Delivery Rate-Cache ... - arXiv

Fundamental Limits of Caching: Improved Delivery Rate-Cache Capacity Trade-off Mohammad Mohammadi Amiri, Student Member, IEEE and

arXiv:1604.03888v1 [cs.IT] 13 Apr 2016

Deniz Gündüz, Senior Member, IEEE

Abstract We consider a centralized coded caching system consisting of a server delivering N popular files, each of size F bits, to K users through an error-free shared link. Each user is equipped with a local cache of capacity M F bits. The contents can be proactively cached into the user caches by the server over low traffic period; however, without the knowledge of the user demands. During the peak traffic period each user requests a single file from the database. The goal is to utilize the user caches in order to minimize the number of bits delivered by the server over a shared link, known as the delivery rate, to satisfy all the user demands. We propose a novel coded caching algorithm for the cache capacity of M =

N −1 K ,

when N and K have a common divisor greater than 1, and satisfy 4 ≤ N < K ≤

3N 2 .

It is shown that the proposed scheme achieves a smaller delivery rate than the existing coded caching schemes in the literature for

1 K

≤M ≤

N K

when N < K
1 as

a common divisor. For N ≤ K, the best known achievable delivery rate-cache capacity trade-off in the literature will be represented by Rb (M ). When N ≤ K