11 research outputs found
Fundamental Limits of Coded Caching: Improved Delivery Rate-Cache Capacity Trade-off
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, is considered. It is assumed that each user is equipped with a local
cache memory with capacity MF bits, and contents can be proactively cached into
these caches over a low traffic period; however, without the knowledge of the
user demands. During the peak traffic period each user requests a single file
from the server. The goal is to minimize the number of bits delivered by the
server over the shared link, known as the delivery rate, over all user demand
combinations. A novel coded caching scheme for the cache capacity of M= (N-1)/K
is proposed. It is shown that the proposed scheme achieves a smaller delivery
rate than the existing coded caching schemes in the literature when K > N >= 3.
Furthermore, we argue that the delivery rate of the proposed scheme is within a
constant multiplicative factor of 2 of the optimal delivery rate for cache
capacities 1/K N >= 3.Comment: To appear in IEEE Transactions on Communication
Content Delivery in Erasure Broadcast Channels with Cache and Feedback
We study a content delivery problem in a K-user erasure broadcast channel
such that a content providing server wishes to deliver requested files to
users, each equipped with a cache of a finite memory. Assuming that the
transmitter has state feedback and user caches can be filled during off-peak
hours reliably by the decentralized content placement, we characterize the
achievable rate region as a function of the memory sizes and the erasure
probabilities. The proposed delivery scheme, based on the broadcasting scheme
by Wang and Gatzianas et al., exploits the receiver side information
established during the placement phase. Our results can be extended to
centralized content placement as well as multi-antenna broadcast channels with
state feedback.Comment: 29 pages, 7 figures. A short version has been submitted to ISIT 201
Coded Caching for a Large Number Of Users
Information theoretic analysis of a coded caching system is considered, in
which a server with a database of N equal-size files, each F bits long, serves
K users. Each user is assumed to have a local cache that can store M files,
i.e., capacity of MF bits. Proactive caching to user terminals is considered,
in which the caches are filled by the server in advance during the placement
phase, without knowing the user requests. Each user requests a single file, and
all the requests are satisfied simultaneously through a shared error-free link
during the delivery phase.
First, centralized coded caching is studied assuming both the number and the
identity of the active users in the delivery phase are known by the server
during the placement phase. A novel group-based centralized coded caching (GBC)
scheme is proposed for a cache capacity of M = N/K. It is shown that this
scheme achieves a smaller delivery rate than all the known schemes in the
literature. The improvement is then extended to a wider range of cache
capacities through memory-sharing between the proposed scheme and other known
schemes in the literature. Next, the proposed centralized coded caching idea is
exploited in the decentralized setting, in which the identities of the users
that participate in the delivery phase are assumed to be unknown during the
placement phase. It is shown that the proposed decentralized caching scheme
also achieves a delivery rate smaller than the state-of-the-art. Numerical
simulations are also presented to corroborate our theoretical results