34 research outputs found
On Caching with More Users than Files
Caching appears to be an efficient way to reduce peak hour network traffic
congestion by storing some content at the user's cache without knowledge of
later demands. Recently, Maddah-Ali and Niesen proposed a two-phase, placement
and delivery phase, coded caching strategy for centralized systems (where
coordination among users is possible in the placement phase), and for
decentralized systems. This paper investigates the same setup under the further
assumption that the number of users is larger than the number of files. By
using the same uncoded placement strategy of Maddah-Ali and Niesen, a novel
coded delivery strategy is proposed to profit from the multicasting
opportunities that arise because a file may be demanded by multiple users. The
proposed delivery method is proved to be optimal under the constraint of
uncoded placement for centralized systems with two files, moreover it is shown
to outperform known caching strategies for both centralized and decentralized
systems.Comment: 6 pages, 3 figures, submitted to ISIT 201
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