  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.
