  Decentralized proactive caching and coded delivery is studied in a content
delivery network, where each user is equipped with a cache memory, not
necessarily of equal capacity. Cache memories are filled in advance during the
off-peak traffic period in a decentralized manner, i.e., without the knowledge
of the number of active users, their identities, or their particular demands.
User demands are revealed during the peak traffic period, and are served
simultaneously through an error-free shared link. The goal is to find the
minimum delivery rate during the peak traffic period that is sufficient to
satisfy all possible demand combinations. A group-based decentralized caching
and coded delivery scheme is proposed, and it is shown to improve upon the
state-of-the-art in terms of the minimum required delivery rate when there are
more users in the system than files. Numerical results indicate that the
improvement is more significant as the cache capacities of the users become
more skewed. A new lower bound on the delivery rate is also presented, which
provides a tighter bound than the classical cut-set bound.
