  We consider a centralized caching network, where a server serves several
groups of users, each having a common shared homogeneous fixed-size cache and
requesting arbitrary multiple files. An existing coded prefetching scheme is
employed where each file is broken into multiple fragments and each cache
stores multiple coded packets each formed by XORing fragments from different
files. For such a system, we propose an efficient file delivery scheme with
explicit constructions by the server to meet the arbitrary multi-requests of
all user-groups. Specifically, the stored coded packets of each cache are
classified into four types based on the composition of the file fragments
encoded. A delivery strategy is developed, which separately delivers part of
each packet type first and then combinatorially delivers the remaining
different packet types in the last stage. The rate as well as the worst rate of
the proposed delivery scheme are analyzed. We show that our caching model and
delivery scheme can incorporate some existing coded caching schemes as special
cases. Moreover, for the special case of uniform requests and uncoded
prefetching, we make a comparison with existing results, and show that our
approach can achieve a lower delivery rate. We also provide numerical results
on the delivery rate for the proposed scheme.
