Three-User D2D Coded Caching With Two Random Requesters and One Sender

We propose a new D2D centralized coded caching problem, named the 3-user D2D coded caching with two random requesters and one sender (2RR1S), where in the delivery phase, any two of the three users will make file requests, and the user that does not make file request is the designated sender. We find the optimal scheme, denoted as the 2RRIS scheme, for any number of files
$N$
. To examine the usefulness of the proposed model and scheme, we adapt the 2RR1S scheme to three scenarios. The first one is the 3-user D2D coded caching model proposed by Ji et al. By characterizing the optimal rate-memory tradeoff for the 3-user D2D coded caching when
$N=2$
, we show that the adapted 2RR1S scheme is in fact optimal when the cache size is medium. The second scenario is request-random D2D coded caching. Adapting the 2RR1S scheme to this scenario, we show the superiority of our adapted scheme for medium to large cache size. The third scenario is K-user D2D coded caching with
$K-s$
random requesters and
$s$
senders, for which an achievability result is obtained by generalizing the 2RR1S scheme.