Multi-Antenna Coded Caching for Multi-Access Networks with Cyclic Wrap-Around

This work explores a multiple transmit antenna setting in a multi-access coded caching (MACC) network where each user accesses more than one cache. A MACC network has
$K$
users and
$K$
caches, and each user has access to
$r < K$
consecutive caches in a cyclic wrap-around manner. There are
$L$
antennas at the server, and each cache has a normalized size of
$M/N\leq 1$
. The cyclic wrap-around MACC network with a single antenna at the server has been a well-investigated topic, and several coded caching schemes and improved lower bounds on the performance are known for the same. However, this MACC network has not yet been studied under multi-antenna settings in the coded caching literature. We study the multi-antenna MACC problem and propose a solution for the same by constructing a pair of arrays called caching and delivery arrays. We present three constructions of caching and delivery arrays for different scenarios and obtain corresponding multi-antenna MACC schemes for the same. Two schemes resulting from the above constructions achieve optimal performance under uncoded placement and one-shot delivery. The optimality is shown by matching the performance of the multi-antenna MACC scheme to that of an optimal multi-antenna scheme for a dedicated cache network having an identical number of users, and each user having a normalized cache size of
$rM/N$
. Further, as a special case, one of the proposed schemes subsumes an existing optimal MACC scheme for the single-antenna setting.