Two-Dimensional Multi-Access Coded Caching with Multiple Transmit Antennas

This work introduces a multi-antenna coded caching problem in a two-dimensional multi-access network, where a server with L transmit antennas and N files communicates to K_1K_2 users, each with a single receive antenna, through a wireless broadcast link. The network consists of K_1K_2 cache nodes and K_1K_2 users. The cache nodes, each with capacity M, are placed on a rectangular grid with K_1 rows and K_2 columns, and the users are placed regularly on the square grid such that a user can access r^2 neighbouring caches in a cyclic wrap-around fashion. For a given cache memory M, the goal of the coded caching problem is to serve the user demands with a minimum delivery time. We propose a solution for the aforementioned coded caching problem by designing two arrays: a caching array and a delivery array. Further, we present two classes of caching and delivery arrays and obtain corresponding multi-access coded caching schemes. The first scheme achieves a normalized delivery time (NDT) K_1K_2(1-r^2M/N)/L+K_1K_2M/N. The second scheme achieves an NDT K_1K_2(1-r^2M/N)/L+K_1K_2r^2M/N when M/N=1/K_1K_2 and L=K_1K_2-r^2, which is optimal under uncoded placement and one-shot delivery.