Multiple-antenna Placement Delivery Array with Cyclic Placement

This paper studies the cache-aided multiple-input single-output (MISO) broadcast problem with one-shot linear delivery, where a server with L antennas and N files is connected to K single-antenna users (each with a memory of M files) through a wireless broadcast channel, with the objective to maximize the sum Degree-of-Freedom (sum-DoF) in the whole system. Recently, a construction structure, referred to as Multiple-antenna Placement Delivery Array (MAPDA), was proposed to construct coded caching schemes for this cacheaided MISO broadcast problem based on the joint design of coded caching and zero-forcing (ZF) precoding. In this paper, we first propose an upper bound on the sum-DoF of any MAPDA scheme given a fixed cache placement. Then, under a class of cyclic placements which leads to subpacketizations on the files linear with K, we propose two MAPDAs for the case L < KM/N achieving the sum-DoF 2L, which is order optimal within a factor of 2 when M/N ≤ 1/2 compared to the upper bound under the cyclic placement.