Content Delivery in MIMO Broadcast Channels with Decentralized Coded Caching.

Caching at the wireless edge is an effective way to trade the scarce communication bandwidth with the more sustainable storage size through traffic time shifting. Multiple-input multiple-output (MIMO), on the other hand, can bring spatial multiplexing gain in wireless channels. This work is to investigate the combined effect of MIMO and caching in a three-user cache-aided MIMO broadcast channel, where the base station is equipped with.. antennas and each user is equipped with.. antennas. Decentralized coded caching is adopted in this paper, which converts the content delivery phase to a transmission problem in a broadcast channel with general message sets. We first derive an achievable degrees of freedom (DoF) region of the three-user MIMO broadcast channel with general message sets. Based on this region, we then obtain an achievable normalized delivery time (NDT), which illustrates the spatial multiplexing gain of MIMO through simultaneous transmission of multiple multicast messages intended to different user sets. It is shown that the achievable NDT is optimal at certain cases and is within a multiplicative gap of 3 from the optimum at other cases.