Incomplete CSI Acquisition for Size-Constrained Massive MIMO Systems with User Mobility

We propose a low-complexity approach for the downlink of physically-constrained massive multiple-input multiple-output (MIMO) systems with user mobility. We examine a channel state information (CSI) acquisition strategy that exploits both the spatial and temporal correlation among the channels of adjacent base station antennas. The proposed strategy solely collects CSI for a subset of antennas and time frames. Then full CSI is approximated using CSI of adjacent antennas and previous frames. This critically reduces the CSI acquisition complexity while sacrificing CSI quality, and hence introduces a scalable performance-complexity tradeo-off. The numerical results demonstrate that, for practical mobile speeds, the proposed scheme reduces the computational complexity and enhances the energy efficiency of massive MIMO base stations against systems with complete CSI, while approximately preserving performance.