Spatial Division Selectivity for High Density Users with Millimeter-Wave Massive Collocated- and Distributed-MIMO

Massive multiple input and multiple output (MIMO) can enhance the cell capacity. Although massive MIMO using space division multiplexing has been developed, the cell capacity for densely populated users has had limited investigation. This paper describes experimental measurements and mathematical analysis of spatial division selectivity using collocated-MIMO (C-MIMO) and distributed-MIMO (D-MIMO) systems. We measure signal to noise ratio (SNR) of down link (DL) multi-user transmission using zero-forcing precoding in over the air environments at 28 GHz by changing user equipment (UE) density. Additionally, mathematical analysis reveals that the beam width causes the differences of spatial division selectivity between C-MIMO and D-MIMO. The experimental and mathematical results demonstrate that C-MIMO degrades the DL SNR as the UE density increases, whereas D-MIMO maintains the high SNR even in the high UE density. D-MIMO enables to enhance the cell capacity in densely populated user environments.