  To meet the future demand for huge traffic volume of wireless data service,
the research on the fifth generation (5G) mobile communication systems has been
undertaken in recent years. It is expected that the spectral and energy
efficiencies in 5G mobile communication systems should be ten-fold higher than
the ones in the fourth generation (4G) mobile communication systems. Therefore,
it is important to further exploit the potential of spatial multiplexing of
multiple antennas. In the last twenty years, multiple-input multiple-output
(MIMO) antenna techniques have been considered as the key techniques to
increase the capacity of wireless communication systems. When a large-scale
antenna array (which is also called massive MIMO) is equipped in a
base-station, or a large number of distributed antennas (which is also called
large-scale distributed MIMO) are deployed, the spectral and energy
efficiencies can be further improved by using spatial domain multiple access.
This paper provides an overview of massive MIMO and large-scale distributed
MIMO systems, including spectral efficiency analysis, channel state information
(CSI) acquisition, wireless transmission technology, and resource allocation.
