Introduction - If you have any usage issues, please Google them yourself
Massive multiple-input multiple-output technology has been considered a breakthrough in wireless
communication systems. It consists of equipping a base station with a large number of antennas to serve many active
users in the same time–frequency block. Among its underlying advantages is the possibility to focus transmitted signal
energy into very short-range areas, which will provide huge improvements in terms of system capacity. However,
while this new concept renders many interesting benefits, it brings up new challenges that have called the attention of
both industry and academia: channel state information acquisition, channel feedback, instantaneous reciprocity,
statistical reciprocity, architectures, and hardware impairments, just to mention a few. This paper presents an overview
of the basic concepts of massive multiple-input multiple-output, with a focus on the challenges and opportunities,
based on contemporary research.