The fourth generation wireless communication
systems have been deployed or are soon to
be deployed in many countries. However, with
an explosion of wireless mobile devices and services,
there are still some challenges that cannot
be accommodated even by 4G, such as the spectrum
crisis and high energy consumption. Wireless
system designers have been facing the
continuously increasing demand for high data
rates and mobility required by new wireless
applications and therefore have started research
on fifth generation wireless systems that are
expected to be deployed beyond 2020. In this
article, we propose a potential cellular architecture
that separates indoor and outdoor scenarios,
and discuss various promising technologies
for 5G wireless communication systems, such as
massive MIMO, energy-efficient communications,
cognitive radio networks, and visible light
communications. Future challenges facing these
potential technologies are also discussed.