Abstract—What will 5G be? What it will not be is an incremental
advance on 4G. The previous four generations of cellular
technology have each been a major paradigm shift that has
broken backward compatibility. Indeed, 5G will need to be a
paradigm shift that includes very high carrier frequencies with
massive bandwidths, extreme base station and device densities,
and unprecedented numbers of antennas. However, unlike the
previous four generations, it will also be highly integrative: tying
any new 5G air interface and spectrum together with LTE and
WiFi to provide universal high-rate coverage and a seamless user
experience. To support this, the core network will also have to
reach unprecedented levels of flexibility and intelligence, spectrum
regulation will need to be rethought and improved, and energy
and cost efficiencies will become even more critical considerations.
This paper discusses all of these topics, identifying key challenges
for future research and preliminary 5G standardization activities,
while providing a comprehensive overview of the current literature,
and in particular of the papers appearing in this special issue.