In this article, we summarize the 5G mobile
communication requirements and challenges.
First, essential requirements for 5G are pointed
out, including higher traffic volume, indoor or
hotspot traffic, and spectrum, energy, and cost
efficiency. Along with these changes of requirements,
we present a potential step change for
the evolution toward 5G, which shows that
macro-local coexisting and coordinating paths
will replace one macro-dominated path as in 4G
and before. We hereafter discuss emerging technologies
for 5G within international mobile
telecommunications. Challenges and directions
in hardware, including integrated circuits and
passive components, are also discussed. Finally,
a whole picture for the evolution to 5G is predicted
and presented.