  The rapidly increasing number of mobile devices, voluminous data, and higher
data rate are pushing to rethink the current generation of the cellular mobile
communication. The next or fifth generation (5G) cellular networks are expected
to meet high-end requirements. The 5G networks are broadly characterized by
three unique features: ubiquitous connectivity, extremely low latency, and very
high-speed data transfer. The 5G networks would provide novel architectures and
technologies beyond state-of-the-art architectures and technologies. In this
paper, our intent is to find an answer to the question: "what will be done by
5G and how?" We investigate and discuss serious limitations of the fourth
generation (4G) cellular networks and corresponding new features of 5G
networks. We identify challenges in 5G networks, new technologies for 5G
networks, and present a comparative study of the proposed architectures that
can be categorized on the basis of energy-efficiency, network hierarchy, and
network types. Interestingly, the implementation issues, e.g., interference,
QoS, handoff, security-privacy, channel access, and load balancing, hugely
effect the realization of 5G networks. Furthermore, our illustrations highlight
the feasibility of these models through an evaluation of existing
real-experiments and testbeds.
