V. FUTURE CHALLENGES
In existing studies, the small cell network is presented to satisfy the high capacity requirement
for hot areas in cellular networks. Therefore, the large wireless traffic is just transmitted in limited
hot areas. In this case, a little burst backhaul traffic can be directly returned back to the core
network through the conventional cellular network architecture. With the massive MIMO and
millimeter wave communication technologies emerging into 5G networks, the cell size of 5G
networks has to become smaller. Furthermore, the large wireless traffic is transmitted in 5G
networks. Moreover, the 5G network will become an ultra dense cell network with small cells.
Clustering
As a consequence, it is a great challenge for future 5G wireless backhaul networks to forward
massive wireless traffic to core networks in a low cost and high energy efficiency manner. Some
potential challenges are presented in the following context.
The first challenge is how to design a new backhaul network architecture and protocols for
ultra dense cell deployment scenarios. As we discussed in the last paragraph, small cells and ultra
dense deployment will become the main features in future 5G networks. In this case, the number
of small cells will obviously increase in the unit area. As a consequence, the corresponding
backhaul traffic will increase exponentially at the gateway if the conventional centralized control
model is adopted in the 5G backhaul network architecture. The massive backhaul traffic not
only makes a congestion but also collapses the backhaul network. It looks that the distributed