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 returned directly 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. As a consequence, it is a great challenge for future 5G wireless backhaul networks to forward massive wireless traffic to core networks in a lowcost and highly energy-efficient manner. Some potential challenges are presented in the following context.