we need to be able to answer the question of how to forward hundreds of gigabits backhaul traffic in ultra dense
cell networks with guaranteed quality of service (QoS) and affordable energy consumption by sustainable systems. With the exponentially increasing demand for wireless data traffic in recent years, it is infeasible for current cellular system architectures to satisfy gigabit-level data traffic in an economical and ecological way [3]. One of the solutions is the small cell network, which is densely deployed by self-organizing, lowcost, and low-power small cell base stations (SBSs). In early studies, a low number of small cells is adopted to improve the signal-to-interference-and-noise ratio (SINR) of wireless links in limited hot areas, embedded in conventional cellular networks. In this case, a little burst backhaul traffic originating from small cells can be forwarded into the core network by the traditional backhual link of cellular networks. When small cells are ultra densely deployed in cellular networks, it is a key problem to forward massive backhaul traffic into the core network. Moreover, there is concern that the large number of small cells will cause the signaling load on the network nodes to increase due to frequent handovers and degraded mobility robustness due to increased handover and radio link failures [4]. The impact of small cell deployments on mobility performance in Long Term Evolution (LTE)-Advanced systems was investigated by system-level simulations [5]. Simulation results implied that the handover optimization technique can effectively