The System Model With massive MIMO and millimeter wave communication technologies, the small cell scenario is an unavoidable solution for the future 5G network. In this article, two small cell backhaul solutions are presented to evaluate the throughput and energy efficiency of 5G wireless backhaul networks. The first backhaul solution is marked as the central solution in Fig. 1. A macrocell BS (MBS) is assumed to be located in the macrocell center, and SBSs are assumed to be uniformly distributed in the macrocell. All SBSs are configured with the same transmission power and coverage. In Fig. 1, the wireless backhaul traffic of small cells is transmitted to the MBS by millimeter wave communication links, and then the aggregated backhaul traffic at the MBS is forwarded to the core network by fiber to the cell (FTTC) links. There are two logical interfaces, S1 and X2, which are used for forwarding backhaul traffic in the central solution. S1 serves as a feeder for user data from the advance gateway to the MBS, and the advance gateway is the entrance to the core network. X2 enables mutual information exchange among small cells. The detailed scenario and logical architecture are illustrated in Figs. 1a and 1b.