bands for 5G systems than are currently used for existing mobile services. The frequencies as high as 300 GHz, according to some reports, have the potential of supporting extremely wide- band 5G applications. However, due to their radio propagation characteristics, these bands are likely to be utilized primarily in small cells and may have only limited practical usage outside urban areas. To ensure 5G services provide good coverage that extends beyond small urban hotspots, it will be important to ensure that the suitable spectrum is available in sub-1 GHz region. Significant cooperation among mobile industry leaders, standards devel- oping organizations, and national/regional regulatory bodies is required to pave the way for large-scale commercial 5G deployments in 2020 and beyond. Progressive refarming of existing mobile bands should be possible and permitted to accommodate future 5G services and to ensure spectrum is used as efficiently as possible. The success of refarming is best illustrated by the 1800 MHz band which is now the most common LTE band worldwide and was previously used for 2G services. A secondary effect of densification of the network with high-data-rate links is the need to improve backhaul transport. Today, optical fiber is the preferred backhaul option. However, as networks grow to become denser with the deployment of more small cells, licensed fixed or point-to-multipoint (PMP) mmWave wireless backhaul may emerge as the most flexible and viable solution. For example, an operator (leveraging guaranteed QoS with licensed PMP) with a 10 Gbps + hub could aggregate backhaul traffic from multiple base stations. The economies of this scenario improve as more base stations are added progressively through network densification. Millimeter wave communications technologies in the 60 GHz and 70-80 GHz frequency range for high capacity in the last mile and pre-aggrega- tion backhaul have been explored in the literature [27,48]. Table 6 provides the existing Introduction and Background lxxxix Table 6: Ma