Thus, spectrum extension and network densification are highly correlated. However, when we look into higher frequency bands, (e.g., beyond 10 GHz), the current LTE radio interface, which was optimized for the existing cellular bands (i.e., around 2 GHz) would not be optimum. Therefore, at a certain point in the future, it would become necessary to redesign the radio interface assuming the requirements for future newly identified spectrum in the World Radio communication conferences (WRC-15) and beyond. From another point of view, the market size for utilizing higher frequency bands needs to be sufficiently large. It is therefore desirable from the operator perspective that higher frequency bands can be used by many UE devices and for many service areas as much as possible. In this sense, higher frequency bands need to be utilized in various deployments, not only for indoor but also for outdoor deployments. Figure 4 shows two typical scenarios for outdoor small cell deployments, that is, normal high traffic spots such as railway stations in suburban areas in which small cells are sparsely deployed, and a super high traffic area such as the downtown area in a large city in which small cells are densely deployed to provide continuous or partial coverage coverage. Furthermore, macrocell deployments using higher frequency bands should be allowed.