mobile data packages become more generous there is less and less incentive for mobile users to seek an alternate Wi-Fi network and instead they use operator network for all their data use. This makes indoor small cell networks a key part of both providing ubiquitous 5G coverage and the network densification required to support the increasing data demand from smartphones. In an outdoor environment small cells are critical components for improving data capac- ity of a network in an urban area as part of a heterogeneous network (HetNet). HetNets are a well-known concept and are networks with an over-arching macro cell with multiple smaller cells providing coverage; the small cells are placed either where extra capacity is needed or where there is a coverage deadspot. These small cells can be fully independent from the macro cell, meaning that a UE must hand over into the small cell, or they can be deployed as a carrier of the macro cell via CA. All of these outdoor scenarios are already used in today's LTE networks, but are expected to expand in usage and importance for 5G as the smartphone data demands continue to increase. Finally, in addition to the market drivers for smartphones and today's mobile networks, small cells are also expected to play an important role as 5G becomes adopted in vertical segments. Many of these vertical segments generating initial interest are private enterprise networks, or indoor networks, for example, smart factories embracing industry 4.0. Both enterprise and indoor networks are typically created from small cells. 4.6 Small Cells 4.6.3 Barriers and Solutions With the many small cell market drivers, which already existed in LTE networks, why aren't small cells already ubiquitous? The answer is that small cells have deployment challenges, and these deployment challenges are a mix of both technical and business oriented. As the small cell industry matures these challenges are being overcome, and this section highlights these barriers and the current status of the solutions to them. Freq