es supporting 2G, 3G, 4G, and 5G air interfaces. As we indicated earlier though, the 5G standard is designed to support flexibility, which means that the deployment form factor options increase. This chapter shows some relevant examples. Integrated small cell The integrated small cell (ISC) in many ways is a massively size-, power-, and cost-optimized version of the all-in-one base station that we described earlier and repeated in Fig. 1-13. Defined as a "base station in a box" and implemented as a "base station on a chip," the ISC is targeting two markets: Coverage limitations. User retention is key to a wireless operator. By implication, user satisfaction needs to be achieved even if this implies additional financial expense. For those users who have coverage issues (dropped calls, too few bars, and low Internet throughput), an ISC can provide in-home solution at a reasonable cost. Backhaul from the ISC to the operator network is provided through (third party) wired Internet connectivity such as DOCSIS/cable, DSL, or other traditional wireline access means. A "femtocell gateway" forms the interface between the ISC network and the core/macro network, allowing firewalling and other gateway functionality to be implemented for network abstraction. Capacity enhancement. High-traffic areas such as the often-used example of the coffee shop impose a high user-count and traffic rate that can be beyond the capacity of the traditional macro base station, especially when the location of the high-traffic area is at/ near the cell edge. First-generation ISC (femtocells) targeted WCDMA and to a wider extent, LTE deploy- ments with small user counts (up to 16) and ~ 100-Mbps throughput in an indoor form fac- tor with passive cooling. RF output power per antenna is ~ 250 mW. Femtocell Low Physical High Physical PDCP/ Ethernet DFE/RF MAC/RLC Layer Layer Transport FIGURE 1-13 Integrated small cell architecture. 18 Open Radio Access Network (O-RAN) Systems Architecture and Design The femtocell concept has never been adopted as wid