small cell products, we need to consider the network architecture options which will impact the choice of the small cell product. The three main architecture solutions are shown in Figure 5.3. The left-most option shows the case with a complete all-in-one small base station including all the protocol layers 1-3. The small cell is directly connected to the packet core with S1 interface. The interworking with the macro cell layer uses X2 interface. The right-most option shows low power radio frequency (RF) head which is connected to the macro cell baseband. The small cell is just RF without any layer 1-3 functions. The interface uses Common Public Radio Interface (CPRI) or Open Base Station Architecture Initiative (OBSAI) between RF head and macro cell. That interface requires high bandwidth and low latency. The core network connection goes only from the macro cell. The low power RF head appears as a new macro cell sector from the core network point of view. This option is referred to as Centralized Radio Access Network (CRAN) or Cloud RAN since the baseband processing can be done in the centralized location. The term 'cloud' is misleading since the latency requirements are tough and the baseband processing must be located relatively close to the RF head and not far-away in the cloud. The middle option is the latest addition to 3GPP specification in Release 12 to support dual connectivity where UE Small Cell Deployment Options Traffic requirements More capacity needed Small cells needed for due to fast traffic growth more capacity Small cells needed for Higher data rates required better coverage Implementation Evolution ofdigital Small cells become even processing capability smaller and lower cost 3GPP features Interference, mobility and Small cells and HetNet SON features in 3GPP become simpler Wireless backhaul Sub-6 GHz wireless Small cell rollout backhaul available becomes faster Figure 5.2 Drivers and enablers for small cell deployments Release 12 dual All-in-one base station Low power RF head connectivity (((