on Remote RF Active antenna Active antenna cabinet installation with baseband Passive Passive Active Active antenna antenna antenna antenna + baseband RF cable RF cable Fiber Fiber Fiber baseband eCPRI in cabinet Baseband Baseband Base station site Virtualized baseband Figure 8.8 Evolution of base station site. operators are building the sites. Figure 8.8 illustrates evolutionary steps in the base sta- tion site. The traditional solution on the left has a large base station cabinet housing RF and baseband units. RF cable connects RF units to passive antenna. The drawbacks of this solution are long RF cables with high losses and bulky base station cabinets with complex installation. The next phase brought RF units close to the antenna, which min- imizes RF cable loss. This solution is also known as remote RF installation. Also, the baseband unit can be located within a small casing, which makes the installation work more flexible. The antenna has been a passive component in the first two evolutionary phases. The third phase made the antenna an active component by integrating RF com- ponents inside the antenna. An active antenna and a baseband unit are connected with optical fiber, where the interface is typically Common Public Radio Interface (CPRI). An active antenna brings a number of benefits: RF losses can be minimized, beamform- ing can be enabled, and installation can be simplified as RF cables or connectors are not required. The fourth step in the site solution evolution is the integration of part of the baseband processing with the active antenna and the rest in the virtualized local cloud. Low-latency baseband is integrated with the antenna, and more latency-tolerant baseband can be centralized. The detailed functionality split depends on the fiber capa- bility. The interface options between baseband sections are described in Chapter 5, and the main options are called F1 and eCPRI. The fourth step makes the base station site extremely lean: it is just an antenna with a fiber connection to the virtualized 