n the operator network planning. A synchronization solution is needed in the small cell: frequency synchronization for Release 8 frequency division duplex (FDD) and time synchronization for time division duplex LTE Small Cell Optimization NOKIA Figure 6.3 Nokia Flexi Zone Outdoor Micro/Pico small cell base station (TDD). Time synchronization is needed also for many LTE-Advanced FDD features. The synchronization can utilize satellite-based global positioning system (GPS) or backhaul- based IEEE 1588v2 or Synchronous Ethernet. Flexible backhaul options are needed to support different deployment options. The small base station should be able to take benefit of many different types of backhaul solu- tion, such as microwave radio, optical or electrical Ethernet, or passive optical network (PON). Self-organizing network (SON) features are important in any new base stations, but espe- cially important in the small cells since the number of small cells can be high and the cost of deployment needs to be low. SON includes self-configuration and self-optimization features. Future evolution to multi-band capability, carrier aggregation and LTE-Advanced features is preferred. An example micro cell product is illustrated in Figure 6.3. The product is targeted for both outdoor and indoor installations. A more detailed list of features is shown in Table 6.1. Pico Base Stations The coverage challenge in in-building premises has accentuated in recent times due to the use of modern building materials that significantly attenuate the radio signals from outdoor cells. While the micro base station, possibly powered-down, can be used in harsh indoor envi- ronments such as train and bus stations, more cost-optimized small cell solutions such as pico base stations are required for enterprise and office environment. At RF transmission levels of local area base station - 250 mW or less - health concerns due to radio frequency emissions are avoided. Indoor pico base stations typically use office LAN cabling for backhaul, either existing or 