itecture and Design High- High- High- Option 1 Option 2 Option 3 Option 4 Option 5 Option 6 Option 7 Option 8 High- High- High- FIGURE 1-18 3GPP functional splits. Signal Conditioning and Filtering PRACH Channel Estimate/Equali De-modulation FIGURE 1-19 Compute complexity for physical layer processing in 4G/5G standardized use case. Implementation complexity. There is a benefit to a low-complexity radio head (size, weight, power, and design efforts are low) which tends to be supported with a lower level (Option 7/Option 8) split. Feature support. Centralization of processing can allow for more advanced features to be implemented such as Coordinated Multipoint Processing. Resource sharing. As we discussed, one of the prime objectives of early C-RAN initiatives was resource pooling/sharing given that peak versus average use of RF resources. Let's discuss each one of this in a bit more detail for each functional split, observe Fig. 1-19: Split 8. This is the traditional 3G/4G/5G macro base station split that we discussed ear- lier with the full scope of 3GPP physical layer specifications implemented in the base sta- tion. In this implementation, the only digital functionality left in the radio head is up/down Chapter 1 Open radio access network overview 23 sampling and DFE including signal conditioning and filtering which are simple in nature (but computationally potentially complex as we will discuss later). The radio head is little standard specific. Interface to the radio head historically has been proprietary: even though CPRI and OBSAI standards are publicly available, their "optional features" effectively make them proprietary, blocking interoperability between base station and radio head vendors. The fronthaul link carries baseband IQ samples in a digital form, in a time division multi- plexing format, which provides time/frequency synchronization to the radio head as well. Given the baseband interface, the throughput of the fronthaul is constant and defined by the antenna/carrier configuration: bandwidth (BW