capsulation eCPRI decapsulation Code Block Concatenation Scrambling Ethernet MAC De-Scrambling Modulation De-Modulation Layer Mapping De-Scrambling Precoding De-Modulation Timing/1588 Layer De-Mapping Channel Estimate, Equalize Resource Element De-Map Offload/FPGA To RU FIGURE 4-10 Alternative server PCle/offload scenario for eCPRI and forward error correction. These custom designs often employ the same components/component families as server- based designs but are more flexible on component choice (custom, after all) as well as inter- connect/interfacing. The starting point of design of an optimized hardware solution is to assess the connectiv- ity requirement. We give an example depiction below for a low-end cell-site solution in Fig. -11: Like for the server-based product, the main component in the CU/DU Digital Baseband unit is a programmable (processor) solution. But also, here, for the unit to become a DU, we need to solve some challenges that are unique to the DU application: Time/frequency synchronization Fronthaul and mid/backhaul IO Forward error correction and other acceleration. 152 Open Radio Access Network (O-RAN) Systems Architecture and Design Cell Site DU/CU 3-RU subsystem 2x10GbE Antennas (optional) 10+10 GbE Failover eCPRI/7-2x 4R4T, TDD/FDD IEEE1588/PtP DU/CU 2x1/10GbE Digital Baseband Failover, 2x10GbE Antennas cascade, ring 2x10GbE Antennas Cell Site DU/CU Baseband Unit 3 X 4 antenna (optional) integrated CU functionality (optional) Integrated switch/route (CSR) FIGURE 4-11 Cell site CU/DU + radio unit (RU) subsystem, IO requirements. Given the more embedded nature of these optimized hardware implementations, we have more options for implementation. We split the processing stages into the following key functional components and list out their implementation options (Fig. 4-12): Fronthaul IO covers eCPRI protocol support including I/Q packet and eCPRI framing/de- framing. Optionally, this can include support for eCPRI switching to be able to connect multiple baseband devices to each other. Im