ased fronthaul interface to the Distributed/Baseband Unit and interface conversion from external optical link to board-level interface to Digital Signal Processing components b. Includes termination of network-based timing (IEEE1588/Synchronous Ethernet) C. Includes Operation and Maintenance (OAM) and related "slow path" functions d. We assume a Time Domain, IQ based interface between Baseband/Digital Unit (DU) and RU, where time-to-frequency domain conversion is done inside the RU- corresponding to the O-RAN 7-2x split defined earlier. Chapter 4 Hardware architecture choices 2. Lower Physical Layer a. Implements the Digital Signal Processing that converts the eCPRI information (frequency domain I/Q data) into time-domain analog I/Q that can be transmitted by the RF subsystem b. This typically (for category "B" RUs in the <6 GHz marker) includes the beamforming functionality associated with user-to-antenna mapping C. Includes time-to-frequency domain conversion (FFT) functions. 3. Digital Front End a. Includes Digital Up/Down Conversion, Crest Factor Reduction and Digital Predistortion functions, specifically for <6 GHz implementations. 4. RF Subsystem a. Implements the analog conversion from baseband IQ to (IF and) RF and the antenna Receive (Rx) and Transmit (Tx) functions including analog beamforming. Note how the picture above shows which components are naturally centralized (specifi- cally beamforming) and which components are explicitly unique to each antenna path. The centralized nature of the beamforming component comes from the fact that in the uplink (receive) direction, this function is implemented as a matrix multiplication between all antenna data and antenna weights to produce the per-Layer (user) samples that are further processed in the DU. This processing stage is difficult to break down into an easily scalable solution involving multiple physical devices. This beamforming aspect can complicate the partitioning, especially when building Massive MIMO systems. eCPRI termination This component is ve