the beamforming operation and with number of antennas after the beamforming operation. In an IO-constrained scenario where the number of physical antennas is higher than the number of logical layers, Option 7-2 becomes an obvious partitioning candidate. Stretching this even further, we note that in the downlink (only!), operations of layer mapping and precoding are relatively of low-complexity and need low computational effort. Moving to Option 7-3 takes advantage of this by sending unmodulated bits from the base station to the radio head, thus lowering IO bandwidth even more. This option only applies to the downlink because in the uplink direction, channel estimation/equali- zation (which are the equivalent functions in the receiver) are still done in the 24 Open Radio Access Network (O-RAN) Systems Architecture and Design DL From MAC UL To MAC CRC Attachment Code Block Concatenation Code Block Segmentation CRC validation Forward Error Correction Forward Error Correction Rate Matching Rate De-Matching Code Block Concatenation Scrambling De-Scrambling Modulation De-Modulation Option 7-3 (DL Only) Layer Mapping Layer De-Mapping Precoding Channel Estimate, Equalize Option 7-2 Resource Element Mapping Resource Element De-Map Beam Forming Beam Forming Option 7-1 iFFT + Cyclic Prefix FFT + Cyclic Prefix Option 8 Digital Front End Digital Front End To RF From RF FIGURE 1-20 Option 7 and Option 8 splits. Precoding Precoding Option 7-2 Pepperon Laker Resource Element Mapping Resource Element Mapping Beam Forming Option 7-1 iFFT + Cyclic Prefix iFFT + Cyclic Prefix Option 8 Peppermint Digital Front End Digital Front End To RF To RF FIGURE 1-21 Option 7 splits. Chapter 1 Open radio access network overview 25 (centralized) base station. As we will see later, in use cases with asymmetrical throughput requirements (more downlink than uplink), this can be a good candidate. Remainder split options (6.1) are above the physical layer as shown in Fig. 1-22. Option 6 is a MAC/PHY split where messages between both stacks are exchang