er at the receiving antennas. For the precoding, the weighting parameters are predefined by 3GPP. The last processing block is the iFFT function, which transfers the frequency-domain I/Q samples into time-domain I/Q samples to be transmitted over the air by Tx antenna. Out of many possible split options, O-RAN has chosen the option 7-2x, which provides a good trade-off, balancing the requirements of reducing fronthaul transport bandwidth and the desire to simplify the radio unit implementation. In particular, it was deemed important to make the RU independent of future 3GPP specification updates, SO that it would be possible to implement it entirely in hardware. Therefore, in the split option 7-2x (ORAN-WG4.CUS.0) most of the 3GPP-specific functions of PHY processing reside in the DU, whereas the O-RAN radio unit (O-RU) hosts the following PHY functions: Beamforming CP addition/removal FFT/iFFT functions. The O-RAN Distribution Unit (O-DU) hosts RLC, MAC and the rest of the physical layer functions (3GPP TS 38.211, 3GPP TS 38.212): Scrambling/descrambling Modulation/demodulation RE mapping/demapping. For the 7-2x split, the lower physical functions within O-RU are generic and not affected by the future 3GPP spec changes, which will reduce O-RU OPEX and maintenance costs. 4.5 Lower-Layer Split O-RAN fronthaul transmits the spatial I/Q data streams instead of antenna I/Q data streams (as in, e.g. split 8). Typically, the number of spatial streams is less than the number of antennas, significantly reducing the transport bandwidth requirement. It is especially beneficial for the base station using a massive MIMO antenna system, which has much larger number of antennas than the spatial streams. The downside of this design choice is that many physical layer functions reside in the O-RU, which requires more processing capabilities and makes the O-RU design somewhat more complex. The single-split option 7-2x chosen by O-RAN allows two types of O-RU radio categories. The first O-RU type is called Category "A," where the p