aul delay may affect HARQ timing and scheduling. 4 NG-RAN Architecture Note: this is the option that is standardized in the Small Cell Forum, see Section 4.7 for details. Option 7 In this option, also referred to as intra-PHY split, part of physical layer function and RF are in the DU. The remaining parts of the PHY and all the protocol stack are in the CU. Multiple PHY partitioning options have been considered (and even more options are tech- nically possible), in particular: Option 7-1 In this option, in the uplink, Fast Fourier Transform (FFT), cyclic prefix (CP) removal, and possibly Physical Random Access Channel (PRACH) filtering functions reside in the DU, the rest of the PHY functions reside in the CU. In the downlink, iFFT and CP addition functions reside in the DU, the rest of PHY functions reside in the CU. The main benefit is that this option allows the implementation of advanced receivers. Option 7-2 In this option, in the uplink, FFT, CP removal, resource de-mapping, and possibly pre- filtering functions reside in the DU, the rest of the PHY functions reside in the CU. In the downlink, inverse FFT (iFFT), CP addition, resource mapping, and precoding functions reside in the DU; the rest of the PHY functions reside in the CU. Note: this is the option selected for standardization by the O-RAN Alliance for the low-level split. More details can be found in Section 4.5. Option 7-3 (Only for DL) In this option, only the encoder resides in the CU, and the rest of the PHY functions reside in the DU. The main benefit is that it reduces the fronthaul requirements in terms of throughput to the baseband bitrates as the payload for Option 7-3 is encoded data. Option 8 In this option, also referred to as PHY-RF split, RF functionality is in the DU and all the upper layers are in the CU. The main benefit is that the interface between CU and DU is relatively simple (as the interface needs to convey mostly I/Q data samples, together with some control and syn- chronization information); however, it has the most string