 using Options 7/8, if any, is negligible. Each high-band deployment site would typically need one or more BBUs/DUs using a lower-layer split. Additionally, since high-band deployments tend to be dense, the number of BBUs/DUs required would be higher leading to higher requirements in terms of space, power, and cooling at the BBU pool locations. This leads to higher real estate and infrastructure costs making lower-layer split less attractive for high-band deployment scenarios. 7 NG-RAN Deployment Considerations RRH/RU BBU Pool Central Office Fronthaul gNB-DUs 3GPP F1 gNB-CU Option 2 split Option 7 Figure 7.3 Two-level split NG-RAN architecture suitable for sub-6 GHz frequencies. 7.4.6 Choice of a NG-RAN Split Architecture Here we consider typical 5G RAN deployment architectures for sub-6 GHz (including low and mid-bands) and high-band scenarios considering the various factors discussed in the earlier sections. 7.4.6.1 Sub-6 GHz Case Sub-6 GHz (low- and mid-frequency ranges) radio deployments with larger propagation distances and respectable pooling gains can benefit from using both the higher-layer Option 2 split and lower-layer Option 7/8 split in a hierarchical architecture as shown in Figure 7.3. This would involve two levels of centralization: first sector carriers from multiple remote radio heads (or RUs) can be connected to a local BBU (i.e. DU) pool using Option 7/8, which can be then further centralized using split Option 2 in a telco central office. Lower-layer split Options 7/8 are appropriate for sub-6 GHz frequencies where it is impor- tant to obtain the coordinated processing gains using mechanisms such as Coordinated Multi-Point (CoMP) Tx and Rx. The resulting fronthaul requirements in terms of FHBW and latency are manageable using current optical transport technologies. Furthermore, the benefits of baseband pooling can be realized and both CUs and DUs can be virtualized 7.4.6.2 High-Band (mmWave) Case As discussed above, high frequency range deployments are characterized by larger band- widths and 