per RU. 7.4 Deployment Considerations # of CUs per 100 km radius service area VS. RTT CU-DU RTT (us) Figure 7.2 Estimate number of CUs as a function of transport network round-trip time. 7.4.5 Baseband Pooling Baseband pooling is one of the two main advantages of centralized NG-RAN (based on split architectures mentioned above), with the other one being centralized radio resource coordination and scheduling. In the past, most of the baseband compute, especially PHY/Medium Access Control (MAC)/Radio Link Control (RLC) parts of the protocol stack were done in specialized hardware specifically designed for that purpose. However, the processing capability of general-purpose processors has evolved, and specialized accelerators have been added to these. As a result, general-purpose hardware has evolved to such an extent that it can be used for baseband compute including MAC and RLC layers (and to some degree even PHY). These advancements, together with standardization of network interfaces between split NG-RAN nodes, open the possibility of virtualiza- tion (see Section 6.2) of the entire RAN protocol stack and the resulting savings for operators. Lower-layer split can enable baseband consolidation through pooling of multiple base- bands at a centralized location. Consider an example case where a base band unit (BBU), which can be a combined CU and DU using the terminology defined in this book, is imple- mented using a general-purpose compute that has the compute capacity to handle 100 sub-6 GHz cells (sector carriers) and assume that each deployment site has 10 cells. A cen- tralized NG-RAN architecture based on Options 7/8 can lead to pooling of resources across 10 different sites and result in a 10 times resource reduction for BBUs. This shows that pool- ing of BBUs using lower-layer split can lead to heavy savings for operators by reducing the number of BBUs required for a certain deployment area. On the other hand, high-band cells require much higher compute capacity per sector carrier. Therefore, the pooling gain