Functional splits are nothing new. They were initially outlined in 3GPP Release 14 and defined in 3GPP release 15 and where new terminology, interfaces and functional modules were introduced. But why is this RU, DU, CU functional split concept becoming so fundamental in Open RAN?
Let us start with some basics.
Previous RAN architectures (2G, 3G and 4G) were based on a “monolithic” building blocks, where few interactions happened between logical nodes. Since the earliest phases of the New Radio (NR) study, however, it was felt that splitting up the gNB (the NR logical node) between Central Units (CUs) and Distributed Units (DUs) would bring flexibility.