RAN decomposition and centralized RAN

RAN decomposition is the term used for the evolution of monolithic RAN to a combination of centralized and distributed RAN architectures. The monolithic RAN encompasses RRH (Remote Radio Head) and BBU (Base Band Unit), forming the eNB/gNB entity, which by its very nature distributes all the functions at the radio location. The decomposition separates the functions of the BBU into the CU (Centralized Unit or Control Unit), the DU (Distributed Unit), and the RU (Radio Unit or Remote Radio Unit (RRU)). This separation is generally known as split, and can be applied at multiple points in the connection between these entities.

Much of the decomposition is encompassed by the term Cloud RAN, which is interchangeable with Centralized RAN (or C-RAN). Simply speaking, C-RAN is a centralized, cloud computing-based architecture for radio access networks that supports 2G, 3G, 4G, 5G and future wireless communication standards. Its name comes from the four Cs in the main characteristics of C-RAN system: clean, centralized processing, collaborative radio, and a real-time Cloud Radio Access Network. C-RAN is the fundamental basis for 5G radio services going forward. While 5G radio is not mandated to be based on C-RAN, it is the path that the industry is following.

Cloud RAN is virtualized RAN or vRAN that is designed for cloud-based deployment and therefore virtualized. Having the decomposed RAN, and basing this on cloud computing-based technologies, provides massive flexibility to the MNO.