# Self-Organizing Networks for 5G and Beyond: A View from the Top
## 5 Future SON Research Directions for B5G
### NFV and SON (vSON) for 5G Networks--RAN Virtualization/C-RAN Architectures and SON  
The telecommunications industry managed to develop critical network function entities such as Evolved Packet Core (EPC) in the case of LTE which is an indication that it can  
Figure 11: Non-roaming 5G architecture. be applied in 5G network entities as well [90; 91]. An example is the migration from virtual Evolved Packet Core (vEPC) the Stand-alone for 5G core (SA) [92]. Since very critical parts of a network can be virtualized and legacy hardware tends to be replaced by virtualized solutions, SON platform virtualization over NFV seems to be intelligent, cost effective and fast in terms of deployment; however, performance metrics must be carefully examined since the interaction of a SON system with the OSS of a mobile network in real time and in terms of time response is very critical. Companies such as Cellwise have already deployed virtualized SON solutions [93]. Virtual SON (V-SON) as an extension of the NFV and SDN architecture has been suggested as one of the key drivers for SON deployment in B5G networks. This can occur either in a centralized or in a distributed/hybrid architecture approach, enabling the provision of SONaaS (SON as a service) [94; 95; 11; 8]. The basic architectural functional blocks of an NFV architecture are the following [96]:  
* Virtualized Network Function (VNF): VNF refers to a standard network function, non-virtualized prior to NFV introduction, which can be fully or partially virtualized. Typical examples might be the MME or AMF, the SGW (Serving Gateway), or even the eNodeB/gNB. In our case, SON might be one of the VNFs [95]. * Element Management (EM): Refers to the management operations strategy of the VNFs. * NFV Infrastructure (NFVI): VNFI refers to the common hardware resources (servers and storage) that host the NVFs. Routers, switches and wireless links interconnecting the main servers can be regarded as part of the NFV infrastructure as well. Moreover, C-RAN (Cloud-RAN), or Centralized-RAN, was first proposed as an architecture by China Mobile Research Institute in April 2010 providing a unified, centralized, and cloud computing solution, leading to the virtualization of the RAN part of 2G, 3G, 4G, and 5G networks [97]. Network operators can benefit from C-RAN since it can provide higher spectrum efficiency, interference, and capacity management, load balancing/traffic peaks handling, energy consumption, and CAPEX/OPEX savings [98; 99; 100]. The former is the outcome of the centralized or partially centralized operation of a Base Band (BB) pool gathering basic RAN functions and serving multiple radio units. The possible architectures are initially based on the assignment and sharing of the functionalities of the BBU (Baseband Unit) and Remote Radio Head (RRH) (referred as Remote Radio Unit (RRU) as well). There are two basic approaches: In the first approach full centralization is provided, since the baseband unit provides layer 1, layer 2, and layer 3 functionalities, while in the second approach (partial centralization) the RRH provides the BBU functionalities leading to partial centralization [98; 99; 100]. The traditional strong relation of the BBU with the RRU where the latter coexist in the same site does not exist anymore since an RRU might belong to different BBUs and the functionality of a \"Virtual BTS\" is introduced. This is the key correlation point of C-RAN with Network Function Virtualization (NFV). In our opinion, the combination of C-RAN with C-SON is a key enabler for future B5G networks, while with the rise of C-RAN it is possible that additional scenarios and use cases for C-SON systems might appear. The rationale behind this is that C-SON systems shall be able to monitor in a more centralized manner metrics and parameters related to the Baseband Units hardware operation and possibly new SON applications focusing on hardware management can be developed.