# Self-Organizing Networks for 5G and Beyond: A View from the Top
## 2 SON Operation Rationale, Use Cases, Standardization, Architectures and Dimensioning
### Principles of Dimensioning and Designing a SON System  
SON systems' initial dimensioning is based on the collection of existing RAN characteristics through a RAN audit providing key information about the existing policies followed, while it is the most important activity and the basic factor to decide the system architecture and the applications that should be applied. More specifically, in order to decide on the system architecture, we must receive an initial input and define the basic needs no matter what the network technology is that we want to apply SON to (2G/3G/4G/5G). Essential information that must be collected from the network for the needs of system dimensioning and architecture design can be found in the following:  
1. Network features applied in the RAN per vendor. 2. RAN parameter settings/values. Key points include: * Handover and reselection policy. * Admission control policy (admission control is the process that evaluates the existing resources to check if these are sufficient, prior to the establishment of a new connection). * Load balancing policy (load balancing aims to transfer the load from overloaded cells to the neighboring less loaded ones so that end-user experience and network performance is improved). * Scrambling codes planning strategy in UMTS and Physical Cell ID (PCI) planning strategy in LTE and 5G. * Neighbor relation planning strategy (unidirectional/bidirectional) for Intra-Frequency/Inter-Frequency and Inter-RAT and number of maximum neighbors per cell for all technologies. * Number of maximum number of cells supported per BSC/RNC/MME/AMF. * Inter-carrier Layer Management Strategy (LMS). * Frequency bands and number of carriers used per technology (UMTS 2100 MHz, LTE 900 MHz, 1800 MHz, 2600 MHz, etc., according to the spectrum usage acquisition and spectrum refarming policy for 5G). 3. Radio Frequency (RF) hardware equipment in the network (antenna types, Remote Electrical Tilt (RET) types). 4. Pre-SON network KPIs and the expected result after SON deployment. 5. Performance Monitoring (PM) counters activated per vendor. 6. Desired IP planning information for SON platform by considering all needed interconnections and ports that must be open. Figure 5: SON loop, basic phases, and lifecycle. Current and expected OSS dimensioning information. (Moreover, full read/write execution rights to the OSS assigned to the SON orchestrator should be ensured.) * The geolocation information (latitude and longitude) of the cells as well as antenna azimuth information. * Possible network expansion and site rehoming plans from a BSC/RNC/MME/AMF to a neighboring one, or the use of new RAN technologies. * Network size in terms of the number of subscribers and number of active cells per technology, number of network controllers (BSCs, RNCs, MMEs, and AMFs) and number of OSS systems per vendor. A typical real case scenario for a medium-sized operator in Europe prior to 5G commercial launch might include 6,000,000 subscribers in total, 60,000 GSM cells, 90,000 UMTS cells, 80,000 LTE cells, 25 BSCs and RNCs and 5 MMEs. The number of OSS subsystems depends on the different vendors an operator might use. Table 1 can be used as input to the SON dimensioning and design process for a real network including 2G/3G and LTE technologies and correlates the applied handover, admission control, and load balancing policies with specific SON applications. The same rationale applies in 5G networks as well, leading to the outcome that IRAT policies, admission control and load balancing parameters are the initial factors to consider. Through using the RAN audit and information collection as the dimensioning input, the equivalent output regards the optimum architecture design of a 2G/3G/4G/5G SON system. Basic system design decisions include:  
1. Decision regarding the hardware infrastructure needs of the SON system to be deployed and prediction for possible hardware expansion (mainly based on the input collected regarding the number of cells per technology as well as existing network controllers (BSC/RNC/MME/AMF). 2.