# On Analyzing Beamforming Implementation in O-RAN 5G
## 2 Related Work
### O-RAN Functional Units and Nodes  
**O-CU (Open Center Unit). ** The O-CU defined by 3 GPP standards provides support for higher layers of the protocol stack. There is a single O-CU for each gNB. O-CU is connected to potentially multiple O-DUs via the F1 interface, while the O-DU is connected only to one O-CU. The centralized unit is a logical node that includes the gNB functions such as transfer of user data, mobility control, RAN sharing (MORAN), positioning, session management, etc. The O-CU performs the layer three functions, including radio resource control (RRC), packet data convergence protocol (PDCP), service data adaptation protocol (SDAP), etc., and operates on several interfaces such as X2-U, F1-U, NG-U, etc. [8; 9]. **O-DU (Open Distributed Unit). ** The O-DU is a commercial off-the-shelf (COTS) edge server that includes both baseband processing and radio frequency (RF) functions. It hosts radio link control (RLC), MAC, and a physical layer with network function virtualization or containers, as shown in Figure 1. O-DU supports one or more cells, and each O-DU can support one or more beams to provide the operating support for O-RU by user (U), control (C), synchronization (S), and management (M) planes through front-haul interface [10; 11; 12]. Figure 1: O-RAN architecture (base station disaggregation and openness). **O-RU (Open Radio Unit). ** The O-RU hosts the lower PHY Layer Baseband Processing and RF Front End (RF FE), and it is designed to support multiple 3 GPP split options. In O-RAN, the O-RU suggested being implanted based on Split Option 7-2x to achieve generic lower physical functions while avoiding impact from future 3 GPP specifications changes. This should reduce O-RU OPEX and maintenance costs. The 7-2x split allows two types of O-RU radio categories in order to provide flexibility for a system designer, which will be able to implement the most suitable option depending on their needs. The first O-RU type is called Category \"A\", and it hosts the precoding in the O-DU; the second type is the Category \"B\", which hosts the precoding in the O-RU. This split has the benefit of hosting the beamforming in one unit, with the cyclic-prefix (CP) addition/removal and Fast Fourier Transform (FFT)/Inverse Fast Fourier Transform (IFFT) functions integrated with multiple-in multiple-out (MIMO), as shown in Figure 1[10; 11; 12]. **O-Cloud (Open-Cloud). ** O-Cloud is a cloud computing platform comprising a combination of physical infrastructure nodes that meet O-RAN requirements to host the relevant O-RAN nodes (i.e., Near-RT RIC, O-CU-CP, O-CU-UP, and O-DU). On the other hand, O-Cloud must support software components (such as operating system, virtual machine monitor, container runtime, etc. ), management, and orchestration functions. **O-CU-CP (O-RAN Central Unit-Control Plane). ** The O-CU-CP is a logical node that terminates the NG-c, X2-c, Xn-c, F1-c, and E1 interfaces, besides the RRC and PDCP protocols across the UE by hosting RRC and control plane part of PDCP. **O-CU-UP (O-RAN Central Unit-User Plane). ** The O-CU-UP is a logical node that terminates the NG-u, X2-u, S1-u, Xn-u, F1-u, and E1 interfaces, besides the PDCP and SDAP protocols across the UE by hosting SDAP and User Plane part of PDCP. **Non-RT RIC (Non-Real-Time RAN Intelligent Controller). ** Non-RT RIC is a logical function inside the service and management orchestration (SMO) in O-RAN architecture and provides the A1 interface to the near-real-time RIC. Non-RT RIC provides policy-based guidance by supporting intelligent RAN optimization, machine learning (ML) model management, and enrichment information to enable O-RAN optimization. One of the important functions in non-RT RIC is the implementation of intelligent radio resource management in the non-real-time interval (i.e., greater than 1 s) [13; 14; 15]. **Near-RT RIC (Near-Real-Time RAN Intelligent Controller or nRT RIC).