5G:Open RAN and O-RAN in Brief

5G:Open RAN and O-RAN in Brief

The O-RAN Reference Architecture is designed to enable next generation RAN infrastructures. It is designed with the principles of intelligence and openness, the O-RAN architecture is the foundation for building the virtualized RAN on open hardware, with embedded AI-powered radio control, that has been envisioned by operators around the globe.

The architecture is based on well-defined, standardized interfaces to enable an open, inter-operable supply chain ecosystem in full support of and complimentary to standards promoted by 3GPP and other industry standards organizations.

It has following functional blocks:

• Orchestration/NMS layer with  Non Real Time RAN Intelligent Controller
• RAN Intelligent Controller (RIC) near-Real Time function layer
• Multi-RAT CU protocol stack Function
• DU and RRU Function

Split RAN architecture was originally defined by 3GPP to address URLLC (Ultra Reliable Low Latency Communication) and eMBB (Enhanced Mobile Broadband) requirements. O-RAN is defining or clarifying the usage of the interfaces between:

1. Orchestrator and RAN components – A1 interface.

2. RIC (RAN Intelligent Controller) and CU/DU – E2 Interface.

3. CU-CP (control plane) and CU-UP (user plane) – E1 Interface.

4. CU-DU – F1 interface.

5. DU-RU (radio unit) – Open FrontHaul.

6. Orchestrator and Cloud Platform (O-Cloud) – O2 Interface.

Orchestration/NMS layer with  Non Real Time RAN Intelligent Controller

Non-RT control functionality (> 1s) and near-Real Time (near-RT) control functions(<1s) are decoupled in the RIC. Non-RT functions include service and policy management, RAN analytics and model-training for the near-RT RAN functionality. Trained models and real-time control functions produced in the RIC non-RT are distributed to the RIC near-RT for runtime execution.

• O-RAN specification defined an A1 interface between Orchestration/NMS layer with RIC non-RT and eNB/gNB containing RIC near-RT.
• Network management applications in non-RT RIC receives and act on highly reliable data from the modular Control Unit (CU) and Distributed Unit (DU) in a standardized format over A1 Interface.
• AI-enabled policies and ML-based models generated messages in RIC non-RT  and conveyed to RIC near-RT.
• The core algorithm of non-RT RIC is owned and deployed by network operators
• This algorithms provides the capability to modify the RAN behaviors based by deployment of different models optimized to individual operator policies and optimization objectives

RAN Intelligent Controller (RIC) near-Real Time function layer

The O-RAN reference architecture provides next generation RRM with embedded intelligence,while optionally accommodating legacy RRM. This resides within the RIC Near RT function layer. The RIC near-RT is completely compatible with legacy RRM and its design is started to enhancing the operational challenging functions such as per-UE controlled load-balancing, RB management, interference detection and mitigation.

This layer has following functions

• It provides new functions leveraging embedded intelligence,such as QoS management, connectivity management and seamless handover control.
• The RIC near-RT delivers a robust, secure, and scalable platform that allows for flexible on-boarding of third-party control-applications.
• RIC near-RT functions leverages a database called the Radio-Network Information Base (R-NIB) which captures the near real-time state of the underlying network
• It feeds various RAN measurements data, to the near-RT RIC to facilitate radio resource management
• It also provides initiate configuration commands  to CU/DU.
• The near-RT RIC can be provided by traditional TEMs or 3rd-party players
• RIC near-RT receives an AI model from RIC non-RT and  execute it to change the functional behavior of the network

Interface Reference Points (A1 & E2)

• A1, as described above, is the interface between non-RT RIC and modular CU which contains near-RT RIC.
• E2 is a standard interface between the near-RT RIC and CU/DU in the context of an O-RAN architecture.

Multi-RAT CU protocol stack Function

• The function of the Multi-RAT protocol stack supports 4G, 5G and other protocol processing.
• The basic functions of the protocol stack are implemented according to the control commands issued by the near-RT RIC module e.g. handovers
• Multi-RAT CU function shall be deployed on virtualization platform
• This virtualization provides a highly-efficient execution environment for CU and near-RT RIC, with the ability to distribute capacity across multiple network elements with security isolation, virtual resource allocation, accelerator resource encapsulation, etc. benefits
• The current architecture is using  existing interface definitions for F1/E1/X2/Xn provided by 3GPP
• This interfaces can be enhanced to support inter operation among multi-vendors and the CU provided by TEMs offer a regional CP and UP anchor for DUs

DU and RRU Function

• The DU and RRU function includes real-time L2 functions, base band processing and radio frequency processing
• The interface between the DU and the RRU provides standard function segmentation, including the DU-RRU lower layer split interface (Open front-haul Interface), and the CU-DU higher layer split interface (F1), which ensures inter-operability between different TEMs