Open RAN (O-RAN) Reference Architecture

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6 years ago

O-RAN Tutorial

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.

O-RAN Reference Architecture

O-RAN reference Architecture is shown in below picture

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

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

Source:

O-RAN Alliance