Sign in Subscribe

OpenRAN - Where to Split

Last updated on 

OpenRAN, or Open Radio Access Network, is an emerging network architecture for mobile communication that aims to disaggregate and open up the traditionally integrated and proprietary RAN (Radio Access Network) components. The goal is to promote interoperability, flexibility, and innovation by allowing different vendors' equipment to work together seamlessly. In OpenRAN, the network functions are split into different components, and this splitting involves defining specific interfaces between these components.

The key components of a traditional RAN include the Radio Unit (RU), Distributed Unit (DU), and Centralized Unit (CU). OpenRAN introduces the concept of functional splits, which determine the separation points between these components. There are several functional splits defined in the OpenRAN architecture, and two of the most important ones are the O-RAN Fronthaul and O-RAN Midhaul.

  1. O-RAN Fronthaul:
    • Purpose: The fronthaul is the interface between the Radio Unit (RU) and the Distributed Unit (DU). It carries the baseband signals from the RU to the DU.
    • Functional Split: O-RAN defines two options for the fronthaul split:
      • Option 7.2: This is a higher-layer split where the RU performs functions like channel coding, modulation, and demodulation. The DU handles functions like MAC (Medium Access Control), RLC (Radio Link Control), and part of the PDCP (Packet Data Convergence Protocol).
      • Option 2: This is a lower-layer split where the RU handles lower-layer functions like the physical layer processing, while the DU handles the higher-layer functions.
  2. O-RAN Midhaul:
    • Purpose: The midhaul is the interface between the Distributed Unit (DU) and the Centralized Unit (CU). It carries the baseband signals from the DU to the CU.
    • Functional Split: O-RAN defines a split called "Midhaul User Plane" (Midhaul-UP) where the DU and CU are separated into different locations, but the split is not as extreme as the fronthaul. The DU still performs some higher-layer functions, and the CU handles the centralized processing.
  3. O-RAN Control Plane:
    • Purpose: In addition to the user plane splits (fronthaul and midhaul), there is a control plane split between the CU and the DU. This involves separating the control functions from the user data processing functions.
    • Functional Split: The O-RAN architecture defines a control plane split into the O-CU-CP (Centralized Unit Control Plane) and the O-DU-CP (Distributed Unit Control Plane). This separation enables flexibility and scalability in the network.

It's important to note that these splits enable network operators to choose different vendors for each component, fostering a more competitive and innovative ecosystem. The OpenRAN architecture is designed to be flexible, allowing operators to deploy and scale their networks more efficiently and cost-effectively. The specific choice of functional splits may depend on factors such as deployment scenarios, network requirements, and the desired level of interoperability and flexibility.