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CU/DU Separation

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The CU/DU (Centralized Unit/Distributed Unit) separation is a concept related to the architecture of 5G networks. It represents a shift from the traditional architecture where the baseband processing is performed within the base station to a new architecture where the baseband processing can be split into two parts: the CU and the DU.

Traditional Base Station Architecture:

In the traditional architecture, the base station (or eNodeB in LTE terminology) contains both the radio unit (RF processing) and the baseband unit (BBU), where the digital signal processing and other baseband tasks are performed.

CU/DU Split Architecture:

  1. Centralized Unit (CU):
    • The CU is responsible for higher-layer functions and coordination across multiple DUs.
    • It takes care of tasks like scheduling, user mobility management, and radio resource management.
    • The CU is located in a centralized location and can manage multiple DUs distributed over a wider area.
  2. Distributed Unit (DU):
    • The DU is responsible for lower-layer functions such as radio frequency (RF) processing, analog-to-digital conversion, and some parts of the digital signal processing (DSP).
    • DUs are distributed closer to the radio units, allowing for reduced latency and more efficient processing of radio signals.
    • They handle the actual transmission and reception of radio signals.

Benefits:

  1. Flexibility: By separating the CU and DU, operators can scale their networks more efficiently. They can deploy DUs where needed without having to deploy a full base station, which can be cost-effective.
  2. Lower Latency: By distributing some of the processing closer to the edge (near the user equipment), latency can be reduced, which is crucial for applications like augmented reality, autonomous vehicles, and real-time gaming.
  3. Resource Optimization: With CU/DU separation, resources can be dynamically allocated based on demand. The CU can coordinate with multiple DUs and optimize the use of radio resources.
  4. Ease of Maintenance and Upgrades: Operators can upgrade or maintain individual components (CU or DU) without affecting the entire network. This modularity simplifies maintenance and reduces downtime.

Technical Aspects:

  1. Fronthaul Interface: The connection between CU and DU is typically established using a high-capacity, low-latency fronthaul interface. This interface must support the transmission of massive amounts of data between the CU and multiple DUs.
  2. Protocol Stack: The protocol stack for the CU and DU is defined to ensure seamless communication. Protocols like the Common Public Radio Interface (CPRI) or the newer eCPRI (enhanced CPRI) are used for fronthaul communication.
  3. Coordination and Synchronization: Ensuring proper coordination and synchronization between CU and DU is crucial to maintain the quality of service (QoS). Precise timing synchronization is essential for functions like beamforming and interference management.