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5G NR gNB High Layer Split

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5G New Radio (NR) introduces a new architecture that supports various deployment scenarios, from dense urban areas to remote rural locations. One of the architectural concepts in 5G NR is the High Layer Split (HLS), which is crucial for achieving the desired flexibility, efficiency, and performance in 5G networks.

What is the High Layer Split (HLS)?

In the context of 5G NR, the term "split" refers to the division of the functionalities between the Central Unit (CU) and the Distributed Unit (DU) of the gNB (Next Generation NodeB or base station). The High Layer Split (HLS) specifically means that more functions are moved to the DU compared to a low-layer split.

Technical Details:

  1. Function Distribution:
    • Central Unit (CU): In an HLS scenario, the CU is responsible mainly for higher-layer functionalities such as Radio Resource Management (RRM), session management, and user-plane protocol terminations. The CU acts as a central point of control and coordination for multiple DUs.
    • Distributed Unit (DU): The DU handles lower-layer functionalities, including the physical layer processing, radio frequency (RF) functions, and some MAC (Medium Access Control) layer functionalities. Essentially, the DU is closer to the radio unit and handles tasks that require real-time processing and low-latency operations.
  2. Advantages:
    • Flexibility: HLS provides more flexibility in terms of deployment scenarios. Operators can optimize network resources better by distributing functionalities according to specific requirements.
    • Scalability: By separating higher-layer and lower-layer functions, scaling becomes more efficient. Operators can scale the network by adding more DUs or CUs based on demand.
    • Performance: HLS can lead to improved latency and throughput performance, especially in scenarios where real-time processing at the radio edge is critical.
    • Cost-Efficiency: The distribution of functions allows for more cost-effective hardware deployment. For instance, specialized hardware tailored for real-time processing can be used in DUs, while general-purpose hardware can serve in CUs.
  3. Challenges:
    • Coordination Overhead: Since functionalities are split between CU and DU, efficient coordination mechanisms must be in place to ensure seamless operation. This requires robust interfaces and protocols between CU and DU.
    • Complexity: Managing a split architecture can introduce complexities in network planning, operation, and maintenance. Proper tools and expertise are essential to manage and troubleshoot the system effectively.

Conclusion:

The High Layer Split (HLS) in 5G NR's gNB architecture signifies a shift in how network functionalities are distributed between the Central Unit (CU) and Distributed Unit (DU). By offloading more responsibilities to the DU, 5G networks can achieve greater flexibility, scalability, and performance advantages. However, this comes with the challenge of managing increased complexity and ensuring efficient coordination between CU and DU components.