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5G NR gNB Logical Architecture and Its Functional Splits

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The 5G New Radio (NR) gNB (gNodeB) logical architecture is a key element in the 5G network that provides radio access to user devices. The gNB is responsible for the transmission and reception of radio signals, as well as managing the radio resources within the 5G network. The gNB logical architecture is designed to be flexible, scalable, and capable of supporting a wide range of deployment scenarios.

The gNB logical architecture consists of various functional elements that work together to enable the delivery of high-speed and low-latency services. The key elements of the 5G NR gNB logical architecture include the following:

  1. Central Unit (CU):
    • The CU is responsible for the overall control of the gNB. It manages and coordinates the radio resources, performs radio resource management, and controls the mobility of devices within the cell.
    • The CU is further divided into two subcomponents: the Central Unit - Distributed (CU-CP) and the Central Unit - Centralized (CU-UP).
    • The CU-CP handles the control plane functions, while the CU-UP is responsible for the user plane functions.
  2. Distributed Unit (DU):
    • The DU is responsible for the lower-layer processing of the radio signals. It performs functions such as modulation, coding, and decoding of the radio signals.
    • Similar to the CU, the DU is also divided into two subcomponents: the Distributed Unit - Centralized (DU-CP) and the Distributed Unit - Distributed (DU-UP).
    • The DU-CP handles control plane processing, while the DU-UP is responsible for user plane processing.
  3. Radio Unit (RU):
    • The RU is responsible for the radio transmission and reception. It includes the antennas and RF (Radio Frequency) components.
    • The RU communicates with the DU to send and receive data and control signals.
  4. gNB-CU/DU Interface:
    • This interface facilitates communication between the CU and the DU. It is standardized to allow interoperability between different vendors' equipment.
    • The interface is defined by functional splits, which determine how the control and user plane functions are distributed between the CU and DU.

Functional Splits:

  • The functional splits define how the processing functions are distributed between different elements of the gNB architecture.
  • There are two main functional splits:
    • CU-DU Split: This split defines the separation between the control plane (CU) and user plane (DU) functions. It allows for flexibility in the deployment of the network, enabling the CU and DU to be located at different physical locations.
    • DU-RU Split: This split defines the separation between the lower-layer processing (DU) and the radio transmission/reception (RU). It allows for the DU to be located closer to the antennas, facilitating the use of centralized processing resources.

5G NR gNB logical architecture is a modular and flexible system that consists of the CU, DU, RU, and standardized interfaces. The functional splits between these elements provide flexibility in deployment and enable efficient use of resources in different network scenarios.