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CU, DU, RU (5G RAN)

A 5G Radio Access Network (RAN) is divided into three functional parts: The CU, DU and RU. This is the role that each plays:


  1. Centralized Unit (CU): The CU is responsible for the non-real-time, higher Layer 2 (L2) and Layer 3 (L3) functions. It supports protocol layers like SDAP (only in 5G), RRC, and PDCP. Multiple CUs can be implemented on a shared hardware platform, taking advantage of cloud computing and Network Function Virtualization (NFV)[4].
  2. Distributed Unit (DU): The DU handles real-time Layer 1 (L1) and lower L2 functions, including baseband processing and RF functions. It supports RLC, MAC, and the physical layer. A single CU can connect to multiple DUs, and each DU can support one or more cells[4].
  3. Radio Unit (RU): The RU is essentially the radio hardware unit responsible for converting radio signals sent to and from the antenna into a digital signal for transmission over packet networks. It handles tasks related to the digital front end (DFE) and the lower Physical Layer (PHY), including digital beamforming functionality. Key considerations in the design of an RU include its size, weight, and power consumption, as these factors directly impact the deployment and operational efficiency of the network.


Each of these functional parts can be placed in the same or in different locations. This is referred to as the "functional split." The flexibility afforded by the ability to split the functional units allows a network architect to design an optimal configuration, depending on the environment and application.


Citations:

[1] https://www.5gworldpro.com/blog/2021/06/13/functional-split-ru-cu-and-du/

[2] https://www.rcrwireless.com/20200708/fundamentals/open-ran-101-ru-du-cu-reader-forum

[3] https://www.linkedin.com/pulse/what-5g-ru-lance-brown

[4] https://youtube.com/watch?v=cevTmmcAHy0

[5] https://teletopix.org/5g/what-is-the-difference-between-ru-and-du-in-5g/

[6] https://www.5gtechnologyworld.com/open-ran-functional-splits-explained/

[7] https://support.huawei.com/enterprise/en/doc/EDOC1100203226/c22e1b0e/overview-of-ru-5g


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