The Road from CPRI to eCPRI/ORAN Fronthual
May 31, 2023

As we know that RAN, Radio Access Network, is divided into two main components:
-> Baseband Unit (BBU).
-> Radio Unit (RU).

The move from D-RAN to C-RAN then v-RAN and O-RAN depends on how to deploy these two RAN components. MNOs want to #centralize the RAN control functions to improve overall performance, gain efficiencies, and reduce costs.

Before continuing reading, please read this article first:

Centralizing RAN elements enables a many-to-one relationship between BBU control functions and the RRHs. Capabilities such as carrier aggregation, Coordinated Multi-Point (CoMP), and X2 handover are simplified when RAN functions are centralized. This also results in improved performance for mobile users.

Split RAN architecture (Source: Ciena)

In a 3GPP radio system, baseband functions include both a real-time processing part and a non-real-time processing part.

  • Real-time baseband handles radio functions such as dynamic resource allocation (scheduler), gNB measurement, configuration and provisioning, radio admission control, and others.
  • Non-real-time baseband handles radio functions like inter-cell Radio Resource Management (RRM), Resource Block (RB) Control, and connection mobility and continuity functions.

Baseband functions are mapped into Distributed Units (DUs) for real-time baseband processing and Centralized Units (CU) for non-real-time processing.

🧧The fronthaul network between RRHs and BBUs/DUs carries extremely latency-sensitive Common Public Radio Interface (CPRI) radio control traffic for 4G LTE radios and eCPRI or Open RAN (O-RAN) fronthaul radio control messages for 5G NR and ng-LTE radios. CPRI fronthaul traffic is a serialized constant bitstream technology traditionally carried over dedicated fiber or WDM.

📗 CPRI requires more than an order of magnitude higher bandwidth than it delivers in effective user throughput. Since this bandwidth inefficiency does not scale with higher-capacity radios and MIMO antenna technology.

📗 New technologies have emerged to replace CPRI, such as IEEE 1914.3 Radio-over-Ethernet (RoE), O-RAN Fronthaul, and eCPRI.  With 5G, eCPRI and O-RAN fronthaul were defined as a more bandwidth-efficient fronthaul interface from inception, supporting both Ethernet-based or UDP-based transport mechanisms.

🔔 Why CPRI is not used in 5G Networks?

🔔 Why does 5G need to move from CPRI to eCPRI?

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