CPRI vs eCPRI: Key Differences Explained for 5G

This article compares CPRI and eCPRI, highlighting the key differences between them, especially in the context of 5G wireless technology. CPRI is typically used in older systems, while eCPRI is designed for 5G.

Introduction

• CPRI (Common Public Radio Interface): Defines the interface specification between the REC (Radio Equipment Control) and RE (Radio Equipment) of radio base stations in cellular networks. It’s a standard for transporting baseband I/Q signals to the radio unit in traditional Base Stations (BS) and supports various standards like GSM, WCDMA, and LTE.
• eCPRI: The successor to CPRI, designed for 5G systems, LTE-Advanced, and LTE-Advanced Pro. It defines the connection between eREC and eRE via a fronthaul transport network.

The primary goal behind developing CPRI and eCPRI is to provide Mobile Network Operators (MNOs) with deployment flexibility. This is achieved by simplifying the Base Station (BS) architecture, dividing its functionality into two modules:

• eREC (evolved Radio Equipment Control): Contains part of the PHY layer functions and upper layer functions of the air interface.
• eRE (evolved Radio Equipment): Contains the remaining PHY layer functions and the analog radio frequency (ARF) functions.

These components can be physically separated, with the eRE placed near the RF antenna and the eREC located remotely, connected by a transport network.

CPRI (Common Public Radio Interface)

Figure 1: CPRI Interface Definition

Figure 2: Typical CPRI Network Elements

Here are some key features of CPRI:

• Point-to-Point Interface: CPRI uses a direct connection between a master and slave port via optical or electrical cables.
• No Networking Layer Functions: CPRI does not support networking layer functions.
• Topology Dependent on REC/RE: The network topologies in CPRI depend on the functions of the REC and RE.
• Supported Logical Connections:
  • Point to Point (One REC with one RE)
  • Point to Multi-Point (One REC with several REs)
• REC/RE Handles Advanced Functions: Redundancy, security, and QoS functions are managed by the REC/RE.

eCPRI

Figure 3: eCPRI Interface Definition

Function: The eCPRI interface enables efficient and flexible radio data transmission over packet-based fronthaul transport networks like IP or Ethernet.

Figure 4: Typical eCPRI Network Elements

Key features of eCPRI include:

• Network Elements: The network comprises eCPRI nodes (eRECs/eREs), the transport network, and other elements like GM/BC for timing and EMS/NMS for network management.
• No Master/Slave at Physical Level: eCPRI does not classify ports as master or slave at the physical level.
  • SAP S: Master of PTP and synchronous ethernet is generally not eREC.
  • SAP CM: Some parts of the M-plane may be managed by EMS/NMS.
• eCPRI Layering: The eCPRI layer operates above the transport networking layer.
• Transport Network Flexibility: The transport network can include local networks, such as local switches from eREC/eRE vendors.
• Supported Logical Connections:
  • Point to Point
  • Point to Multi-point
  • Multi-point to Multi-point
• Transport Network Protocols: eCPRI nodes need to implement appropriate transport network layer protocols to support redundancy, security, and QoS.
• Reduced Data Rate Requirements: Compared to CPRI, eCPRI reduces data rate requirements between the eREC and eRE by using flexible functional decomposition while maintaining the complexity of the eRE.
• Flexible Functional Split: eCPRI offers more flexibility in positioning the functional split within the Physical layer of the BS (i.e., gNB or eNB) compared to CPRI.

For more details, refer to the advantages and disadvantages of the eCPRI interface.

References

• CPRI Specification V7.0 (2015-10-09)
• eCPRI Specification V1.0 (2017-08-22)