What is CPRI and eCPRI in optical modules for 5G?

CPRI (Common Public Radio Interface) and eCPRI (enhanced CPRI) are specifications for fronthaul in mobile networks, connecting radio units to baseband processing.

CPRI Basics

• Defined 2003 for 3G/4G fronthaul
• Time-Division Multiplexed (TDM) protocol
• Constant bit rate, tight timing
• Rates: 614.4M, 1.2G, 2.4G, 4.9G, 6.1G, 9.8G, 10.1G, 12.1G, 24.3G

CPRI Optical Modules

• Specialized SFP/SFP+ for CPRI rates
• Industrial temperature grade (-40 to +85°C)
• Cell tower deployment
• Available in single-fiber (BiDi) variants
• Common distances: 300m, 10km, 20km, 40km

eCPRI — the 5G Evolution

• Introduced 2017 for 5G
• Packet-based (Ethernet transport)
• Split MAC/PHY between RU and DU
• Lower bandwidth requirement
• Uses standard Ethernet optics

eCPRI Advantages

• Higher aggregation efficiency
• Standard 25G/100G optics reusable
• Statistical multiplexing possible
• Integration with existing IP networks

Time Synchronization

Both CPRI and eCPRI require precise timing:

• CPRI: inherent in TDM
• eCPRI: requires PTP (IEEE 1588) with G.8275.1 telecom profile
• Time error budget <100 ns typically

Fronthaul Distance

• Traditional CPRI: up to ~20 km (round-trip delay limit)
• eCPRI: similar limits due to synchronization
• Longer distances need distributed baseband architectures

Common Optics Used

Deployment Considerations

• Industrial temperature range for outdoor cabinets
• Support for PTP time synchronization
• BiDi options where fiber is limited
• Vendor compatibility with radio equipment