Board and RRU optical module

Optical modules connect the BBU and RRU in mobile base stations, enabling high-speed data transmission over fiber with support for industrial environments.

Overview of BBU and RRU

In mobile communication networks, a base station is typically divided into two main parts: the BBU (Baseband Unit), responsible for signal processing, and the RRU (Remote Radio Unit), responsible for transmitting and receiving radio signals . The BBU is usually located indoors in a climate-controlled environment, while the RRU is mounted outdoors on telecom towers, exposed to extreme temperatures and weather conditions .

Role of Optical Modules

Optical modules serve as the transmission medium between the BBU and RRU, converting electrical signals into optical signals for fiber transmission and vice versa . They are essential for maintaining high-speed, long-distance communication between the indoor and outdoor units. In 4G networks, optical modules typically support data rates from 1.25G to 10G, while in 5G networks, higher rates such as 25G are common .

Types and Specifications

• 4G Networks: Optical modules range from 1.25G SFP to 10G SFP+, with wavelengths around 850nm, operating temperatures of 0–75°C, and transmission distances up to 550m for multimode fiber .
• 5G Networks: Optical modules often use CPRI or eCPRI interfaces with higher data rates (25G), supporting industrial temperature ranges due to outdoor deployment .
• Fiber Requirements: RRUs typically require 2–6 core optical fibers, and passive wavelength division multiplexing (CWDM) is often used to optimize fiber usage and enable serial networking between multiple RRUs .

Operational Considerations

• Temperature and Environment: RRUs operate in unregulated outdoor conditions, so optical modules must support industrial temperature ranges, sometimes as low as -40°C or lower in extreme climates .
• Power and Fault Management: Optical modules can trigger alarms if there are transmit/receive faults, often linked to RRU power issues or unstable voltage, which can affect the RF maintenance link .
• Deployment: The BBU-RRU connection is critical for network performance, and proper installation of optical modules and fibers ensures reliable data transmission and minimal downtime .

Summary

Optical modules are a key component in distributed base station architectures, enabling high-speed, reliable communication between BBUs and RRUs. They must meet specific data rate, temperature, and environmental requirements to ensure stable operation in both 4G and 5G networks, supporting the growing demand for mobile data and network expansion .