RRU Cascaded Optical Modules

RRU cascaded optical modules are used to connect multiple RRUs in series, enabling efficient signal transmission and bypass protection in wireless networks.Understanding RRU Cascading

RRU cascading involves connecting multiple RRUs using CPRI optical cables so that they share the same SFP port on the baseband processing unit (BBU) or UBRI board . This allows several RRUs to operate in a single sector while minimizing the number of required ports. Cascading is commonly used in chain, tree, or ring topologies depending on network design requirements .

Optical Module Connections

Each RRU typically has two optical modules: a first and a second module. In normal mode, the first optical module transmits and receives signals to and from the internal processing module, while the second module handles the next RRU in the cascade . The optical modules are connected via CPRI fiber cables, ensuring proper alignment of transmitting (TX) and receiving (RX) ports .

Steps for Cascading

1. Identify the SFP ports on the BBU or UBRI board that will serve the cascaded RRUs.
2. Connect the first RRU to the SFP port using a CPRI optical cable.
3. Link subsequent RRUs in series by connecting the second optical module of the upstream RRU to the first optical module of the downstream RRU.
4. Verify TX/RX alignment to ensure proper signal flow.

Bypass Protection

Cascaded RRUs can be vulnerable if one unit fails. To enhance reliability, a bypass protection unit can be used . In bypass mode, the transmitting port of the first optical module is connected to the receiving port of the second optical module, effectively bypassing the faulty RRU. This is typically implemented using a CML cross-point switch or FPGA-based switch to maintain signal continuity.

Practical Considerations

• Ensure proper cabling and avoid excessive bending of optical fibers to prevent signal loss.
• Check LED indicators on the RRU panels to confirm operational status .
• Use RRU interconnection for RF signals if multiple RRUs share the same antenna system, connecting RX_in/out ports with RF jumpers .
• Follow manufacturer guidelines for hardware installation, maintenance, and safety, especially when handling high-voltage or tower-mounted equipment . By following these steps, you can deploy cascaded RRUs efficiently, maintain network reliability, and implement bypass protection to minimize downtime in case of RRU failure.