Should the optical module be placed in BBU or AAU

In modern 5G networks, optical modules are typically installed in both AAUs and DUs, while BBUs mainly handle centralized processing and connect via fiber.Optical Module Placement OverviewBBU (Baseband Unit): The BBU serves as the core processing unit, handling baseband signal processing, modulation, encoding, and network control. It is usually located in a centralized site such as a telecom shelter or data center and connects to AAUs or RRUs via fiber optics using CPRI or eCPRI interfaces . While BBUs manage signal processing, they do not directly host optical modules for transmission; instead, they rely on optical modules in the fronthaul to connect to remote units . AAU (Active Antenna Unit): The AAU integrates the RRU and antenna, supporting 5G features like massive MIMO and beamforming. Optical modules are installed in AAUs to handle high-speed optical transmission between the AAU and the DU or BBU. In 5G pre-transmission applications, colored optical modules in AAUs enable WDM (Wavelength Division Multiplexing), allowing multiple optical signals to share a single fiber without interference, which reduces link costs and simplifies deployment .Practical DeploymentDistributed Sites: The BBU is placed in the machine room at the base of the tower, while the AAU is mounted on the tower or rooftop. Optical modules in the AAU transmit physical layer data to the DU or BBU over fiber .Centralized or Co-located Deployment: In 5G, DUs and CUs may be centralized, but AAUs still require optical modules for high-speed fronthaul connections. The optical modules in AAUs handle bidirectional transmission and WDM functions, supporting multiple sectors and high-bandwidth requirements .SummaryBBU: Centralized processing, connects via fiber; optical modules are generally not installed here for fronthaul transmission.AAU: Located near the antenna, hosts optical modules for high-speed fiber transmission, WDM, and multi-sector connectivity.Best Practice: Place optical modules in AAUs (and DUs if applicable) to optimize 5G fronthaul performance, reduce signal loss, and simplify network architecture . This deployment ensures efficient high-speed data transmission, supports massive MIMO, and aligns with modern 5G network architecture standards.