The transmission bearer connecting BBU and RRU equipment is optical module and optical fiber. PAM4 (4-Level Pulse Amplitude Modulation): This is the predominant modulation technique used in 400G modules. The base station can be divided into two modules: the RRU for transmitting signals and the BBU for processing signals. The BBU is small and. 400G, 800G, and 1. However, 400G remains more cost-effective for. A1: 400g optical transceivers are optical modules that are mainly used for photoelectric conversion with a transmission rate of 400Gbps. Operating at the physical layer of the OSI model, optical modules are core devices in optical. 400G optical modules are high-speed transceivers using PAM4 modulation and multi-lane architectures to enable ultra-high bandwidth connectivity.