The indoor baseband processing unit is a widely used distributed base station architecture in 3G networks. RRU and BBU need to be connected via optical fiber. One BBU can support multiple RRUs. The multi-channel solution of BBU+RRU can effectively solve the indoor coverage problem of large venues.

Main functions of BBU: BBU is the baseband processing unit of the base station. Provide external interfaces to complete the system's resource management, operation and maintenance, environmental monitoring and other functions. BBU includes the main control unit FSMF module, baseband extension FBBA and transmission extension FTIF.

Features: unique multi-channel algorithm to achieve spatial isolation and reduce interference; coverage capacity can be planned independently; reduce dependence on trunk amplifiers; baseband capacity can be shared and has large expansion space; optical fiber has no loss, backbone deployment is convenient, and RRU deployment is flexible. But the disadvantage is that it is necessary to add an optoelectronic conversion unit, the optical fiber is easily damaged, and armor is required. The difference between TD-SCDMA indoor power distribution system and other 3G systems is that TD-SCDMA is time division duplex (TDD), WCDMA and cdma2000 are frequency division duplex (FDD), and the technical systems of the air interface are also different, so their indoor power distribution systems are also different.

Data transmission direction: For the downlink direction: the optical fiber is directly connected from the BBU to the RRU, and the baseband digital signal is transmitted between the BBU and the RRU. In this way, the base station can control the user's signal to be transmitted from the designated RRU channel, which can greatly reduce the impact on other channels in the community. User interference.

For the uplink direction: the user's mobile phone signal is received by the nearest channel and then transmitted from the channel to the base station through optical fiber, which can also greatly reduce the interference between users on different channels. The BBU+RRU solution is very flexible in capacity allocation. According to capacity requirements, the BBU can be configured to support capacity expansion from 1/6 carrier per channel to 3 carriers without changing the RRU and indoor distribution system.