Downlink transmitter of LTE base station system and data processing method thereof

The invention discloses a downlink transmitter of a long term evolution (LTE) base station system. The downlink transmitter comprises a base band unit (BBU) and a remote radio unit (RRU), wherein the BBU and the RRU are connected by an Ir ( interface between the RRU and the BBU). The BBU is used for carrying out bit-level processing and modulation processing on original data and sending the processed data to the RRU by the Ir; and the RRU including an inverse fast fourier transform (IFFT)/inverse discrete fourier transform (IDFT) module is used for receiving the data sent by the BBU through the Ir, carrying out IFFT or IDFT processing on the data and emitting the data. Correspondingly, the invention also discloses a data processing method of the downlink transmitter. The sampling rate and the data bit width are reduced. Therefore, the Ir downlink data transmission flow is effectively reduced, the cost of transmission from the BBU to the RRU is lowered, and the optical fiber resources laid at the Ir are saved; and thus an objective of saving of the equipment cost and the maintenance cost is achieved.