Embodiments of the present invention disclose a base station, including: a first channel state information acquiring module, configured to acquire channel state information of dimension-reduced channel subspace by means of level-one channel state information measurement; a set determining module, configured to: schedule the user equipment, and determine a set of user equipment involved in multiple-input multiple-output; a second channel state information acquiring module, configured to: perform level-two channel state information measurement on user equipment in the set of user equipment to acquire state information of a dimension-reduced real-time channel; and a data sending module, configured to: process downlink data and a user-specific demodulation reference signal by means of two-level precoding, and send processed downlink data and a processed user-specific demodulation reference signal to the user equipment in the set of user equipment.