The present invention discloses a solution including: receiving channel quality fed back by at least two user terminals; determining, according to the received channel quality fed back by the at least two user terminals, a user terminal that needs to be served by each transmit antenna of a base station device; for user terminals served by a same transmit antenna, configuring, according to channel quality fed back by the user terminals served by the same transmit antenna, a constellation expansion modulation scheme for each user terminal served by the same transmit antenna, and determining an intra-stream power allocation factor and an initial phase rotation coefficient of the transmit antenna; and processing, by using the modulation scheme, a signal to be sent to the user terminal, and transmitting the processed signal to the user terminal according to the intra-stream power allocation factor and the initial phase rotation coefficient.