A transmitter for maximizing coding gain by transmitting an input symbol sequence through a plurality of transmit antennas method according to feedback CQIs from a receiver in a 3 Tx-rate 2 communication system. In the transmitter, an S/P converter converts serial modulated data to parallel modulated data. A coder mode decider determines a transmission mode based on the channel quality indicator of each transmit antenna fed back from a receiver. A coder transmits the parallel modulated data through the three transmit antennas according to the determined transmission mode.