We propose a transmit power optimization method for distributed transmit antenna space-time block coded orthogonal frequency division multiplexing (STBC-OFDM) systems in multipath Rayleigh fading channels with multiple residual frequency offsets (RFOs).We assume that the transmitter is equipped with two distributed transmit antennas and the receiver uses the decision-feedback detector.The proposed method is designed to minimize the lower bound of the average bit error ratio (BER) and the optimal transmit power for each transmit antenna is calculated according to the average channel power gains

the RFOs variance

and the noise variance.Simulation results show that the proposed method can save the transmit power while enhancing the BER performance compared with the conventional full power transmit method.