A method for transmitting a data signal by a transmission unit of a wireless multiple-input/multiple-output (MIMO) communication system. The communication system includes the transmission unit and a reception unit, the transmission unit having a plurality of transmission antennas and the reception unit having a plurality of reception antennas. The method includes performing a first transmission of a data signal, the first transmission including transmitting the data signal by each one of the plurality of transmission antennas, and performing a second transmission of the data signal at a time later than the first transmission, the second transmission including transmitting at least one spectrally modified signal variant of the data signal by at least one antenna of the plurality of transmission antennas.