The present invention discloses a method for selecting a transmission scheme in a multiple-input-multiple-output (MIMO) wireless communications system. The method comprises receiving a downlink request to transmit a data stream to a wireless station, checking the availability of channel state information (CSI) associated with the wireless station, determining the validity characteristic of beamforming weighting vectors associated with the wireless station, selecting a transmission scheme from a plurality of predetermined transmission schemes based on the availability of the CSI and the validity characteristic of the beamforming weighting vectors.