Orthogonalization of quasi-orthogonal space-time block codes in multipath fading environments by using feedback

To combat the detrimental effect of the frequency-selective fading channel and the intersymbol interference in quasi-orthogonal space-time block codes (QO-STBCs), two feedback algorithms combined with multicarrier modulation scheme are proposed. One of the algorithms rotates the phase of the transmitted signal from certain antennas in a prescribed way. The other algorithm is based on selecting certain antennas and switching-off the others according a channel quality measure. A highly practical setup with only two bits of feedback can achieve considerable performance gain over the open-loop QO-STBC.