Performance analysis of code selection algorithm based on quasi-orthogonal space-time block code

A quasi-orthogonal space-time block code (QO-STBC) has a rate one but a loss of diversity gain, compared with an orthogonal space-time block code such as Alamouti code. In this study, a code selection algorithm between QO-STBCs is proposed for a diversity gain improvement of a system based on a QO-STBC with four transmit antennas. The proposed algorithm improves diversity gain without a rate loss and provides better performance than the conventional closed-loop algorithm based on QO-STBC. Advantageously, the proposed algorithm can be applied to simple linear receivers, such as the zero-forcing receiver and minimum mean square error receiver, instead of the maximum likelihood receiver, which has a high computational complexity problem. The probability density function of two signal-to-interference and noise ratios (SINRs) is derived and by the derived pdf, an approximated bit error rate (BER) performance of the proposed system is also derived. The BER performance of the proposed system outperforms previous algorithms at least by about 0.5-dB SNR gain at BER 10^-4.