Performance criteria analysis and further performance results for quasi-orthogonal space-time block codes

Orthogonal space-time block codes (OSTBC) exploits the multiple-input multiple-output (MIMO) communication systems in order to obtain the diversity for high link reliability. Unfortunately, it is not possible to construct an OSTBC with a transmission rate equal to one for more than two transmit antennas. A way to achieve the transmission rates equal to one is to use the quasi-orthogonal STBC (QSTBC). In previous works, it was shown by simulations that the performance of QSTBC can be improved by rotating the constellation of some symbols in the so called transmit matrix. We analyze two different performance criteria proposed in the literature concerning this rotation. We derive an optima with respect to these criteria and show their impact on the bit error rate (BER). Furthermore, we derive some analytical results for the BER-performance.