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

Orthogonal Space-Time Block Codes (OSTBC) exploit multipleinput multiple-output (MIMO) communication systems in order to obtain diversity for high link reliability. Unfortunately, it is not possible to construct OSTBC with transmission rate equal one for more than two transmit antennas. A way to achieve transmission rates equal one is to use 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. In this paper, we analyze two different performance criteria proposed in the literature concerning this rotation. We derive optima in respect of these criteria and show their impact on the bit error rate (BER). Furthermore, we derive some analytical results for the BER-performance.