Heterogeneous constellation based QOSTBC for improving property of QRD-MLD

Orthogonal space-time block code (OSTBC) can achieve full diversity with a simple MLD, but the rate of OSTBC only achieves 3/4 of the maximum rate when applying more than two transmit antennas. To solve this problem, a quasi-orthogonal STBC (QOSTBC) scheme has been proposed. Even though a QOSTBC scheme can achieve the full rate, there are interference terms resulting from neighboring signals during detection. The existing QOSTBC using the pairs of transmitted symbols can be detected with two parallel MLD. Therefore, MLD based QOSTBC has higher complexity than OSTBC. To reduce the detection complexity, in this paper, we propose the heterogeneous constellation based QOSTBC for improving the detection property of QRD-MLD with maintaining a simple decoding structure.