Optimizing Quasi-Orthogonal STBC Through Group-Constrained Linear Transformation

Abstract — In this paper, we first derive the generic algebraic structure of a Quasi-Orthogonal STBC (QO-STBC). Next we propose Group-Constrained Linear Transformation (GCLT) as a mean to optimize the diversity and coding gains of a QO-STBC. Compared with the constellation rotation (CR) technique reported in the literature, we show that QO-STBC with GCLT requires only half the number of symbols for joint detection in the maximum-likelihood (ML) decoder when square or rectangular QAM constellations are used, hence it has lower decoding complexity than QO-STBC with CR. We also derive analytically the optimum GCLT Parameters for QO-STBC with generic square or rectangular QAM constellation for four and eight transmit antennas. The resultant QO-STBCs with GCLT can achieve full transmit diversity, and they have negligible performance loss compared with QO-STBCs with CR at the same code rate. Keywords- constellation rotation; group-constrained linear transformation; quasi-orthogonality constraint; quasi-orthogonal space-time block code. I

Accepted for publication in IEE Proc. Communications Optimizing Quasi-Orthogonal STBC Through Group-Constrained Linear Transformation

Abstract — In this paper, we first derive the generic algebraic structure of a Quasi-Orthogonal STBC (QO-STBC). Next we propose Group-Constrained Linear Transformation (GCLT) as a means to optimize the diversity and coding gains of a QO-STBC with square or rectangular QAM constellations. Compared with QO-STBC with constellation rotation (CR), we show that QO-STBC with GCLT requires only half the number of symbols for joint detection, hence lower maximum-likelihood decoding complexity. We also derive analytically the optimum GCLT parameters for QO-STBC with square QAM constellation. The optimized QO-STBCs with GCLT are able to achieve full transmit diversity, and have negligible performance loss compared with QO-STBCs with CR at the same code rate