Quasi-Orthogonal STBC Using Stretched Constellations for Low Detection Complexity

Space-time block codes (STBC) from orthogonal designs have been proposed by Alamouti and Tarokh-Jafarkhani-Calderbank, achieving full diversity in the order of the number of transmit antennas. However, orthogonal STBC always result in a symbol rate less than one, if complex symbols are transmitted from more than 2 antennas. Jafarkhani, Tirkkonen-Boariu-Hottinen and Papadias-Foschini have suggested to use quasi-orthogonal STBC (QO-STBC), and it has been shown by various authors that these schemes achieve transmission rate 1 and full diversity, if selected symbols are chosen from suitably rotated constellations. The schemes can, however, lead to a high detection complexity, which has been recently addressed through co-ordinate interleaved orthogonal designs (CIOD) and minimum detection complexity (MDC) QO-STBC, though leading to a slight degradation in performance. In this paper, we present a novel QO-STBC scheme that uses stretched, i.e. non-linearly preprocessed symbol constellations, achieving full diversity and a performance comparable to that of CIOD and MDC, while further reducing detection complexity.