Low complexity MMSE-QRD-based ML decoder for quasi-orthogonal STBC scheme in MIMO wireless communications systems with four-transmit antennas

This work proposes a MMSE-QR decomposition-based (MMSE-QRD) low-complexity maximum-likelihood (ML) decoders for quasi-orthogonal space-time block code (QOSTBC) with 4 transmit antennas, denoted as MMSE-QRD LCML decoder. By stacking received symbols from different received symbol period together and applying QR decomposition on extended channel matrix (D. Wubben et al., 2001) resulting special format of matrix R, the proposed decoders is able to reduce complexity by decouple decoding as H. Jafarkhani (2001). In addition, by using the same principle of Minh-Tuan Le et al. (2005) to jointly detect signals, the MMSE-QRD LCML decoder is able to not only significantly reduce the computational load but also obtain ML performance