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In this letter, we present a new maximum likelihood (ML) decoding algorithm for space time block codes (STBCs) that employ multidimensional constellations. We start with a lattice representation for STBCs which transforms complex channel models into real matrix equations. Based on the lattice representation, we propose a new decoding algorithm for quasi-orthogonal STBCs (QO-STBC) which allows simple ML decoding with performance identical to the conventional ML decoder. Multidimensional rotated constellations are constructed for the QO-STBCs to achieve full diversity. As a consequence, for quasi-orthogonal designs with an arbitrary number of transmit antennas N(Nges4), the proposed decoding scheme achieves full rate and full diversity while reducing the decoding complexity from O(Mc N/2) to O(Mc N/4) in a Mc-QAM constellation.
Date of Publication: January 2009