Efficient quasi-orthogonal space-time block codes for five and six transmit antennas

Space-time block codes offer transmit diversity in multiple antenna systems. Orthogonal and quasi-orthogonal space-time block codes have been developed for improving the performance of wireless communication systems. Orthogonal designs have full diversity and allow symbol-wise maximum likelyhood decoding. However, their code rate is strictly less than one for more than two transmit antennas. Quasi-orthogonal designs achieve a code rate of one, but diversity is sacrificed and decoding becomes more complex. Signal constellation rotation based quasi-orthogonal codes provide full diversity, but the code rate depends on the orthogonal design. This paper proposes two new constellation-rotation based quasi-orthogonal space-time block codes, one for five transmit antennas and one for six transmit antennas. The proposed codes achieve full diversity as well as a code rate of one. The new codes are presented with extensive simulation results to back the superiority of the codes developed. Our improved codes are found to perform better than the existing codes.