Research On Improved Quasi-orthogonal Space-time Block Code

Space time block code is an important skill of channel codings in MIMO system. Because the space time block code (STBC), which can give full-diversity, have simple structure and channel estimation, and relative lower decoding complexity, it got extensive research in recent years. But the complex OSTBC can not provide full-rate transmission when the transmitter antennas are more than two and this system have achieved full-diversity. In order to solve this problem, Jarkarkhani proposed the conception and construction of quasi-orthogonal space-time block code (QOSTBC) .This kind of space-time block coding is assumed that the channel state information (CSI) is available at receiver. However, it is difficult and costly to estimate CSI, and sometimes it is impossible under certain situation in which the receiver is in a quick moving environment or a rapid changing environment. So, the differential space-time coding which do not need the CSI at receiver and can be decoded by the adjacent receiver signals has been proposed. The transmitted matrices must satisfy some restriction for the procession of differential modulation (e.g. for the differential unitary space-time coding, the transmit matrices must be unitary). Since the orthogonal space-time block codes (OSTBC) satisfy unitary matrices, the most studies about DSTC are differential OSTBC in the past years. But the QOSTBC can not satisfy unitary matrices, how to design a full-rate and high performance differential modulation based on quasi-orthogonal codes is important. So, this paper will study differential QOSTBC deeply.Firstly, this thesis according to the rank criterion, a full-rate full-diversity QOSTBC is obtained by Givens matrix rotation and constellations rotation processing on Jafakhaini coding. The simulation results show that the BER(Bit Error Rate)of this new coding can get better performance than conventional QOSTBC.Secondly, we propose a new differential QOSTBC scheme using M-PSK modulation, which uses a rotation coefficient to construct a group of unitary matrices for differential modulation. This new scheme has large Euclidean distance and can improve the transmit performance for large number of receive antennas. Since the new scheme can not achieve full rank, our proposed differential scheme is less efficient than other differential quasi-orthogonal space-time schemes for single receive antenna.Lastly, this paper propose another new differential QOSTBC scheme using Givens matrices rotating and constellations rotating, which constructs a group of unitary matrices for differential modulation. The new scheme can achieve full rank, our proposed differential scheme is more efficient than rotating coefficient differential QOSTBC scheme. This new differential QOSTBC scheme has lower decoding complexity than other differential quasi-orthogonal space-time schemes.