| With the development of communication technology, the frequency resources are becoming increasingly tense, whereas requirements of quality, speed and reliability of wireless communication system become higher than before. Hence, how to effectively make use of the frequency resources to transmit information becomes the focus of wireless communication. By employing multiple antennas at the transmitter and receiver, MIMO system can improve the system capacity, bandwidth utilization and the reliability of data transmission, so as to improve system performance greatly. Therefore, MIMO has been widely accepted as a core technology of the next generation wireless communication system. However, in practical applications, it is difficult for a mobile terminal to equip with multiple antennas due to the factors of power consumption, size and cost constraints. In this case, cooperative diversity technology which forms a virtual MIMO system by mutually sharing the antennas among adjacent single-antenna terminals provides a good idea for the wide application of MIMO technology. Adopting space-time coding technology in cooperative communication systems, spatial diversity and coding gain can be obtained so as to improving the system performance further. To sum up, this paper mainly focuses on QOSTBC(Quasi-Orthogonal Space-Time Block Code) and space-time cooperative diversity technology of MIMO system, the specific arrangements are as follows.Firstly, the principle of space-time block code is introduced especially the design criteria of orthogonal space-time block codes, realization of Alamouti transmit diversity scheme and two design methods of full diversity QOSTBCs are mainly discussed. By simulating the performance of different codes in Matlab platform, we find QOSTBC has more broad application prospects. Then according to the traditional decoding algorithm of QOSTBC, two improved decoding schemes are put forward. The improved schemes which are based on the decomposing of the channel matrix and the elementary transformation of channel matrix with QR decomposition have better tradeoff ability between decoding complexity, speed and system performance.Secondly, through combining the space-time block codes mentioned above with cooperative diversity technology, the space-time cooperation technology is introduced and studied in depth. Through MATLAB simulation, several cooperative diversity schemes are analyzed and the performance of space-time cooperative schemes based on Alamouti coding under different protocols are researched. Then, this paper points out the synchronization error can be barely avoided owing to the relays’ distributed characteristics. However, the synchronization error leads to deep fading of the SER performance. Hence, several solutions are introduced. At last, an improved scheme based on PIC detection which combined the received signal in broadcasting phase with that in cooperative phase is proposed. The simulation result demonstrates that owing to the full use of the information from DT link, the proposed scheme reduces the SER of the system further, especially in lower SNR stage where the SER performance is identical to the synchronization system. |
