Research On Space-Time Block Coding Technique In MIMO System

Space-time codes based on MIMO is almost the unique solution for future bandwidth-limited high-speed wireless communication systems. This novel transmit diversity technique, which combines channel coding modulation and signal processing at receive terminal, can make full use of the fading multi-path in the wireless communication systems so as to mitigate the signal attenuation. This technique is mainly designed to combat channel fading in downlink transmission by combining the technique of channel coding and that of array diversity, hence increasing the capacity of wireless communications systems and giving diversity gain and coding gain to them.This thesis investigates several issues related to this hot research topic, the main research results are as follows:(1) The performance of the STBC (Space-Time Block Code) has been studied. Several orthogonal-STBC's performance under different spectrum utilization rate are simulated.(2) A quasi-orthogonal STBC has been improved. Only when the transmit antennas are two, orthogonal design of STBC signals in the case of complex can achieve full-rate transmission. So the quasi-orthogonal design of STBC has come to attention for full-rate transmission purpose. In this thesis, we start analysis and research around quasi-orthogonal STBC. By adding the weights which are related to the channel situation information at the transmitter, the encoding scheme of quasi-orthogonal STBC is improved, and the full-rate transmission is implemented.(3) In order to get STBC coding gain, the STBC and LDPC will be concatenated in this thesis. The STBC can provide diversity gain but can not provide coding gain, while the LDPC codes have good performance close to capacity limits and provide good coding gain. So, in this thesis, the LDPC code and STBC code are combined. The simulation results show that the concatenation scheme can improve the coding gain for the better.