Study On Double Space-time Transmit Diversity Technique

Multiple input multiple output (MIMO) technology can be used to improved the capacity, bit error ratio and frequency efficiency significantly without extra frequency bandwidths and transmitted power, so it is the key technology of new generation broadband wireless mobile communication system. Double space-time transmit diversity (DSTTD) is a space-time coding technology combining Alamouti's scheme and spatial multiplexing, which can obtain both diversity gain and multiplexing gain. Due to its simple receiver structure and robustness against correlated fading channels, DSTTD system has received considerable attention and has being in IEEE802.16e and become a part of the broadband wireless mobile communication standard. So it is a very significant topic to investigate DSTTD system performance improvement from different environment and discuss the system performance impact of channel estimation errors.In order to mitigate inter-symbol interference (ISI) caused by frequency selective fading channels, the thesis discusses DSTTD-OFDM system combined with OFDM and analyzes system model and the basic detection algorithm ZF-DF. Using the simplified approach of QR decomposition, a low complexity ZF-DF detection method is also discussed. At the same time, multiple antenna shuffling modes of DSTTD system with antenna shuffling scheme for improving the system performance in correlated fading channels are theoretically derived. And the performance between two criteria for each shuffling mode is simulated and compared. Furthermore, it is shown that the criteria of the maximization of the minimum post-processing SNR can perform a better performance.Under the environment of independent and identically distributed channels, to further improve diversity gain of DSTTD system, a DSTTD-SSD system combined signal space diversity is proposed. The system transmitter achieves multi-dimensional signal space diversity through constellation rotation and the receiver designs a joint detection method of iterative structure based on the idea of soft interference cancellation. The joint detection method acquires low complexity quasi-optimal likelihood detection using vector Gaussian approximation algorithm and scalar Gaussian approximation algorithm. Simulation results show that the proposed system using iterative detection method provides at least 2dB performance improvement at low SNR, which can effectively improve system capability against fading. DSTTD system mainly bases on perfect channel estimation while channel estimation always has errors. In order to overcome the issue, an assessment method of the impact of channel estimation errors on DSTTD system performance is proposed. Using the deducing method of matrix transformation, a mostly affecting factor called interference matrix is put forward. The thesis constructs the error matrixes and concludes that independent and identically distributed channels are more resistant to estimation bias than correlated fading channels under the same estimation errors. Simulations involving the impact of performance on different scenarios error matrixes are done and the results are shown that the system performance caused by error matrixes of different channel estimation errors is equivalent to the practical situation. Numerical simulations indicate that error matrix analysis method is valid and reasonable.