| The key physical layer technology of the next generation broadband wireless MIMO communication system, importantly represented by the technology of channel estimation (contain pilot design) and iterative detection is one of the hot research directions in wireless communication. On the one hand, the performance of channel estimation (contain pilot design) and iterative detection is suffered different degrees of deterioration, influenced by the spatial correlation, the time correlation, and all kinds of wireless fading of the MIMO channel, resulting that the reliability of system can't be guaranteed and high spectral efficiency of system can't be fully exploited. So the development and application of wireless MIMO system are limited. On the other hand, by further improving and optimizing the design for the technology of channel estimation (contain pilot design) and iterative detection, so that the performance and capacity of system are overall increased, and deeply drive the research, development and application of the next generation broadband wireless MIMO communication system-MIMO OFDM system.In this dissertation, we take the wireless MIMO system as the study of background, closely around the actual environmental characteristics of the wireless MIMO channel and the wireless link transmission infrastructure and its design requirements for MIMO OFDM system. On the basis of analyzing and mining a number of problems in key technologies of baseband transmission for current MIMO OFDM system, a serious research on the pilot design, based on pilot-assisted channel estimation and iterative detection to improve the performance of the wireless link transmission for MIMO OFDM system. Precisely, the work can be divided into the following four parts.1. For MIMO channel spatial correlation impact on the optimization design of pilot, consider taking fully the spatial correlation into the optimization design of the pilot, an optimal pilot sequence based on spatial correlation for MIMO OFDM system is proposed, the structure of the optimal pilot sequence is concluded and analyzed, the numerical analysis and comparison of the channel mutual information between the optimal pilot sequence and other pilot sequences in a variety of spatial correlation conditions are presented.2. In order to further enhance the performance improvement of channel estimation which the optimization design of pilot brings to, the idea of joint optimization of multi-objective criteria applied to the pilot design, a frequency domain LMMSE channel estimator based on multi-criteria optimization design of the pilot is proposed, the closed-form solution for the optimal pilot sequence is derived, and the numerical analysis to the pilot overhead, the PAR and the corresponding channel estimation performance of the optimal pilot sequence is presented. In order to suppress the degradation of the channel estimation performance due to the virtual sub-carrier presence in part-load MIMO OFDM system, a time-domain LS channel estimator based on uniform type pilot optimized is proposed, and the optimal power allocation and the sub-optimal location of the distribution are derived, the simulation analysis and comparison of NMSE and BER performance between the optimized pilot and other uniform type of pilots are presented. 3. In order to take full advatange of the channel space-time correlation which can enhance the channel estimation performance, an algorithm of channel estimation based on space-time correlation for MIMO OFDM system is proposed, and the optimal weight matrix of the space-time filter is derived, the simulation analysis of the multiple filter parameters impact on algorithm performance and comparison of NMSE and BER performance between the algorithm and the MA algorithm are further presented. For large delay spread channel conditions, in order to suppress the deterioration of the channel estimation performance due to limited pilot subcarriers, an algorithm of channel estimation based on the joint estimation of TOA and DPS for MIMO OFDM system is proposed, and the conditions of multi-path delay adapting to the algorithm is derived, the simulation analysis of the NMSE and BER performances between this algorithm and other channel estimation algorithms in a variety of large delay spread channel conditions is presented. For large Doppler spread channel conditions, in order to suppress the deterioration of the channel estimation and detection performance caused by severe ICI interference, a joint algorithm of channel estimation in fast time-varying environments for MIMO OFDM system is proposed, and the LB of the estimation mean square error is derived, at the same time, the complexity of the algorithm is analyzed. Finally, the simulation analysis of the NMSE and BER performances between this algorithm and other channel estimation algorithms in a variety of large Doppler spread channel conditions is presented.4. In order to solve the problem that the spatial correlation and channel estimation error will reduce the extraction accuracy of the soft information in Turbo-BLAST detection, an optimal MMSE-PIC iterative detection algorithm based the soft-output is proposed, and the closed-form solution for the optimal weight vector of the MMSE filter is derived, the simulation analysis of the BER performance between this algorithm and the traditional iterative detection algorithm in the presence of the spatial correlation and channel estimation error is presented, further the complexity of the algorithm is analyzed.
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