Research On Iterative Detection Of MIMO-LDPC System

Low-Density Parity-Check (LDPC) code is a class of channel code with excellent error control performance. Multi-input multi-output (MIMO) technic improves the spectrum utilization greatly. The spatial domain is utilized to increase the capacity of the system. Iterative detection of MIMO-LDPC system is studied to improve the system performance.Firstly, the model of wireless fading channel is introduced. The performance of Rayleigh fading channel is analyzed. The basic transmit diversity technic against the fading channel is presented. The fundamental principles and common structures of MIMO systems are also introduced. The VBLAST MIMO system is investigated due to the simple structure for spatial multiplexing and higher throughputs. The hard-detection algorithm of the system is studied.Thereafter, the basic encoding and decoding algorithms of LDPC codes are investigated. The extrinsic information transfer (EXIT) chart is introduced as a tool of optimizing the design of LDPC codes. Because of the good structure for fast encoding, dual-diagonal structured QC-LDPC codes are investigated. The construct method is studied and the process of code construction is detailed. The code constructed outperforms 0.2 dB than the code in WiMAX standard of the same length and rate.Next, the soft-detection algorithm of the MIMO system is studied. The MIMO detector and the LDPC decoder work iteratively. Because of the unacceptable complexity of the ML detection algorithm which performs best, the tradeoff between performance and complexity is considered. The MMSE-based soft-detection algorithm has relatively lower complexity while the performance degrade is larger. MMSE-SIC algorithm is proposed for better performance. In order to further improve the performance, the joint Gaussian approach (JGA) is used to replace the Gaussian approximate in the MMSE algorithm. For the purpose of reducing the complexity of the inverse computation in both MMSE and JGA algorithm, simplified algorithms are proposed.Finally, the research is extended to the multipath channel. MMSE and JGA based soft-detection algorithms on multipath channel is investigated. The complexity of detection increases with the increase of multipath number exponentially. Simplified algorithms are also studied and the detailed algorithm process is given. According to the simulation (?), the simplified algorithm reduces the detection complexity greatly, while the performance degrade is within 0.1 dB.