Research On Non-binary LDPC Code And Its MIMO-Concatenated Technology

The development of broadband wireless communication systems faces the challenges such as limited bandwidth and complicated transmission environments. MIMO technology, excellent channel coding schemes and other key technologies of the physical layer can meet the demands of the spectral efficiency and the transmitting reliability of broadband wireless communication systems. Therefore, it is necessary and urgent to do research in this field. MIMO technology greatly improves the transmitting gain and increases the data rate without extra cost of the transmitting power and bandwidth, and hence can be widely applied. Non-binary LDPC code, the best channel code currently, shows better anti random and burst error performance than the binary LDPC code, and thus is worth studying.The dissertation focuses on the research of MIMO technology and non-binary LDPC codes. The construction of non-binary LDPC codes, the iterative MIMO detectors based on non-binary LDPC codes and the concatenated system design of MIMO and non-binary LDPC code have been researched in the dissertation.Firstly, the fundamental of MIMO technology and non-binary LDPC codes is introduced. For MIMO technology, the channel model is introduced, the channel capacity is analyzed and the diversity and multiplexing techniques are elaborated. As to non-binary LDPC codes, the basic concepts and the fundamental representations via parity-check matrices and Tanner graphs are introduced. The fast encoding parity-check matrix structure and the corresponding encoding algorithm are presented. Three basic decoding algorithms are introduced, too.Then, the construction of Quasi-cyclic (QC) non-binary LDPC codes is studied, mainly on the searching of optimized degree distributions, the mother matrix extension of QC non-binary LDPC codes and the replacement of the non-binary elements in the extended binary matrix. In order to optimize the degree distributions, a statistical-based density evolution algorithm is proposed and then applied to guide the construction of SeIRA QC non-binary LDPC codes. The girth and circle connectivity are taken into account in the extension of the mother matrix. The replacement of the non-binary elements is also studied to further lower the error floor. Based on others’ work, a new framework is derived, which brings the formation condition of the circles and the replacement of non-binary elements together. Simulation results show that the construction method proposed is effective.Next, iterative MIMO detectors based on non-binary LDPC codes are studied, mainly on two low-complexity iterative detection algorithms, the MMSE algorithm and the JGA algorithm. In order to improve the system performance, the successive interference cancellation (SIC) technique and the iterative interference cancellation (IIC) technique based on LLR are also studied. The IIC technique is applied to the MMSE detector and the JGA detector. The MMSE algorithm and the JGA algorithm based on the IIC technique are proposed. To avoid the high complexity of matrix inversion in both the algorithms, simplified algorithms of the IIC-MMSE algorithm and the IIC-JGA algorithm are investigated. The matrix inversion complexity of the detectors is greatly reduced, with an acceptable system performance degradation. Then, the IIC-MMSE detector and the IIC-JGA detector in the multipath channel are researched. Both the detectors have a higher detection complexity than the detectors in the single path channel and need to be simplified. Simplified algorithms are proposed in the dissertation with a much lower complexity and an acceptable system performance degradation. Proper parameters can be chosen to balance the system performance and the detection complexity.Finally, the concatenated system design of MIMO and non-binary LDPC code is studied, mainly on the non-binary symbol based MIMO detection algorithm, mapping strategies with low detection complexity and the simplified detection algorithm. The output of the MAP-based detector is non-binary symbol level, and can be directly used by the LDPC decoder. For the situation that the order of the Galois field and that of the modulation is not equal and one code symbol is mapped into different MIMO transmitting vectors, two low-complexity high-performance mapping strategies are proposed. The simplified detection algorithm for the mapping strategies is given, with a much lower complexity and almost no loss on system performance.