Research On LDPC Codes Coding And Decoding Algorithm Based On LTE-Advanced Systems

LTE-Advanced system is the backwards-compatible evolution of LTE system, which is a 3GPP standard for meeting the requirements of ITU IMT-Advanced (4G). LTE-Advanced is required to support 1Gbps rate channel coding techniques, and to maintain compatibility with R8 LTE. Since the original modulation coded in the original band and application scenarios must be supported in the new band and application scenarios, currently, the new channel coding (LDPC codes) scheme is considered. Low density parity check (LDPC) codes have the characteristic that is close to Shannon limit, additionally, because of their good performance and flexibility, the LDPC codes have been increasingly recoganized by reseachers for their great potentianality on applications.It is necessary to study the enhancement of efficient coding techniques suitable for LTE-Advanced system, in order to achieve the optimal combination of the code performance and implementation complexity, meanwhile, to improve coding gain and reduce the coding complexity, as well as to save storage space. Therefore, the goal of this thesis is to futher study on in-depth LDPC Codec algorithms based on LTE-Advanced system.In this thesis, the long-term evolution of the system (LTE) and LTE-Advanced System development progress is reviewed at first, also the advantages and the status quo of LDPC codes are analysed. Based on fundatmental theory of LDPC codes introduced, the approach constructing LDPC codes and related basic codec algorithms are studied in this thesis. Subsequently, based on Potevio and Beijing University of Posts and Telecommunications of the mother code, the LDPC codes with a different code length and low bit rate are constructed. It is verified that such LDPC codes are compatible with the original LTE channel coding technology, and also the channel coding options of LTE-Advanced system are proposed. Finally, for the expansion methods of low bit-rate LDPC codes, two kinds of improved fast encoding algorithms are presented for an expanded LDPC codes in this thesis.Then, the distance Belief-Propagation decoding algorithm based on the LDPC-OFDM system is analyzed. In addition, the Belief-Propagation decoding algorithm based on Euclidean distance is proposed. Meanwhile the LogBP decoding algorithm is implemented in multi-level modulation. The simulation result shows that the LDPC codes applied in a multi-level modulation of the OFDM system is effective. Lastly, system performance with different parameters is analyzed in this thesis.Finally, the calculation of the initial information, as well as Belief-Propagation information from the check node to node based on LDPC decoding algorithm is researched. Several improved LDPC decoding algorithms are illustrated, including the Normalized Min-Sum algorithm, Offset Min-Sum algorithm and linear fitting Log-BP algorithm. The end, in order to compare LDPC codes performances under different decoding algorithms, simulations are carried out in LTE-PDSCH channels, so that the programs for LDPC decoding algorithm are determined, which is suitable for LTE-Advanced system.