Analysis And Design Of Protograph LDPC-coded Bit-interleaved Coded Modulation Systems

As a type of high spectrum-efficiency and reliability transmission techniques,bit-interleaved coded modulation(BICM)has a significant amount of attention.In the past two decades,the research of BICM technology mainly focuses on three aspects:channel coding,bit interleaving and modulation.As the most widely used channel coding scheme,low-density parity-check(LDPC)code has often been adopted by BICM system.However,LDPC codes suffer from several drawbacks,e.g.,non-extensible code rate,relatively high encoding/decoding complexities,error-floor phenomenon,etc.As a subclass of LDPC codes,protograph LDPC(PLDPC)codes not only can overcome the drawbacks of conventional LDPC codes,but also can be easily designed and implemented.Besides,spatially coupled protograph LDPC(SC-PLDPC)codes derived from PLDPC codes combine the characteristics of block codes and convolutional codes,and thus can achieve better iterative decoding performance.In addition to the channel coding scheme,the design of the bit interleaver and modulator can further optimize the performance of BICM systems.Therefore,this thesis studies the design of bit-interleaving and constellation schemes for PLDPC-coded BICM systems.Moreover,we adopt the extrinsic information transfer(EXIT)algorithm to analyze the system performance.The main research contents of this thesis are as follows:(1)The basic principle and encoding/decoding algorithm of LDPC codes are studied,and the construction methods of PLDPC codes and SC-PLDPC codes are summarized.Moreover,the framework of BICM with and without iterative feedback are analyzed,and the system models of PLDPC-coded BICM are established.In addition,the performance of the system is analyzed through a protograph-based EXIT(PEXIT)algorithm.(2)The existing bit interleaver designs based on PLDPC-BICM system are analyzed in detail.By associating the unequal error protection(UEP)mechanism of the BICM systems with the convergence characteristics of SC-PLDPC codes,an interleaver design scheme based on mutual information(MI)analysis is proposed,namely spatial position match mapping(SPMM)scheme.Using the BICM-aided PEXIT algorithm,the decoding thresholds are analyzed,and the corresponding simulation experiments of system error performance are completed.Theoretical analysis and simulation results show that the convergence performance of the SC-PLDPC codes after SPMM interleaving has been significantly improved.(3)Based on the PLDPC coded BICM system,a protograph-based adaptive irregular mapping scheme(PAIM)scheme is proposed.According to the harmonic mean of square Euclidean distances of the non-feedback and ideal-feedback situations,the adaptive constellation mappings mixed with Gray mapping are designed.Theoretical analysis and bit error rate(BER)simulation results show that the irregular mapping scheme effectively improves the error performance of PLDPC-coded BICM systems.