Design Of Spatially Coupled LDPC Codes For Block-Fading Channels

With the popularity of mobile communications and the improvement of people's life,people have increasing demands for the reliability and effectiveness of communication transmission.As an important part of the communication system,channel coding technology is a key means to improve the reliability of communication transmission,and it has been a research hotspot for the majority of communication workers.Among communication channel models,block-fading(BF)channel is the closest model to the real wireless channel transmission scenario,and it has more technical challenges due to its non-ergodic relative to Gaussian and ergodic fading channels.Therefore,the research of channel coding technology over block-fading channel has important practical significance.Due to the performance of approaching the Shannon limit and lower error floor,since the low density parity check(LDPC)codes have found to reach the Shannon capacity limit,research on coding design and application around LDPC codes has been inexhaustible.Among them,spatially coupled LDPC(SC-LDPC)codes constructed based on the regular LDPC codes have been proved to have "threshold saturation" characteristics and have attracted much attention from researchers.In this thesis,we focus on the design of SC-LDPC codes for block-fading channels.First,the principle of encoding and decoding,and the analysis methods of SC-LDPC codes are studied.From the perspectives of protograph and base matrix,the structural characteristics of SC-LDPC codes are analyzed.Based on the characteristics of the block-fading channel model,the performance metrics and analysis methods of channel codes under block-fading channels are studied.Secondly,symmetric-edge exchanged SC-LDPC(SEE-SC-LDPC)codes is proposed for block-fading channels with F=2.By exchanging partial edge connections on variable nodes with axisymmetric center position,we obtain a matrix with strong correlation between different fading blocks,which can effectively avoid the outage occurrence caused by deep fades on the transmission of codewords.The edge exchange method need neither to change the degree distribution of the original codes and nor to add any extra check node resulting rate loss.We obtain infinite-length performance via PEXIT(Protograph-based EXtrinsic Information Transfer)algorithm,which shows that the performance of this code ensembles can approach the outage limit.Furthermore,the finite-length performance simulation results obtained through belief propagation(BP)decoding show that the proposed codes can achieve full diversity and good coding gain.Finally,connecting consecutive multi-SC-LDPC(CC-MSC-LDPC)codes is proposed which can be flexibly designed for block-fading channel conditions with different F-values.First,the construction scheme of CC-MSC-LDPC codes is given for F=2.Then,the construction scheme is expanded for block-fading channels with different F-values.Two different expansion schemes are described with F=3 as an example.The CC-MSC-LDPC codes is also constructed by exchanging edge connections.However,unlike the SEE-SC-LDPC codes,the CC-MSC-LDPC codes is a multi-chain code.By exchanging the edge connections of variable nodes at the same location of subchains,multiple subchains are coupled to form a code set with strong correlation between different fading blocks.Simulation results show that when F=2,the CC-MSC-LDPC codes can achieve full diversity,and has faster decoding convergence rate than the SEE-SC-LDPC codes.And it is also shown that the CC-MSC-LDPC codes expansion scheme can reach outage limit when F=3.