Research On Construction Of QC-LDPC Erasure Codes Based On Protograph

In order to solve the problem of time delay caused by the retransmission system in network communication,the forward error correction coding technique is applied to the erasure channel,and the error correction code applied to the erasure channel is called the erasure code.Low density parity check(LDPC)erasure code based on sparse matrix has linear coding and decoding time complexity,and the decoding threshold approximates the excellent performance of erasure channel capacity.However,the QC-LDPC erasure codes based on quasi cyclic structure have more research value because of their advantages such as high efficiency coding and low storage.In this thesis,a code type structure with bit rate compatibility and adaptable to time-variation as well as a spatial coupling pattern that can resist long burst deletion errors in transmission are constructed.The specific works are as follows:Based on the protograph,a method of constructing QC-LDPC erasure code which can realize bit rate compatibility is proposed.In this structure,the parity nodes have been added to the proposed model which satisfies the constraints,so it can realize the bit rate compatibility characteristics where the information bits remain unchanged and the bit rate is flexible.In this thesis,the constraints of adding nodes to the protograph is given,which ensures that the extended series of code words have linear minimum code distance and low decoding threshold.Compared to the conventional PEG extension method,the base matrix of BIBD base group is extended according to certain mathematical rules,which makes the constructed LDPC code have quasi-cyclic characteristics,which greatly reduces the coding complexity and makes it easier to realize the hardware.The simulation results under the BEC channel show that the code can change flexibly between 0.5 and 0.8 when the information bits are kept constant,and have good ‘waterfall' characteristics and no obvious error level.Based on the protograph spatial coupling structure,a method of constructing QC-LDPC erasure code against long burst deletion error is proposed.Firstly,a special diagonal structure with spatial coupling structure is used to construct a matrix with resistive long burst characteristics.Firstly,by using the special diagonal structure of the spatial coupling structure,the matrix is constructed by means of block expansion.Then,the SC-QC-LDPC code is constructed by filling the position vector of the BIBD-LDPC code into the base matrix.The proposed method inherits the advantages of the spatial coupling structure to the Shannon limit,and the quasi-cyclic structure makes it have lower coding complexity.The simulation results on the BEC channel show that the decoding threshold of the code is only 0.024 to the Shannon limit when the bit rate is 0.833.In addition,compared with the QC-LDPC constructed by the BCSD method,the code words constructed in this thesis have a greater zero coverage at the same bit rate and the same code length,and have better resistance to long burst deletion errors.