Research On Design And Performance Of QC-LDPC Codes Based On Protograph

Quasi-Cyclic Low-Density Parity-Check?QC-LDPC?codes are a kind of structured linear block codes,with the parity check matrices taking into account sparse and quasi-cyclic characteristics.And the current various communication systems have a higher demand for the reliability of signal transmission.Compared to general code construction methods,the QC-LDPC codes constructed based on the protograph can effectively avoid short loops,thus has better error correction performance.This thesis revolves around the construction of QC-LDPC codes,and two construction methods based on protograph are proposed.Furthermore,the performance of the constructed codes is simulated and analyzed.The main research works are presented as follows:1.A construction method of QC-LDPC codes based on the protograph is proposed,and the parity check matrix constructed by this method has no cycles of length 4.First,using Yang Hui triangle structure deformation to establish the shift matrix.Then,the established shift matrix is applied to the quasi-cyclic expansion of the basic protograph.Finally,the YH-YMT-QC-LDPC code is constructed,the performance of which is simulated and analyzed.The simulation results show that factors such as the code length,and maximum number of iterations before the decoding,can affect the bit error rate?BER?of the codes.And compared with other patterns,the net coding gain?NCG?of YH-YMT-QC-LDPC codes is significantly improved.2.Based on the finite field,a construction method of the protograph QC-LDPC codes with a rate compatibility feature is proposed.By fissioning and adding pairs of nodes to the basic protograph,a compatible initial matrix is designed,and then the basic matrix is extended to a check matrix using the finite field,thereby constructing a multi-rate MYMT-QC-LDPC code.The simulation results show that in the case of the same code length,the lower the code rate of the codes,the better its performance.When the BER is 10^-6,in the same simulation environment,the NCG of the proposed MYMT-QC-LDPC?4000,2000?code is improved 0.35 dB than YH-YMT-QC-LDPC?4000,2000?code with same code length and code rate,and about 0.45dB than RC-QC-LDPC?4000,2000?code.In addition,the MYMT-QC-LDPC?4000,3000?code with a code rate of 0.75 is also verified to have better error correction performance.Based on the above analysis,the MYMT-QC-LDPC code constructed by using this method can not only select the code rate flexibly according to demand,but also obtain a higher net coding gain.