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通过原型图的循环提升可方便地构造准循环低密度奇偶校验(QC-LDPC)码.为了保证QC-LDPC码的性能,消除Tanner图中的短环,首先设计一种算法用于找出原型图中的有害短环,然后提出一种贪婪算法用于对提升后的校验矩阵中的单位循环位移子阵分配适合的循环位移量.与已有的DES算法相比,所提出的贪婪算法在分配循环位移量时施加了更多的限制条件来提升性能,仿真结果表明它比DES算法能消除更多的短环.当提升因子为2的整数次幂时,证明了所得QC-LDPC码的校验阵可转化成分块下三角阵的形式.利用该性质,由原型图循环提升得到的QC-LDPC码仅需对基矩阵做预处理就可以实现编码,极大地降低了QC-LDPC码的编码复杂度.
In order to ensure the performance of QC-LDPC codes and eliminate the short loop in the Tanner graph, an algorithm is first designed to find out the QC-LDPC codes Then, a greedy algorithm is proposed to allocate a suitable cyclic displacement to the cyclic shift matrix in the improved parity check matrix.Compared with the existing DES algorithm, the proposed greedy The algorithm imposes more restrictions on the allocation of cyclic shift to improve performance, and the simulation results show that it can eliminate more short loops than the DES algorithm. When the lifting factor is an integer power of 2, it proves that the obtained QC-LDPC The code check matrix can be transformed into the form of sub-block lower triangular matrix.Using this property, the QC-LDPC code which is circularly promoted by the prototype can be encoded only by preprocessing the basis matrix, thus greatly reducing the QC-LDPC Code complexity of the code.