Article Contents
Article Contents

# QC-LDPC construction free of small size elementary trapping sets based on multiplicative subgroups of a finite field

The authors were partially funded by the Natural Sciences and Engineering Research Council (NSERC) of Canada

• Trapping sets significantly influence the performance of low-density parity-check codes. An $(a, b)$ elementary trapping set (ETS) causes high decoding failure rate and exert a strong influence on the error floor of the code, where $a$ and $b$ denote the size and the number of unsatisfied check-nodes in the ETS, respectively. The smallest size of an ETS in $(3, n)$-regular LDPC codes with girth 6 is 4. In this paper, we provide sufficient conditions to construct fully connected $(3, n)$-regular algebraic-based QC-LDPC codes with girth 6 whose Tanner graphs are free of $(a, b)$ ETSs with $a\leq5$ and $b\leq2$. We apply these sufficient conditions to the exponent matrix of a new algebraic-based QC-LDPC code with girth at least 6. As a result, we obtain the maximum size of a submatrix of the exponent matrix which satisfies the sufficient conditions and yields a Tanner graph free of those ETSs with small size. Some algebraic-based QC-LDPC code constructions with girth 6 in the literature are special cases of our construction. Our experimental results show that removing ETSs with small size contribute to have better performance curves in the error floor region.

Mathematics Subject Classification: Primary: 58F15, 58F17; Secondary: 53C35.

 Citation:

• Figure 1.  A (5, 3) EAS with $\gamma = 4$ and its corresponding variable node graph

Figure 2.  The variable node graphs of $(4, 0)$, $(4, 2)$ and $(5, 1)$ ETSs with girth 6

Figure 3.  The comparison of the performance curves of two $(3, 4)$-regular QC-LDPC codes with the same length. The exponent matrices of both codes, $C1$ and $C2$, are submatrices of B in (10)

Table 1.  Row indices $(i, j, k);\ i, j, k\in\{0, 1, 2, 3, 4\}$ and column indices $(c_1, c_2, c_3, c_4);\ c_i\in\{0, 1, \dots, 16\}$ of ${\mathbf B}$ in (10) to construct non-isomorphic $(3, 4)$-regular QC-LDPC codes with girth 6 and free of $(a, b)$ ETSs with $a\leq5$ and $b\leq2$

 $row\ indices$ $column\ indices$ $(1, 2, 3)$ $(1, 2, 7, 10), \ (1, 3, 4, 13), \ (1, 3, 4, 14), \ (1, 3, 13, 14)$ $(1, 2, 3)$ $(1, 4, 5, 16), \ (1, 5, 8, 16), \ (1, 5, 10, 16), \ (1, 5, 12, 15)$

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