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Wireless Communications and Mobile Computing

Design of Nonbinary LDPC Cycle Codes with Large Girth from Circulants and Finite Fields

Hengzhou Xu, Huaan Li, Jixun Gao, Guixiang Zhang, Hai Jiang Zhu, Xiao‐Dong Zhang

Published Jan 1, 2021• 0 citations
Publisher

Abstract

In this paper, we study a class of nonbinary LDPC (NBLDPC) codes whose parity‐check matrices have column weight 2, called NBLDPC cycle codes. We propose a design framework of (2, ρ)‐regular binary quasi‐cyclic (QC) LDPC codes and then construct NBLDPC cycle codes of large girth based on circulants and finite fields by randomly choosing the nonzero field elements in their parity‐check matrices. For enlarging the girth values, our approach is twofold. First, we give an exhaustive search of circulants with column/row weight ρ and design a masking matrix with good cycle distribution based on the edge‐node relation in undirected graphs. Second, according to the designed masking matrix, we construct the exponent matrix based on finite fields. The iterative decoding performances of the constructed codes on the additive white Gaussian noise (AWGN) channel are finally provided.

DOI
10.1155/2021/4099918

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In this paper, we study a class of nonbinary LDPC (NBLDPC) codes whose parity‐check matrices have column weight 2, called NBLDPC cycle codes. We propose a design framework of (2, ρ)‐regular binary quasi‐cyclic (QC) LDPC codes and then construct NBLDPC cycle codes of large girth based on circulants and finite fields by randomly choosing the nonzero field elements in their parity‐check matrices. For enlarging the girth values, our approach is twofold. First, we give an exhaustive search of circulants with column/row weight ρ and design a masking matrix with good cycle distribution based on the edge‐node relation in undirected graphs. Second, according to the designed masking matrix, we construct the exponent matrix based on finite fields. The iterative decoding performances of the constructed codes on the additive white Gaussian noise (AWGN) channel are finally provided.
For any row weight L , a novel class of (8, L ) quasi‐cyclic low‐density parity‐check (QC‐LDPC) codes is deterministically constructed with girth eight. Compared with a similar construction, the proposed (7, L ) and (8, L ) QC‐LDPC codes exist for any circulant permutation matrix of size P ≥ ( L − 1)( L 2 + 3 L /4 + 3/4) + 1 and P ≥ ( L − 1)( L 2 + 3 L /4 + 7/4) +1, which remarkably improve the existing bounds of ( L − 1)( L 2 + L ) +1 and ( L − 1)( L 2 + L + 1) +1, respectively. Moreover, for any column weight J , any row weight L and any common difference, a construction for ( J , L ) QC‐LDPC codes with girth eight is also proposed. This construction has high flexibility with respect to the design of code rate and code length. Simulation results show that the novel codes with moderate lengths perform well in the additive white Gaussian noise channel.
This paper,based on algebra and graph,proposes a method for constructing structured low-density parity-check(LDPC) codes.In this method,the authors design a connected graph with three kinds of special path to ensure that the Tanner graph of the parity check matrix mapped from the connected graph is without short cycles.The construction method results in two classes of(3,k)-regular quasi-cyclic LDPC codes with girth 8 and 12 respectively.Furthermore,by extending this construction method,two classes of LDPC codes with column weight 2,whose girths are respectively 16 and 24,can be obtained.The simulation studies show that these codes can achieve better performance than randomly constructed regular LDPC codes over AWGN channels with iterative decoding.At the BER of 10-5,the new proposed(3,6)-regular(4356,2205) QC-LDPC code performs 1.48dB from the Shannon limit.Moreover,it outperforms the random regular LDPC code of comparable parameters by 0.1dB.For the new proposed structured LDPC codes with column weight 2,they can achieve about 2dB coding gains with respect to the random regular LDPC codes with similar block lengths and code rates.
In this paper, we focus on the design of a type of low- density parity-check (LDPC) codes called cycle codes whose parity-check matrix have exactly weight-2 columns. An approach to design nonbinary LDPC cycle codes with good performance is presented based on cycle entropy defined here. This method can obtain an elegant distribution of the nonbinary elements over the Galois Field GF(q) among the cycles whose length is exactly equal to the girth. Simulation results demonstrate that the LDPC codes designed with the proposed algorithm perform better than the randomly-constructed nonbinary LDPC cycle codes.
The algebraic method for constructing nonbinary quasi-cyclic(QC) low-density parity-check(LDPC) codes based on balanced incomplete block designs(BIBD) is presented.The generalized nonbinary location vector is proposed on constructions.A nonbinary matrix,which consists of nonbinary circulant submatrices,is formed by generalized two-dimensional matrix dispersion considering the generalized nonbinary location vector and BIBD method.The codes constructed by this method have girths at least 6.Experimental results show that significant coding gains are achieved over Reed-Solomon codes of the same parameters under the Additive White Gaussian Noise(AWGN) channel with iterative decoding Fast Fourier Transform based q-ary Sum-Product Algorithm(FFT-QSPA).And a good performance is also achieved over nonbinary Mackay LDPC codes with almost the same conditions.
In this paper, we construct nonbinary quasi-cyclic low-density parity-check (QC-LDPC) codes whose parity check matrices consist of an array of square sub-matrices which are either zero matrices or circulant permutation matrices. We propose a novel method to design the shift offset values of the circulant permutation sub-matrices, so that the code length can vary while maintaining a large girth. Extensive Monte Carlo simulations demonstrate that the obtained codes of a wide range of rates (from 1/2 to 8/9) with length from 1000 to 10000 bits have very good performance over both AWGN and Rayleigh fading channels. Furthermore, the proposed method is extended to design multiple nonbinary QC-LDPC codes simultaneously where each individual code can achieve large girth with variable lengths. The proposed codes are appealing to practical adaptive systems where the block length and code rate need to be adaptively adjusted depending on traffic characteristics and channel conditions.
In this paper a new low complexity method for constructing binary quasi-cyclic low-density parity-check (QC-LDPC) codes is introduced. In the proposed method, each block-column of the parity check matrix H is made by a circulant matrix in a way that the associated Tanner graph is free of cycle four. Each circulant matrix in H is made by a generator column. The generator columns should be selected in a way that each associated circulant matrix and every two distinct circulant matrices are free of cycle four. The generator columns are made by row distance sets. An algorithm for generating distance sets and obtaining circulant matrices with columns of weight three is presented separately. Simplicity of construction and having a good flexible family of quasi cyclic LDPC codes both in rate and length are the main properties of the proposed method. The performance of the proposed codes is compared with that of the random-like and Array LDPC codes over an AWGN channel. Simulation results show that from the performance perspective, the constructed codes are competitive with random-like and Array LDPC codes.