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A Method for Geometric Construction of Low-density Parity-check Codes

Xiaoguang Wang

Published Jan 1, 2008• 0 citations
OpenAlex

Abstract

A new method for geometric construction of QC-LDPC is proposed. The parity-check matrix constructed through this method has a girth more than eight,which promises good performance. Since the parity-check matrix is composed of cyclic sub-matrices,the hardware encoder is simple. Simulations show that this type of LDPC codes has remarkable performance with low encoding complexity.

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IEEE Symposium on Industrial Electronics & Applications (ISIEA)•Oct 1, 2009•5 citations
A new method for geometric construction of QC-LDPC is proposed. The parity-check matrix constructed through this method has a girth more than eight,which promises good performance. Since the parity-check matrix is composed of cyclic sub-matrices,the hardware encoder is simple. Simulations show that this type of LDPC codes has remarkable performance with low encoding complexity.
A design algorithm of regular check matrix for Low-Density Parity-Check(LDPC)codes is proposed in this paper.The proposed approach is to design 3 sub-matrices,and each of the sub-matrices is combined by the cyclic shift matrices of the identity matrix,then to combine these sub-matrices into a desired parity check matrix according to our approach.Using the check algorithms of the short cycles to find the combinations of shifting operators by which the parity check matrix desires has no girth- four and no girth-six.The simulation results in AWGN channel show that the BER performance of these codes obtained by the generator matrix derived from the proposed check matrices to encode the random information bits is as good as that of random LDPC codes.
A construction method for girth‐eight quasi‐cyclic low‐density parity‐check codes (QC‐LDPCs) with low encoding complexity is proposed in this study. To avoid short cycles and further improve the performance of the authors proposed codes, the greatest common divisor (GCD)‐based method is utilised to construct the information part with girth‐eight of the parity‐check matrix with systematic form. Furthermore, the quasi‐dual‐diagonal structure is adopted as the parity part of the parity‐check matrix for fast encoding, which not only maintains the parity‐check matrix with girth‐eight, but also efficiently decreases the encoding complexity of their proposed codes. Simulation results show that their proposed codes perform better than Mackay's codes and the QC‐LDPCs constructed by the GCD‐based method, and have comparable performance compared with progressive edge growth based QC‐LDPCs. Besides, their proposed codes have lower encoding complexity due to the property of fast encoding.
There is an important breakthrough in the field of forward error correction techniques, low-density parity-check (LDPC) codes. These codes have potential to approach the Shannon limit with reliable performance on a given channel, known as the channel capacity. Recently, researchers pay much more attention towards LDPC codes because its performance is better than Turbo codes. However, the LDPC code is the best when it is an irregular code and uses with a very large block-length. Although, the short block-length LDPC codes perform not so well, they are easy to implement in various practical applications. Therefore, there is still a demand of new development on the encoding side of LDPC codes for various ranges of code rate and code length so as to capable of using in many applications.This thesis proposes the development of quasi-cyclic (QC) LDPC codes for column weight 3. In the first part of this thesis, we propose a new construction algorithm of QC-LDPC codes for medium to large block-length by combining QC-LDPC codes of small block-length as their component codes, via Chinese remainder theorem (CRT). Such component codes were constructed by permuting each column block sequentially to attain the desire local girth. After combining all component codes to generate an expanded parity-check matrix, the resulting girth is greater than or at least equal to the maximum girth of the component codes. Simulation results show that our proposed construction method of the parity-check matrix significantly outperforms the other well-known existing methods in terms of low error-floor, simple structure, high performance, and can reduce encoding complexity.In addition, this thesis also proposes two new construction methods for QC-LDPC codes, namely a base matrix method and a subtraction based method. A base matrix based method is a simple, less computational complexity method for constructing the exponent matrix (3, K) of girth 8, 10 and 12 of QC-LDPC codes. Another method is a subtraction method, which has a similar exponent matrix as a base matrix method and has a girth at least 8. Results indicate that the LDPC codes constructed from these two methods have flexibility for arbitrary block-column length K and have a similar BER performance if compared to existing methods.
For any column weight J and any row weight L, a novel framework is proposed such that a girth-eight (J,L) quasi-cyclic low-density parity-check (QC-LDPC) code with any block length above a lower bound can be constructed via a simple inequality in terms of greatest common divisor (GCD). The main advantage is that the construction of a class of (J,L) girth-eight QC-LDPC codes is transformed into a rather simple task, searching for J integers satisfying the so-called GCD constraint for L. Combining the new method with masking matrices, a class of type-1 QC-LDPC codes is presented with girth at least eight. Simulation results show that the type-1 codes perform better than the random QC-LDPC codes and quadratic-congruence-based QC-LDPC codes for moderate block lengths and low code rates.
A new method for constructing quasi-cyclic (QC) low-density parity-check (LDPC) codes based on the structural properties of Euclidean geometries is presented. The proposed method changes the incidence vectors of some lines in the original Euclidean geometry method to construct much more parity check matrices and results in a large class of QC-LDPC codes with girth of at least 6. Simulations show that some codes in this class have better performance and lower error floor than the original Euclidean geometry codes.
This paper proposes a new technique for constructing the Quasi-Cyclic low density parity check (QC-LDPC) codes based on row division method. The new codes offer more flexibility in term of girth, code rates and codeword length. In this method of code construction, the rows are used to form as the distance graph. Then they are transformed to a parity-check matrix in order to acquire the desired girth. The new QC-LDPC codes show good bit-error rate performance as compared to the renowned Mackay codes for given values of Eb/Noby 0.12 dB at BER of10-7.