Computation of Groebner Basis for Systematic Encoding of Generalized Quasi-Cyclic Codes

For R a Galois ring and m 1, . . . , m l positive integers, a generalized quasi-cyclic (GQC) code over R of block lengths (m 1, m 2, . . . , m l ) and length $${\sum_{i=1}^lm_i}$$ is an R[x]-submodule of $${R[x]/(x^{m_1}-1)\times\cdots \times R[x]/(x^{m_l}-1)}$$. Suppose m 1, . . . , m l are all coprime to the characteristic of R and let {g 1, . . . , g t } be the set of all monic basic irreducible polynomials in the factorizations of $${x^{m_i}-1}$$ (1 ≤ i ≤ l). Then the GQC codes over R of block lengths (m 1, m 2, . . . , m l ) and length $${\sum_{i=1}^lm_i}$$ are identified with $${{\mathcal G}_1\times\cdots\times {\mathcal G}_t}$$, where $${{\mathcal G}_j}$$ is an R[x]/(g j )-submodule of $${(R[x]/(g_j))^{n_j}}$$, where n j is the number of i for which g j appears in the factorization of $${x^{m_i}-1}$$ into monic basic irreducible polynomials. This identification then leads to an enumeration of such GQC codes. An analogous result is also obtained for the 1-generator GQC codes. A notion of a parity-check polynomial is given when R is a finite field, and the number of GQC codes with a given parity-check polynomial is determined. Finally, an algorithm is given to compute the number of GQC codes of given block lengths.

Structure and performance of generalized quasi-cyclic codes

In this paper, we investigate the properties of the point-line incidence matrix of a finite affine plane and present a construction of quasicyclic LDPC codes based on submatrices of the incidence matrix. The codes from the point-line incidence matrices of the affine and projective geometries perform very well with iterative decoding algorithms for low-density parity-check (LDPC) codes.

1-Generator quasi-cyclic codes over [formula omitted

Using algebraic techniques, one of the co-authors has designed a [155,64, 20] low density parity check code based on permutation matrices. This code is quasi-cyclic by construction and hence admits a convolutional representation. A set of low density parity check convolutional codes is derived from this quasi-cyclic code and its generalizations. The performance of these convolutional codes is investigated when decoded using belief propagation on their corresponding graph representations.

In this paper, we study no 4-cycle, high-rate LDPC codes based on finite geometries for use in data storage devices and prove that these codes cannot be classified as quasi-cyclic (QC) codes but should be considered as broader generalized quasi-cyclic (GQC) codes. Because of the GQC structure of such codes, they can be systematically encoded using Groebner bases and their encoder can be implemented using simple feedback-shift registers. In order to demonstrate the efficiency of the encoder, we show that the hardware complexity of the serial-in serial-out encoder architecture of these codes is of linear order O(n). To encode a binary codeword of length n, less than 2n adders and 3n memory elements are required. Furthermore, we evaluated the error performances of these codes with sum product algorithm (SPA) decoding over additive white Gaussian noise (AWGN) channels. At a bit error rate (BER) of 10^-5, they perform 1-dB away from the Shannon limit after 10 decoding iterations.

Quantum error correction is the basic technique for realization of quantum communication and quantum computation. So far, the theories of quantum error correction have become more and more perfect, and many counterpart of classical error correction coding technique have been found in quantum area. In this article, we proposed a new method of construction of parity check matrix of quantum low density parity check (LDPC) codes which based on classical quasi-cyclic LDPC codes, and selected the quantum code (3,8)(16,6) as the example to illustrate the construction of quantum code. We also gave its completing circuit by controlled-not gate and Hadamard gate.

Two new design approaches for constructing Low-Density Parity-Check (LDPC) codes are proposed. One is used to design regular Quasi-Cyclic LDPC (QC-LDPC) codes with girth at least 8. The other is used to design irregular LDPC codes. Both of their parity-check matrices are composed of Circulant Permutation Matrices (CPMs). When iteratively decoded with the Sum-Product Algorithm (SPA), these proposed codes exhibit good performances over the AWGN channel.

In this paper we present a method to search q circulant matrices; the concatenation of these circulant matrices with circulant identity matrix generates quasi-cyclic codes with high various code rate q/(q+1) (q an integer). This method searches circulant matrices in order to find the good quasi-cyclic code (QCC) having the largest minimum distance. A modified simulated annealing algorithm is used as an evaluator tool of the minimum distance of the obtained QCC codes. Based on this method we found 16 good quasi-cyclic codes with rates (1/2, 2/3 and 3/4), their estimated minimum distance reaches the lower bounds of codes considered to be the better linear block codes in Brouwer’s database.

In this paper we propose a novel method for designing irregular quasi-cyclic low-density parity-check (LDPC) codes from Balanced Incomplete Block Designs (BIBDpsilas). The design method hinges around finding the optimum degree profile by minimizing the threshold using density evolution. The approach for designing short block length codes is robust for practical implementation and has been found to exhibit considerable performance gain that may be attributed to a good degree profile for the codes. The design takes into consideration the code rate and code length as variable parameters. The simulation results for the designed codes are compared with regular and irregular quasi-cyclic BIBD based LDPC codes and found a relatively higher performance in terms of BER.

A low-density parity-check (LDPC) code whose parity-check matrix consists of weight-2 columns is known as a cycle code. In this letter, we propose a construction of nonbinary quasi-cyclic (QC) LDPC cycle codes based on Singer perfect difference set. The Tanner graph has girth 12 and the code length achieves the Gallager lower bound. We further show that constructed codes have exactly a minimum symbol Hamming distance 6. Simulation results show that the proposed codes perform better than random nonbinary LDPC cycle codes.

The combination of multiple-input multiple-output (MIMO) and bit-interleaved coded modulation (BICM)/BICM with iterative demapping (BICM-ID) is one of the key technologies to meet the high-transmission-rate requirement of the next generation broadcasting systems. However, conventional low-density parity check (LDPC) coded MIMO BICM schemes always show poor performance with iterative demapping, and vice versa. In this paper, a subset of spatially coupled codes, finite-length spatially coupled (SC-) quasi-cyclic (QC-) LDPC code, is proposed and the universality of spatially coupled codes is utilized to achieve a good tradeoff between MIMO BICM and BICM-ID schemes. Due to the specific code structure of SC-QC-LDPC, the tool of multi-edge type density evolution (MET-DE) is employed for the performance analysis and code optimization. As an example, a finite-length SC-QC-LDPC code is optimized in binary-input additive white Gaussian noise channel, and then bit error rate simulations are carried out to verify the universality of the designed code in MIMO BICM and BICM-ID schemes.

When a nontrivial permutation of a Hermitian code is given, the code will have a module structure over a polynomial ring of one variable. By exploiting the theory of Grobner bases for modules, a novel and elegant systematic encoding scheme for Her- mitian codes is proposed by Heegard et al.. The goal of this paper is to develop a serial-in-serial-out hardware architecture, similar to a classical cyclic encoder, for such a systematic encoding scheme. Moreover, we demonstrate that under a specific permutation, the upper bounds of the numbers of memory elements and constant multipliers in the proposed architecture are both proportional to , where is the length of the Hermitian code. To encode a codeword of length , this architecture takes clock cycles without any latency. Therefore, the hardware complexity of the proposed architecture is much less than that of the brute-force systematic encoding by matrix multiplication.

Low-density parity check (LDPC) codes are a significant class of classical codes with many applications. Several good LDPC codes have been constructed using random, algebraic, and finite geometries approaches, with containing cycles of length at least six in their Tanner graphs. However, it is impossible to design a self-orthogonal parity check matrix of an LDPC code without introducing cycles of length four. In this paper, a new class of quantum LDPC codes based on lines and points of finite geometries is constructed. The parity check matrices of these codes are adapted to be self-orthogonal with containing only one cycle of length four. Also, the column and row weights, and bounds on the minimum distance of these codes are given. As a consequence, the encoding and decoding algorithms of these codes as well as their performance over various quantum depolarizing channels will be investigated.

DOI: 10.1049/cp:20061337 ISBN: 0 86341 644 6 Location: Hangzhou, China Conference date: 6-9 Nov. 2006 Format: PDF The BER performance of presented quasi-cyclic (QC) low-density parity-check (LDPC) codes is not good as that of randomly constructed LDPC codes, while the lack of structure of randomly constructed LDPC codes implies serious disadvantages in terms of storing and accessing a large parity-check matrix. To solve the problems, this paper proposes a design of good quasi-cyclic (QC) low-density parity-check (LDPC) codes, the obtained algebraically structured codes have large minimum distances and good BER performance. The proposed design is based on index matrices, which determines the shifts of the circulant matrices of the sparse parity-check matrices. Compared with the presented design of QC LDPC codes, the designed QC LDPC codes are free from girth 4, sometimes free from girth 6, and have much larger minimum distances. Based on the algebraic code structure, the conditions of the girth and minimum distance of the codes are found. The BER performance of the designed QC LDPC block codes compares with that of randomly constructed LDPC codes for any block lengths. Better BER performance is obtained by increasing the circulant size of the base QC code. Simulations verify the construction of the QC LDPC codes to be valid. (4 pages) Inspec keywords: AWGN channels; error statistics; channel coding; algebraic codes; parity check codes; sparse matrices Subjects: Algebra; Other topics in statistics; Codes