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International Conference on Information Systems and Advanced Technologies (ICISAT)

Construction Methods and Performance Evaluation of Regular LDPC Convolutional Codes

Oulfa Laouar, Nadir Derouiche, Imed Amamra

Published Dec 27, 2021• 1 citation
Publisher

Abstract

In this paper, we present three construction methods of systematic regular LDPC-CCs based on randomly or algebraically structured sparse matrices. We provide an overview of LDPC-CCs and compares between Gallager’s, Mackay-Neal and Quasi-Cyclic (QC) construction methods, which are a good choice for many wireless applications due to their errors correction efficiency and low decoding complexity. At a rate-1/2, for the same size of the parity matrix to obtain the same encoding and decoding complexity, and using the Bit Flipping (BF) decoding algorithm over Additive White Gaussian Noise (AWGN) channel, we simulated the BER performance of a (3,6) regular LDPC convolutional codes, where the results showed that Gallager’s construction method (random) outperforms Mackay-Neal and QC ones.

DOI
10.1109/icisat54145.2021.9678497

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In this paper, we present three construction methods of systematic regular LDPC-CCs based on randomly or algebraically structured sparse matrices. We provide an overview of LDPC-CCs and compares between Gallager’s, Mackay-Neal and Quasi-Cyclic (QC) construction methods, which are a good choice for many wireless applications due to their errors correction efficiency and low decoding complexity. At a rate-1/2, for the same size of the parity matrix to obtain the same encoding and decoding complexity, and using the Bit Flipping (BF) decoding algorithm over Additive White Gaussian Noise (AWGN) channel, we simulated the BER performance of a (3,6) regular LDPC convolutional codes, where the results showed that Gallager’s construction method (random) outperforms Mackay-Neal and QC ones.
Low Density Parity Check (LDPC) codes are one of the most powerful error correction codes available today. Its Shannon capability that closely matches performance and lower decoding complexity has made them the best choice for many wired and wireless applications. This Paper provides an overview of the LDPC codes and compares the Gallager method, the Reed-Solomon-based algebraic method, and the combinatorial Progressive Growth (PEG) method for constructing regular LDPC codes and also Overlapped and Modified overlapped message passing algorithm for Non-Quasi Cyclic(NQC) LDPC codes.
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Low-density parity-check (LDPC) block codes invented by Gallager in 1962 achieve exceptional error performance on a wide variety of communication channels. LDPC convolutional codes are the convolutional counterparts of LDPC block codes. This dissertation describes techniques for the design of LDPC convolutional codes, and analyzes their distance properties and iterative decoding convergence thresholds. The construction of time invariant LDPC convolutional codes by unwrapping the Tanner graph of algebraically constructed quasi-cyclic LDPC codes is described. The convolutional codes outperform the quasi-cyclic codes from which they are derived. The design of parity-check matrices for time invariant LDPC convolutional codes by the polynomial extension of a base matrix is proposed. An upper bound on free distance, proving that time invariant LDPC codes are not asymptotically good, is obtained. The Tanner graph is used to describe a pipelined message passing based iterative decoder for LDPC convolutional codes that outputs decoding results continuously. The performance of LDPC block and convolutional codes are compared for fixed decoding parameters like computational complexity, processor complexity, and decoding delay. In each case, the LDPC convolutional code performance is at least as good as that of LDPC block codes. An analog circuit to implement pipelined decoding of LDPC convolutional codes is proposed. The distance properties of a permutation matrix based (time varying) ensemble of (J,K) regular LDPC convolutional codes is investigated. It is proved that these codes (for J > 2) have free distance increasing linearly with constraint length, i.e., they are asymptotically good. Further, the asymptotic free distance to constraint length ratio for the convolutional codes is several times larger than the minimum distance to block length ratio for corresponding LDPC block codes. Iterative decoding of terminated LDPC convolutional codes, based on the ensemble mentioned above, is analyzed, assuming transmission over a binary erasure channel. The structured irregularity of the codes leads to significantly better convergence thresholds compared to corresponding LDPC block codes. At the calculated thresholds, both the bit and block error probability can be made arbitrarily small. The results obtained suggest that the thresholds approach capacity with increasing J.
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Time-invariant low-density parity-check convolutional codes (TI LDPC-CCs) can be represented by a polynomial-domain parity-check matrix derived from the corresponding quasi-cyclic (QC) LDPC block codes (LDPC-BCs), while time-varying (TV) LDPC-CCs can be obtained by unwrapping the parity-check matrices of LDPC-BCs. The cycle enumerators for TI and TV LDPC-CCs are compared. Based on the analysis of the graphical structures of short cycles in HT(D), we introduce a method of designing the polynomial syndrome former matrix HCRT(D) for LDPC-CCs. It eliminates short cycles and shows improved decoding performance on an additive white Gaussian noise (AWGN) channel with lower bit error ratio (BER) curves.