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arXiv:2010.07538 · IEEE Information Theory Workshop (ITW)

Matched Quantized Min-Sum Decoding of Low-Density Parity-Check Codes

Emna Ben Yacoub

Published Apr 11, 2021• 1 citation
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Abstract

A quantized message passing decoding algorithm for low-density parity-check codes is presented. The algorithm relies on the min approximation at the check nodes, and on modelling the variable node inbound messages as observations of an extrinsic discrete memoryless channel. The performance of the algorithm is analyzed and compared to quantized min-sum decoding by means of density evolution, and almost closes the gap with the performance of the sum-product algorithm. A stability analysis is derived, which highlights the role played by degree-3 variable nodes in the stability condition. Finite-length simulation results confirm large gains predicted by the asymptotic analysis.

DOI
10.1109/itw46852.2021.9457667

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A quantized message passing decoding algorithm for low-density parity-check codes is presented. The algorithm relies on the min approximation at the check nodes, and on modelling the variable node inbound messages as observations of an extrinsic discrete memoryless channel. The performance of the algorithm is analyzed and compared to quantized min-sum decoding by means of density evolution, and almost closes the gap with the performance of the sum-product algorithm. A stability analysis is derived, which highlights the role played by degree-3 variable nodes in the stability condition. Finite-length simulation results confirm large gains predicted by the asymptotic analysis.
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This paper examines ways to recoup the performance loss incurred when using the min-sum approximation instead of the exact sum-product algorithm for decoding low-density parity check codes (LDPCs). Approximations to the correction factor exactly expressing the difference between these two decoding algorithms exist for degree 3 check nodes, and can be applied to higher degree nodes by subdividing them into component degree 3 nodes. However, this results in replication of the approximation. An asymptotic expression for the correction factor at a check node of any degree is derived in this paper, and used to develop two simple approximations to the correction factor, matched to the check node degree. One has very low complexity, and both only need be applied once per check node extrinsic message. Simulation results are presented for each check node approximation when decoding a regular and an irregular LDPC. Both degree-matched check node approximations achieve sum-product decoding performance
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A new low-complexity message passing algorithm is described for decoding low-density parity-check (LDPC) codes by exchanging binary messages. The algorithm computes the local maximum-likelihood binary message (LMLBM) at each symbol node, given the combination of local channel information and partial syndrome components from adjacent parity check nodes. When channel information is quantized, the locally ML messages are pre-computed and stored in a dynamic global lookup table. The proposed algorithm uses memoryless extrinsic messages so that density evolution thresholds can be directly computed. Thresholds are obtained for regular ensembles, predicting good performance on quantized binary-input additive white Gaussian noise (biAWGN) channels.
To improve performance and reduce computation complexity of the low-density parity-check (LDPC) codes, a min-sum based differential decoding algorithm is proposed. The main principle is that the messages passing in the bipartite graph of the codes are the probability differences and the updates of the check nodes adopt min sum algorithm. Simulation results show that the proposed algorithm can achieve about 0.4dB performance gain over the UMP BP-Based decoding algorithm at bit error rate (BER) of under an additive white Gaussian noise (AWGN) channel. And it can obtain good performance very close to that of the BP decoding algorithm with much lower complexity.