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Optics and Photonics Journal

Research of Multi-Rate LDPC Decoding in Optical Communication System

Wenhao Jin, Chunwu Liu

Published Jan 1, 2020• 1 citation
Publisher

Abstract

Low-density parity-check code (LDPC) not only has good performance approaching the Shannon limit, but also has low decoding complexity and flexible structure. It is a research hot-spot in the field of channel coding in recent years and has a wide range of application prospects in optical communication systems. In this paper, the decoding aspects and performance of LDPC codes are analyzed and compared according to the bit error rate (BER) of LDPC codes. The computer simulation was carried out under additive white Gaussian noise (AWGN) channel and binary phase shift keying (BPSK) modulation. Through theoretical analysis and simulation results, this paper explores the way of multi-rate LDPC decoding.

DOI
10.4236/opj.2020.106019

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•Jan 1, 2013•0 citations
Low-density parity-check code (LDPC) not only has good performance approaching the Shannon limit, but also has low decoding complexity and flexible structure. It is a research hot-spot in the field of channel coding in recent years and has a wide range of application prospects in optical communication systems. In this paper, the decoding aspects and performance of LDPC codes are analyzed and compared according to the bit error rate (BER) of LDPC codes. The computer simulation was carried out under additive white Gaussian noise (AWGN) channel and binary phase shift keying (BPSK) modulation. Through theoretical analysis and simulation results, this paper explores the way of multi-rate LDPC decoding.
Low-Density Parity-Check (LDPC) codes are error correcting codes with good performance in communications systems. LDPC codes, however, have heavy computational complexity. In this paper, we find out how many iterations are required for sufficient performance of LDPC codes. The Additive White Gaussian Noise (AWGN) channel model and a log-domain Sum-Product (SP) algorithm are used. Experiments measure Bit Error Rate (BER) at each iteration in given SNRs. The result of performance evaluation, the best performance is showed when the number of iteration is 25 at 5 ㏈.
We study the decoding performance of low-density parity-check (LDPC) code based on Watermark scheme under different percentages of water-mark bits over 100 Gb/s differential quadrature phase shift keying (DQPSK) high-speed optical communication system. We also find the optimum percentage of water-mark bits according to the performance comparison. Simulation result shows an improvement of 0.5 dB net code gain by using the optimum Watermark scheme at a post-forward error correction bit error rate (BER) of 10-9, comparing with the traditional log-likelihood ratios belief propagation decoding algorithm. Also, for the same BER, there is a decrease in the number of iterations used in LDPC decoding.
Quasi-cyclic low-density parity-check(QC-LDPC) codes have excellent performance,but in order to obtain the optimal performance on a specific channel,the decoding method needs to be modified to adapt to the corresponding channel model.In this paper,we apply QC-LDPC codes into the channel based on avalanche photodiode(APD) receiver in the space optical communication system.The main work is to analyze the error performance and modify the belief propagation(BP) iterative decoding algorithm that uses probability density function(PDF) of the output sequences in the multiplicative noise channel model.We introduce a new method to compute the log-likelihood ratio(LLR) initialization for the LLR-BP decoding in the APD receiver channel.The simulation results show that the adaptation of QC-LDPC decoding on the accurate Webb-Gaussian model has better performance than that on approximate asymmetric Gaussian model,and almost no additional hardware complexity is increased.Moreover,the former can bring more than 1 dB net coding gain compared with the latter at the bit error rate(BER) of 10-6 under ideal channel conditions.
Channel coding technique is a fundamental building block in any modern communication system to realize reliable, fast, and secure data transmission. At the same time, it is a challenging and crucial task, as the data transmission happens in a channel where noise, fading, and other impairments are present. The Low-Density Parity-Check (LDPC) codes give substantial results close to the Shannon limit when the complexity and processing delay time are unlimited. In this paper, the performance of the LDPC decoding with four algorithms was investigated. The investigated four algorithms were Belief Propagation (BP), Layered Belief Propagation (LBP), Normalized min-sum (NMS), and Offset min-sum (OMS). These algorithms were examined for code rates ranging from 1/3 to 9/10 and message block lengths (64, 512, 1024, and 5120) bits. The simulation results revealed the flexibility of these decoders in supporting these code rates and block lengths, which enables their usage in a wide range of applications and scenarios for fifth-generation (5G) wireless communication. In addition, the effect of the maximum number of decoding iterations on the error correction performance was investigated, and a gain of 5.6 dB can be obtained by using 32 decoding iterations at BER=2*10-3 instead of one decoding iteration. The results showed that the decoders performed better for longer message blocks than for short message blocks, and less power was required for transmitting longer messages. Finally, the comparison results of their performance in terms of bit error rate (BER) under the same conditions showed a gain of 0.8 dB using LBP at BER= 10-5 compared with the NMS decoding algorithm.
Abstract: In this paper, we perform an analysis on the min-max decoding algorithm for nonbinary LDPC (lowdensity parity-check) codes and propose serial min-max decoding algorithm. After that, combining with the weighted processing of the variable node message, we propose serial min-max decoding algorithm based on variable weighting for nonbinary LDPC codes. In the end, we perform a detailed analysis on the features of optical communication and show the simulation model in optical communication system. The simulation indicates that when the bit error rate is 10-3 and used in optical communication, compared with serial min-max decoding algorithm, traditional min-max decoding algorithm and traditional min-sum algorithm, serial min-max decoding algorithm based on variable weighting can offer additional coding gain 0.2 dB, 0.3 dB and 0.4 dB respectively in (AWGN) additional white Gaussian noise channel and under (OOK) on-off keying modulation. Copyright © 2013 IFSA.