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IET Communications

Low-density parity-check code for high-speed fibre-optic communication and its experimental verification

Bo Xu, Jiandong Xie

Published Jun 24, 2010• 5 citations
Publisher

Abstract

Although low-density parity-check (LDPC) code has been proved as a powerful forward error correction code for fibre optic communication, its soft-decoding requires high quantisation resolution which is difficult to achieve for high-speed fibre-optic communication systems. A modification to LDPC decoding algorithms is proposed to effectively improve the performance at quantisation resolution as low as two-bit or one-bit. The good decoding performance of LDPC code for error correction is confirmed by experiment. Compared with the RS(255, 239) code commonly used in optical fibre communication, a Q-factor improvement of 2-dB is obtained in the experiment for an LDPC code with quasi-cyclic structure at the same redundancy as the RS code. Furthermore, the impacts of sampling phase and channel estimation using real data over the decoding performance are analysed.

DOI
10.1049/iet-com.2009.0534

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Although low-density parity-check (LDPC) code has been proved as a powerful forward error correction code for fibre optic communication, its soft-decoding requires high quantisation resolution which is difficult to achieve for high-speed fibre-optic communication systems. A modification to LDPC decoding algorithms is proposed to effectively improve the performance at quantisation resolution as low as two-bit or one-bit. The good decoding performance of LDPC code for error correction is confirmed by experiment. Compared with the RS(255, 239) code commonly used in optical fibre communication, a Q-factor improvement of 2-dB is obtained in the experiment for an LDPC code with quasi-cyclic structure at the same redundancy as the RS code. Furthermore, the impacts of sampling phase and channel estimation using real data over the decoding performance are analysed.
Low-density parity-check (LDPC) codes are linear block codes. It is called low density parity check code because their parity-check matrix contains only a few 1’s in comparison to the amount of 0’s. These codes were first introduced by Gallager. It is a very powerful code for forward error correction system. The presently used LDPC code in optical fibre communication systems is not meeting the requirements of the high speed fibre optics communication systems. So the LDPC code can be modified and with which the quality factor can be improved. This modification is beneficial for the high speed fibre optic communication systems. We present here a comprehensive review of decoding algorithm of modified Low density parity check code useful in Optical fibre communication. BP and the MS decoding algorithms which are modified decoding algorithm are use for a better performance in high speed fibre optic communication.
The performance of a high-throughput long-distance communication system such as an optical transmission system is limited by the Net Coding Gain (NCG) of the Forward Error Correction (FEC) system. Summarizing the previous research works, Low-Density Parity-Check (LDPC) codes form one of the most promising FEC schemes to be applied in high-throughput communication systems. Designing a practical channel coding scheme with high code rate, low complexity, high throughput and extremely low error floor has always been a very challenging problem. Quasi-cyclic low-density parity-check (QC-LDPC) codes have been promising candidates to fulfill the above requirements but the implementation issues remain. In this paper, we propose a layered QC-LDPC decoder architecture with high code rate, low complexity, high throughput and excellent error performance. The architecture has been implemented using FPGA and the error performance has been shown to be good.
Forward error correcting codes are successfully implemented in high speed communication for error-free transmission with high data rate. One such code is Low Density Parity Check (LDPC) code. In this paper, Quasi Cyclic (QC) construction of LDPC code is used and we investigate the performance of various decoding algorithms of QC-LDPC code. Their performances in terms of error correction and complexity are compared. The speed of convergence of various decoding algorithms of LDPC code is analyzed by using the Density Evolution theory. With this thresholding in iterations, the BER performances of different algorithms are simulated. Our results show that the same BER performance can be achieved with reduced number of iterations or the speed of the system can be improved without much sacrifice in BER performance.
Forward error correction is as one of the key technologies enabling the next-generation high-speed fiber optical communications. Quasi-cyclic (QC) low-density parity-check (LDPC) codes have been considered as one of the promising candidates due to their large coding gain performance and low implementation complexity. In this paper, we present our designed QC-LDPC code with girth 10 and 25% overhead based on pairwise balanced design. By FPGAbased emulation, we demonstrate that the 5-bit soft-decision LDPC decoder can achieve 11.8dB net coding gain with no error floor at BER of 10-15 avoiding using any outer code or post-processing method. We believe that the proposed single QC-LDPC code is a promising solution for 400Gb/s optical communication systems and beyond.
The increasing popularity of optical communication systems emphasizes the need for effective errorcorrection solutions, including high-efficiency hardware decoder designs and codes with strong performance. Within optical communication networks, Low-Density Parity-Check (LDPC) codes utilizing sparse matrices and decoded through the Bit-Flipping (BF) algorithm, known for its hard iterative decoding approach are extensively utilized. These codes effectively balance decoding complexity with error-correction performance.This paper focuses on comparing the optical performance of LDPC codes with and without the BF decoding algorithm using two simulation software packages: MATLAB and OptiSystem 7.0. The comparison is conducted across different wavelengths and quality factors. Through this study, we evaluate the advantages of LDPC codes in terms of error-rate reduction and enhancing the reliability of optical transmission.
In the paper, we construct the non-binary quasi-cyclic low-density parity check (NB-QC-LDPC) code from the quasi-cyclic low-density parity check (QC-LDPC) code. The NB-QC-LDPC code over the Galois field GF(4) is suitable for 100Gb/s optical communication systems with QPSK or DQPSK modulation formats. We also study the bit error ratio (BER) performance of the NB-QC-LDPC code by using the Log-Fourier Sum and Product decoding algorithm (LFSPA). The numerical results show that the NB-QC-LDPC code with code length 500 can provide approximately 5.5dB coding gain at the BER of 910- and outperform QC-LDPC code by 0.7dB.