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IEEE Latin-American Conference on Communications

Design and FPGA verification of a quasi-cyclic LDPC code for optical communication systems

Bergero Genaro, Damián A. Morero, Ariel L. Pola, Mario A. Castrillón, Mario R. Hueda

Published Nov 1, 2016• 1 citation
Publisher

Abstract

Powerful forward error correction codes such as quasi-cyclic low density parity check (QC-LDPC) are required in next-generation coherent optical communication systems [1]. This work describes the design and experimental verification of a high net coding gain (NCG), low complexity QC-LDPC code. Towards this end, we develop a field programmable gate array (FPGA) based platform specially designed for optimization and performance evaluation of LDPC codes. The proposed FPGA framework includes several features such as the capability of changing the internal resolution of the decoder algorithm or capturing error patterns for error-floor analysis. Experimental results derived from the FPGA platform show that the designed QC-LDPC code is able to achieve an NCG of 11.6 dB at a bit-error-rate (BER) of 10-15with an overhead of 25% and a codeword length of only 16K bits.

DOI
10.1109/latincom.2016.7811566

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Powerful forward error correction codes such as quasi-cyclic low density parity check (QC-LDPC) are required in next-generation coherent optical communication systems [1]. This work describes the design and experimental verification of a high net coding gain (NCG), low complexity QC-LDPC code. Towards this end, we develop a field programmable gate array (FPGA) based platform specially designed for optimization and performance evaluation of LDPC codes. The proposed FPGA framework includes several features such as the capability of changing the internal resolution of the decoder algorithm or capturing error patterns for error-floor analysis. Experimental results derived from the FPGA platform show that the designed QC-LDPC code is able to achieve an NCG of 11.6 dB at a bit-error-rate (BER) of 10-15with an overhead of 25% and a codeword length of only 16K bits.
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 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.
To meet the increasing requirement on the transmission characteristics of optical communication systems,based on the structure of parity-check matrix of Richardson-Urbanke algorithm,a lowercomplexity constructing method is proposed for the quasi-cyclic low-density parity-check(QC-LDPC) codes in the optical communication systems,and a QC-LDPC(4288,4020) code with 93.7% higher code-rate is also constructed.Simulation shows that the constructed QC-LDPC(4288,4020) code has net coding gain of about 1.7 dB over the classic RS(255,239) code which has been widely used for optical communication systems and 0.3 dB more than that of SCG-LDPC(3969,3720) code with the same 93.7% higher code-rate,and the NCG of the QC-LDPC(4288,4020) code is about 1.3 dB away from the Shannon limit at bit error rate BER of 10-7;furthermore,the error floor of QC-LDPC(4288,4020) code is lower than that of the randomly constructed LDPC(4288,4020) with the column weight of 3.
We propose a rate-adaptive forward error correction (FEC) scheme based on spatially-coupled (SC) LDPC codes derived from quasi-cyclic (QC) LDPC codes with its field-programmable gate array (FPGA) architecture. By FPGA emulation, we show that, with comparable computational complexity, the proposed LDPC codes provide larger coding gain and smaller error floor compare to the QC-LDPC base code. As a result, due to its hardware friendly structure, they are presented to be a promising candidate for the next-generation intelligent optical communication systems such as long-haul optical transmission system.
Based on finite field(GF(q)) additive group,a novel construction method with the advantages of simple construction and easy implementation of quasi-cyclic low-density parity-check(QC-LDPC) codes for optical communication systems is proposed in order to meet the increasing requirement on the transmission characteristics.The novel construction method can flexibly adjust the code-length and code-rate,and furthermore,the complexity of the encoding and decoding in lower.A regular QC-LDPC(4599,4307) code to be suitable for optical communication systems is constructed by applying the proposed method.The simulation results show that at the condition of the bit error rate(BER) of 10-7 and the same code rate of 93.7%,the net coding gain(NCG) of the constructed QC-LDPC(4599,4307) code is 2.2 dB more than that of the classic RS(255,239) code which has widely been applied in optical communication systems,and 0.47 dB and 0.25 dB more than those of the SCG-LDPC(3969,3720) code constructed by the systematically constructed gallager(SCG) construction method and the irregular QC-LDPC(3843,3603) code respectively,and is 1 dB away from the Shannon limit.Therefore,the novel QC-LDPC(4599,4307) code has superior error-correction performance and is more suitable for the high-speed long-haul optical communication systems.
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.