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Optical Fiber Communication Conference

Reduced-Complexity Decoding Algorithm for LDPC Codes for Practical Circuit Implementation in Optical Communications

Yoshikuni Miyata, Rui Sakai, Wataru Matsumoto, Hideo Yoshida, Takashi Mizuochi

Published Mar 1, 2007• 17 citations
Publisher

Abstract

For superior, practical decoding of LDPC based FEC, a cyclic approximated delta-minimum algorithm is proposed. Simulation shows that 3-bit soft-decision decoding provides a required Q of 6.2 dB at 10-6BER with only 16 iterations.
DOI
10.1109/ofc.2007.4348865

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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.
Very powerful long low-density parity-check (LDPC) codes, such as the ITU G.975.1 Standard (32643, 30592) LDPC Code [1], have been considered for optical communications. Traditional implementations of such long codes result in circuits requiring millions of interconnections, which are not affordable. This thesis investigates the performance of the hard-decision differential decoding with binary message-passing (DD-BMP) algorithm [2], a low-complexity algorithm requiring a minimal number of wires due to its binary messages. Our simulation results for the ITU G.975.1 standard demonstrate that hard-decision DD-BMP algorithm outperforms the results provided in the standard, and that the gap between the decoding performance of hard-decision DD-BMP and hard-decision sum-product is small at high signal-to-noise ratios (SNR). We also present a novel design methodology for implementing a soft-decision decoder by exploiting the code's structure. An implementation-efficient architecture is presented using a partially-parallel adaptation of the min-sum algorithm known as the line-passing algorithm. The line-passing algorithm makes soft-decision decoding available while requiring a minimal number of interconnections, which is attractive for long-haul optical communication systems.