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In this paper, we compare performance of three classes of forward error correction schemes for 40-Gb/s optical transmission systems. The first class is based on the concatenation of Reed-Solomon codes and this is employed in the state-of-the-art fiber-optics communication systems. The second class is the turbo product codes with Bose-Chaudhuri-Hocquenghen component codes. The application of these codes in optical communication systems was extensively studied by Sab and Lemarie, and Mizuochi The third class is the low-density parity-check (LDPC) codes that have attracted much attention over the past decade. We present enhanced decoding algorithms for Turbo product codes and LDPC codes that use probability density function of output sequences instead of calculating initial likelihood ratios assuming (inaccurate) Gaussian or chi-square approximation. The analysis in this paper shows that the LDPC codes perform better than the other codes in the waterfall region at bit error rates as low as 10-9. We also presented error floors results obtained by analyzing decoding failures of hard-decision iterative decoders [ABSTRACT FROM PUBLISHER]

A bandwidth- and power-efficient modulation scheme using M-ary differential phase-shift keying (DPSK)/differential quadrature amplitude modulation (DQAM) and low-density parity-check (LDPC) codes as component codes in a multilevel coding (MLC) is proposed for optical transmission systems with direct detection. An MLC scheme with 2 b/s/Hz spectral efficiency based on block-circulant component codes provides the coding gain of 12.3 dB when compared to uncoded 8-DPSK, and 8.3 dB when compared to uncoded 4-DPSK (QDPSK). [ABSTRACT FROM PUBLISHER]

In an earlier paper, we reported that the low-density parity-check (LDPC) codes from finite planes outperform any other known forward error-correction (FEC) scheme for optical communications. However, the number of different LDPC codes of code rate above 0.8 is rather small. As a natural extension of the prior work, in this paper, we consider LDPC codes on m flats derived from projective and affine geometries, which outperform codes from finite planes. The codes on m flats also provide a greater selection of structured LDPC codes of rate 0.8 or higher. The performance of the codes in a long-haul optical-communication system was assessed using an advanced simulator able to capture all important transmission impairments. Specifically, they achieve a coding gain of 10 dB at a bit error rate (BER) of 10-9, outperforming, therefore, the best turbo product codes proposed for optical communications. In addition, the simulator implements a fixed-point (FP) iterative decoder that allows control of the precision of the soft information used in the decoder. Such quantization is required to facilitate hardware implementations of the iterative decoder, and the high-speed operations for long-haul optical transmission systems. The loss in performance due to reduced precision of the soft information can be as low as 0.2 dB. [ABSTRACT FROM PUBLISHER]

This paper is concerned with investigating the performance of regular and irregular, randomlike and structured generalized low-density parity-check (GLDPC) codes for long-haul transmission. The proposed GLDPC codes outperform currently known turbo and low-density parity-check (LDPC) coding schemes with comparable parameters utilized in optical communication systems. For a GLDPC coding scheme with 23.6% redundancy, the largest so far reported coding gain of at least 11dB (at 40 Gb/s) is demonstrated. [ABSTRACT FROM PUBLISHER]

A novel family of structured low-density parity-check (LDPC) codes with block-circulant parity-check matrices that consist of permutation blocks is proposed. The codes from this family are based on new combinatorial objects termed cycle-invariant difference sets, and they have low storage requirements, fast encoding algorithms, and girth of at least six. Most importantly, they tend to outperform many other known structured LDPCs of comparable rate and length. [ABSTRACT FROM PUBLISHER]

The possibility of 100-Gb/s transmission over 25-GHz bandwidth using orthogonal frequency-division multiplexing (OFDM) is demonstrated. It is shown that 100-Gb/s transmission over 3840 km can be achieved using single-sideband quadrature-phase-shift keying OFDM transmission and low-density parity-check codes [ABSTRACT FROM PUBLISHER]

We propose an efficient coded modulation scheme for multiple input/multiple output free-space optical systems with Q-ary pulse-position modulation. It is based on multilevel coding and low-density parity-check codes as component codes. The proposed scheme provides excellent coding gain in the regime of strong atmospheric turbulence. [ABSTRACT FROM PUBLISHER]

We propose a class of moderate-length nonbinary low-density parity-check (LDPC) codes for long-haul high-speed optical transmission systems. In particular, we present an LDPC code with 12.59% redundancy that achieves a 9.9-dB coding gain at a bit-error rate of 10-10. A similar coding gain is obtained for a long nonbinary LDPC code with a redundancy of only 6.7%. [ABSTRACT FROM PUBLISHER]