| 1. |
- Sheikh, Alireza, 1989, et al.
(author)
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Achievable Information Rates for Coded Modulation With Hard Decision Decoding for Coherent Fiber-Optic Systems
- 2017
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In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 35:23, s. 5069-5078
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Journal article (peer-reviewed)abstract
- We analyze the achievable information rates (AIRs) for coded modulation schemes with quadrature amplitude modulation constellations with both bitwise and symbolwise decoders, corresponding to the case where a binary code is used in combination with a higher order modulation using the bit-interleaved coded modulation (BICM) paradigm and to the case where a nonbinary code over a field matched to the constellation size is used, respectively. In particular, we consider hard decision decoding, which is the preferable option for fiber-optic communication systems where decoding complexity is a concern. Recently, Liga et al. analyzed the AIRs for bitwise and symbolwise decoders considering what the authors called hard decision decoder, which, however, exploits soft information of the transition probabilities of discrete-input discrete-output channel resulting from the hard detection. As such, the complexity of the decoder is essentially the same as the complexity of a soft decision decoder. In this paper, we analyze instead the AIRs for the standard hard decision decoder, commonly used in practice, where the decoding is based on the Hamming distance metric. We show that if standard hard decision decoding is used, bitwise decoders yield significantly higher AIRs than the symbolwise decoders. As a result, contrary to the conclusion by Liga et al., binary decoders together with the BICM paradigm are preferable for spectrally efficient fiber-optic systems. We also design binary and nonbinary staircase codes and show that, in agreement with the AIRs, binary codes yield better performance.
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| 2. |
- Sheikh, Alireza, 1989, et al.
(author)
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Dispersion Compensation FIR Filter with Improved Robustness to Coefficient Quantization Errors
- 2016
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In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 34:22, s. 5110-5117
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Journal article (peer-reviewed)abstract
- In this paper, we propose a new finite impulseresponse (FIR) filter for chromatic dispersion compensation which is given in closed form. We identify a relation between the out-of-band gain and the in-band error when the filter is implemented with finite-precision arithmetic. In particular, a large out-of-band gain makes the filter more sensitive tocoefficient quantization errors due to finite precision digital signal processing. To improve robustness to coefficient quantization errors, our proposed filter is designed based on confining the out-of-band gain. By means of simulations, we show that our filter outperforms other existing FIR filters. The performance gain improves with increasing modulation order and decreasing number of bits used to represent the filter taps.
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| 3. |
- Sheikh, Alireza, 1989, et al.
(author)
-
Novel High-Throughput Decoding Algorithms for Product and Staircase Codes based on Error-and-Erasure Decoding
- 2021
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In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 39:15, s. 4909-4922
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Journal article (peer-reviewed)abstract
- Product codes (PCs) and staircase codes (SCCs) are conventionally decoded based on bounded distance decoding (BDD) of the component codes and iterating between row and column decoders. The performance of iterative BDD (iBDD) can be improved using soft-aided (hybrid) algorithms. Among these, iBDD with combined reliability (iBDD-CR) has been recently proposed for PCs, yielding sizeable performance gains at the expense of a minor increase in complexity compared to iBDD. In this paper, we first extend iBDD-CR to SCCs. We then propose two novel decoding algorithms for PCs and SCCs which improve upon iBDD-CR. The new algorithms use an extra decoding attempt based on error and erasure decoding of the component codes. The proposed algorithms require only the exchange of hard messages between component decoders, making them an attractive solution for ultra high-throughput fiber-optic systems. Simulation results show that our algorithms based on two decoding attempts achieve gains of up to 0.88 dB for both PCs and SCCs. This corresponds to a 33% optical reach enhancement over iBDD with bit-interleaved coded modulation using 256 quadrature amplitude modulation.
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| 4. |
- Sheikh, Alireza, 1989, et al.
(author)
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Probabilistic Amplitude Shaping with Hard Decision Decoding and Staircase Codes
- 2018
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In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 36:9, s. 1689-1697
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Journal article (peer-reviewed)abstract
- We consider probabilistic amplitude shaping (PAS) as a means of increasing the spectral efficiency of fiber-optic communication systems. In contrast to previous works in the literature, we consider probabilistic shaping with hard decision decoding (HDD). In particular, we apply the PAS recently introduced by Böcherer et al. to a coded modulation (CM) scheme with bit-wise HDD that uses a staircase code as the forward error correction code. We show that the CM scheme with PAS and staircase codes yields significant gains in spectral efficiency with respect to the baseline scheme using a staircase code and a standard constellation with uniformly distributed signal points. Using a single staircase code, the proposed scheme achieves performance within 0.57–1.44 dB of the corresponding achievable information rate for a wide range of spectral efficiencies.
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| 5. |
- Sheikh, Alireza, 1989, et al.
(author)
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Refined Reliability Combining for Binary Message Passing Decoding of Product Codes
- 2021
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In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 39:15, s. 4958-4973
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Journal article (peer-reviewed)abstract
- We propose a novel soft-aided iterative decoding algorithm for product codes (PCs). The proposed algorithm, named iterative bounded distance decoding with combined reliability (iBDD-CR), enhances the conventional iterative bounded distance decoding (iBDD) of PCs by exploiting some level of soft information. In particular, iBDD-CR can be seen as a modification of iBDD where the hard decisions of the row and column decoders are made based on a reliability estimate of the BDD outputs. The reliability estimates are derived by analyzing the extrinsic message passing of generalized low-density-parity check (GLDPC) ensembles, which encompass PCs. We perform a density evolution analysis of iBDD-CR for transmission over the additive white Gaussian noise channel for the GLDPC ensemble. We consider both binary transmission and bit-interleaved coded modulation with quadrature amplitude modulation. We show that iBDD-CR achieves performance gains up to 0.51 dB compared to iBDD with the same internal decoder data flow. This makes the algorithm an attractive solution for very high-throughput applications such as fiber-optic communications.
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