| 1. |
- Buchberger, Andreas, 1990, et al.
(författare)
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Probabilistic Eigenvalue Shaping for Nonlinear Fourier Transform Transmission
- 2018
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 36:20, s. 4799-4807
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Tidskriftsartikel (refereegranskat)abstract
- We consider a nonlinear Fourier transform (NFT)-based transmission scheme, where data is embedded into the imaginary part of the nonlinear discrete spectrum. Inspired by probabilistic amplitude shaping, we propose a probabilistic eigenvalue shaping (PES) scheme as a means to increase the data rate of the system. We exploit the fact that for an NFT-based transmission scheme the pulses in the time domain are of unequal duration by transmitting them with a dynamic symbol interval and find a capacity-achieving distribution. The PES scheme shapes the information symbols according to the capacity-achieving distribution and transmits them together with the parity symbols at the output of a low-density parity-check encoder, suitably modulated, via time-sharing. We furthermore derive an achievable rate for the proposed PES scheme. We verify our results with simulations of the discrete-time model as well as with split-step Fourier simulations.
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| 2. |
- He, Zonglong, 1994, et al.
(författare)
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Periodicity-Enabled Size Reduction of Symbol Based Predistortion for High-Order QAM
- 2022
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; In press
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Tidskriftsartikel (refereegranskat)abstract
- We experimentally demonstrate a novel size reduction approach for symbol-based look-up table (LUT) digital predistortion (DPD) of the transmitter impairments taking advantage of the periodicity in the pattern-dependent distortions. Compared to other reduced-size LUT schemes, the proposed method can significantly lessen the storage memory requirements with negligible performance penalty for high-order modulation formats. To further alleviate the storage memory restriction, a twice reduced-size LUT scheme is proposed to provide further size reduction. Importantly, given a targeted memory length, we verify the importance of averaging over sufficient occurrences of the patterns to obtain a well-performing LUT. Moreover, it is necessary to evaluate the performance of LUT-based DPD using random data. Finally, we demonstrate a neural network (NN) based nonlinear predistortion technique, which achieves nearly identical performance to the full-size LUT for all employed constellations and is robust against a change of modulation format. The proposed techniques are verified in a back-to-back transmission experiment of 20 Gbaud 64-QAM, 256-QAM, and 1024-QAM signals considering 3 and 5 symbol memory. The performance of the LUT-based DPD is further validated in a noise loading experiment.
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| 3. |
- Häger, Christian, 1986, et al.
(författare)
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Terminated and Tailbiting Spatially-Coupled Codes with Optimized Bit Mappings for Spectrally Efficient Fiber-Optical Systems
- 2015
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 33:7, s. 1275-1285
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Tidskriftsartikel (refereegranskat)abstract
- We study the design of spectrally efficient fiber- optical communication systems based on different spatially cou- pled (SC) forward error correction (FEC) schemes. In particular, we optimize the allocation of the coded bits from the FEC encoder to the modulation bits of the signal constellation. Two SC code classes are considered. The codes in the first class are protograph-based low-density parity-check (LDPC) codes which are decoded using iterative soft-decision decoding. The codes in the second class are generalized LDPC codes which are decoded using iterative hard-decision decoding. For both code classes, the bit allocation is optimized for the terminated and tailbiting SC cases based on a density evolution analysis. An optimized bit allocation can significantly improve the performance of tailbiting SC codes codes over the baseline sequential allocation, up to the point where they have a comparable gap to capacity as their terminated counterparts, at a lower FEC overhead. For the considered terminated SC codes, the optimization only results in marginal performance improvements, suggesting that in this case a sequential allocation is close to optimal.
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| 4. |
- Sheikh, Alireza, 1989, et al.
(författare)
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Achievable Information Rates for Coded Modulation With Hard Decision Decoding for Coherent Fiber-Optic Systems
- 2017
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 35:23, s. 5069-5078
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Sheikh, Alireza, 1989, et al.
(författare)
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Dispersion Compensation FIR Filter with Improved Robustness to Coefficient Quantization Errors
- 2016
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 34:22, s. 5110-5117
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Sheikh, Alireza, 1989, et al.
(författare)
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Novel High-Throughput Decoding Algorithms for Product and Staircase Codes based on Error-and-Erasure Decoding
- 2021
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 39:15, s. 4909-4922
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Sheikh, Alireza, 1989, et al.
(författare)
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Probabilistic Amplitude Shaping with Hard Decision Decoding and Staircase Codes
- 2018
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 36:9, s. 1689-1697
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Sheikh, Alireza, 1989, et al.
(författare)
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Refined Reliability Combining for Binary Message Passing Decoding of Product Codes
- 2021
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 39:15, s. 4958-4973
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Steiner, Fabian Roland, et al.
(författare)
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One and Two Bit Message Passing for SC-LDPC Codes with Higher-Order Modulation
- 2019
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 37:23, s. 5914-5925
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Tidskriftsartikel (refereegranskat)abstract
- Low complexity decoding algorithms are necessary to meet data rate requirements in excess of 1 Tbps. In this paper, we study one and two bit message passing algorithms for belief propagation decoding of low-density parity-check (LDPC) codes and analyze them by density evolution. The variable nodes exploit soft information from the channel output, and to decrease the data flow, the messages exchanged between check and variable nodes are represented by one or two bits. The newly proposed quaternary message passing (QMP) algorithm is compared asymptotically and in finite length simulations to binary message passing (BMP) and ternary message passing (TMP) for spectrally efficient communication with higher-order modulation and probabilistic amplitude shaping (PAS). To showcase the potential for high throughput forward error correction, spatially coupled LDPC codes and a target spectral efficiency of 3 bits/QAM symbol are considered. Gains of about 0.7 dB and 0.1 dB are observed compared to BMP and TMP, respectively. The gap to unquantized belief propagation decoding is reduced to about 0.75 dB. For smaller code rates, the gain of QMP compared to TMP is more pronounced and amounts to 0.24 dB in the considered example.
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