| 1. |
- Beygi, Lotfollah, 1977, et al.
(författare)
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A Discrete-Time Model for Uncompensated Single-Channel Fiber-Optical Links
- 2012
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Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 60:11, s. 3440-3450
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Tidskriftsartikel (refereegranskat)abstract
- An analytical discrete-time model is introduced for single-wavelength polarization multiplexed nonlinear fiber-optical channels based on the symmetrized split-step Fourier method (SSFM). According to this model, for high enough symbol rates, a fiber-optic link can be described as a linear dispersive channel with additive white Gaussian noise (AWGN) and a complex scaling. The variance of this AWGN noise and the attenuation are computed analytically as a function of input power and channel parameters. The results illustrate a cubic growth of the noise variance with input power. Moreover, the cross effect between the two polarizations and the interaction of amplifier noise and the transmitted signal due to the nonlinear Kerr effect are described. In particular, it is found that the channel noise variance in one polarization is affected twice as much by the transmitted power in that polarization than by the transmitted power in the orthogonal polarization.The effect of pulse shaping is also investigated through numerical simulations. Finally, it is shown that the analytical performance results based on the new model are in close agreement with numerical results obtained using the SSFM for a symbol rate of 28 Gbaud and above.
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| 2. |
- Beygi, Lotfollah, 1977, et al.
(författare)
-
A novel multilevel coded modulation scheme for fiber optical channel with nonlinear phase noise
- 2010
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Ingår i: Proc. Global Communications Conference, Miami, FL. - 9781424456383
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Konferensbidrag (refereegranskat)abstract
- A multilevel coded modulation (MLCM) system in the presence of nonlinear phase noise for fiber optical communication is introduced. The proposed scheme exploits a 16-point ring constellation with nonlinear post compensation of the self phase modulation produced via the Kerr effect. A new set partitioning based on the Ungerboeck approach is introduced to maintain unequal error protection in amplitude and phase direction. The rate allocation for the MLCM component codes for different fiber lengths and transmit powers are done numerically. Simulation results show that the proposed MLCM system provides up to 2 dB gain over a forward error correcting scheme for a block error rates around 10-9, with the same overhead (7%) and complexity. ©2010 IEEE.
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| 3. |
- Beygi, Lotfollah, 1977, et al.
(författare)
-
A novel rate allocation method for multilevel coded modulation
- 2010
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Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. - 9781424469604 ; , s. 1983-1987
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Konferensbidrag (refereegranskat)abstract
- We present a new rate allocation scheme for multilevelcoded modulation based on the minimization of the totalblock error rate (BLER). The proposed method uses affine codecomponents and hard decision multistage decoding. Exhaustivesearch for the rate allocation which minimizes the total BLERjustifies the near-optimum performance of the introduced methodin moderate to high SNRs. Compared to previous approaches thisnew rate allocation scheme can improve the performance of thesystem by 1 dB at BLER = 10−6 for 16-QAM with Ungerboeck setpartitioning. Interestingly, our results indicate that the optimumrate allocation is a function of the SNR. Finally, the performanceof some specific codes are evaluated by simulation and unionbounds to verify the theoretical results.
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| 4. |
- Beygi, Lotfollah, 1977, et al.
(författare)
-
Adaptive Coded Modulation for Nonlinear Fiber-Optical Channels
- 2012
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Ingår i: 2012 IEEE Globecom Workshops, Anaheim, USA, 3-7 December 2012. - 9781467349420 ; , s. 331-335
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Konferensbidrag (refereegranskat)abstract
- A low complexity hybrid polar low-density parity check (LDPC) coded modulation (CM) scheme is introduced for a single-wavelength fiber-optical channel. In the proposed scheme, we exploit a low complexity probabilistic shaping together with a four-dimensional (4D) mapping to reduce the complexity of a 4D non-binary LDPC CM scheme for fiber-optic channels. The proposed scheme has a flexible structure and it can be used as an adaptive-rate CM scheme. The numerical results show that the forward error correction (FEC) threshold of the introduced CM scheme can be significantly improved by probabilistic shaping with a negligible increase in the system complexity. In particular, the FEC threshold for the uncoded symbol error rate of the introduced CM scheme with 4D 16-ary quadrature amplitude modulation can be improved from 0.058 to 0.072 by exploiting a shaping overhead (redundancy) of 0.016 for an information bit error rate of 10^{-5}.
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| 5. |
- Beygi, Lotfollah, 1977
(författare)
-
Channel-Aware Multilevel Coded Modulation for Coherent Fiber-Optic Communications
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The past decades have shown an ever-increasing demand for high-rate Internet services, motivating a great effort to increase the spectral efficiency of optical networks. In general, fiber-optic links are non-Gaussian, and in contrast to additive white Gaussian noise (AWGN) channels, there is no standard framework for quantifying fundamental limits or designing capacity-approaching coding schemes for such channels. In this thesis, some steps are taken toward this challenging goal by first developing a channel model for fiber-optic links and, second, using an information-theoretic design framework to investigate joint design of forward error correction and multilevel modulation, so-called coded modulation (CM), techniques for these channels.We extend the signal statistics of highly nonlinear single-polarization fiber-optic links with negligible dispersion to the polarization-multiplexed case. Taking chromatic dispersion into account, we derive an analytical discrete-time model for single- wavelength, polarization-multiplexed, non-dispersion-managed (non-DM) links. According to this model, for high enough symbol rates, a fiber-optic link can be described as a linear dispersive channel with AWGN and a complex constant scaling.We exploit the proposed channel model for highly nonlinear fiber-optic links to devise a new channel-aware multilevel CM scheme based on the minimization of the total block error rate. We introduce a CM system with an N-dimensional constellation constructed from the Cartesian product of N identical one-dimensional constellations. The multidimensional scheme shows better trade-off between complexity and performance than a one-dimensional multilevel CM scheme.By invoking the introduced channel model for the dispersive non-DM links, we present a four-dimensional CM scheme, which shows a better trade-off between digital signal processing complexity and transparent reach than existing methods. This CM scheme together with a probabilistic signal shaping method is used to devise a rate-adaptive scheme with a single low-density parity-check code. The performance evaluation of the proposed CM scheme for a single-channel transmission fiber-optic system justifies the improvement of the system spectral efficiency for a wide range of transparent reaches, observing more than 1 dB performance gain compared to existing methods.
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| 6. |
- Beygi, Lotfollah, 1977, et al.
(författare)
-
Coded Modulation for Fiber-Optic Networks
- 2014
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Ingår i: IEEE Signal Processing Magazine. - 1558-0792 .- 1053-5888.
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Tidskriftsartikel (refereegranskat)abstract
- In this tutorial, we study the joint design of forward error correction and modulation for fiber-optic communications. To this end, we use an information-theoretic design framework to investigate coded modulation (CM) techniques for standard additive white Gaussian noise channels and fiber-optic channels. This design guideline helps us to provide a comprehensive overview of the CM schemes in the literature. Then, by invoking recent advances in optical channel modeling for non-dispersion-managed links, we discuss two- and four-dimensional CM schemes. Moreover, we discuss the electronic computational complexity and hardware constraints of CM schemes for optical communications. Finally, we address CM schemes with signal shaping and rate-adaptation capabilities to accommodate the data transmission scheme to optical links with different signal qualities.
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| 7. |
- Beygi, Lotfollah, 1977
(författare)
-
Coded Modulation Techniques in Fiber-Optical Communications
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Today's high demand for increasing the data transmission rate motivates a great challenge to improve the spectral efficiency of fiber-optical channels. In order to achieve a higher spectral efficiency, exploiting an advanced coded modulation scheme is inevitable. Since a general fiber-optic link is a non-Gaussian channel with nonlinear behavior, new coded modulation schemes need to be designed for these non-Gaussian channels. The performance of many binary classic codes such as Reed-Solomon and capacity-achieving codes such as low density parity-check codes and turbo codes, originally designed for the additive white Gaussian noise channel (AWGN), has been evaluated in fiber-optical channels. However, the design of error-correcting codes for such a non-Gaussian fiber-optical channel is complicated and is not well investigated in the literature. Multilevel coded modulation (MLCM) uses low complexity multistage decoding, which is a suitable structure for a very high-rate fiber-optical communication system. We propose a new rate-allocation method for the MLCM scheme [Paper A] based on the minimization of the total block error rate. The proposed approach uses Reed--Solomon component codes and hard decision multistage decoding. A multidimensional MLCM system with an $N$-dimensional constellation constructed from the Cartesian product of $N$ identical one-dimensional constellations is introduced in [Paper B]. According to our analysis, the multidimensional scheme shows better trade-off between complexity and performance than a one-dimensional MLCM. Exploiting the results in Papers A and B, we present a novel MLCM scheme for a non-Gaussian dispersion-managed fiber channel [Paper C]. This MLCM scheme is designed with a ring constellation and nonlinear post-compensation of the self-phase modulation produced via the Kerr effect. In this scheme, a new set partitioning based on the Ungerboeck approach is introduced to maintain unequal error protection in amplitude and phase. In contrast to AWGN channels, increasing the minimum Euclidean distance is not a valid criterion to design a coded system for such fiber-optical channels. Finally, the joint probability density function of the received amplitudes and phases of a dispersion-managed fiber-optical channel is derived in [Paper D]. This analysis is performed for dual-polarization transmission with both lumped and distributed amplifications. The derived statistics can be used to design an ML receiver for data transmission systems in these channels.
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| 8. |
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| 9. |
- Beygi, Lotfollah, 1977, et al.
(författare)
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On nonlinearly-induced noise in single-channel optical links with digital backpropagation
- 2013
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 21:22, s. 26376-26386
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we investigate the performance limits of electronic chromatic dispersion compensation (EDC) and digital backpropagation (DBP) for a single-channel non-dispersion-managed fiber-optical link. A known analytical method to derive the performance of the system with EDC is extended to derive a first-order approximation for the performance of the system with DBP. In contrast to the cubic growth of the variance of the nonlinear noise-like interference, often called nonlinear noise, with input power for EDC, a quadratic growth is observed with DBP using this approximation. Finally, we provide numerical results to verify the accuracy of the proposed approach and compare it with existing analytical models.
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| 10. |
- Beygi, Lotfollah, 1977, et al.
(författare)
-
On the dimensionality of multilevel coded modulation in the high SNR regime
- 2010
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Ingår i: IEEE Communications Letters. - 1558-2558 .- 1089-7798. ; 14:11, s. 1056-1058
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the dimensionality of the multilevel coded modulation (MLCM) scheme is addressed. This study is done for an MLCM scheme with a N-dimensional (ND) constellation constructed from the Cartesian product of N identical 1D constellations in the high SNR regime. It is demonstrated that multidimensional MLCM with Reed--Solomon code components has better trade-off between coding gain and complexity than a 1D scheme. Specifically, a 4D MLCM system gains 1.4~dB over a 1D MLCM system with lower complexity at a block error of 10^{-6}. The gain increases to 2.5~dB asymptotically.
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