| 1. |
- Czegledi, Cristian Bogdan, 1988, et al.
(författare)
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Bandlimited Power-Efficient Signaling and Pulse Design for Intensity Modulation
- 2014
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Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 62:9, s. 3274-3284
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a new method for power-efficient intersymbol interference-free transmission over the bandlimited intensity-modulation direct-detection channel is proposed. A new time-varying bias signal is added to the transmitted signal to make it nonnegative and provide a more power-efficient transmission than the previously considered constant bias. To exploit the benefits of the new signaling method, Nyquist and root-Nyquist pulses suitable for the use with this kind of bias are designed using two different methods. In the first method, new pulses are obtained by adding Nyquist pulses in the time domain with different combining coefficients, whereas in the second method, the pulses are obtained by the design of their frequency response. Analytical expressions for the asymptotic optical power efficiency and symbol error rate of the proposed schemes are derived and evaluated. At a spectral efficiency of 1~b/s/Hz, using on-off keying modulation and the proposed bias signal and pulses, up to 0.628 dB gains in asymptotic power efficiency can be achieved compared to the previously best known signaling scheme, which is based on squared sinc pulse shaping.
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| 2. |
- Czegledi, Cristian Bogdan, 1988, et al.
(författare)
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Bandlimited Power-Efficient Signaling for Intensity Modulation
- 2014
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Ingår i: European Conference on Optical Communication, ECOC 2014; Cannes; France; 21 September 2014 through 25 September 2014. - 9782954944401
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Konferensbidrag (refereegranskat)abstract
- A new, power-efficient signaling method for intersymbol interference-free transmission over the bandlimited intensity-modulation direct-detection channel is proposed. The method utilizes pulse-amplitude modulation with a sinusoidal bias function and is more power-efficient than previously known methods.
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| 3. |
- Czegledi, Cristian Bogdan, 1988, et al.
(författare)
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Digital backpropagation accounting for polarization-mode dispersion
- 2017
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 25:3, s. 1903-1915
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Tidskriftsartikel (refereegranskat)abstract
- Digital backpropagation (DBP) is a promising digital-domain technique to mitigate Kerr-induced nonlinear interference. While it successfully removes deterministic signal-signal interactions, the performance of ideal DBP is limited by stochastic effects, such as polarizationmode dispersion (PMD). In this paper, we consider an ideal full-field DBP implementation and modify it to additionally account for PMD; reversing the PMD effects in the backward propagation by passing the reverse propagated signal also through PMD sections, which concatenated equal the inverse of the PMD in the forward propagation. These PMD sections are calculated analytically at the receiver based on the total accumulated PMD of the link estimated from channel equalizers. Numerical simulations show that, accounting for nonlinear polarization-related interactions in the modified DBP algorithm, additional signal-to-noise ratio gains of 1.1 dB are obtained for transmission over 1000 km.
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| 4. |
- Czegledi, Cristian Bogdan, 1988
(författare)
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Modeling and Compensation of Polarization Effects in Fiber-Optic Communication Systems
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Optical communication systems that exploit the orthogonality between two polarizations of light convey information over optical fibers by modulating data over the two polarizations. In an idealized scenario, the two polarizations propagate through the fiber without interfering. However, this is not the case for practical fibers, which suffer from various imperfections that lead to polarization-related interference between the two polarizations. This thesis is concerned with polarization effects that arise in communication systems over optical fibers. In particular, we consider modeling and compensation of such effects, and their impact on and improvement of nonlinearity mitigation algorithms. The impact of an impairment on the performance of a transmission system can be understood via a channel model, which should describe the behavior of the channel as accurately as possible. A theoretical framework is introduced to model the stochastic nature of the state of polarization during transmission. The model generalizes the one-dimensional carrier phase noise random walk to higher dimensions, modeling the phase noise and state of polarization drift jointly as rotations of the electric field and it has been successfully verified using experimental data. Thereafter, the model is extended to account for polarization-mode dispersion and its temporal random fluctuations. Such models will be increasingly important in simulating and optimizing future systems, where sophisticated digital signal processing will be natural parts. The typical digital signal processing solution to mitigate phase noise and drift of the state of polarization consists of two separate blocks that track each phenomenon independently and have been developed without taking into account mathematical models describing the impairments. Based on the proposed model for the state of polarization, we study a blind tracking algorithm to compensate for these impairments. The algorithm dynamically recovers the carrier phase and state of polarization jointly for an arbitrary modulation format. Simulation results show the effectiveness of the proposed algorithm, having a fast convergence rate and an excellent tolerance to phase and polarization noise. The optical fiber is a nonlinear medium with respect to the intensity of the incident light. This effect leads to nonlinear interference as the intensity of light increases, which made nonlinear interference mitigation techniques to be an intensively studied topic. Typically, these techniques do not take into account polarization-mode dispersion, which becomes detrimental as the nonlinear effects interact with polarization-mode dispersion. We study digital-domain nonlinear interference mitigation algorithms that take into account polarization-mode dispersion by i) reversing the polarization effects concurrently with reversing the nonlinear effects and by ii) mitigating only the polarization-insensitive nonlinear contributions. These algorithms will be increasingly important in future optical systems capable of performing large bandwidth nonlinear interference mitigation, where even small amounts of polarization-mode dispersion become a limiting factor.
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| 5. |
- Czegledi, Cristian Bogdan, 1988
(författare)
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Modeling and Tracking of Stochastic Polarization Drifts in Fiber-Optic Systems
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the past decade, accessing information has become easier than ever, leading to a rapid growth in popularity of social media, online gaming, and multimedia broadcast systems. These and other services put pressure on the Internet service providers to support high-speed Internet connections and motivate the need for faster communication systems. Fiber-optic communications are the backbone of the Internet and accommodate for this demand by evolving from the traditional intensity-modulated systems to modern coherent detection, which makes use of digital signal processing to encode the data onto multiple phase and amplitude levels of the optical carrier. Although coherent systems enable the use of high-order modulation formats, the improved spectral efficiency comes at the cost of a reduced tolerance to impairments. These impairments are mitigated using digital signal processing algorithms, which, ideally, should be designed such that the impairments are optimally compensated in order to maximize performance. The impact of an impairment on the performance of a transmission system can be understood via a channel model, which should describe the behavior of the channel as accurately as possible. In this thesis, we consider modeling and compensation of the carrier phase noise and state of polarization drift in coherent fiber-optic systems. A theoretical framework is introduced to model the stochastic nature of the state of polarization during transmission. The model generalizes the one-dimensional carrier phase noise random walk to higher dimensions, modeling the phase noise and state of polarization drift jointly as rotations of the optical field and it has been successfully verified using experimental data. Such a model will be increasingly important in simulating and optimizing future systems, where sophisticated digital signal processing will be natural parts. The proposed polarization drift model is the first of its kind, as prior work either models polarization drift as a deterministic process or focuses on polarization-mode dispersion in systems where the state of polarization does not affect the receiver's performance. The typical digital signal processing solution to mitigate the phase noise and the drift of the state of polarization consists of two separate blocks that track each phenomenon independently. Such algorithms have been developed without taking into account mathematical models describing the impairments. Based on the proposed model, we study a blind tracking algorithm to compensate for these impairments. The algorithm dynamically recovers the carrier phase and state of polarization jointly for an arbitrary modulation format. Simulation results show the effectiveness of the proposed algorithm, having a fast convergence rate and an excellent tolerance to phase noise and dynamic drift of the polarization. The computational complexity of the algorithm is lower compared to state-of-the-art algorithms at similar or better performance, which makes it a strong candidate for future optical systems.
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| 6. |
- Czegledi, Cristian Bogdan, 1988, et al.
(författare)
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Modified Digital Backpropagation Accounting for Polarization-Mode Dispersion
- 2017
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Ingår i: Optical Fiber Communication Conference. - 9781943580231
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Konferensbidrag (refereegranskat)abstract
- We propose a modified DBP algorithm accounting for PMD. The accumulated PMD at the receiver is factorized into several PMD sections, and inserted into the DBP routine to distributively compensate for PMD, outperforming the conventional approach by 1.1 dB in SNR.
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| 7. |
- Czegledi, Cristian Bogdan, 1988, et al.
(författare)
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Modulation Format Independent Joint Polarization and Phase Tracking for Coherent Receivers
- 2016
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 13:14, s. 3354-3364
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Tidskriftsartikel (refereegranskat)abstract
- © 1983-2012 IEEE. The state of polarization and the carrier phase drift dynamically during transmission in a random fashion in coherent optical fiber communications. The typical digital signal processing solution to mitigate these impairments consists of two separate blocks that track each phenomenon independently. Such algorithms have been developed without taking into account mathematical models describing the impairments. We study a blind, model-based tracking algorithm to compensate for these impairments. The algorithm dynamically recovers the carrier phase and state of polarization jointly for an arbitrary modulation format. Simulation results show the effectiveness of the proposed algorithm, having a fast convergence rate and an excellent tolerance to phase noise and dynamic drift of the polarization at low complexity, which make the algorithm a strong candidate for future optical systems.
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| 8. |
- Czegledi, Cristian Bogdan, 1988, et al.
(författare)
-
Polarization Drift Channel Model for Coherent Fibre-Optic Systems
- 2016
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 6, s. 21217-
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical framework is introduced to model the dynamical changes of the state of polarization during transmission in coherent fibre-optic systems. The model generalizes the one-dimensional phase noise random walk to higher dimensions, accounting for random polarization drifts, emulating a random walk on the Poincare sphere, which has been successfully verified using experimental data. The model is described in the Jones, Stokes and real four-dimensional formalisms, and the mapping between them is derived. Such a model will be increasingly important in simulating and optimizing future systems, where polarization-multiplexed transmission and sophisticated digital signal processing will be natural parts. The proposed polarization drift model is the first of its kind as prior work either models polarization drift as a deterministic process or focuses on polarization-mode dispersion in systems where the state of polarization does not affect the receiver performance. We expect the model to be useful in a wide-range of photonics applications where stochastic polarization fluctuation is an issue.
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| 9. |
- Czegledi, Cristian Bogdan, 1988, et al.
(författare)
-
Polarization-Mode Dispersion Aware Digital Backpropagation
- 2016
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Ingår i: 42nd European Conference on Optical Communication, ECOC 2016; Dusseldorf; Germany; 18 September 2016 through 22 September 2016. - 9783800742745 ; , s. 1091-1093
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Konferensbidrag (refereegranskat)abstract
- We study a modified DBP algorithm that accounts for PMD. Based on the accumulated PMD at the receiver, the algorithm distributively compensates for PMD in the reverse propagation and outperforms the conventional approach by up to 2.1 dB.
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| 10. |
- Czegledi, Cristian Bogdan, 1988, et al.
(författare)
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Symbol-by-Symbol Joint Polarization and Phase Tracking in Coherent Receivers
- 2015
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Ingår i: Optical Fiber Communication Conference, OFC 2015; Los Angeles Convention CenterLos Angeles; United States; 22 March 2015 through 26 March 2015. - Washington, D.C. : OSA. - 9781557529374 - 9781557529374
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Konferensbidrag (refereegranskat)abstract
- An analytical model to describe the combined drift of the state of polarization and absolute phase is presented. To compensate for this drift, a novel, modulation format independent algorithm is proposed, which outperforms state-of-the-art algorithms.
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