| 1. |
- Farsi, Mohammad, 1994, et al.
(författare)
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Capacity Bounds under Imperfect Polarization Tracking
- 2022
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Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 70:11, s. 7240-7249
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Tidskriftsartikel (refereegranskat)abstract
- In optical fiber communication, due to the random variation of the environment, the state of polarization (SOP) fluctuates randomly with time leading to distortion and performance degradation. The memory-less SOP fluctuations can be regarded as a two-by-two random unitary matrix. In this paper, for what we believe to be the first time, the capacity of the polarization drift channel under an average power constraint with imperfect channel knowledge is characterized. An achievable information rate (AIR) is derived when imperfect channel knowledge is available and is shown to be highly dependent on the channel estimation technique. It is also shown that a tighter lower bound can be achieved when a unitary estimation of the channel is available. However, the conventional estimation algorithms do not guarantee a unitary channel estimation. Therefore, by considering the unitary constraint of the channel, a data-aided channel estimator based on the Kabsch algorithm is proposed, and its performance is numerically evaluated in terms of AIR. Monte Carlo simulations show that Kabsch outperforms the least-square error algorithm. In particular, with complex, Gaussian inputs and eight pilot symbols per block, Kabsch improves the AIR by 0.20 to 0.30 bits/symbol throughout the range of studied signal-to-noise ratios.
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| 2. |
- Farsi, Mohammad, 1994, et al.
(författare)
-
Improved Polarization Tracking in the Presence of PDL
- 2022
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Ingår i: European Conference on Optical Communication, ECOC. - 9781957171159
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Konferensbidrag (refereegranskat)abstract
- We propose a novel tracking algorithm for optical channels suffering from fast state of polarization (SOP) rotations and polarization-dependent loss (PDL). Unlike gradient descent-based algorithms that require step size adjustment when the channel conditions change, our algorithm performs similarly or better without parameter tuning.
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| 3. |
- Farsi, Mohammad, 1994, et al.
(författare)
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Learning to Extract Distributed Polarization Sensing Data from Noisy Jones Matrices
- 2024
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Ingår i: 2024 Optical Fiber Communication Conference and Exhibition, OFC 2024 - Proceeding. - 2162-2701. - 9781957171326
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Konferensbidrag (refereegranskat)abstract
- We consider the problem of recovering spatially resolved polarization information from receiver Jones matrices. We introduce a physics-based learning approach, improving noise resilience compared to previous inverse scattering methods, while highlighting challenges related to model overparameterization.
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| 4. |
- Farsi, Mohammad, 1994
(författare)
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Phase Noise and Polarization Effects in Fiber-Optic Communication Systems: Modeling, Compensation, Capacity, and Sensing
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High data rate optical communications are susceptible to phase noise and state of polarization (SOP) perturbations. The dynamic nature of phase noise and SOP fluctuations requires a comprehensive investigation of their effects on the channel capacity and the development of robust and efficient communication technologies. This thesis unravels phase and polarization challenges in optical communication systems by characterizing polarization drift channels, introducing polarization tracking algorithms, utilizing polarization data for fiber sensing, and investigating capacity implications. The SOP drifts at a much slower rate than typical transmission rates in buried or underwater fibers. Thus, we first characterize the capacity of the block-constant polarization drift channel under an average power constraint and imperfect channel knowledge. An achievable information rate is derived, showing strong dependence on the channel estimation technique. A novel data-aided channel estimator is proposed, enforcing the unitary constraint, and its superior performance is validated through Monte Carlo simulations. However, in aerial fibers, the SOP drift does not follow the block-constant assumption and can drift quickly over time. Hence, the next contribution involves investigating the robustness of polarization tracking algorithms in the presence of fast SOP drift and polarization-dependent loss. Novel tracking algorithms are proposed, showing a higher tolerance to SOP drift compared to the gradient descent-based algorithms without the need for parameter tuning. Thereafter, we explore the application of polarization for fiber sensing by proposing a physics-based learning approach. The proposed approach shows lower sensitivity to additive noise compared to previous inverse scattering methods. Next, we turn our attention to phase noise and investigate the capacity of a discrete-time multiple-input-multiple-output channel with correlated phase noises originating from electro-optic frequency combs (EO-comb). We derive capacity bounds and show that the multiplexing gain is M - 1 where M is the number of channels. Moreover, a constant gap between the bounds is observed in the high signal-to-noise ratio regime, which vanishes for the special case of M =2. Finally, we study optimal pilot placement for channels impaired by phase noise from EO-combs. Contrary to regular multichannel systems, it is demonstrated that allocating the first and last channels for pilots is optimal under a fixed pilot overhead.
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| 5. |
- Farsi, Mohammad, 1994, et al.
(författare)
-
Pilot distributions for phase noise estimation in electro-optic frequency comb systems
- 2023
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Ingår i: European Conference on Optical Communication, ECOC.
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Konferensbidrag (refereegranskat)abstract
- We explore the optimal pilot positioning for phase tracking in electro-optic frequency comb setups. We show that, in contrast to previous results for regular multichannel systems, allocating the first and the last channels for pilots is optimal given a fixed pilot overhead.
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| 6. |
- Farsi, Mohammad, 1994, et al.
(författare)
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Polarization Tracking in the Presence of PDL and Fast Temporal Drift
- 2022
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 40:19, s. 6408-6416
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we analyze the effectiveness of polarization tracking algorithms in optical transmission systems suffering from fast state of polarization (SOP) rotations and polarization-dependent loss (PDL). While most of the gradient descent (GD)-based algorithms in the literature may require step size adjustment when the channel condition changes, we propose tracking algorithms that can perform similarly or better without parameter tuning. Numerical simulation results show higher robustness of the proposed algorithms to SOP and PDL drift compared to GD-based algorithms, making them promising candidates to be used in aerial fiber links where the SOP can potentially drift rapidly, and therefore becomes challenging to track.
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