119 research outputs found
Decision-Feedback Detection Strategy for Nonlinear Frequency-Division Multiplexing
By exploiting a causality property of the nonlinear Fourier transform, a
novel decision-feedback detection strategy for nonlinear frequency-division
multiplexing (NFDM) systems is introduced. The performance of the proposed
strategy is investigated both by simulations and by theoretical bounds and
approximations, showing that it achieves a considerable performance improvement
compared to previously adopted techniques in terms of Q-factor. The obtained
improvement demonstrates that, by tailoring the detection strategy to the
peculiar properties of the nonlinear Fourier transform, it is possible to boost
the performance of NFDM systems and overcome current limitations imposed by the
use of more conventional detection techniques suitable for the linear regime
Why Noise and Dispersion may Seriously Hamper Nonlinear Frequency-Division Multiplexing
The performance of optical fiber systems based on nonlinear
frequency-division multiplexing (NFDM) or on more conventional transmission
techniques is compared through numerical simulations. Some critical issues
affecting NFDM systems-namely, the strict requirements needed to avoid burst
interaction due to signal dispersion and the unfavorable dependence of
performance on burst length-are investigated, highlighting their potentially
disruptive effect in terms of spectral efficiency. Two digital processing
techniques are finally proposed to halve the guard time between NFDM symbol
bursts and reduce the size of the processing window at the receiver, increasing
spectral efficiency and reducing computational complexity.Comment: The manuscript has been submitted to Photonics Technology Letters for
publicatio
A Novel Detection Strategy for Nonlinear Frequency-Division Multiplexing
A novel decision feedback detection strategy exploiting a causality property
of the nonlinear Fourier transform is introduced. The novel strategy achieves a
considerable performance improvement compared to previously adopted strategies
in terms of Q-factor.Comment: The work has been submitted to the Optical Fiber Communication (OFC)
Conference 201
Accurate statistical performance evaluation of EDC techniques on 10 Gb/s multimode fiber links
Abstract--- We perform a statistical investigation (based on the Cambridge 108-fiber set) of the performance limits of different electronic dispersion compensation (EDC) techniques in terms of their robustness to modal dispersion, considering the impact of connection offsets in 10GBASE-LRM (long reach multimode) systems with connection offsets. We also investigate the effectiveness of an accurate and fast analytical method to take into account any amount of intersymbol interference based on Gaussian quadrature rules, thus allowing a thorough statistical investigation of the performance of different EDC techniques
Scope and Limitations of the Nonlinear Shannon Limit
The concept and significance of the so called nonlinear Shannon limit are reviewed and their relation to the channel capacity is analyzed from an information theory point of view. It is shown that this is a limit (if at all) holding only for conventional detection strategies. Indeed, it should only be considered as a limit to the information rate that can be achieved with a given modulation/detection scheme. By virtue of some simple examples and theoretical results, it is also shown that, using the same approximated models commonly adopted for deriving the nonlinear Shannon limit, the information rate can be arbitrarily increased by increasing the input power. To this aim, the validity of some popular approximations to the output distribution is also examined to show that their application outside the scope for which they were devised can lead to pitfalls. To the best of our belief, the existence of a true nonlinear Shannon limit has still not been demonstrated, and the problem of determining the channel capacity of a fiber-optic system in the presence of Kerr nonlinearities is still an open issue
On the error probability evaluation in lightwave systems with optical amplification
We review the time domain, frequency domain, and Fourier series Karhunen–Loéve series expansion (KLSE) methods for exact BER evaluation in intensity- and phase-modulated direct-detection optically amplified systems.We compare their complexity and computational efficiency, and discuss the most relevant implementation issues. We show that the method based on a Fourier series expansion has the simplest implementation and requires the minimum number of eigenvalues to converge to the exact BER value for various kind of optical filters. For this method, we also introduce an equivalent form of the moment generating function, that avoids the singularity for eigenvalues equal to zero, and derive an alternative expansion where signal and noise are expanded on the same orthonormal basis
Narrow filtered DPSK implements order-1 CAPS optical line coding
A novel family of optical line codes has been presented elsewhere, here referred to as combined amplitude-phase shift (CAPS) codes. We show here that narrow filtering of a differential phase shift keying signal with bandwidth equal to about 2/3 of the bit rate turns out to closely implement the order-1 CAPS line coding. Performance of the two systems is compared for various types of optical filters
Nonlinearity Mitigation in WDM Systems: Models, Strategies, and Achievable Rates
After reviewing models and mitigation strategies for interchannel nonlinear
interference (NLI), we focus on the frequency-resolved logarithmic perturbation
model to study the coherence properties of NLI. Based on this study, we devise
an NLI mitigation strategy which exploits the synergic effect of phase and
polarization noise compensation (PPN) and subcarrier multiplexing with
symbol-rate optimization. This synergy persists even for high-order modulation
alphabets and Gaussian symbols. A particle method for the computation of the
resulting achievable information rate and spectral efficiency (SE) is presented
and employed to lower-bound the channel capacity. The dependence of the SE on
the link length, amplifier spacing, and presence or absence of inline
dispersion compensation is studied. Single-polarization and dual-polarization
scenarios with either independent or joint processing of the two polarizations
are considered. Numerical results show that, in links with ideal distributed
amplification, an SE gain of about 1 bit/s/Hz/polarization can be obtained (or,
in alternative, the system reach can be doubled at a given SE) with respect to
single-carrier systems without PPN mitigation. The gain is lower with lumped
amplification, increases with the number of spans, decreases with the span
length, and is further reduced by in-line dispersion compensation. For
instance, considering a dispersion-unmanaged link with lumped amplification and
an amplifier spacing of 60 km, the SE after 80 spans can be be increased from
4.5 to 4.8 bit/s/Hz/polarization, or the reach raised up to 100 spans (+25%)
for a fixed SE.Comment: Submitted to Journal of Lightwave Technolog
Improved Detection Strategies for Nonlinear Frequency-Division Multiplexing
Two novel detection strategies for nonlinear Fourier transform-based
transmission schemes are proposed. We show, through numerical simulations, that
both strategies achieve a good performance improvement (up to 3 dB and 5 dB)
with respect to conventional detection, respectively without or only moderately
increasing the computational complexity of the receiver.Comment: This work will be presented at PIERS 2018 in Toyama, Japan, and has
been submitted for publication in the conference proceeding
Nonlinear Probabilistic Constellation Shaping with Sequence Selection
Probabilistic shaping is a pragmatic approach to improve the performance of
coherent optical fiber communication systems. In the nonlinear regime, the
advantages offered by probabilistic shaping might increase thanks to the
opportunity to obtain an additional nonlinear shaping gain. Unfortunately, the
optimization of conventional shaping techniques, such as probabilistic
amplitude shaping (PAS), yields a relevant nonlinear shaping gain only in
scenarios of limited practical interest. In this manuscript we use sequence
selection to investigate the potential, opportunities, and challenges offered
by nonlinear probabilistic shaping. First, we show that ideal sequence
selection is able to provide up to 0.13 bit/s/Hz gain with respect to PAS with
an optimized blocklength. However, this additional gain is obtained only if the
selection metric accounts for the signs of the symbols: they must be known to
compute the selection metric, but there is no need to shape them. Furthermore,
we show that the selection depends in a non-critical way on the symbol rate and
link length: the sequences selected for a certain scenario still provide a
relevant gain if these are modified. Then, we analyze and compare several
practical implementations of sequence selection by taking into account
interaction with forward error correction (FEC) and complexity. Overall, the
single block and the multi block FEC-independent bit scrambling are the best
options, with a gain up to 0.08 bit/s/Hz. The main challenge and limitation to
their practical implementation remains the evaluation of the metric, whose
complexity is currently too high. Finally, we show that the nonlinear shaping
gain provided by sequence selection persists when carrier phase recovery is
included.Comment: The manuscript has been submitted for publication to the Journal of
Lightwave Technolog
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