37 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
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
On the Nonlinear Shaping Gain with Probabilistic Shaping and Carrier Phase Recovery
The performance of different probabilistic amplitude shaping (PAS) techniques
in the nonlinear regime is investigated, highlighting its dependence on the PAS
block length and the interaction with carrier phase recovery (CPR). Different
PAS implementations are considered, based on different distribution matching
(DM) techniques-namely, sphere shaping, shell mapping with different number of
shells, and constant composition DM-and amplitude-to-symbol maps. When CPR is
not included, PAS with optimal block length provides a nonlinear shaping gain
with respect to a linearly optimized PAS (with infinite block length); among
the considered DM techniques, the largest gain is obtained with sphere shaping.
On the other hand, the nonlinear shaping gain becomes smaller, or completely
vanishes, when CPR is included, meaning that in this case all the considered
implementations achieve a similar performance for a sufficiently long block
length. Similar results are obtained in different link configurations (1x180km,
15x80km, and 27x80km single-mode-fiber links), and also including laser phase
noise, except when in-line dispersion compensation is used. Furthermore, we
define a new metric, the nonlinear phase noise (NPN) metric, which is based on
the frequency resolved logarithmic perturbation models and explains the
interaction of CPR and PAS. We show that the NPN metric is highly correlated
with the performance of the system. Our results suggest that, in general, the
optimization of PAS in the nonlinear regime should always account for the
presence of a CPR algorithm. In this case, the reduction of the rate loss
(obtained by using sphere shaping and increasing the DM block length) turns out
to be more important than the mitigation of the nonlinear phase noise (obtained
by using constant-energy DMs and reducing the block length), the latter being
already granted by the CPR algorithm.Comment: Accepter for publication to the Journal of Lightwave Technologies on
January 202
New Lower Bounds on the Capacity of Optical Fiber Channels via Optimized Shaping and Detection
Constellation shaping is a practical and effective technique to improve the
performance and the rate adaptivity of optical communication systems. In
principle, it could also be used to mitigate the impact of nonlinear effects,
possibly increasing the information rate beyond the current limit dictated by
fiber nonlinearity. However, this appealing idea is frustrated by the
difficulty of designing an effective shaping strategy that takes into account
the nonlinearity and long memory of the fiber channel, as well as the possible
interplay with other nonlinearity mitigation strategies. As a result, only
little progress has been made so far, while the optimal shaping distribution
and the ultimate channel capacity remain unknown. In this work, we describe a
novel technique to optimize the shaping distribution in a very general setting
and high-dimensional space. For a simplified block-memoryless nonlinear optical
channel, the capacity lower bound obtained by the proposed technique can be
expressed analytically, establishing the conditions for an unbounded growth of
capacity with power. In a more realistic scenario, the technique can be
implemented by a rejection sampling algorithm driven by a suitable cost
function, and the corresponding achievable information rate estimated
numerically. The combination of the proposed technique with an improved
(non-Gaussian) decoding metric yields a new capacity lower bound for the
dual-polarization WDM channel.Comment: Submitted to IEEE Journal of Lightwave Technology on November 30th,
202