8,103 research outputs found
A survey on fiber nonlinearity compensation for 400 Gbps and beyond optical communication systems
Optical communication systems represent the backbone of modern communication
networks. Since their deployment, different fiber technologies have been used
to deal with optical fiber impairments such as dispersion-shifted fibers and
dispersion-compensation fibers. In recent years, thanks to the introduction of
coherent detection based systems, fiber impairments can be mitigated using
digital signal processing (DSP) algorithms. Coherent systems are used in the
current 100 Gbps wavelength-division multiplexing (WDM) standard technology.
They allow the increase of spectral efficiency by using multi-level modulation
formats, and are combined with DSP techniques to combat the linear fiber
distortions. In addition to linear impairments, the next generation 400 Gbps/1
Tbps WDM systems are also more affected by the fiber nonlinearity due to the
Kerr effect. At high input power, the fiber nonlinear effects become more
important and their compensation is required to improve the transmission
performance. Several approaches have been proposed to deal with the fiber
nonlinearity. In this paper, after a brief description of the Kerr-induced
nonlinear effects, a survey on the fiber nonlinearity compensation (NLC)
techniques is provided. We focus on the well-known NLC techniques and discuss
their performance, as well as their implementation and complexity. An extension
of the inter-subcarrier nonlinear interference canceler approach is also
proposed. A performance evaluation of the well-known NLC techniques and the
proposed approach is provided in the context of Nyquist and super-Nyquist
superchannel systems.Comment: Accepted in the IEEE Communications Surveys and Tutorial
Simultaneous multislice acquisition with multi-contrast segmented EPI for separation of signal contributions in dynamic contrast-enhanced imaging
We present a method to efficiently separate signal in magnetic resonance imaging (MRI) into a base signal S0, representing the mainly T1-weighted component without T2*-relaxation, and its T2*-weighted counterpart by the rapid acquisition of multiple contrasts for advanced pharmacokinetic modelling. This is achieved by incorporating simultaneous multislice (SMS) imaging into a multi-contrast, segmented echo planar imaging (EPI) sequence to allow extended spatial coverage, which covers larger body regions without time penalty. Simultaneous acquisition of four slices was combined with segmented EPI for fast imaging with three gradient echo times in a preclinical perfusion study. Six female domestic pigs, German-landrace or hybrid-form, were scanned for 11 minutes respectively during administration of gadolinium-based contrast agent. Influences of reconstruction methods and training data were investigated. The separation into T1- and T2*-dependent signal contributions was achieved by fitting a standard analytical model to the acquired multi-echo data. The application of SMS yielded sufficient temporal resolution for the detection of the arterial input function in major vessels, while anatomical coverage allowed perfusion analysis of muscle tissue. The separation of the MR signal into T1- and T2*-dependent components allowed the correction of susceptibility related changes. We demonstrate a novel sequence for dynamic contrast-enhanced MRI that meets the requirements of temporal resolution (Ît < 1.5 s) and image quality. The incorporation of SMS into multi-contrast, segmented EPI can overcome existing limitations of dynamic contrast enhancement and dynamic susceptibility contrast methods, when applied separately. The new approach allows both techniques to be combined in a single acquisition with a large spatial coverage
Sub-Nyquist Field Trial Using Time Frequency Packed DP-QPSK Super-Channel Within Fixed ITU-T Grid
Sub-Nyquist time frequency packing technique was demonstrated for the first
time in a super channel field trial transmission over long-haul distances. The
technique allows a limited spectral occupancy even with low order modulation
formats. The transmission was successfully performed on a deployed Australian
link between Sydney and Melbourne which included 995 km of uncompensated SMF
with coexistent traffic. 40 and 100 Gb/s co-propagating channels were
transmitted together with the super-channel in a 50 GHz ITU-T grid without
additional penalty. The super-channel consisted of eight sub-channels with
low-level modulation format, i.e. DP-QPSK, guaranteeing better OSNR robustness
and reduced complexity with respect to higher order formats. At the receiver
side, coherent detection was used together with iterative maximum-a-posteriori
(MAP) detection and decoding. A 975 Gb/s DP-QPSK super-channel was successfully
transmitted between Sydney and Melbourne within four 50GHz WSS channels (200
GHz). A maximum potential SE of 5.58 bit/s/Hz was achieved with an OSNR=15.8
dB, comparable to the OSNR of the installed 100 Gb/s channels. The system
reliability was proven through long term measurements. In addition, by closing
the link in a loop back configuration, a potential SE*d product of 9254
bit/s/Hz*km was achieved
LArPix: Demonstration of low-power 3D pixelated charge readout for liquid argon time projection chambers
We report the demonstration of a low-power pixelated readout system designed
for three-dimensional ionization charge detection and digital readout of liquid
argon time projection chambers (LArTPCs). Unambiguous 3D charge readout was
achieved using a custom-designed system-on-a-chip ASIC (LArPix) to uniquely
instrument each pad in a pixelated array of charge-collection pads. The LArPix
ASIC, manufactured in 180 nm bulk CMOS, provides 32 channels of
charge-sensitive amplification with self-triggered digitization and multiplexed
readout at temperatures from 80 K to 300 K. Using an 832-channel LArPix-based
readout system with 3 mm spacing between pads, we demonstrated low-noise
(500 e RMS equivalent noise charge) and very low-power (100
W/channel) ionization signal detection and readout. The readout was used
to successfully measure the three-dimensional ionization distributions of
cosmic rays passing through a LArTPC, free from the ambiguities of existing
projective techniques. The system design relies on standard printed circuit
board manufacturing techniques, enabling scalable and low-cost production of
large-area readout systems using common commercial facilities. This
demonstration overcomes a critical technical obstacle for operation of LArTPCs
in high-occupancy environments, such as the near detector site of the Deep
Underground Neutrino Experiment (DUNE).Comment: 19 pages, 10 figures, 1 ancillary animation. V3 includes minor
revisions based on referee comment
Dexterity for Channel Capacity Enhancement in MU-MIMO by Abrogating Interference
The looming field of Multi user Multiple-input Multiple-output (MU-MIMO) communication system has faced a challenge with precoding techniques for achieving increased channel capacity of their less inhaling of signals, imperfect knowing of channel state information, loss of signals by noise ,time complexity etc. in downlink systems which results in interference to the users. Hence straight forwarding from the issues, the paper newly introduce2LB-FR precoding technique which holds Linde-Lyoldâs (LL)algorithm to increase data transmission by consuming large amount of signals with space and the Bernoulli distribution with Bayes decision (BB) to allot the perfect channel state; l information during transmission that eliminates co-interference. Holding Floyd Rasta (FR) algorithm expels the noise if added and takes the shortest required path by acquiring all the possible routes available in single execution which decreases delay. By the overall implementation, the proposed work pomped that in short time ,the capacity of the channel get enhanced with interference cancellation
Optimization of micropillar sequences for fluid flow sculpting
Inertial fluid flow deformation around pillars in a microchannel is a new
method for controlling fluid flow. Sequences of pillars have been shown to
produce a rich phase space with a wide variety of flow transformations.
Previous work has successfully demonstrated manual design of pillar sequences
to achieve desired transformations of the flow cross-section, with experimental
validation. However, such a method is not ideal for seeking out complex
sculpted shapes as the search space quickly becomes too large for efficient
manual discovery. We explore fast, automated optimization methods to solve this
problem. We formulate the inertial flow physics in microchannels with different
micropillar configurations as a set of state transition matrix operations.
These state transition matrices are constructed from experimentally validated
streamtraces. This facilitates modeling the effect of a sequence of
micropillars as nested matrix-matrix products, which have very efficient
numerical implementations. With this new forward model, arbitrary micropillar
sequences can be rapidly simulated with various inlet configurations, allowing
optimization routines quick access to a large search space. We integrate this
framework with the genetic algorithm and showcase its applicability by
designing micropillar sequences for various useful transformations. We
computationally discover micropillar sequences for complex transformations that
are substantially shorter than manually designed sequences. We also determine
sequences for novel transformations that were difficult to manually design.
Finally, we experimentally validate these computational designs by fabricating
devices and comparing predictions with the results from confocal microscopy
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