1,720,966 research outputs found
Quality parameter for coherent transmissions with Gaussian-distributed nonlinear noise
No full textBy assuming the nonlinear noise as a signal-independent
circular Gaussian noise, a typical case in non-dispersion managed links
with coherent multilevel modulation formats, we provide several analytical
properties of a new quality parameter – playing the role of the signal to
noise ratio (SNR) at the sampling gate in the coherent receiver – which
carry over to the Q-factor versus power (or “bell”) curves. We show that
the maximum Q is reached at an optimal power, the nonlinear threshold, at
which the amplified spontaneous emission (ASE) noise power is twice the
nonlinear noise power, and the SNR penalty with respect to linear propagation
is 10Log(32
) = 1.76 dB, although the Q-penalty is somewhat larger
and increases at lower Q-factors, as we verify for the polarization-division
multiplexing quadrature phase shift keying (PDM-QPSK) format. As we
vary the ASE power, the maxima of the SNR vs. power curves are shown
to slide along a straight-line with slope -2 dB/dB. A similar behavior is
followed by the Q-factor maxima, although for PDM-QPSK the local slope
is around -2.7 dB/dB for Q-values of practical interest
Modeling Nonlinearity in Coherent Transmissions with Dominant Interpulse-Four-Wave-Mixing
No full textBy extending a well-established time-domain perturbation approach to dual-polarization propagation, we provide an analytical framework to predict the nonlinear interference (NLI) variance, i.e., the variance induced by nonlinearity on the sampled field, and the nonlinear threshold (NLT) in coherent transmissions with dominant intrachannel four-wave-mixing (IFWM). Such a framework applies to non dispersion managed (NDM) very long-haul coherent optical systems at nowadays typical baudrates of tens of Gigabaud, as well as to dispersion-managed (DM) systems at even higher baudrates, whenever IFWM is not removed by nonlinear equalization and is thus the dominant nonlinearity. The NLI variance formula has two fitting parameters which can be calibrated from simulations. From the NLI variance formula, analytical expressions of the NLT for both DM and NDM systems are derived and checked against recent NLT Monte-Carlo simulations
Revisiting Binary Sequence Length Requirements to Accurately Emulate Optical Transmission Systems in Highly Dispersive Regime
No full textWhen increasing channel bit rate beyond 10Gb/s or when operating over fiber lines with sparse or no in-line dispersion
compensation, Kerr-like non-linear effects can be considered as second order with respect to dispersive effects, because
pulse broadening can expand over numerous neighbor pulses, before optical non-linear effects imprint their signature
noticeably. To accurately emulate the interactions between pulses in this case, a few studies emphasized that Pseudo-
Random Binary Sequences (PRBS) should be used, with exponential dependence of the required PRBS length on bit rate
and accumulated dispersion. In this paper, we explain our strategy to numerically estimate the required number of
random, noisy bits for Monte-Carlo simulations, and show that it weakly increases in presence of pulse to pulse
correlations and commonly tolerated levels of non-linearities (i.e. leading to transmission penalties as high as 1.5dB, for
reference BERs of 10-2, 10-3 or 10-5) . Then we determine the actual required PRBS length that yields the same
(sufficient) BER accuracy as the MC method. We demonstrate its actual dependence on BER, and show that MC theory
provides a reliable upper bound in FEC-assisted, highly dispersive systems
System and method for selecting an optical path in an optical network
No full textThe invention proposes a system and method
for selecting an optimal optical path through
which to transmit an optical signal, the optimal
optical path is one of a plurality of optical paths in
a transparent optical network. Each of the
plurality of optical paths includes a plurality of
optical elements. For each of the plurality of
optical paths,a first optical signal to noise ratio is
determined for each optical element in the
respective optical path. Then, for each of the
plurality of optical paths, nonlinear distortions
caused by each optical element in the respective
optical path are modelled as Gaussian noise and a
second optical signal to noise ratio associated with
the modelled Gaussian noise is determined.
Finally, the optimal optical path is selected using the sums of the first and second
optical signal to noise ratios, respectively
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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