6,293 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
TARANET: Traffic-Analysis Resistant Anonymity at the NETwork layer
Modern low-latency anonymity systems, no matter whether constructed as an
overlay or implemented at the network layer, offer limited security guarantees
against traffic analysis. On the other hand, high-latency anonymity systems
offer strong security guarantees at the cost of computational overhead and long
delays, which are excessive for interactive applications. We propose TARANET,
an anonymity system that implements protection against traffic analysis at the
network layer, and limits the incurred latency and overhead. In TARANET's setup
phase, traffic analysis is thwarted by mixing. In the data transmission phase,
end hosts and ASes coordinate to shape traffic into constant-rate transmission
using packet splitting. Our prototype implementation shows that TARANET can
forward anonymous traffic at over 50~Gbps using commodity hardware
A Quantitative Theory of Bottleneck Structures for Data Networks
The conventional view of the congestion control problem in data networks is
based on the principle that a flow's performance is uniquely determined by the
state of its bottleneck link, regardless of the topological properties of the
network. However, recent work has shown that the behavior of
congestion-controlled networks is better explained by models that account for
the interactions between bottleneck links. These interactions are captured by a
latent \textit{bottleneck structure}, a model describing the complex ripple
effects that changes in one part of the network exert on the other parts. In
this paper, we present a \textit{quantitative} theory of bottleneck structures
(QTBS), a mathematical and engineering framework comprising a family of
polynomial-time algorithms that can be used to reason about a wide variety of
network optimization problems, including routing, capacity planning and flow
control. QTBS can contribute to traffic engineering by making clear predictions
about the relative performance of alternative flow routes, and by providing
numerical recommendations for the optimal rate settings of traffic shapers. A
particularly novel result in the domain of capacity planning indicates that
previously established rules for the design of folded-Clos networks are
suboptimal when flows are congestion controlled. We show that QTBS can be used
to derive the optimal rules for this important class of topologies, and
empirically demonstrate the correctness and efficacy of these results using the
BBR and Cubic congestion-control algorithms
Response theory: a trajectory-based approach
We collect recent results on deriving useful response relations also for
nonequilibrium systems. The approach is based on dynamical ensembles,
determined by an action on trajectory space. (Anti)Symmetry under time-reversal
separates two complementary contributions in the response, one entropic the
other frenetic. Under time-reversal invariance of the unperturbed reference
process, only the entropic term is present in the response, giving the standard
fluctuation-dissipation relations in equilibrium. For nonequilibrium reference
ensembles, the frenetic term contributes essentially and is responsible for new
phenomena. We discuss modifications in the Sutherland-Einstein relation, the
occurence of negative differential mobilities and the saturation of response.
We also indicate how the Einstein relation between noise and friction gets
violated for probes coupled to a nonequilibrium environment. We end with some
discussion on the situation for quantum phenomena, but the bulk of the text
concerns classical mesoscopic (open) systems. The choice of many simple
examples is trying to make the notes pedagogical, to introduce an important
area of research in nonequilibrium statistical mechanics
Study into movement of wide span tractors (vehicles) used in controlled traffic farming
Wide span tractors/vehicles have good prospects as the mechanisation means for controlled traffic farming. The efficiency of the practical application of wide span tractors (vehicles) depends on the availability of the substantiated scientific basis or the theoretical basis for the research into their key properties, including among other factors the smoothness of movement. The aim of the research is to improve the smoothness of movement of wide span tractors (vehicles) by substantiating their configuration, design-and-process and other parameters as well as the properties of the longitudinal profile of the agricultural background irregularities in the ruts of the laid-down process track. The smoothness of
movement of the wide span tractor (vehicle) as a dynamic system travelling in the ruts of the permanent process track substantially depends on the structure of the latter’s longitudinal profile, the stiffness of tyres on the supporting wheels, while the dynamics of the vertical oscillations of the process section depends on its operating weight
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