986 research outputs found
Labeling Diversity for 2x2 WLAN Coded-Cooperative Networks
Labelling diversity is an efficient technique recently proposed in the literature and aims to improve the bit error rate(BER) performance of wireless local area network (WLAN) systems with two transmit and two receive antennas without increasing the transmit power and bandwidth requirements. In this paper, we employ labelling diversity with different space-time channel codes such as convolutional, turbo and low density parity check (LDPC) for both point-to-point and coded-cooperative communication scenarios. Joint iterative decoding schemes for distributed turbo and LDPC codes are also presented. BER performance bounds at an error floor (EF) region are derived and verified with the help of numerical simulations for both cooperative and non-cooperative schemes. Numerical simulations show that the coded-cooperative schemes with labelling diversity achieve better BER performances and use of labelling diversity at the source node significantly lowers relay outage probability and hence the overall BER performance of the coded-cooperative scheme is improved manifolds
Adaptive Network Coding for Scheduling Real-time Traffic with Hard Deadlines
We study adaptive network coding (NC) for scheduling real-time traffic over a
single-hop wireless network. To meet the hard deadlines of real-time traffic,
it is critical to strike a balance between maximizing the throughput and
minimizing the risk that the entire block of coded packets may not be decodable
by the deadline. Thus motivated, we explore adaptive NC, where the block size
is adapted based on the remaining time to the deadline, by casting this
sequential block size adaptation problem as a finite-horizon Markov decision
process. One interesting finding is that the optimal block size and its
corresponding action space monotonically decrease as the deadline approaches,
and the optimal block size is bounded by the "greedy" block size. These unique
structures make it possible to narrow down the search space of dynamic
programming, building on which we develop a monotonicity-based backward
induction algorithm (MBIA) that can solve for the optimal block size in
polynomial time. Since channel erasure probabilities would be time-varying in a
mobile network, we further develop a joint real-time scheduling and channel
learning scheme with adaptive NC that can adapt to channel dynamics. We also
generalize the analysis to multiple flows with hard deadlines and long-term
delivery ratio constraints, devise a low-complexity online scheduling algorithm
integrated with the MBIA, and then establish its asymptotical
throughput-optimality. In addition to analysis and simulation results, we
perform high fidelity wireless emulation tests with real radio transmissions to
demonstrate the feasibility of the MBIA in finding the optimal block size in
real time.Comment: 11 pages, 13 figure
Asymptotics toward viscous contact waves for solutions of the Landau equation
In the paper, we are concerned with the large time asymptotics toward the
viscous contact waves for solutions of the Landau equation with physically
realistic Coulomb interactions. Precisely, for the corresponding Cauchy problem
in the spatially one-dimensional setting, we construct the unique
global-in-time solution near a local Maxwellian whose fluid quantities are the
viscous contact waves in the sense of hydrodynamics and also prove that the
solution tends toward such local Maxwellian in large time. The result is proved
by elaborate energy estimates and seems the first one on the dynamical
stability of contact waves for the Landau equation. One key point of the proof
is to introduce a new time-velocity weight function that includes an
exponential factor of the form with where and are given positive
constants and is defined by the energy dissipation rate of the
solution itself. The time derivative of such weight function is able to induce
an extra quartic dissipation term for treating the large-velocity growth in the
nonlinear estimates due to degeneration of the linearized Landau operator in
the Coulomb case. Note that in our problem the explicit time-decay of solutions
around contact waves is unavailable but no longer needed under the crucial use
of the above weight function, which is different from the situation in [11,
14].Comment: 60 pages. Comments are most welcome. Slight modifications have been
made to simplify some estimates using the conservation of mas
KdV limit for the Vlasov-Poisson-Landau system
Two fundamental models in plasma physics are given by the
Vlasov-Poisson-Landau system and the compressible Euler-Poisson system which
both capture the complex dynamics of plasmas under the self-consistent electric
field interactions at the kinetic and fluid levels, respectively. Although
there have been extensive studies on the long wave limit of the Euler-Poisson
system towards Korteweg-de Vries equations, few results on this topic are known
for the Vlasov-Poisson-Landau system due to the complexity of the system and
its underlying multiscale feature. In this article, we derive and justify the
Korteweg-de Vries equations from the Vlasov-Poisson-Landau system modelling the
motion of ions under the Maxwell-Boltzmann relation. Specifically, under the
Gardner-Morikawa transformation with and
being the Knudsen number, we construct smooth solutions of the
rescaled Vlasov-Poisson-Landau system over an arbitrary finite time interval
that can converge uniformly to smooth solutions of the Korteweg-de Vries
equations as . Moreover, the explicit rate of convergence in
is also obtained. The proof is obtained by an appropriately chosen
scaling and the intricate weighted energy method through the micro-macro
decomposition around local Maxwellians.Comment: 68 pages. All comments are welcome. arXiv admin note: text overlap
with arXiv:2212.0765
Moir\'e Magnetic Exchange Interactions in Twisted Magnets
Besides moir\'e superlattice, twisting can also generate moir\'e magnetic
exchange interactions (MMEIs) in van der Waals magnets. However, due to the
extreme complexity and twist-angle-dependent sensitivity, all existing models
fail to capture the MMEIs, preventing the understanding of MMEIs-induced new
physics. Here, we develop a microscopic moir\'e spin Hamiltonian that enables
the effective description of MMEIs via a sliding-mapping approach in twisted
magnets, as demonstrated in twisted bilayer CrI3. Unexpectedly, we discover
that the emergence of MMEIs can create an unprecedented magnetic skyrmion
bubble (SkB) with non-conversed helicity, named as moir\'e-type SkB,
representing a unique spin texture solely generated by MMEIs and ready to be
detected under the current experimental conditions. Importantly, the size and
population of SkBs can be finely controlled by twist angle, a key step for
skyrmion-based quantum computing and information storage. Furthermore, we
reveal that the MMEIs can be effectively manipulated by the substrate-induced
interfacial Dzyaloshinskii-Moriya interaction, modulating the
twist-angle-dependent magnetic phase diagram, which solves the outstanding
disagreements between prior theories and experiments and verifies our theory.Comment: 17 pages, 5 figure
Investing with Fast Thinking
Using data from a major online peer-to-peer lending market, we document that investors follow a simple rule of thumb under time pressure: they rush to invest in loans with high interest rates without sufficiently examining credit ratings, which are freely available on the trading interface. Our experiments show that making credit rating information more salient “nudges” investors into better decisions. Firsthand experience matters for learning for non-informational reasons: An investor responds differently when observing a default of her own loan, relative to observing a default of another investor’s loan
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