10,017 research outputs found
Heterogeneous Networks with Power-Domain NOMA: Coverage, Throughput and Power Allocation Analysis
In a heterogeneous cellular network (HetNet), consider that a base station in
the HetNet is able to simultaneously schedule and serve K users in the downlink
by performing the power-domain non-orthogonal multiple access (NOMA) scheme.
This paper aims at the preliminary study on the downlink coverage and
throughput performances of the HetNet with the non-cooperative and the
(proposed) cooperative NOMA schemes. First, the coverage probability and link
throughput of K users in each cell are studied and their accurate expressions
are derived for the non-cooperative NOMA scheme in which no BSs are coordinated
to jointly transmit the NOMA signals for a particular user. We show that the
coverage and link throughput can be largely reduced if transmit power
allocations among the K users do not satisfy the constraint derived. Next, we
analyze the coverage and link throughput of K users for the cooperative NOMA
scheme in which the void BSs without users are coordinated to enhance the
farthest NOMA user in a cell. The derived accurate results show that
cooperative NOMA can significantly improve the coverage and link throughput of
all users. Finally, we show that there exist optimal power allocation schemes
that maximize the average cell coverage and throughput under some derived power
allocation constraints and numerical results validate our analytical findings.Comment: 31 pages, 4 figure
Spin transfer in high energy fragmentation processes
We point out that measuring longitudinal polarizations of different hyperons
produced in lepton induced reactions are ideal to study the spin transfer of
the fragtmenting quark to produced hadron in high energy hadronization
processes. We briefly summarize the method used in calculating the hyperon
polarizations in these processes, then present some of the results for e+e- and
e-p or \nu p reactions obtained using two different pictures for the spin
structure of hyperon: that drawn from polarized deep inelastic lepton-nucleon
scattering data or that using SU(6) symmetric wave functions. The results show
in particular that measurements of such polarizations should provide useful
information to the question of which picture is more suitable in describing the
spin effects in the fragmentation processes.Comment: Talk given at the 14th International Spin Symposium, 5 page
Minimum Cuts and Shortest Cycles in Directed Planar Graphs via Noncrossing Shortest Paths
Let be an -node simple directed planar graph with nonnegative edge
weights. We study the fundamental problems of computing (1) a global cut of
with minimum weight and (2) a~cycle of with minimum weight. The best
previously known algorithm for the former problem, running in
time, can be obtained from the algorithm of \Lacki, Nussbaum, Sankowski, and
Wulff-Nilsen for single-source all-sinks maximum flows. The best previously
known result for the latter problem is the -time algorithm of
Wulff-Nilsen. By exploiting duality between the two problems in planar graphs,
we solve both problems in time via a divide-and-conquer
algorithm that finds a shortest non-degenerate cycle. The kernel of our result
is an -time algorithm for computing noncrossing shortest paths
among nodes well ordered on a common face of a directed plane graph, which is
extended from the algorithm of Italiano, Nussbaum, Sankowski, and Wulff-Nilsen
for an undirected plane graph.Comment: 25 pages, 14 figure
On Secrecy Capacity of Fast Fading MIMOME Wiretap Channels With Statistical CSIT
In this paper, we consider secure transmissions in ergodic Rayleigh
fast-faded multiple-input multiple-output multiple-antenna-eavesdropper
(MIMOME) wiretap channels with only statistical channel state information at
the transmitter (CSIT). When the legitimate receiver has more (or equal)
antennas than the eavesdropper, we prove the first MIMOME secrecy capacity with
partial CSIT by establishing a new secrecy capacity upper-bound. The key step
is to form an MIMOME degraded channel by dividing the legitimate receiver's
channel matrix into two submatrices, and setting one of the submatrices to be
the same as the eavesdropper's channel matrix. Next, under the total power
constraint over all transmit antennas, we analytically solve the channel-input
covariance matrix optimization problem to fully characterize the MIMOME secrecy
capacity. Typically, the MIMOME optimization problems are non-concave. However,
thank to the proposed degraded channel, we can transform the stochastic MIMOME
optimization problem to be a Schur-concave one and then find its solution.
Besides total power constraint, we also investigate the secrecy capacity when
the transmitter is subject to the practical per-antenna power constraint. The
corresponding optimization problem is even more difficult since it is not
Schuar-concave. Under the two power constraints considered, the corresponding
MIMOME secrecy capacities can both scale with the signal-to-noise ratios (SNR)
when the difference between numbers of antennas at legitimate receiver and
eavesdropper are large enough. However, when the legitimate receiver and
eavesdropper have a single antenna each, such SNR scalings do not exist for
both cases.Comment: submitted to IEEE Transactions on Wireless Communication
Ultra-Reliable and Low-Latency Communications Using Proactive Multi-cell Association
Attaining reliable communications traditionally relies on a closed-loop
methodology but inevitably incurs a good amount of networking latency thanks to
complicated feedback mechanism and signaling storm. Such a closed-loop
methodology thus shackles the current cellular network with a tradeoff between
high reliability and low latency. To completely avoid the latency induced by
closed-loop communication, this paper aims to study how to jointly employ
open-loop communication and multi-cell association in a heterogeneous network
(HetNet) so as to achieve ultra-reliable and low-latency communications. We
first introduce how mobile users in a HetNet adopt the proposed proactive
multi-cell association (PMCA) scheme to form their virtual cell that consists
of multiple access points (APs) and then analyze the communication reliability
and latency performances. We show that the communication reliability can be
significantly improved by the PMCA scheme and maximized by optimizing the
densities of the users and the APs. The analyses of the uplink and downlink
delays are also accomplished, which show that extremely low latency can be
fulfilled in the virtual cell of a single user if the PMCA scheme is adopted
and the radio resources of each AP are appropriately allocated.Comment: 18 pages, 9 figures, journal publicatio
Investigating the quark flavor dependence of the chiral magnetic effect with a multiphase transport model
Because the properties of the QCD phase transition and the chiral magnetic
effect (CME) depend on the number of quark flavors () and quark mass,
relativistic heavy-ion collisions provide a natural environment to investigate
the flavor features if quark deconfinement occurs. We introduce an initial
two-flavor or three-flavor dipole charge separation into a multiphase transport
(AMPT) model to investigate the flavor dependence of the CME. By taking
advantage of the recent ALICE data of charge azimuthal correlations with
identified hadrons, we attempt to disentangle two-flavor and three-flavor CME
scenarios in Pb+Pb collisions at 2.76 TeV. We find that the experimental data
show a certain potential to distinguish the two scenarios, therefore we further
suggest to collect more data to clarify the possible flavor dependence in
future experiments.Comment: 12 pages, 4 figures; final published versio
Larkin-Ovchinikov superfluidity in time-reversal symmetric bilayer Fermi gases
Larkin-Ovchinnikov (LO) state which combines the superfluidity and spatial
periodicity of pairing order parameter and exhibits the supersolid properties
has been attracting intense attention in both condensed matter physics and
ultracold atoms. Conventionally, realization of LO state from an intrinsic
s-wave interacting system necessitates to break the time-reversal (TR) and
sometimes spatial-inversion (SI) symmetries. Here we report a novel prediction
that the LO state can be realized in a TR and SI symmetric system representing
a bilayer Fermi gas subjected to a laserassisted interlayer tunneling. We show
that the intralayer s-wave atomic interaction acts effectively like a p-wave
interaction in the pseudospin space. This provides distinctive pairing effects
in the present system with pseudspin spin-orbit coupling, and leads to a
spontaneous density-modulation of the pairing order predicted in a very broad
parameter regime. Unlike the conventional schemes, our results do not rely on
the spin imbalance or external Zeeman fields, showing a highly feasible way to
observe the long-sought-after LO superfluid phase using the laser-assisted
bilayer Fermi gases.Comment: 10 pages, 5 figure
Hacking on decoy-state quantum key distribution system with partial phase randomization
Quantum key distribution (QKD) provides means for unconditional secure key
transmission between two distant parties. However, in practical
implementations, it suffers from quantum hacking due to device imperfections.
Here we propose a hybrid measurement attack, with only linear optics, homodyne
detection, and single photon detection, to the widely used vacuum+weak decoy
state QKD system when the phase of source is partially randomized. Our analysis
shows that, in some parameter regimes, the proposed attack would result in an
entanglement breaking channel but still be able to trick the legitimate users
to believe they have transmitted secure keys. That is, the eavesdropper is able
to steal all the key information without discovered by the users. Thus, our
proposal reveals that partial phase randomization is not sufficient to
guarantee the security of phase-encoding QKD systems with weak coherent states.Comment: 12 pages,4 figure
Longitudinal polarization of hyperons in high jets in singly polarized pp collisions at high energies
We calculate the longitudinal polarizations of hyperons in high
jets in collisions in which one of the protons is longitudinally polarized
at RHIC energies using different models for the spin transfer in fragmentation
process. The results show that the measurements of these polarizations can be
used to study the spin transfer in high energy fragmentation processes in
general and to test the different models in particular. Our results show
especially that the magnitude of the polarization of is rather small
whereas that of is considerably larger in the large rapidity region.
The differences between the results from different pictures for
polarizations is also much larger. Hence, the measurement of
polarization should be more effective to distinguish between different models
especially the SU(6) or the DIS picture for spin transfer in fragmentation
processes.Comment: 26 pages, 11 figures; to appear in Phys. Rev.
A Broad Learning Approach for Context-Aware Mobile Application Recommendation
With the rapid development of mobile apps, the availability of a large number
of mobile apps in application stores brings challenge to locate appropriate
apps for users. Providing accurate mobile app recommendation for users becomes
an imperative task. Conventional approaches mainly focus on learning users'
preferences and app features to predict the user-app ratings. However, most of
them did not consider the interactions among the context information of apps.
To address this issue, we propose a broad learning approach for
\textbf{C}ontext-\textbf{A}ware app recommendation with \textbf{T}ensor
\textbf{A}nalysis (CATA). Specifically, we utilize a tensor-based framework to
effectively integrate user's preference, app category information and
multi-view features to facilitate the performance of app rating prediction. The
multidimensional structure is employed to capture the hidden relationships
between multiple app categories with multi-view features. We develop an
efficient factorization method which applies Tucker decomposition to learn the
full-order interactions within multiple categories and features. Furthermore,
we employ a group norm regularization to learn the group-wise
feature importance of each view with respect to each app category. Experiments
on two real-world mobile app datasets demonstrate the effectiveness of the
proposed method
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