627 research outputs found
Energy-Efficient Optimization for Physical Layer Security in Multi-Antenna Downlink Networks with QoS Guarantee
In this letter, we consider a multi-antenna downlink network where a secure
user (SU) coexists with a passive eavesdropper. There are two design
requirements for such a network. First, the information should be transferred
in a secret and efficient manner. Second, the quality of service (QoS), i.e.
delay sensitivity, should be take into consideration to satisfy the demands of
real-time wireless services. In order to fulfill the two requirements, we
combine the physical layer security technique based on switched beam
beamforming with an energy-efficient power allocation. The problem is
formulated as the maximization of the secrecy energy efficiency subject to
delay and power constraints. By solving the optimization problem, we derive an
energy-efficient power allocation scheme. Numerical results validate the
effectiveness of the proposed scheme.Comment: 4 pages, 3 figure
Optimal Power Allocation for Secure Communications in Large-Scale MIMO Relaying Systems
In this paper, we address the problem of optimal power allocation at the
relay in two-hop secure communications. In order to solve the challenging issue
of short-distance interception in secure communications, the benefit of
large-scale MIMO (LS-MIMO) relaying techniques is exploited to improve the
secrecy performance significantly, even in the case without eavesdropper
channel state information (CSI). The focus of this paper is on the analysis and
design of optimal power allocation for the relay, so as to maximize the secrecy
outage capacity. We reveal the condition that the secrecy outage capacity is
positive, prove that there is one and only one optimal power, and present an
optimal power allocation scheme. Moreover, the asymptotic characteristics of
the secrecy outage capacity is carried out to provide some clear insights for
secrecy performance optimization. Finally, simulation results validate the
effectiveness of the proposed scheme.Comment: 6 pages, 6 figures, ICC 201
Energy-Efficient Power Allocation for Secure Communications in Large-Scale MIMO Relaying Systems
In this paper, we address the problem of energy-efficient power allocation
for secure communications in an amplify-and-forward (AF) large-scale
multiple-input multiple-output (LS-MIMO) relaying system in presence of a
passive eavesdropper. The benefits of an AF LS-MIMO relay are exploited to
significantly improve the secrecy performance, especially the secrecy energy
efficiency (bit per Joule). We first analyze the impact of transmit power at
the relay on the secrecy outage capacity, and prove that the secrecy outage
capacity is a concave function of transmit power under very practical
assumptions, i.e. no eavesdropper channel state information (CSI) and imperfect
legitimate CSI. Then, we propose an energy-efficient power allocation scheme to
maximize the secrecy energy efficiency. Finally, simulation results validate
the advantage of the proposed energy-efficient scheme compared to the capacity
maximization scheme.Comment: 6 pages, 5 figure
Large-Scale MIMO Relaying Techniques for Physical Layer Security: AF or DF?
In this paper, we consider a large scale multiple input multiple output
(LS-MIMO) relaying system, where an information source sends the message to its
intended destination aided by an LS-MIMO relay, while a passive eavesdropper
tries to intercept the information forwarded by the relay. The advantage of a
large scale antenna array is exploited to improve spectral efficiency and
enhance wireless security. In particular, the challenging issue incurred by
short-distance interception is well addressed. Under very practical
assumptions, i.e., no eavesdropper channel state information (CSI) and
imperfect legitimate CSI at the relay, this paper gives a thorough secrecy
performance analysis and comparison of two classic relaying techniques, i.e.,
amplify-and-forward (AF) and decode-and-forward (DF). Furthermore, asymptotical
analysis is carried out to provide clear insights on the secrecy performance
for such an LS-MIMO relaying system. We show that under large transmit powers,
AF is a better choice than DF from the perspectives of both secrecy performance
and implementation complexity, and prove that there exits an optimal transmit
power at medium regime that maximizes the secrecy outage capacity.Comment: arXiv admin note: text overlap with arXiv:1401.304
Efficient Multi-User Computation Offloading for Mobile-Edge Cloud Computing
Mobile-edge cloud computing is a new paradigm to provide cloud computing
capabilities at the edge of pervasive radio access networks in close proximity
to mobile users. In this paper, we first study the multi-user computation
offloading problem for mobile-edge cloud computing in a multi-channel wireless
interference environment. We show that it is NP-hard to compute a centralized
optimal solution, and hence adopt a game theoretic approach for achieving
efficient computation offloading in a distributed manner. We formulate the
distributed computation offloading decision making problem among mobile device
users as a multi-user computation offloading game. We analyze the structural
property of the game and show that the game admits a Nash equilibrium and
possesses the finite improvement property. We then design a distributed
computation offloading algorithm that can achieve a Nash equilibrium, derive
the upper bound of the convergence time, and quantify its efficiency ratio over
the centralized optimal solutions in terms of two important performance
metrics. We further extend our study to the scenario of multi-user computation
offloading in the multi-channel wireless contention environment. Numerical
results corroborate that the proposed algorithm can achieve superior
computation offloading performance and scale well as the user size increases.Comment: The paper has been accepted by IEEE/ACM Transactions on Networking,
Sept. 2015. arXiv admin note: substantial text overlap with arXiv:1404.320
Topological Phase with Critical-Type Nodal Line State in Intermetallic CaPd
In recent years, realizing new topological phase of matter has been a hot
topic in the fields of physics and materials science. Topological semimetals
and metals can conventionally be classified into two types: type-I and type-II
according to the tilting degree of the fermion cone. Here, it is the first time
to report a new topological metal phase with the critical-type nodal line
between type-I and type-II nodal line. The critical-type nodal line shows a
unique nontrivial band crossing which is composed of a at band and a dispersive
band and leads to a new fermionic state. We propose intermetallic CaPd can be
an existing topological metal for the new fermionic state, characterized with
critical-type nodal line in the bulk and drumhead band structure on the
surface. Our work not only promotes the concept of critical-type nodal line,
but also provides the material realization to study its exotic properties in
future experiments
Ideal inner nodal chain semimetals in Li2XY (X = Ca, Ba; Y = Si, Ge) materials
The chain-type nodal loops in the reciprocal space can generate exotic nodal
chain fermions. Here, we report that Li2XY (X = Ca, Ba; Y = Si, Ge) compounds
are ideal inner nodal chain semimetals. Their band structures are composed of
two connecting nodal loops with either hybrid or type-I band dispersion. The
signatures of the nodal chain, such as the nontrivial surface states, are quite
pronounced in these Li2XY compounds since there is only a single inner nodal
chain without other extraneous bands near the Fermi level. These compounds are
existing materials and ambient-stable, which is available to realize the
experimental detection of inner nodal chain fermions or further the practical
applications.Comment: 5 pages, 4 figure
Face Alignment Across Large Poses: A 3D Solution
Face alignment, which fits a face model to an image and extracts the semantic
meanings of facial pixels, has been an important topic in CV community.
However, most algorithms are designed for faces in small to medium poses (below
45 degree), lacking the ability to align faces in large poses up to 90 degree.
The challenges are three-fold: Firstly, the commonly used landmark-based face
model assumes that all the landmarks are visible and is therefore not suitable
for profile views. Secondly, the face appearance varies more dramatically
across large poses, ranging from frontal view to profile view. Thirdly,
labelling landmarks in large poses is extremely challenging since the invisible
landmarks have to be guessed. In this paper, we propose a solution to the three
problems in an new alignment framework, called 3D Dense Face Alignment (3DDFA),
in which a dense 3D face model is fitted to the image via convolutional neutral
network (CNN). We also propose a method to synthesize large-scale training
samples in profile views to solve the third problem of data labelling.
Experiments on the challenging AFLW database show that our approach achieves
significant improvements over state-of-the-art methods.Comment: 11 pages, 10 figure
From Multiple Nodal Chain to Dirac/Weyl Semimetal and Topological Insulator in Ternary Hexagonal Materials
Dirac semimetal (DSM) hosts four-fold degenerate isolated band-crossing
points with linear dispersion, around which the quasiparticles resemble the
relativistic Dirac Fermions. It can be described by a 4 * 4 massless Dirac
Hamiltonian which can be decomposed into a pair of Weyl points or gaped into an
insulator. Thus, crystal symmetry is critical to guarantee the stable
existence. On the contrary, by breaking crystal symmetry, a DSM may transform
into a Weyl semimetal (WSM) or a topological insulator (TI). Here, by taking
hexagonal LiAuSe as an example, we find that it is a starfruit shaped multiple
nodal chain semimetal in the absence of spin-orbit coupling(SOC). In the
presence of SOC, it is an ideal DSM naturally with the Dirac points locating at
Fermi level exactly, and it would transform into WSM phase by introducing
external Zeeman field or by magnetic doping with rare-earth atom Sm. It could
also transform into TI state by breaking rotational symmetry. Our studies show
that DSM is a critical point for topological phase transition, and the
conclusion can apply to most of the DSM materials, not limited to the hexagonal
material LiAuSe.Comment: 21 pages, 7 figure
Mn2C monolayer: hydrogenation/oxygenation induced strong room-temperature ferromagnetism and potential applications
Two-dimensional ferromagnetic materials with strong ferromagnetism and high
Curie temperature are significantly desired for the applications of nanoscale
devices. Here, based on first-principles computations, we report
hydrogenated/oxygenated Mn2C monolayer is a such material with strong
room-temperature ferromagnetism. The bare Mn2C monolayer is an
antiferromagnetic metal with the local magnetic moment of Mn ~ 3{\mu}B.
However, the antiferromagnetic coupling of Mn atoms can transform into the
ferromagnetic order under hydrogenation/oxygenation. Especially, the magnetic
moments in hydrogenated/oxygenated Mn2C monolayer can be as large as 6 {\mu}B
per unit cell, and the Curie temperatures are above 290K. Beside the potential
applications in spintronic devices, our work suggests that Mn2C monolayer is
also promising to be used in hydrogen/oxygen detection and removal devices
- …