2,653 research outputs found
A note on closedness of the sum of two closed subspaces in a Banach space
Let be a Banach space, and be two closed subspaces of . We
present several necessary and sufficient conditions for the closedness of
( is not necessarily direct sum)
On completeness of the space of weighted pseudo almost automorphic functions
In this paper, we prove that for every , the
space of weighted pseudo almost automorphic functions is complete under the
supremum norm. This gives an affirmative answer to a key and fundamental
problem for weighted pseudo almost automorphic functions, and fills a gap in
the proof of [J. Funct. Anal. 258, No. 1, 196-207 (2010)].Comment: 8 page
Optimal Power Allocation for Artificial Noise under Imperfect CSI against Spatially Random Eavesdroppers
In this correspondence, we study the secure multiantenna transmission with
artificial noise (AN) under imperfect channel state information in the presence
of spatially randomly distributed eavesdroppers. We derive the optimal
solutions of the power allocation between the information signal and the AN for
minimizing the secrecy outage probability (SOP) under a target secrecy rate and
for maximizing the secrecy rate under a SOP constraint, respectively. Moreover,
we provide an interesting insight that channel estimation error affects the
optimal power allocation strategy in opposite ways for the above two
objectives. When the estimation error increases, more power should be allocated
to the information signal if we aim to decrease the rate-constrained SOP,
whereas more power should be allocated to the AN if we aim to increase the
SOP-constrained secrecy rate.Comment: 7 pages, 6 figure
Improving Anti-Eavesdropping Ability without Eavesdropper's CSI: A Practical Secure Transmission Design Perspective
This letter studies the practical design of secure transmissions without
knowing eavesdropper's channel state information (ECSI). An ECSI-irrelevant
metric is introduced to quantize the intrinsic anti-eavesdropping ability (AEA)
that the transmitter has on confronting the eavesdropper via secrecy encoding
together with artificial-noise-aided signaling. Non-adaptive and adaptive
transmission schemes are proposed to maximize the AEA with the optimal encoding
rates and power allocation presented in closed-form expressions. Analyses and
numerical results show that maximizing the AEA is equivalent to minimizing the
secrecy outage probability (SOP) for the worst case by ignoring eavesdropper's
receiver noise. Therefore, the AEA is a useful alternative to the SOP for
assessing and designing secure transmissions when the ECSI cannot be prior
known.Comment: 4 pages, 2 figures, to be published on IEEE Wireless Communications
Letters (WCL
Delivery-Secrecy Tradeoff for Cache-Enabled Stochastic Networks: Content Placement Optimization
Wireless caching has been widely recognized as a promising technique for
efficient content delivery. In this paper, by taking different file secrecy
levels into consideration, physical-layer security oriented content placement
is optimized in a stochastic cache-enabled cellular network. We propose an
analytical framework to investigate the nontrivial file delivery-secrecy
tradeoff. Specifically, we first derive the closed-form expressions for the
file hit and secrecy probabilities. The global optimal probabilistic content
placement policy is then analytically derived in terms of hit probability
maximization under file secrecy constraints. Numerical results are demonstrated
to verify our analytical findings and show that the targeted file secrecy
levels are crucial in balancing the file delivery-secrecy tradeoff.Comment: 5 pages, 4 figures, accepted to be published in IEEE Transactions on
Vehicular Technolog
Secure and Energy-Efficient Transmissions in Cache-Enabled Heterogeneous Cellular Networks: Performance Analysis and Optimization
This paper studies physical-layer security for a cache-enabled heterogeneous
cellular network comprised of a macro base station and multiple small base
stations (SBSs). We investigate a joint design on caching placement and file
delivery for realizing secure and energy-efficient transmissions against
randomly distributed eavesdroppers. We propose a novel hybrid "most popular
content" and "largest content diversity" caching placement policy to distribute
files of different popularities. Depending on the availability and placement of
the requested file, we employ three cooperative transmission schemes, namely,
distributed beamforming, frequency-domain orthogonal transmission, and best SBS
relaying, respectively. We derive analytical expressions for the connection
outage probability and secrecy outage probability for each transmission scheme.
Afterwards, we design the optimal transmission rates and caching allocation
successively to achieve a maximal overall secrecy throughput and secrecy energy
efficiency, respectively. Numerical results verify the theoretical analyses and
demonstrate the superiority of the proposed hybrid caching policy.Comment: 13 pages in double-column, 9 figures, accepted for publication on
IEEE Transactions on Communication
Uniqueness of the inverse reaction coefficient problems for nonlocal diffusion models
In this paper, we consider the inverse reaction coefficient problems (IRCPs)
for nonlocal diffusion equation and multi-term time-fractional nonlocal
diffusion equation from the average nonlocal flux data in external reaction
region. Based on the nonlocal maximum principle we established, the uniqueness
theorem for IRCPs are proved
Identification of the degradation coefficient for an anomalous diffusion process in hydrology
In hydrology, the degradation coefficient is one of the key parameters to
describe the water quality change and to determine the water carrying capacity.
This paper is devoted to identify the degradation coefficient in an anomalous
diffusion process by using the average flux data at the accessible part of
boundary. The main challenges in inverse degradation coefficient problems
(IDCP) is the average flux measurement data only provide very limited
information and cause the severe ill-posedness of IDCP. Firstly, we prove the
average flux measurement data can uniquely determine the degradation
coefficient. The existence and uniqueness of weak solution for the direct
problem are established, and the Lipschitz continuity of the corresponding
forward operator is also obtained. Secondly, to overcome the ill-posedness, we
combine the variational regularization method with Laplace approximations (LA)
to solve the IDCP. This hybrid method is essentially the combination of
deterministic regularization method and stochastic method. Thus, it is able to
calculate the minimizer (MAP point) more rapidly and accurately, but also
enables captures the statistics information and quantifying the uncertainty of
the solution. Furthermore, the existence, stability and convergence of the
minimizer of the variational problem are proved. The convergence rate estimate
between the LA posterior distribution and the actual posterior distribution in
the sense of Hellinger distance is given, and the skewness are introduced for
characterizing the symmetry or slope of LA solution, especially the
relationship with the symmetry of the measurement data. Finally, the
one-dimensional and two-dimensional numerical examples are presented to confirm
the efficiency and robustness of the proposed method
Adaptive Full-Duplex Jamming Receiver for Secure D2D Links in Random Networks
Device-to-device (D2D) communication raises new transmission secrecy
protection challenges, since conventional physical layer security approaches,
such as multiple antennas and cooperation techniques, are invalid due to its
resource/size constraints. The full-duplex (FD) jamming receiver, which
radiates jamming signals to confuse eavesdroppers when receiving the desired
signal simultaneously, is a promising candidate. Unlike existing endeavors that
assume the FD jamming receiver always improves the secrecy performance compared
with the half-duplex (HD) receiver, we show that this assumption highly depends
on the instantaneous residual self-interference cancellation level and may be
invalid. We propose an adaptive jamming receiver operating in a switched FD/HD
mode for a D2D link in random networks. Subject to the secrecy outage
probability constraint, we optimize the transceiver parameters, such as
signal/jamming powers, secrecy rates and mode switch criteria, to maximize the
secrecy throughput. Most of the optimization operations are taken off-line and
only very limited on-line calculations are required to make the scheme with low
complexity. Furthermore, some interesting insights are provided, such as the
secrecy throughput is a quasi-concave function. Numerical results are
demonstrated to verify our theoretical findings, and to show its superiority
compared with the receiver operating in the FD or HD mode only
Energy-Efficient Transmission Design in Non-Orthogonal Multiple Access
Non-orthogonal multiple access (NOMA) is considered as a promising technology
for improving the spectral efficiency (SE) in 5G. In this correspondence, we
study the benefit of NOMA in enhancing energy efficiency (EE) for a multi-user
downlink transmission, where the EE is defined as the ratio of the achievable
sum rate of the users to the total power consumption. Our goal is to maximize
the EE subject to a minimum required data rate for each user, which leads to a
non-convex fractional programming problem. To solve it, we first establish the
feasible range of the transmitting power that is able to support each user's
data rate requirement. Then, we propose an EE-optimal power allocation strategy
that maximizes the EE. Our numerical results show that NOMA has superior EE
performance in comparison with conventional orthogonal multiple access (OMA)
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