120 research outputs found
Covert Wireless Communication with a Poisson Field of Interferers
In this paper, we study covert communication in wireless networks consisting
of a transmitter, Alice, an intended receiver, Bob, a warden, Willie, and a
Poisson field of interferers. Bob and Willie are subject to uncertain shot
noise due to the ambient signals from interferers in the network. With the aid
of stochastic geometry, we analyze the throughput of the covert communication
between Alice and Bob subject to given requirements on the covertness against
Willie and the reliability of decoding at Bob. We consider non-fading and
fading channels. We analytically obtain interesting findings on the impacts of
the density and the transmit power of the concurrent interferers on the covert
throughput. That is, the density and the transmit power of the interferers have
no impact on the covert throughput as long as the network stays in the
interference-limited regime, for both the non-fading and the fading cases. When
the interference is sufficiently small and comparable with the receiver noise,
the covert throughput increases as the density or the transmit power of the
concurrent interferers increases
Regularized Channel Inversion for Simultaneous Confidential Broadcasting and Power Transfer: A Large System Analysis
We propose for the first time new transmission
schemes based on linear precoding to enable simultaneous confidential
broadcasting and power transfer (SCBPT) in a multiuser
multi-input single-output (MISO) network, where a BS with N
antennas simultaneously transmits power and confidential messages
to K single-antenna users. We first design two transmission
schemes based on the rules of regularized channel inversion
(RCI) for both power splitting (PS) and time switching (TS)
receiver architectures, namely, RCI-PS and RCI-TS schemes.
For each scheme, we derive channel-independent expressions to
approximate the secrecy sum rate and the harvested power in
the large-system regime where K, N → ∞ with a fixed ratio
β = K/N. Based on the large-system results, we jointly optimize
the regularization parameter of the RCI and the PS ratio or the
TS ratio such that the secrecy sum rate is maximized subject
to an energy-harvesting constraint. We then present the tradeoff
between the secrecy sum rate and the harvested power achieved
by each scheme, and find that neither scheme always outperforms
the other one. Motivated by this fact, we design an RCI-hybrid
scheme based on the RCI and a newly proposed hybrid receiver
architecture. The hybrid receiver architecture takes advantages
of both the PS and TS receiver architectures. We show that the
RCI-hybrid scheme outperforms both the RCI-PS and RCI-TS
schemes.ARC Discovery Projects Grant DP15010390
Covert communication with finite blocklength in AWGN channels
Covert communication is to achieve a reliable transmission
from a transmitter to a receiver while guaranteeing an
arbitrarily small probability of this transmission being detected
by a warden. In this work, we study the covert communication
in AWGN channels with finite blocklength, in which the number
of channel uses is finite. Specifically, we analytically prove that
the entire block (all available channel uses) should be utilized to
maximize the effective throughput of the transmission subject
to a predetermined covert requirement. This is a nontrivial
result because more channel uses results in more observations
at the warden for detecting the transmission. We also determine
the maximum allowable transmit power per channel use, which
is shown to decrease as the blocklength increases. Despite the
decrease in the maximum allowable transmit power per channel
use, the maximum allowable total power over the entire block is
proved to increase with the blocklength, which leads to the fact
that the effective throughput increases with the blocklength.ARC Discovery Projects Grant DP15010390
Efficient Multi-objective Evolutionary 3D Neural Architecture Search for COVID-19 Detection with Chest CT Scans
COVID-19 pandemic has spread globally for months. Due to its long incubation
period and high testing cost, there is no clue showing its spread speed is
slowing down, and hence a faster testing method is in dire need. This paper
proposes an efficient Evolutionary Multi-objective neural ARchitecture Search
(EMARS) framework, which can automatically search for 3D neural architectures
based on a well-designed search space for COVID-19 chest CT scan
classification. Within the framework, we use weight sharing strategy to
significantly improve the search efficiency and finish the search process in 8
hours. We also propose a new objective, namely potential, which is of benefit
to improve the search process's robustness. With the objectives of accuracy,
potential, and model size, we find a lightweight model (3.39 MB), which
outperforms three baseline human-designed models, i.e., ResNet3D101 (325.21
MB), DenseNet3D121 (43.06 MB), and MC3\_18 (43.84 MB). Besides, our
well-designed search space enables the class activation mapping algorithm to be
easily embedded into all searched models, which can provide the
interpretability for medical diagnosis by visualizing the judgment based on the
models to locate the lesion areas.Comment: Neural Architecture Search, Evolutionary Algorithm, COVID-19, C
On Covert Communication With Noise Uncertainty
Prior studies on covert communication with noise
uncertainty adopted a worst-case approach from the warden’s
perspective. That is, the worst-case detection performance of the
warden is used to assess covertness, which is overly optimistic.
Instead of simply considering the worst limit, in this work,
we take the distribution of noise uncertainty into account to
evaluate the overall covertness in a statistical sense. Specifically,
we define new metrics for measuring the covertness, which are
then adopted to analyze the maximum achievable rate for a given
covertness requirement under both bounded and unbounded
noise uncertainty models.ARC Discovery Projects Grant DP15010390
Correlation-Based Power Allocation for Secure Transmission with Artificial Noise
We examine for the first time the impact of
transmitter-side correlation on the secure transmission with
artificial noise (AN), based on which a new power allocation
strategy for AN is devised for physical layer security enhancement.
Specifically, we design a correlation-based power allocation
(CPA) for AN, of which the optimality in terms of achieving the
minimum secrecy outage probability is analytically proved in
the large system regime with the number of transmit antennas
approaching infinity. Our numerical results demonstrate that
the CPA is nearly optimal and can significantly outperform the
widely-used uniform power allocation (UPA) even for a moderate
(finite) number of correlated transmit antennas. Our numerical
results also reveal a fundamental difference between the secrecy
performance of the CPA and that of the UPA. When the number
of correlated transmit antennas increases, we find that the secrecy
outage probability of the CPA always reduces while the secrecy
outage probability of the UPA suffers from a saturation point.ARC Discovery Projects Grant DP15010390
Delay-Intolerant Covert Communications with Either Fixed or Random Transmit Power
In this paper, we study delay-intolerant covert communications in additive white Gaussian noise (AWGN) channels with a finite block length, i.e., a finite number of channel uses. Considering the maximum allowable number of channel uses to be N, it is not immediately clear whether the actual number of channel uses, denoted by n, should be as large as N or smaller for covert communications. This is because a smaller n reduces a warden’s chance to detect the communications due to fewer observations, but also reduces the chance to transmit information. We show that n=N is indeed optimal to maximize the amount of information bits that can be transmitted, subject to any covert communication constraint in terms of the warden’s detection error probability. To better make use of the warden’s uncertainty due to the finite block length, we also propose to use uniformly distributed random transmit power to enhance covert communications. Our examination shows that the amount of information that can be covertly transmitted logarithmically increases with the number of random power levels, which indicates that most of the benefit of using random transmit power is achieved with just a few different power levels.This work was supported by the Australian Research Council’s Discovery Projects under Grant DP180104062
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