15 research outputs found
Covert Communications with a Full-Duplex Receiver over Wireless Fading Channels
In this work, we propose a covert communication
scheme where the transmitter attempts to hide its transmission to
a full-duplex receiver, from a warden that is to detect this covert
transmission using a radiometer. Specifically, we first derive the
detection error rate at the warden, based on which the optimal
detection threshold for its radiometer is analytically determined
and its expected detection error rate over wireless fading channels
is achieved in a closed-form expression. Our analysis indicates
that the artificial noise deliberately produced by the receiver
with a random transmit power, although causes self-interference,
offers the capability of achieving a positive effective covert rate
for any transmit power (can be infinity) subject to any given
covertness requirement on the expected detection error rate. This
work is the first study on the use of the full-duplex receiver with
controlled artificial noise for achieving covert communications
and invites further investigation in this regard.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
Sensing Aided Covert Communications: Turning Interference into Allies
In this paper, we investigate the realization of covert communication in a
general radar-communication cooperation system, which includes integrated
sensing and communications as a special example. We explore the possibility of
utilizing the sensing ability of radar to track and jam the aerial adversary
target attempting to detect the transmission. Based on the echoes from the
target, the extended Kalman filtering technique is employed to predict its
trajectory as well as the corresponding channels. Depending on the maneuvering
altitude of adversary target, two channel models are considered, with the aim
of maximizing the covert transmission rate by jointly designing the radar
waveform and communication transmit beamforming vector based on the constructed
channels. For the free-space propagation model, by decoupling the joint design,
we propose an efficient algorithm to guarantee that the target cannot detect
the transmission. For the Rician fading model, since the multi-path components
cannot be estimated, a robust joint transmission scheme is proposed based on
the property of the Kullback-Leibler divergence. The convergence behaviour,
tracking MSE, false alarm and missed detection probabilities, and covert
transmission rate are evaluated. Simulation results show that the proposed
algorithms achieve accurate tracking. For both channel models, the proposed
sensing-assisted covert transmission design is able to guarantee the
covertness, and significantly outperforms the conventional schemes.Comment: 13 pages, 12 figures, submitted to IEEE journals for potential
publicatio
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