61 research outputs found
Optimal Throughput for Covert Communication Over a Classical-Quantum Channel
This paper considers the problem of communication over a memoryless
classical-quantum wiretap channel subject to the constraint that the
eavesdropper on the channel should not be able to learn whether the legitimate
parties are using the channel to communicate or not. Specifically, the relative
entropy between the output quantum states at the eavesdropper when a codeword
is transmitted and when no input is provided must be sufficiently small.
Extending earlier works, this paper proves the "square-root law" for a broad
class of classical-quantum channels: the maximum amount of information that can
be reliably and covertly transmitted over uses of such a channel scales
like . The scaling constant is also determined.Comment: Corrected version of a paper presented at ITW 2016. In the ITW paper,
the denominator in the main formula (10) was incorrect. The current version
corrects this mistake and adds an appendix for its derivatio
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
Finite Blocklength Analysis of Gaussian Random Coding in AWGN Channels under Covert Constraint
This paper considers the achievability and converse bounds on the maximal
channel coding rate at a given blocklength and error probability over AWGN
channels. The problem stems from covert communication with Gaussian codewords.
By re-visiting [18], we first present new and more general achievability bounds
for random coding schemes under maximal or average probability of error
requirements. Such general bounds are then applied to covert communication in
AWGN channels where codewords are generated from Gaussian distribution while
meeting the maximal power constraint. Further comparison is made between the
new achievability bounds and existing one with deterministic codebooks.Comment: 18 page
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
Fundamental Limits of Communication with Low Probability of Detection
This paper considers the problem of communication over a discrete memoryless
channel (DMC) or an additive white Gaussian noise (AWGN) channel subject to the
constraint that the probability that an adversary who observes the channel
outputs can detect the communication is low. Specifically, the relative entropy
between the output distributions when a codeword is transmitted and when no
input is provided to the channel must be sufficiently small. For a DMC whose
output distribution induced by the "off" input symbol is not a mixture of the
output distributions induced by other input symbols, it is shown that the
maximum amount of information that can be transmitted under this criterion
scales like the square root of the blocklength. The same is true for the AWGN
channel. Exact expressions for the scaling constant are also derived.Comment: Version to appear in IEEE Transactions on Information Theory; minor
typos in v2 corrected. Part of this work was presented at ISIT 2015 in Hong
Kon
Finite Blocklength Analysis of Gaussian Random coding in AWGN Channels under Covert constraints II: A Viewpoint of Total Variation Distance
Covert communication over an additive white Gaussian noise (AWGN) channel
with finite block length is investigated in this paper. The attention is on the
covert criterion, which has not been considered in finite block length
circumstance. As an accurate quantity metric of discrimination, the variation
distance with given finite block length n and signal-noise ratio (snr) is
obtained. We give both its analytic solution and expansions which can be easily
evaluated. It is shown that K-L distance, which is frequently adopted as the
metric of discrimination at the adversary in asymptotic regime, is not
convincing in finite block length regime compared with the total variation
distance. Moreover, the convergence rate of the total variation with different
snr is analyzed when the block length tends to infinity. The results will be
very helpful for understanding the behavior of the total variation distance and
practical covert communication
The First and Second Order Asymptotics of Covert Communication over AWGN Channels
This paper investigates the asymptotics of the maximal throughput of
communication over AWGN channels by channel uses under a covert constraint
in terms of an upper bound of Kullback-Leibler divergence (KL
divergence). It is shown that the first and second order asymptotics of the
maximal throughput are and
, respectively.
The technique we use in the achievability is quasi--neighborhood
notion from information geometry. We prove that if the generating distribution
of the codebook is close to Dirac measure in the weak sense, then the
corresponding output distribution at the adversary satisfies covert constraint
in terms of most common divergences. This helps link the local differential
geometry of the distribution of noise with covert constraint. For the converse,
the optimality of Gaussian distribution for minimizing KL divergence under
second order moment constraint is extended from dimension to dimension .
It helps to establish the upper bound on the average power of the code to
satisfy the covert constraint, which further leads to the direct converse bound
in terms of covert metric
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