14,405 research outputs found
The weak Stratonovich integral with respect to fractional Brownian motion with Hurst parameter 1/6
Let be a fractional Brownian motion with Hurst parameter . It is
known that the symmetric Stratonovich-style Riemann sums for do not, in general, converge in probability. We show, however,
that they do converge in law in the Skorohod space of c\`adl\`ag functions.
Moreover, we show that the resulting stochastic integral satisfies a change of
variable formula with a correction term that is an ordinary It\^o integral with
respect to a Brownian motion that is independent of .Comment: 45 page
Haar projection numbers and failure of unconditional convergence in Sobolev spaces
For we determine the precise range of Sobolev spaces for
which the Haar system is an unconditional basis. We also consider the natural
extensions to Triebel-Lizorkin spaces and prove upper and lower bounds for
norms of projection operators depending on properties of the Haar frequency
set
POWER-SUPPLaY: Leaking Data from Air-Gapped Systems by Turning the Power-Supplies Into Speakers
It is known that attackers can exfiltrate data from air-gapped computers
through their speakers via sonic and ultrasonic waves. To eliminate the threat
of such acoustic covert channels in sensitive systems, audio hardware can be
disabled and the use of loudspeakers can be strictly forbidden. Such audio-less
systems are considered to be \textit{audio-gapped}, and hence immune to
acoustic covert channels.
In this paper, we introduce a technique that enable attackers leak data
acoustically from air-gapped and audio-gapped systems. Our developed malware
can exploit the computer power supply unit (PSU) to play sounds and use it as
an out-of-band, secondary speaker with limited capabilities. The malicious code
manipulates the internal \textit{switching frequency} of the power supply and
hence controls the sound waveforms generated from its capacitors and
transformers. Our technique enables producing audio tones in a frequency band
of 0-24khz and playing audio streams (e.g., WAV) from a computer power supply
without the need for audio hardware or speakers. Binary data (files,
keylogging, encryption keys, etc.) can be modulated over the acoustic signals
and sent to a nearby receiver (e.g., smartphone). We show that our technique
works with various types of systems: PC workstations and servers, as well as
embedded systems and IoT devices that have no audio hardware at all. We provide
technical background and discuss implementation details such as signal
generation and data modulation. We show that the POWER-SUPPLaY code can operate
from an ordinary user-mode process and doesn't need any hardware access or
special privileges. Our evaluation shows that using POWER-SUPPLaY, sensitive
data can be exfiltrated from air-gapped and audio-gapped systems from a
distance of five meters away at a maximal bit rates of 50 bit/sec
Spectral Efficient and Energy Aware Clustering in Cellular Networks
The current and envisaged increase of cellular traffic poses new challenges
to Mobile Network Operators (MNO), who must densify their Radio Access Networks
(RAN) while maintaining low Capital Expenditure and Operational Expenditure to
ensure long-term sustainability. In this context, this paper analyses optimal
clustering solutions based on Device-to-Device (D2D) communications to mitigate
partially or completely the need for MNOs to carry out extremely dense RAN
deployments. Specifically, a low complexity algorithm that enables the creation
of spectral efficient clusters among users from different cells, denoted as
enhanced Clustering Optimization for Resources' Efficiency (eCORE) is
presented. Due to the imbalance between uplink and downlink traffic, a
complementary algorithm, known as Clustering algorithm for Load Balancing
(CaLB), is also proposed to create non-spectral efficient clusters when they
result in a capacity increase. Finally, in order to alleviate the energy
overconsumption suffered by cluster heads, the Clustering Energy Efficient
algorithm (CEEa) is also designed to manage the trade-off between the capacity
enhancement and the early battery drain of some users. Results show that the
proposed algorithms increase the network capacity and outperform existing
solutions, while, at the same time, CEEa is able to handle the cluster heads
energy overconsumption
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