85 research outputs found
Wireless-Powered Communication Assisted by Two-Way Relay with Interference Alignment Underlaying Cognitive Radio Network
This study investigates the outage performance of an under-laying
wireless-powered secondary system that reuses the primary users (PU) spectrum
in a multiple-input multiple-output (MIMO) cognitive radio (CR) network. Each
secondary user (SU) harvests energy and receives information simultaneously by
applying power splitting (PS) protocol. The communication between SUs is aided
by a two-way (TW) decode and forward (DF) relay. We formulate a problem to
design the PS ratios at SUs, the power control factor at the secondary relay,
and beamforming matrices at all nodes to minimize the secondary network's
outage probability. To address this problem, we propose a two-step solution.
The first step establishes closedform expressions for the PS ratios at each SU
and secondary relay's power control factor. Furthermore, in the second step,
interference alignment (IA) is used to design proper precoding and decoding
matrices for managing the interference between secondary and primary networks.
We choose IA matrices based on the minimum mean square error (MMSE) iterative
algorithm. The simulation results demonstrate a significant decrease in the
outage probability for the proposed scheme compared to the benchmark schemes,
with an average reduction of more than two orders of magnitude achieved
Improvementvoltage Stability and Load Ability Enhancement by Continuation Power Flow and Bifurcation Theory
Power systems operation becomes more important as the load demand increases all over the world. This rapid increase in load demand forces power systems to operate near critical limits due to economic and environmental constraints. The objective in power systems operation is to serve energy with acceptable voltage and frequency to consumers at minimum cost. This paper studies the important power system phenomenon; voltage stability voltage stability is studies by using continuation power flow method and the effect of compensator, placement of generator and variation of line reactance on the voltage stability have been studied. Voltage collapse scenario is presented which can be a serious result of voltage instability and also the parameters that affected by voltage collapse are discussed. In analysing power system voltage stability, continuation power flow method is utilized which consists of successive load flows. This method is applied to a 14 bus sample test system and load-voltage curves for several buses are obtained. Simulation is done with PSAT in MATLAB. Continuation Power Flow was implemented using Newton-Raphson method. Simulation results show the proper performance of capacitor, variation of line reactance and placement of generator to improve voltage control on the lines and significantly increase the load ability margin of power systems
Impact of Device Orientation on Error Performance of LiFi Systems
Most studies on optical wireless communications (OWCs) have neglected the
effect of random orientation in their performance analysis due to the lack of a
proper model for the random orientation. Our recent empirical-based research
illustrates that the random orientation follows a Laplace distribution for a
static user equipment (UE). In this paper, we analyze the device orientation
and assess its importance on system performance. The reliability of an OWC
channel highly depends on the availability and alignment of line-of-sight (LOS)
links. In this study, the effect of receiver orientation including both polar
and azimuth angles on the LOS channel gain are analyzed. The probability of
establishing a LOS link is investigated and the probability density function
(PDF) of signal-to-noise ratio (SNR) for a randomly-oriented device is derived.
By means of the PDF of SNR, the bit-error ratio (BER) of DC-biased optical
orthogonal frequency division multiplexing (DCO-OFDM) in additive white
Gaussian noise (AWGN) channels is evaluated. A closed-form approximation for
the BER of UE with random orientation is presented which shows a good match
with Monte-Carlo simulation results. Furthermore, the impact of the UE's random
motion on the BER performance has been assessed. Finally, the effect of random
orientation on the average signal-to-interference-plus-noise ratio (SINR) in a
multiple access points (APs) scenario is investigated.Comment: 10 pages, 11 figures, journa
Development of a stability-indicating high performance liquid chromatography method for assay of erythromycin ethylsuccinate in powder for oral suspension dosage form
In this study an effective method was developed to assay erythromycin ethylsuccinate for an oral suspension dosage form. The chromatographic separation was achieved on an X-Terra[superscript ™] C[subscript 18] analytical column. A mixture of acetonitrile–ammonium dihydrogen phosphate buffer (0.025 mol L[superscript -1]) (60:40, V/V) (pH 7.0) was used as the mobile phase, effluent flow rate monitored at 1.0 mL min[superscript −1], and UV detection at 205 nm. In forced degradation studies, the effects of acid, base, oxidation, UV light and temperature were investigated showing no interference in the peak of drug. The proposed method was validated in terms of specificity, linearity, robustness, precision and accuracy. The method was linear at concentrations ranging from 400 to 600 μg mL[superscript −1], precise (intra- and inter-day relative standard deviations <0.65), accurate (mean recovery; 99.5%). The impurities and degradation products of erythromycin ethylsuccinate were selectively determined with good resolution in both the raw material and the final suspension forms. The method could be useful for both routine analytical and quality control assays of erythromycin ethylsuccinate in commercial powder for an oral suspension dosage form and it could be a very powerful tool to investigate the chemical stability of erythromycin ethylsuccinate.Chemi Darou Industrial Compan
Targeted collapse regularized autoencoder for anomaly detection: black hole at the center
Autoencoders have been extensively used in the development of recent anomaly
detection techniques. The premise of their application is based on the notion
that after training the autoencoder on normal training data, anomalous inputs
will exhibit a significant reconstruction error. Consequently, this enables a
clear differentiation between normal and anomalous samples. In practice,
however, it is observed that autoencoders can generalize beyond the normal
class and achieve a small reconstruction error on some of the anomalous
samples. To improve the performance, various techniques propose additional
components and more sophisticated training procedures. In this work, we propose
a remarkably straightforward alternative: instead of adding neural network
components, involved computations, and cumbersome training, we complement the
reconstruction loss with a computationally light term that regulates the norm
of representations in the latent space. The simplicity of our approach
minimizes the requirement for hyperparameter tuning and customization for new
applications which, paired with its permissive data modality constraint,
enhances the potential for successful adoption across a broad range of
applications. We test the method on various visual and tabular benchmarks and
demonstrate that the technique matches and frequently outperforms alternatives.
We also provide a theoretical analysis and numerical simulations that help
demonstrate the underlying process that unfolds during training and how it can
help with anomaly detection. This mitigates the black-box nature of
autoencoder-based anomaly detection algorithms and offers an avenue for further
investigation of advantages, fail cases, and potential new directions.Comment: 16 pages, 4 figures, 4 table
Invoking Deep Learning for Joint Estimation of Indoor LiFi User Position and Orientation
Light-fidelity (LiFi) is a fully-networked bidirectional optical wireless
communication (OWC) that is considered a promising solution for high-speed
indoor connectivity. Unlike in conventional radio frequency wireless systems,
the OWC channel is not isotropic, meaning that the device orientation affects
the channel gain significantly. However, due to the lack of proper channel
models for LiFi systems, many studies have assumed that the receiver is
vertically upward and randomly located within the coverage area, which is not a
realistic assumption from a practical point of view. In this paper, novel
realistic and measurement-based channel models for indoor LiFi systems are
proposed. Precisely, the statistics of the channel gain are derived for the
case of randomly oriented stationary and mobile LiFi receivers. For stationary
users, two channel models are proposed, namely, the modified truncated Laplace
(MTL) model and the modified Beta (MB) model. For LiFi users, two channel
models are proposed, namely, the sum of modified truncated Gaussian (SMTG)
model and the sum of modified Beta (SMB) model. Based on the derived models,
the impact of random orientation and spatial distribution of LiFi users is
investigated, where we show that the aforementioned factors can strongly affect
the channel gain and system performance
Physical Layer Security for Visible Light Communication Systems:A Survey
Due to the dramatic increase in high data rate services and in order to meet
the demands of the fifth-generation (5G) networks, researchers from both
academia and industry are exploring advanced transmission techniques, new
network architectures and new frequency spectrum such as the visible light
spectra. Visible light communication (VLC) particularly is an emerging
technology that has been introduced as a promising solution for 5G and beyond.
Although VLC systems are more immune against interference and less susceptible
to security vulnerabilities since light does not penetrate through walls,
security issues arise naturally in VLC channels due to their open and
broadcasting nature, compared to fiber-optic systems. In addition, since VLC is
considered to be an enabling technology for 5G, and security is one of the 5G
fundamental requirements, security issues should be carefully addressed and
resolved in the VLC context. On the other hand, due to the success of physical
layer security (PLS) in improving the security of radio-frequency (RF) wireless
networks, extending such PLS techniques to VLC systems has been of great
interest. Only two survey papers on security in VLC have been published in the
literature. However, a comparative and unified survey on PLS for VLC from
information theoretic and signal processing point of views is still missing.
This paper covers almost all aspects of PLS for VLC, including different
channel models, input distributions, network configurations,
precoding/signaling strategies, and secrecy capacity and information rates.
Furthermore, we propose a number of timely and open research directions for
PLS-VLC systems, including the application of measurement-based indoor and
outdoor channel models, incorporating user mobility and device orientation into
the channel model, and combining VLC and RF systems to realize the potential of
such technologies
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