10 research outputs found
Chaotic Based Self-Synchronization for RF Steganography Radar/Communication Waveform
In this project, we continue previous CSR project entitled RF Steganography based Joint Radar/Communication Waveform Design to develop a bio-inspired secure low probability detection (LPD) radio frequency (RF) waveform that can serve multiple purposes simultaneously. Previously, we have developed an RF steganography based RF waveform to conceal a secure digital communication within a linear frequency modulated (LFM) chirp radar signal. By exploiting novel reduced phase shift keying modulation and variable symbol duration, the new waveform is resistant to time domain analysis, frequency domain analysis and cyclostationary analysis. However, to demodulate the hidden communication message, the intended receiver has to know the entire sequence of variable symbol duration, or the entire sequence of pseudo-random phases. We are developing a chaotic based self-synchronization scheme to solve this problem and provide enhanced security. Specifically, a chaotic sequence generator is employed to generate an aperiodic chaotic sequence to control the phase of the reduced phase shift keying modulation. The intended receiver only needs to have knowledge of the initial condition of the chaotic sequence generator to generate the entire pseudo-random phase sequence to achieve self-synchronization
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Various modulated hybrid pulse compression for advanced ultrasound technology and its non-destructive testing application
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University LondonUltrasound is a sound wave with a frequency greater than 20 kHz. It obeys the propagation
laws of reflection, refraction, diffraction, and scattering. Because of its excellent
physical properties, ultrasound has been used in a variety of fields, including industry
and medicine. There are many techniques that use ultrasound as detection methods in the
field of non-destructive testing (NDT) and medical treatment. In a typical ultrasound system,
a sine wave or pulse signal with a fit window is considered as the transmitted signal.
This results in low accuracy in some special situations, such as testing high attenuation
material. The signal-to-noise ratio (SNR) is an important parameter for evaluating the
performance of an echo signal or imaging. However, under high attenuation materials or
noisy conditions, SNR will significantly decrease. Under these conditions, valid information
in the received signal will be obscured by noise. This situation can cause errors in
the detection system. In an ultrasound system, increasing the SNR of the echo signal can
reduce detection errors and improve accuracy.
First, in ultrasound systems, a noise reduction method based on pulse compression has
been investigated and applied. Convolution and modulation were used in the proposed
method to generate new hybrid emission signals. The hybrid codes can only be distinguished
by a special matched filter that is related to the emission signals. The echo signals
processed by a special matched filter have a high main lobe and a very low side lobe,
implying that the side lobe level and SNR will increase. When compared to traditional
denoising methods, the proposed method can significantly improve SNR while only requiring
a change in the transmission code without requiring any hardware changes.
Second, in a low voltage ultrasonic testing (UT) system, a hybrid phase modulated code
excitation method based on the Barker and Golay code pairs was proposed and implemented.
In a UT system, the lower the pulsing voltage, the lower the SNR of the signal.
Attempting to reduce the pulsing voltage will result in noisy and unusable results. The
proposed hybrid method can increase main lobe power in low average power transmitted
and received signals. The proposed method has been theoretically examined and then
tested in simulation studies. The experimental results showed that the main lobe level of
the code produced by convolution of Barker code and Golay code pairs is around 30 dB
higher than the simple pulse, and the main lobe of the combined code is around 15 dB
higher than the traditional Barker code, with the sidelobe being the same as the Baker
code that constitutes this combined code. As a result, the combined code’s peak sidelobe
level (PSL) is approximately 5 dB lower than the traditional Barker code. Because of this,
UT devices can be used in real-world applications, even in low-voltage situations.
Third, the torsional wave mode T(0,1) hybrid phase modulated code excitation method
has been proposed and applied in a long range guided wave testing (GWT) system. The
proposed hybrid method combines the Barker and Golay code pair and is modulated by
a fitted sine wave. This method combines the benefits of these two coding methods and
increases code length flexibility. The SNR and PSL of the processed signal are used to assess
the method’s performance. The proposed method has been tested in GWT using both
finite element method (FEM) simulation and real-world testing. The results of pipeline
laboratory testing revealed that the best increasing SNR of BCG is around 33.5 dB when
compared to a simple pulse at 40 kHz, and the peak sidelobe level is around -24 dB. The
proposed method, as well as other traditional methods, were used for pipeline defect detection
testing. The results of the tests showed that the hybrid coded excitation method
can detect notches that are difficult to detect with other methods and effectively improve
the SNR. The applied method’s increasing SNR is around 6 dB, which agrees with the
simulation and laboratory testing results. In UGW testing, the proposed coded excitation
method was highly regarded.
Finally, the non-linear frequency modulated (NLFM) hybrid pulse compression method
has been proposed and implemented in an ultrasound imaging (UI) system. The proposed
code combines the Barker and Golay codes and is modulated using a non-linear
frequency method based on the Zak transform. Theoretical research on signal generation
and decoding has been presented, as well as cyst phantom simulation. The simulation
analysis shows that the novel code method can improve the contrast ratio by 15.96 dB
and the SNR by 36.64 dB when compared to a simple pulse signal. Overall, this study
demonstrated that the proposed novel method can be effectively used in ultrasound detection
methods to improve performance
Analysis and Characterization of an Unclassified RFI Affecting Ionospheric Amplitude Scintillation Index over the Mediterranean Area
Radio Frequency (RF) signals transmitted by Global Navigation Satellite Systems (GNSS) are exploited as signals of opportunity in many scientific activities, ranging from sensing waterways and humidity of the terrain to the monitoring of the ionosphere. The latter can be pursued by processing the GNSS signals through dedicated ground-based monitoring equipment, such as the GNSS Ionospheric Scintillation and Total Electron Content Monitoring (GISTM) receivers. Nonetheless, GNSS signals are susceptible to intentional or unintentional RF interferences (RFIs), which may alter the calculation of the scintillation indices, thus compromising the quality of the scientific data and the reliability of the derived space weather monitoring products. Upon the observation of anomalous scintillation indices computed by a GISTM receiver in the Mediterranean area, the study presents the results of the analysis and characterization of a deliberate, unclassified interferer acting on the L1/E1 GNSS signal bands, observed and captured through an experimental, software defined radio setup. The paper also highlights the adverse impacts of the interferer on the amplitude scintillation indices employed in scientific investigations, and presents a methodology to discriminate among regular and corrupted scintillation data. To support further investigations, a dataset of baseband signals samples affected by the RFI is available at IEEE DataPort
Amplitude and phase sonar calibration and the use of target phase for enhanced acoustic target characterisation
This thesis investigates the incorporation of target phase into sonar signal processing, for enhanced information in the context of acoustical oceanography. A sonar system phase calibration method, which includes both the amplitude and phase response is proposed. The technique is an extension of the widespread standard-target sonar calibration method, based on the use of metallic spheres as standard targets. Frequency domain data processing is used, with target phase measured as a phase angle difference between two frequency components. This approach minimizes the impact of range uncertainties in the calibration process. Calibration accuracy is examined by comparison to theoretical full-wave modal solutions. The system complex response is obtained for an operating frequency of 50 to 150 kHz, and sources of ambiguity are examined. The calibrated broadband sonar system is then used to study the complex scattering of objects important for the modelling of marine organism echoes, such as elastic spheres, fluid-filled shells, cylinders and prolate spheroids. Underlying echo formation mechanisms and their interaction are explored. Phase-sensitive sonar systems could be important for the acquisition of increased levels of information, crucial for the development of automated species identification. Studies of sonar system phase calibration and complex scattering from fundamental shapes are necessary in order to incorporate this type of fully-coherent processing into scientific acoustic instruments
Европейский и национальный контексты в научных исследованиях
В настоящем электронном сборнике «Европейский и национальный контексты в научных исследованиях. Технология» представлены работы молодых ученых по геодезии и картографии, химической технологии и машиностроению, информационным технологиям, строительству и радиотехнике. Предназначены для работников образования, науки и производства. Будут полезны студентам, магистрантам и аспирантам университетов.=In this Electronic collected materials “National and European dimension in research. Technology” works in the fields of geodesy, chemical technology, mechanical engineering, information technology, civil engineering, and radio-engineering are presented. It is intended for trainers, researchers and professionals. It can be useful for university graduate and post-graduate students
RF Steganography via LFM Chirp Radar Signals
A novel radio frequency (RF) steganography scheme is proposed to hide digital communication in linear frequency modulation (LFM) radar signals. This joint radar/communication waveform serves two purposes simultaneously: it performs as the original radar waveform, and it provides a covert communication to legitimate receivers. The proposed RF steganography scheme hides digitally modulated communication information inside an LFM radar signal to prevent enemy from detecting the existence of such hidden information via a new modulation and variable symbol duration design
RF Steganography via LFM Chirp Radar Signals
A novel radio frequency (RF) steganography scheme is proposed to hide digital communication in linear frequency modulation (LFM) radar signals. This joint radar/communication waveform serves two purposes simultaneously: it performs as the original radar waveform, and it provides a covert communication to legitimate receivers. The proposed RF steganography scheme hides digitally modulated communication information inside an LFM radar signal to prevent enemy from detecting the existence of such hidden information via a new modulation and variable symbol duration design