Joint time-frequency representation of simulated earthquake accelerograms via the adaptive chirplet transform

Seismic accelerograms are inherently nonstationary signals since both the intensity and frequency content of seismic events evolve in time. The adaptive chirplet transform is a signal processing technique for joint time-frequency representation of nonstationary data. Analysis of a signal via the adaptive chirplet decomposition in conjunction with the Wigner-Ville distribution yields the so-called adaptive spectrogram which constitutes a valid representation of the signal in the time-frequency plane. In this paper the potential of this technique for capturing the temporal evolution of the frequency content of strong ground motions is assessed. In this regard, simulated nonstationary earthquake accelerograms compatible with an exponentially modulated and appropriately filtered Kanai-Tajimi spectrum are processed using the adaptive chirplet transform. These are samples of a random process whose evolutionary power spectrum can be represented by an analytical expression. It is suggested that the average of the ensemble of the adaptive chirplet spectrograms can be construed as an estimate of the underlying evolutionary power spectrum. The obtained numerical results show, indeed, that the estimated evolutionary power spectrum is in a good agreement with the one defined analytically. This fact points out the potential of the adaptive chirplet analysis for as a tool for capturing localized frequency content of arbitrary data- banks of real seismic accelerograms

Chirplet approximation of band-limited, real signals made easy

In this paper we present algorithms for approximating real band-limited signals by multiple Gaussian Chirps. These algorithms do not rely on matching pursuit ideas. They are hierarchial and, at each stage, the number of terms in a given approximation depends only on the number of positive-valued maxima and negative-valued minima of a signed amplitude function characterizing part of the signal. Like the algorithms used in \cite{gre2} and unlike previous methods, our chirplet approximations require neither a complete dictionary of chirps nor complicated multi-dimensional searches to obtain suitable choices of chirp parameters

Wavefield extraction using multi-channel chirplet decomposition

International audienceIn acoustical and seismic fields, wavefield extraction has alwaysbeen a crucial issue to solve inverse problem. Depending on the experimentalconfiguration, conventional methods of wavefield decomposition might nolonger likely to hold. In this paper, an original approach is proposed based ona multichannel decomposition of the signal into a weighted sum of elementaryfunctions known as chirplets. Each chirplet is described by physical parametersand the collection of chirplets makes up a large adaptable dictionary,so that a chirplet corresponds unambiguously to one wave componen

Protection of information networks based on LoRa technology

The paper deals with modern technology for transmitting short messages over long distances named LoRa, where the transmitted signal uses linear frequency modulation (chirp). The object of the study to define lack of transmitters that it has a design on LoRa technology for assessment their applicable in condition urban city where there are a lot of radiation sources. The goal of the work is the creation of a method of assessing the act the interference conditions that based on measurement bit error rate and signal-noise ratio and via on which to get individual host vulnerability levels. The processing of these signals is carried out by means of a time-frequency transformation. The chirp signal is characterized by 4 parameters: frequencies, time, modulation rate and amplitude. By analogy with the wavelet transform, the processing of chirp signals involves a chirplet decomposition. Since the chirp signals are strongly influenced by mutual interference due to multipath, the article studies the effectiveness of LoRa technology in conditions of mutual interference of radiation sources. The developed method utilized chirplet decomposition and retrieve symbols of a message in the dictionary. The conducted experiments have confirmed the proposed software operability and allow recommending it for use in practice for solving the problems receiving signal. The prospects for further research may include the creation of parallel methods for calculation of the set of proposed indicators, the improvement of software, as well as an experimental study of proposed indicators in real conditions.The paper deals with modern technology for transmitting short messages over long distances named LoRa, where the transmitted signal uses linear frequency modulation (chirp). The object of the study to define lack of transmitters that it has a design on LoRa technology for assessment their applicable in condition urban city where there are a lot of radiation sources. The goal of the work is the creation of a method of assessing the act the interference conditions that based on measurement bit error rate and signal-noise ratio and via on which to get individual host vulnerability levels. The processing of these signals is carried out by means of a time-frequency transformation. The chirp signal is characterized by 4 parameters: frequencies, time, modulation rate and amplitude. By analogy with the wavelet transform, the processing of chirp signals involves a chirplet decomposition. Since the chirp signals are strongly influenced by mutual interference due to multipath, the article studies the effectiveness of LoRa technology in conditions of mutual interference of radiation sources. The developed method utilized chirplet decomposition and retrieve symbols of a message in the dictionary. The conducted experiments have confirmed the proposed software operability and allow recommending it for use in practice for solving the problems receiving signal. The prospects for further research may include the creation of parallel methods for calculation of the set of proposed indicators, the improvement of software, as well as an experimental study of proposed indicators in real conditions.National Aviation Universit

Protection of information networks based on LoRa technology

The paper deals with modern technology for transmitting short messages over long distances named LoRa, where the transmitted signal uses linear frequency modulation (chirp). The object of the study to define lack of transmitters that it has a design on LoRa technology for assessment their applicable in condition urban city where there are a lot of radiation sources. The goal of the work is the creation of a method of assessing the act the interference conditions that based on measurement bit error rate and signal-noise ratio and via on which to get individual host vulnerability levels. The processing of these signals is carried out by means of a time-frequency transformation. The chirp signal is characterized by 4 parameters: frequencies, time, modulation rate and amplitude. By analogy with the wavelet transform, the processing of chirp signals involves a chirplet decomposition. Since the chirp signals are strongly influenced by mutual interference due to multipath, the article studies the effectiveness of LoRa technology in conditions of mutual interference of radiation sources. The developed method utilized chirplet decomposition and retrieve symbols of a message in the dictionary. The conducted experiments have confirmed the proposed software operability and allow recommending it for use in practice for solving the problems receiving signal. The prospects for further research may include the creation of parallel methods for calculation of the set of proposed indicators, the improvement of software, as well as an experimental study of proposed indicators in real conditions.The paper deals with modern technology for transmitting short messages over long distances named LoRa, where the transmitted signal uses linear frequency modulation (chirp). The object of the study to define lack of transmitters that it has a design on LoRa technology for assessment their applicable in condition urban city where there are a lot of radiation sources. The goal of the work is the creation of a method of assessing the act the interference conditions that based on measurement bit error rate and signal-noise ratio and via on which to get individual host vulnerability levels. The processing of these signals is carried out by means of a time-frequency transformation. The chirp signal is characterized by 4 parameters: frequencies, time, modulation rate and amplitude. By analogy with the wavelet transform, the processing of chirp signals involves a chirplet decomposition. Since the chirp signals are strongly influenced by mutual interference due to multipath, the article studies the effectiveness of LoRa technology in conditions of mutual interference of radiation sources. The developed method utilized chirplet decomposition and retrieve symbols of a message in the dictionary. The conducted experiments have confirmed the proposed software operability and allow recommending it for use in practice for solving the problems receiving signal. The prospects for further research may include the creation of parallel methods for calculation of the set of proposed indicators, the improvement of software, as well as an experimental study of proposed indicators in real conditions.National Aviation Universit

Frequency Estimation Using Time-Frequency Based Methods

Any periodic signal can be decomposed into a sum of oscillating functions. Traditionally, cosine and sine segments have been used to represent a single period of the periodic signal (Fourier Series). In more general cases, each of these functions can be represented by a set of spectral parameters such as its amplitude, frequency, phase, and the variability of its instantaneous spectral components. The accuracy of these parameters depends on several processing variables such as resolution, noise level, and bias of the algorithm used. This thesis presents some background of existing frequency estimation techniques and proposes a new technique for estimating the instantaneous frequency of signals using short sinusoid-like basis functions. Furthermore, it also shows that the proposed algorithm can be implemented in a popular embedded DSPmicroprocessor for practical use. This algorithm can also be implemented using more complex features on more resourceful processing processors in order to improve estimation accurac

A Lamb wave signal processing method for damage diagnosis in the plate structure

In this work, a damage location method for plate-like structures is developed based on Lamb wave signal processing using matching pursuit method, which is employed to decompose Lamb wave signals into a linear expansion of several chirplet atoms using a fast realization algorithm. The relationship between Lamb wave dispersion and the chirplet chirp rate is established, which can be used to identify the modes of Lamb waves. Then a method for damage location is developed based on the difference between the baseline and the damaged signals. The effectiveness and accuracy of the proposed method in identifying the modes and in locating defects are demonstrated through experimental tests on the isotropic plate structure and honeycomb sandwich composite structure

Guided-wave signal processing using chirplet matching pursuits and mode correlation for structural health monitoring

Signal processing algorithms for guided wave pulse echo-based structural health monitoring (SHM) must be capable of isolating individual reflections from defects in the structure, if any, which could be overlapping and multimodal. In addition, they should be able to estimate the time–frequency centers, the modes and individual energies of the reflections, which would be used to locate and characterize defects. Finally, they should be computationally efficient and amenable to automated processing. This work addresses these issues with a new algorithm employing chirplet matching pursuits followed by a mode correlation check for single point sensors. Its theoretical advantages over conventional time–frequency representations for SHM are elaborated. Results from numerical simulations and experiments in isotropic plate structures are presented, which show the capability of the proposed algorithm. Finally, the issue of in-plane triangulation is discussed and experimental work done to explore this issue is presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58147/2/sms7_2_014.pd