Chirp Signal Research Articles

Simulation of QPSK-based acoustic telemetry through drillstring

Faster data communication speed is required for better real-time drilling control. The fastest communication method currently in use is acoustic telemetry, with a maximum level of 20 bps. The communication speed is limited because the decay time of the chirp signal is about 1/20 second. In order to overcome the communication limitation due to the chirp signal interval, the QPSK modulation method was applied. This method of transferring data with a phase difference of the carrier frequency is a robust communication method commonly used in digital wireless communication. In this study, the FDTD (finite-difference time-domain) method was applied and the drilling noise taken at drilling sites was added to simulate the actual drilling site environment. According to the study results, the BER (bit error rate) should be less than 0.1 in order to recover data from signals received at the surface. The center frequency of the chirp communication method is about 650 Hz, and at this frequency, the attenuation of the sound wave energy according to the drilling depth is relatively high. To overcome the signal attenuation, it is necessary to install a signal repeater approximately every 1 km. In this study, by lowering the QPSK carrier frequency to 83.5 Hz, it was possible to communicate without a repeater up to a drilling depth of 3 km. In this case, the maximum communication speed possible is 167.5 bps, which is favored for faster and accurate real-time drilling control. In order to enable this communication, measures are required to overcome high level of drilling noise in the low frequency region. A design plan is needed to install acoustic attenuators in the ground receiver and increase the capacity of the signal exciter amplifier and battery in the transmitter section near the drill bit.

Monitoring of corrosion effects in pipes with multi-mode acoustic signals

Current commercial long-range guided wave inspection and monitoring technologies for pipes usually require establishment of certain specific acoustic modes for wave propagation and use a large number of sensors in a certain geometric arrangement (for example, uniformly-spaced arrays of sensors on a collar, placed around a pipe). This paper, in contrast, presents a long-range corrosion detection method in pipes based on multi-mode guided acoustic waves, generated and received using simple, single-element sensors. In this technique, available guided wave modes in any interrogated zone of the structure are automatically down-selected by the medium, and changes in energy distribution over the selected modes are analyzed through signal processing to monitor material loss or addition. To investigate the feasibility of the proposed method, we have performed both experimental and numerical simulation studies on 50.8-mm (2-in)-diameter schedule-40 carbon steel pipes. In these studies, a linear chirp signal is injected in compression mode, perpendicular to the surface of the pipe, generating multi-mode, multi-directional guided waves that travel within the pipe wall. Corrosion effects in the pipes are simulated numerically and experimentally. To reduce errors in the measurement technique due to changes in the local or global temperature of the measured media, a universal temperature compensation algorithm is introduced. The experimental results show good agreement with simulation results, indicating that the proposed multi-mode wave generation and detection in a pipe could be used for long-range detection and monitoring of corrosion effects, such as pipe wall losses or solid material deposits.

A waveform design method for frequency diverse array systems based on diversity linear chirp waveforms

AbstractA frequency diverse array (FDA) radar has attracted wide attention, due to its capability to provide a range-angle dependent beampattern and to scan the spatial without phase shifters or rotating arrays. However, FDA systems will suffer from low echo signal energy or high sidelobe peaks when detecting targets by beamforming based on existing receivers. To reduce the sidelobe peak of detection results while increasing the echo signal energy, in this paper, we propose an FDA radar system based on diversity linear frequency modulation waveforms. Correspondingly, we propose a receiver architecture with a time-variant beamforming chain. The proposed system retains the ability of the FDA system to automatically spatial beam scanning, owing to the frequency increment across elements. By increasing the pulse duration of transmitted signals, we enhance the echo signal energy. By applying the artificial bee colony algorithm to design the bandwidth of each chirp signal, the proposed system reduces the sidelobe level of detection results while increasing pulse width. Numerical simulation results are presented to demonstrate the effectiveness of the proposed system.

High-Resolution ISAR Imaging Under Low SNR With Sparse Stepped-Frequency Chirp Signals

To obtain high-resolution imaging while reducing the radar operating bandwidth under a low signal-to-noise ratio (SNR), this article proposes a genetic method for accurate residual radial motion estimation and well-focused imaging of the sparse stepped-frequency chirp signal (SSFCS). First, the signal model is constructed by incorporating the residual radial motion parameters into the dictionary. Then, high-quality high-resolution range profiles (HRRPs) are synthesized by Beta process regression (BPR), which has enhanced flexibility in data description and superior performance in parameter estimation. In addition, the genetic method updates the population, i.e., the candidates for the residual radial motion parameters, iteratively according to the image entropy to meet the required precision for well-focused imaging. Experimental results of Monte Carlo simulations and imaging results of simulated and measured data have demonstrated that the proposed method achieves more accurate estimation in residual radial motion parameters and better-focused imaging than the available methods.

CHIRP FILTER JAMMING IMMUNITY RESEARCH

The pulse compression technique uses a matched filter to extract an echo signal in the radars receiver. A model of a matched filter for a chirp signal was synthesized using the Simulink Tool of the MATLAB software. Pulse jamming and chirp jamming signals were feed to the input of the matched filter. The output signals were measured. The matched filters degree of suppression of these jamming signals was assessed. Conclusions were made about the jamming immunity of a radar operating with a Chirp matched filter.

Multiple Target Localization Using Wideband Echo Chirp Signals

This work proposes a unique technique for wideband chirp signals-based detection and estimate of the range, velocity, and direction of arrival (DOA) of numerous far-field objects. A wide region is covered by the wideband signal that is created. The targets reflect them, and an echo signal is created. The range, radial velocity, as well as DOA of the echo signal are extracted to identify the objects. Using the LCT, the range, radial velocity, and DOA are determined. The main goals of the system under consideration are to transmit a wide band signal over an area, to detect targets nearby, to obtain an echo signal from a target that has been reflected, and to extract features from the echo signal, such as range, radial velocity, and DOA, in order to achieve superior performance metrics than previous ones.

A pde-Based Analysis of the Spectrogram Image for Instantaneous Frequency Estimation

Instantaneous frequency (IF) is a fundamental feature in multicomponent signals analysis and its estimation is required in many practical applications. This goal can be successfully reached for well separated components, while it still is an open problem in case of interfering modes. Most of the methods addressing this issue are parametric, that is, they apply to a specific IF class. Alternative approaches consist of non-parametric time filtering-based procedures, which do not show robustness to destructive interference—the most critical scenario in crossing modes. In this paper, a method for IF curves estimation is proposed. The case of amplitude and frequency modulated two-component signals is addressed by introducing a spectrogram time-frequency evolution law, whose coefficients depend on signal IFs time derivatives, that is, the chirp rates. The problem is then turned into the resolution of a two-dimensional linear system which provides signal chirp rates; IF curves are then obtained by a simple integration. The method is non-parametric and it results quite robust to destructive interference. An estimate of the estimation error, as well as a numerical study concerning method sensitivity and robustness to noise are also provided in the paper.

Advanced Chirp Transform Spectrometer with Novel Digital Pulse Compression Method for Spectrum Detection

Based on chirp transform and pulse compression technology, chirp transform spectrometers (CTSs) can be used to perform high-resolution and real-time spectrum measurements. Nowadays, they are widely applied for weather and astronomical observations. The surface acoustic wave (SAW) filter is a key device for pulse compression. The system performance is significantly affected by the dispersion characteristics match and the large insertion loss of the SAW filters. In this paper, a linear phase sampling and accumulating (LPSA) algorithm was developed to replace the matched filter for fast pulse compression. By selecting and accumulating the sampling points satisfying a specific periodic phase distribution, the intermediate frequency (IF) chirp signal carrying the information of the input signal could be detected and compressed. Spectrum measurements across the entire operational bandwidth could be performed by shifting the fixed sampling points in the time domain. A two-stage frequency resolution subdivision method was also developed for the fast pulse compression of the sparse spectrum, which was shown to significantly improve the calculation speed. The simulation and experiment results demonstrate that the LPSA method can realize fast pulse compression with adequate high amplitude accuracy and frequency resolution. Compared to existing digital pulse compression technology, this method can significantly reduce the number of required calculations, especially for measurements of sparse signals.

Boosting Chirp Signal Based Aerial Acoustic Communication Under Dynamic Channel Conditions

Aerial acoustic communication attracts substantial attention for its simplicity and cost-effectiveness. Unfortunately, the preferred inaudible transmission has to strike a balance between the transmission rate and communication range, when the Bit-Error-Rate (BER) is under a certain threshold. Additionally, the performance of previous proposals can be deteriorated by dynamic channel conditions including near-far problem, device heterogeneity, and multipath fading. To this end, we propose a High-speed, long-range, and Robust Chirp Spread Spectrum (HRCSS) scheme for inaudible aerial acoustic communication under dynamic channels. HRCSS innovates in the definition of a loose orthogonality condition, and it leverages this orthogonality to overlap multiple chirp carriers in a single time duration to form a data symbol representing multiple bits, thereby substantially promoting the data rate. To further enhance system robustness in long communication ranges and dynamic channel conditions, we construct a lightweight rate adaptation algorithm and design a simple yet efficient normalization method. Experiment results reveal that HRCSS achieves a significant improvement in data rate over existing methods: it delivers 500 bps data rate with a BER of 0.24 percent at 10 m, and achieves 125 bps with zero BER at 20 m. Meanwhile, HRCSS can work adaptively under dynamic channel conditions while still retaining a BER below 3 percent.

Optimizing Thermoacoustic Characterization Experiments for Identifiability Improves Both Parameter Estimation Accuracy and Closed-Loop Controller Robustness Guarantees

ABSTRACT This article examines the degree to which optimizing a Rijke tube experiment can improve the accuracy of thermoacoustic model parameter estimation, thereby facilitating robust stability control. We use a one-dimensional thermoacoustic model to describe the combustion dynamics in a Rijke tube. This model contains two unknown parameters that relate velocity perturbations to heat release rate oscillations, namely, a time delay and amplification factor . The parameters are estimated from experiments where the system input is the acoustic excitation from a loudspeaker and the output is the pressure response captured by a microphone. Our work is grounded in the insight that optimizing an experiment’s design for higher Fisher identifiability leads to more accurate parameter estimates. The novel goal of this paper is to apply this insight in the laboratory using a flame-driven Rijke tube setup. For comparison purposes, we conduct a benchmark experiment with a broadband chirp signal as the excitation input. Next, we excite the Rijke tube at two frequencies optimized for Fisher identifiability. Repeats of both experiments show that the optimal experiment achieves parameter estimates with uncertainties at least one order of magnitude smaller than the benchmark. With smaller parameter estimate uncertainties, an LQG controller designed to attenuate combustion instabilities is able to achieve stronger robustness guarantees, quantified in terms of closed-loop structured singular values that account for parameter estimation uncertainty.

A Local Search Maximum Likelihood Parameter Estimator of Chirp Signal

A local search Maximum Likelihood (ML) parameter estimator for mono-component chirp signal in low Signal-to-Noise Ratio (SNR) conditions is proposed in this paper. The approach combines a deep learning denoising method with a two-step parameter estimator. The denoiser utilizes residual learning assisted Denoising Convolutional Neural Network (DnCNN) to recover the structured signal component, which is used to denoise the original observations. Following the denoising step, we employ a coarse parameter estimator, which is based on the Time-Frequency (TF) distribution, to the denoised signal for approximate estimation of parameters. Then around the coarse results, we do a local search by using the ML technique to achieve fine estimation. Numerical results show that the proposed approach outperforms several methods in terms of parameter estimation accuracy and efficiency.

Developing the concept of autonomous control of the quarry vehicles movement

Introduction. The article presents the results of studies related to the description of the synthesis and further analysis of the dynamic behavior of unmanned vehicles (UMVs) operating at coal opencast mines and other mining enterprises. The relevance of the research topic is dictated by the need to create safe and effective conditions for overburden / mining and mining transportation operations. This is ensured, among other things, by the operation of unmanned heavy-duty dump trucks. Purpose of the work: in the course of the research, a concept was developed for the formation of route parameters and models of the dynamics of movement of UMVs along technological routes. Methodology. The paper describes the technology for generating and processing signals in control subsystems as part of an automated dispatching system and an on-board subsystem for autonomous control of the UMV. Research methods include the study of the shapes and characteristics of current trajectories (CT) in relation to a nominal axial trajectory (NAT). In this case, a current trajectory of the UMV is considered within the framework of the so-called S-frames, which are formed as geolocations on a certain working UMV route from a bench face to the place of unloading and vice versa. As a variable characterizing the UMV behavior on a current trajectory, a 1D-signal with a time dependent frequency is adopted, the nature of the change of which is determined by the CT dynamic shape relative to the NAT. Results. Such chirp signals – together with the wavelet transforms technique introduced into consideration – allow us in a semantically transparent and information-rich videographic form to display and subject to further processing signals characterizing the current behavior of a UMV on a route. The resulting parameters of such secondary wavelet representations of the current UMV dynamics (wavelet maps) are further planned to be used in the subsystem of dynamic modal control of the UMV movement in the open pit. Conclusions. The results of the studies carried out make it possible to form current routes of UMV movement according to the models generated based on the analytical tools accompanying the dynamics of the UMVs, proposed in the work.

Statistically efficient simultaneous amplitude measurement of multiple linear chirp signals

In this article, the amplitude measurement of multiple and simultaneously received linear chirp signals is investigated. The achievable scalability, that is, the maximum number of simultaneously transmitted superimposed signals that a receiver can characterize with a given target accuracy, is explored using simulations. The effect of chirp duration and bandwidth on the estimation accuracy and on the scalability is investigated. The effect of inaccuracies affecting the realized chirp duration and bandwidth is also discussed. It is shown that the scalability of the proposed approach is competitive with respect to multiple access methods, such as frequency-division multiple access or code-division multiple access. It is also shown that accurate amplitude measurements are achievable even when the collected signal is the superimposition of up to 20 chirp signals with amplitudes differing by three orders of magnitude.

A Low-Complexity Time-Domain Method for a Fast and Accurate Measurement of Q-Factor and Resonant Frequency of RF and Microwave Resonators

A new time-domain technique for an accurate and fast measurement of the resonant frequency and Q-factor of resonators is presented. In this technique, the phase slope with respect to frequency of a resonator is characterized and used to specify its Q-factor and resonant frequency. To measure the phase slope, a slow-rate linear chirp signal is generated and passed through the resonator under test. The output signal is amplified and subsequently divided into two equal parts which are delayed by different amounts. Due to the linear time-frequency relationship of the chirp signal, the instantaneous frequencies of the two delayed signals are slightly different at any given time, and their phase difference can determine the resonator's phase slope. Detailed analysis of the proposed approach is presented and its accuracy is verified through simulations and measurements. Based on the measured results, the proposed approach characterizes the resonant frequency and Q-factor by less than 0.6% and 4% error, respectively.

Photonics-Assisted Multi-Band Dual Linear/Nonlinear Chirp Waveform Generation Based on Optical Phase Modulation

A novel photonic scheme for generating multi-band dual-chirp waveforms with linear or nonlinear chirp rates is proposed via two cascaded polarization modulators (PolMs) paralleled with a phase modulator (PM). The cascaded PolMs produce a flat optical frequency comb (OFC) as a multi-frequency reference light, while the PM is driven by the power-function-type baseband signals to obtain the lightwave with different order phase chirp. The phase-chirped lightwave and the multi-frequency reference lightwave are orthogonally coupled by a polarization beam combiner (PBC) and then recombined via a polarization beam splitter (PBS) to make them in-phase in one output port of the PBS and anti-phase in the other. The two recombined lightwaves are detected by a balanced photodetector (BPD), and the different order dual-chirp signals, covering six bands, can be generated in their differential photocurrent without interference components. Compared with the single-chirp signal of the knife-edge-type ambiguity function, the dual-chirp signal with the peak-saliency-type ambiguity function significantly suppresses sidelobe and shows better range-Doppler resolution performance. With the 1GHz-bandwidth and 102.4ns-duration quadratic baseband driving signal, six-band linear dual-chirp signal, centered at 10, 30, 50, 70, 90 and 110GHz, are generated by simulation, and each linear dual-chirp signal has a bandwidth of 4.1GHz, the pulse compression ratio of 465.45 and the peak-to-sidelobe ratio (PSLR) of 12.8dB. As baseband driving signal has higher (3rd) order power, the six-band nonlinear dual-chirp signals with the same central frequencies can also be generated but with increased bandwidth (6.3GHz) and the improved PSLR (15.51dB). Their autocorrelation functions show that compared with the linear chirp signal, the nonlinear chirp signal has better sidelobe suppression capability, which is improve as the degree of nonlinearity increase.

The Influence of ISI and an Improved Algorithm of Channel Estimation in the Chirp System

Chirp signal is widely used in communication, radar, sonar and ultrasonic systems. The impulse response of channel must be estimated in PSK chirp spread spectrum modulation systems which is a chirp signal multiplied by the PSK modulated signal. Due to the influence of filters and multipath channel, the received signal of current symbol will be affected by the interference of the previous symbol and the next symbol, the interference which is called inter-symbol interference (ISI) can degrade the performance of channel estimation and demodulation. In this paper, based on BPSK chirp spread spectrum modulation system, we describe the received model, the channel estimation based on FFT and channel estimation of matched filtering, analyze the impacts of ISI on channel estimation. And we simulate the MSE of channel estimation and the simulation results are consistent with the analysis, then an improved method of channel estimation is proposed based on the analysis of the impact of ISI on channel estimation.

The wavelet transforms technique in the computer-aided system for controlling the quarry unmanned vehicles

Introduction. Purpose of the work. Within the framework of the computer-aided system, a technology has been formed for the method of controlling the current trajectories (CTs) of unmanned vehicles (UMVs) when they move along routes in a quarry in open pit mining. The purpose of the presented studies is to analyze the application of a wavelet transforms technique to the problem of routing unmanned vehicles when they move along routes within open pit roads. Methodology. The results of modeling certainone-dimensional signalscorresponding to the UMV current trajectories when they deviate to the left / right from a nominal axial trajectory (NAT), as well astheir time-frequency representationsin a wavelet medium are presented. An algorithm of the procedure for displaying scalar UMV CT control signals in a complex medium of time-frequency wavelet transforms has been developed and described. Such a transformation allows for a functionally transparent and information-capacious monitoring of the UMV movement and efficiently manage the processes of trajectory routing dump trucks in an open pit. Research results, analysis. The processes of modifying the UMV movement current trajectories under the control of the computer-aided system are generated using wavelet transforms methods. They are based on algorithms for projecting the trajectory signals with a time-dependent frequency (chirp signals) onto a set of wavelet functions as part of a wavelet thesaurus (wavelet dictionary), executing certain wavelet matching pursuit procedures, and displaying the CT scalar signals in a specific multidimensional medium of Cohen’s class time-frequency distributions. The simulation results in the form of the current trajectory (CT-) signals waveforms and their three-dimensional time-frequency representations as Wigner maps showing the UMV movement in a start-stop mode, as well as the signals of formed continuous deviation trajectories when they leave to the left and to the right from the NAT, are presented. An algorithm for the formation of 3D-representations of UMV current trajectory one-dimensional signals is presented. Conclusion. The conclusion is made that the mathematical technique of wavelet transforms is the most expedient and effective means for computer-aided monitoring and controlling the dynamics of UMV movement along routes within open pit roads.

Dispersion distortions of wide spectrum signals during their propagation in the Earth ionosphere

The current trend in the development of radio engineering systems (RES) is to use wide spectrum signals, the application of which provides an increase in the resolution and secrecy of the radar operation, an increase in the speed and volume of transmitted information for communication and telemetry systems. The class of such signals includes ultrashort pulses (USP signals), radio pulses with linear frequency modulation (chirp signals). Also of interest are ultra-wideband (UWB) noise signals (UWBN signals), which have high electromagnetic compatibility, stealth and noise immunity. When designing promising ground-based and space-based RES using wide spectrum signals, an important task is to determine the distortions of their envelope shape and distortions of spectrum, as well as the change in the polarization of the emitted wave when passing through the Earth's ionosphere, since taking these distortions into account will provide conditions for optimal reception. This article presents the numerical assessment results of the expected distortions of the wide spectrum signals main types of the decimeter wavelength range, for middle latitudes at heights from 100 km to 1000 km. The conversion of the emitted pulse into a frequency modulated radio pulse is typical for the USP signal. For a chirp radio pulse with a monotonically increasing frequency, an initial decrease in duration with an increase in amplitude and subsequent stretching in time with further spread is typical (the amplitude change is estimated due to a change in the signal shape without taking into account spread). For a chirp radio pulse with a monotonically falling frequency and a UWBN signal, dispersion distortions manifest themselves as an increase in their duration with a decrease in amplitude. For all signal types under consideration that have passed through the ionosphere, a leading edge lag is observed, the dependences of frequency on time at an altitude of 1000 km are repeated and are close to hyperbolic character, the energy spectra envelope shape of the considered signals is almost not distorted. The polarization plane rotation for signals with a spectrum concentrated in the frequency range above 0.7 GHz does not exceed 45

Multiscale Entropy Analysis of Instantaneous Frequency Variation to Overcome the Cross-Over Artifact in Rhythmic EEG

Generally, for healthy adults, the entropy of electroencephalogram (EEG) signals gradually decreases from wake to sleep stages N1, N2, to N3, and increases during REM. However, some researchers found that multiscale entropy curves of sleep and wakefulness intercept, a cross-over phenomenon whose origin remains unexplored. The objective of the present work is to trace the origin of the cross-over phenomenon and to propose a workaround strategy. We simulated EEG by generating 1/f broadband signal and chirp signals with continuously varying frequencies. We then retrieved the rhythmic component from simulated EEG and real-world EEG and conducted MSE analysis of the instantaneous frequency variation (IFV) of the rhythmic component. The simulation revealed that this interception was ubiquitous in the MSE analysis of simulated EEG with rhythmic components of different frequencies. The cross-over point moved toward larger scale factors with the increasing sampling rate. We found that the MSE curve of IFV from real-world EEG for the wakefulness group was higher than that for sleep, showing no interception. These results suggest that (1) for a rhythmic signal like EEG, MSE analysis of the raw signal is highly affected by the rhythmic component, presenting artificial cross-over curves in sleep EEG study, (2) frequency variation of rhythmic components are complex signal which differs between wakefulness and sleep, in accordance with the complexity loss theory.

Spatially Smoothed TF-Root-MUSIC for DOA Estimation of Coherent and Non-Stationary Sources Under Noisy Conditions

This paper proposes a method for efficient Direction-of-Arrival (DOA) estimation of coherent and non-stationary sources under adverse noise conditions. The method consists of three main parts: 1) derivation of Spatial Time-Frequency Distribution (STFD) matrix; 2) application of the forward-backward spatial smoothing technique; 3) estimating the angles of arrival by solving for the roots of the polynomial. The key significance of the proposed method is that the combination of existing methods and techniques allows an estimation of DOA angles for both coherent and non-stationary source signals under noise. Whereas the individual use of the existing methods does not show adequate performance under these conditions. The experiments allow studying the performance of the proposed method for 1) both coherent and non-coherent clean sinusoidal signals; 2) noisy non-stationary chirp signals; 3) coherent and non-stationary signals under noise. Furthermore, extensive simulations have been carried out to compute the root mean square error (RMSE) performance of the proposed method in comparison with the existing ones. The experiments have been designed for varying number of microphones, level of noise, and value of the time-frequency threshold. As a result of the experiments, we observe the efficacy of the proposed method in comparison with the conventional Root-MUSIC and Time-Frequency MUSIC (TF-MUSIC) methods.