Chirp Signal Research Articles

Chaotic-cavity surface-emitting lasers for optical wireless communication and low-speckle illumination

Though necessary and advantageous in many fields, the high coherence of lasers is detrimental to their performance in certain applications, including illumination, imaging, and projection. This is due to the formation of coherence artifacts, commonly known as speckles, resulting from the interference of randomly scattering spatially coherent photons. It is possible to resolve this issue by increasing the number of mutually incoherent modes emitted from the laser. In vertical-cavity surface-emitting lasers (VCSELs), this can be performed by designing them to have chaotic cavities. This paves the way toward their use in simultaneous illumination and communication scenarios. Herein, we show that chaotic-cavity broad-area VCSELs can achieve significantly broader modulation bandwidths (up to 5 GHz) and higher data rates (up to 12.6 GB/s) compared to other low-coherence light sources, with a lower speckle contrast. We further report a novel technique for lowering the speckle contrast by carefully designing the AC signal used for communication. We show that the apparent spatial coherence is dramatically decreased by inserting a short chirp signal between symbols. Using this method with a chaotic-cavity VCSEL, the number of apparent modes can be up to 450, compared to 88 modes measured from a conventional broad-area VCSEL (a fivefold increase). In light of the recent advances in visible-light VCSELs, this work shows the potential of low-coherence surface-emitting lasers (LCSELs) in simultaneous illumination and optical wireless communication systems since they combine the high speed of lasers with the excellent illumination properties of light-emitting diodes.

Ranging disambiguation of LiDAR using chirped amplitude-modulated phase-shift method.

Ranging ambiguity is the major challenge in most LiDAR techniques with amplitude modulation, which limits the performance of range detection due to the tradeoff between the ranging precision and the unambiguous range. Here we propose a novel disambiguation method using a laser with chirped amplitude modulation (sweeping modulation frequency), which can in theory infinitely expand the unambiguous range and completely solve the ranging ambiguation problem. The usage of the earlier proposed Chirped Amplitude-Modulated Phase-Shift (CAMPS) technique enables us to detect the phase-shift of chirped signals with high precision. Incorporating this technique with the proposed disambiguation method, the absolute distance well beyond the conventional unambiguous range can easily be found with merely <1% frequency sweep range. When certain conditions are met, the Non-Mechanical Spectrally Scanned LiDAR (NMSL) system employing the CAMPS method and the Dispersion-Tuned Swept Laser (DTSL) can also realize disambiguation in non-mechanical line-scanning measurement.

Photonic-Assisted Microwave Frequency Measurement Using High Q-Factor Microdisk with High Accuracy

Frequency measurement plays a crucial role in radar, communication, and various applications. The photonic-assisted frequency measurement method offers several advantages, including resistance to electromagnetic interference, broad bandwidth, and low power consumption. Notably, frequency-to-time mapping enables the measurement of various microwave signal types, such as single-frequency, multiple-frequency, frequency hopping, and chirped signals. However, the accuracy of this method is currently limited due to the absence of resonant devices with high-quality factors, which are essential for achieving higher-precision measurements. In this work, a frequency measurement method based on an ultrahigh-quality-factor microdisk is proposed. By establishing a correlation between the time difference and the frequency to be measured, a reduction in measurement error to below 10 MHz within a frequency measurement range of 3 GHz is realized. Our work introduces a new approach to frequency measurement using optical devices, opening new possibilities in this field.

Impact Assessment of the Chirp Signal Frequency Change Rate on the Energy Secrecy and Noise Immunity

The article deals with the issues of noise immunity and energy secrecy of chirp signals. The purpose of the article is to study the rate of chirp signal frequency change and its influence on signal parameters, such as the envelope and spectrum of the signal, the degree of its energy secrecy and noise immunity. A study was made of the chirp signal frequency change rate influence on the amplitude spectrum of the transmitted signal. The study showed that an increase in the chirp signal frequency change rate leads to an increase in the slope control of the sawtooth voltage. In this case, the width of the amplitude spectrum changes in direct proportion to the change in the frequency band. Based on the results, the assumption was made about the positive effect of increasing the slope of the control signal on noise immunity and energy secrecy. The effect of the chirp signal frequency change rate on the degree of energy secrecy is studied by means of the author's method to estimate the energy of the transmitted symbol. The simulation results showed that the rate of change in the frequency of the chirp signal does not lead to a change in energy and does not affect the degree of energy secrecy. A study was made of the chirp signal frequency change rate influence on the noise immunity of the transmitted signal. It was proposed to investigate a real high-frequency chirp signal using the weighting method on a set of matched filters. The method made it possible to investigate the noise immunity of chirp signals with different parameters and compare the obtained data with the noise immunity of the GMSK signal of the Gonets-M satellite communication system. As a result, some regularities were found that allow us to evaluate the effect of the rate of change in the frequency of the chirp signal on its noise immunity. Comparison of GMSK and chirp signals made it possible to verify the effect of introducing chirp signals into satellite communication systems. As a result of the study, conclusions were drawn about the influence of the choice of chirp signal frequency change rate on noise immunity and energy secrecy.

Adaptive mode decomposition based on the instantaneous frequency basis space

Signal decomposition has attracted increasing interest in various applications in recent years. This paper proposes a new mode decomposition algorithm, called “mode decomposition based on the instantaneous frequency basis space” (IFBMD), to decompose complex chirp signals superposed with multiple-mode signals with a low-frequency instantaneous frequency (IF). In IFBMD, a global optimization algorithm is combined with an alternating iterative computation method to extract the optimal IF of the modes from the low-frequency IF basis space. In addition, to avoid the limitation of a fixed number of modes, an adaptive IFBMD is designed based on a scale-factor iteration approach that can extract modes successively. This new scaling-factor updating method can be widely usable to improve other mode-decomposition algorithms. Compared with other well-known algorithms, IFBMD has been proved to be superior in performance.

Variable-Step Multiscale Fuzzy Dispersion Entropy: A Novel Metric for Signal Analysis.

Fuzzy dispersion entropy (FuzDE) is a newly proposed entropy metric, which combines the superior characteristics of fuzzy entropy (FE) and dispersion entropy (DE) in signal analysis. However, FuzDE only reflects the feature from the original signal, which ignores the hidden information on the time scale. To address this problem, we introduce variable-step multiscale processing in FuzDE and propose variable-step multiscale FuzDE (VSMFuzDE), which realizes the characterization of abundant scale information, and is not limited by the signal length like the traditional multiscale processing. The experimental results for both simulated signals show that VSMFuzDE is more robust, more sensitive to dynamic changes in the chirp signal, and has more separability for noise signals; in addition, the proposed VSMFuzDE displays the best classification performance in both real-world signal experiments compared to the other four entropy metrics, the highest recognition rates of the five gear signals and four ship-radiated noises reached 99.2% and 100%, respectively, which achieves the accurate identification of two different categories of signals.

Improved performance in temperature and speed of TCP artificial muscles for soft wearables robots by length modification

Artificial muscles provide a unique solution for wearable rehabilitation robots (WRRs) because they are compliant, compact, and lightweight. Twisted and coiled polymer actuators (TCPs) are artificial muscles from thermally activated polymer fibres. They present high power density, linearity, stress and strain compared to other artificial muscles. Nevertheless, as TCPs require heat to start, their main barrier for widespread use in WRRs are their slow reaction times and the high temperatures they reach. Previous studies have analysed different parameters, like fibre material, fibre diameter, and various cooling systems, to improve TCP frequency response and working temperature. Nevertheless, the length of the actuator has not been explored as a possible parameter to enhance the actuation performance in this regard. This work focuses on studying the behaviour of TCPs with different lengths and how the performance in frequency response and temperature can be improved using the length as a primary parameter, as they are critical for wearable robots. First, a characterisation of the TCPs was performed. Then, a method to improve frequency response, based on offsets on long actuators was implemented and validated using a chirp signal. The experimental results show that the mechanical characteristics are similar regardless of the actuator’s length. They reached a strain of 10% with a power of 0.16 W cm−1. However, the electrothermal properties changed as the power needed to increase temperature was higher when the actuator was enlarged. Therefore, an improvement in the required temperature was found, able to reduce the temperature with the same frequency response. Regarding the technique to enhance the speed of the actuator, it was possible to increase the frequency by 0.0006 Hz for each mm applied as an offset. Hence, the frequency response for the same displacement was increased linearly as the actuator was elongated.

Cross-correlation vibro-acoustic modulation method for damage detection

The vibroacoustic modulation (VAM) method distinguishes itself from other linear or nonlinear acoustic structure health monitoring methods due to its advantages of high sensitivity, relatively simple implementation, and the capability to detect defects in complex structures. However, the damaged index of VAM—modulation index, which is used for quantifying the damage severity, is highly influenced by the frequency of the probe wave. To increase the reliability and robustness of the VAM method, researchers modified it by replacing the single harmonic probe wave with a chirp signal. The instantaneous frequency of the chirp signal linearly increases with time, allowing the modified VAM method to access the broadband frequency range in a relatively short amount of time. However, the sideband that attributes to the acoustic nonlinearity of the defect would be overwhelmed by the broadband frequency content of the probe wave. Hence, a different algorithm is needed to process the received signal of the modified VAM method. Previous studies have employed short-time Fourier transform, wavelet transform, Hilbert transform, and synchronous demodulation for this purpose. Yet, these signal processing methods do not take into account affection of the phase difference between the probe and pump waves to the final result. To address this issue, this paper proposes using a cross-correlation (CC) approach. The performance of the proposed CC approach and existing methods were compared using simulation and experimental testing, evaluating their ability to detect acoustic nonlinearity.

M-Ary Direct Modulation Chirp Spread Spectrum for Spectrally Efficient Communications

Spread spectrum techniques, such as the Chirp Spread Spectrum (CSS) used by LoRa technology, are important for machine-to-machine communication in the context of the Internet of Things. They offer high processing gain, reliable communication over long ranges, robustness to interference and noise in harsh environments, etc. However, these features are compromised by their poor spectral efficiency, resulting in a very low data transmission rate. This paper deals with a spectrally efficient variant of CSS. The system uses M-ary phase keying to modulate the data and exploits CSS’s properties to transmit the modulated symbols as overlapping chirps. The overlapping of chirp signals may affect the system performance due to inter-symbol interference. Therefore, we analyse the relationship between the number of overlaps and the effect of inter-symbol interference (ISI), and we also determine the BER expression as a function of the number of overlaps. Finally, we derive the optimal number of overlapping symbols that corresponds to the minimum error probability.

The evaluated signal-to-noise ratio for the alternate transmission of different chirp ultrasound to extend the measurable distance in the pulse-echo method

The basic concept of distance measurement using the alternate transmission of two different codes based on the pulse-echo method has been used to obtain an extension of the measurable distance, in which the temporal resolution is not degraded in the one-code transmission. In the alternate transmission, the reflected signals from the object are measured by two correlation signals. The received signal is correlated with each transmitted signal. The truncation and truncated interference noise of signals are generated in the cross-correlation function. Which is a part of the signal components. The signal components are changed according to the transmit signal. In this paper, the signal-to-noise ratio (SNR) of the alternate transmission of the different chirp signals is described and investigated. The highest SNR of the alternate chirp signal is achieved by the high bandwidth and long length of the transmitted signal. Moreover, the different bandwidth of the chirp transmission is simulated. The SNRs of the alternate transmission of different chip signals between the experiment and simulation are compared.

Coding and Coherent Decoding techniques for Continuous Single Slope Cyclic Shift Chirp Signal

Coding and Coherent Decoding techniques for Continuous Single Slope Cyclic Shift Chirp Signal

An adaptive-robust method for simultaneous detection/capture of an object's trajectory in radars with quasi-continuous chirp radiation at an extended speed range

The paper considers the problem of providing long-range observation (detection and capture of the trajectory) of an air object with an extended range of its positive and negative relative velocities, including zero and supersonic, and with interfering reflections from the ground in radars with quasi-continuous radiation at a high pulse repetition rate. The urgency of solving this problem is substantiated, taking into account the increasing requirements for the efficiency, accuracy and noise immunity of observation sessions. A number of factors associated with the expansion of the velocity range are shown, which make it difficult to solve this problem only on the basis of known methods of combined observation of low- and high-speed objects - within the framework of the concept of adaptive-robust observation with unified quasi-continuous radiation with a carrier wave chirp. Multidimensional ambiguity of time-frequency measurements at the time of detection, low information content of the detection stage, lack of speed data against the background of increasing signal delay drift at high speeds, and a number of other destabilizing factors lead to a decrease in the efficiency and accuracy of typical procedures for adaptive-robust trajectory capture. The purpose of the work is to propose a method for long-range observation of an object against the background of interfering reflections from the ground and at an extended range of speeds, including negative ones, which allows: expand the functionality of the radar in the mode of high pulse repetition rate with chirp, providing observation of the object and at a wide sub-range of negative velocities; to increase the accuracy/efficiency of observation sessions, providing an increase in the information content of the stage of primary detection of an object, without additional probing packs and with a minimum of measurement information. In fact, at the detection stage using the proposed method, the range/velocity capture functions are simultaneously implemented, and at an accuracy level that allows one to significantly reduce or exclude from the cyclogram typical adaptive-robust capture procedures traditionally performed after detection. At the same time, under the conditions of a minimum of “real” measurements at the detection stage, as quasi-measurements of the ambiguous delay and rangefinder-Doppler frequency of the chirp signal of the object, information is used about its location in the blind zone of the pulse repetition period (when the receiver is closed for the duration of the pulse radiation) and the blind zone according to frequency (due to the spectrum of interfering reflections from the ground). Simulation mathematical modeling of algorithms for simultaneous detection/capture, synthesized on the basis of the proposed method, has been carried out for a wide range of speeds and ranges of initial detection of an approaching/retreating object. Statistical processing of the simulation results and a comparative analysis with the statistical characteristics obtained by modeling typical sequential procedures for adaptive-robust detection and capture in range and speed are performed. The operability and efficiency of the proposed method were confirmed, and, first of all, in situations with a single ambiguous time-frequency measurement during the initial detection of an object, i.e., with a minimum of measurement information at the detection stage. The results obtained in the work can be used to improve the algorithmic and software of the developed/modernized radars with quasi-continuous chirp radiation, and no additional requirements are put forward for the radar hardware.

РЕАЛИЗАЦИЯ СОГЛАСОВАННОГО ФИЛЬТРА В ЧАСТОТНОЙ ОБЛАСТИ НА ПЛИС

The use of filters matched to radio signals is quite common in radar, which helps to improverange resolution, as well as in communication systems and many other radio engineering systems,allowing you to increase the output signal-to-noise ratio (SNR). Designing digital devices on fieldprogrammable gate array (FPGA) allows us to configure them quite flexibly and create prototypesof radio engineering systems for further implementation of DSP algorithms, on applicationspecificintegrated circuits (ASIC ), GPU, CPU, etc. FPGA digital devices are most used in lowpower mobile systems, while ASICs show the highest performance with high development costs.In this work, special attention is paid to the design and implementation of a filter matched to acomplex chirp signal in the frequency domain on an FPGA using the Xilinx System Generator forDSP library of Matlab/Simulink. The results of the hardware-software model operation are presentedin paper both for a single point object and for three point objects with different sampleddelays. The dependence of the output on the input SNR for a linear and quadratic envelope detectoris shown. The analytical curve SNROUT(SNRIN) is compared with the curve obtained using thedeveloped hardware-software model implemented on the FPGA. The paper shows the benefits ofusing Xilinx System Generator for rapid prototyping of DSPs on FPGAs, and it provides an analysisof the used FPGA resources for the developed matched filter.

Ultrasonic guided waves as an indicator for the state-of-charge of Li-ion batteries

Conventional battery management systems rely on cell voltage, current, and temperature to predict the battery state-of-charge and state-of-health, but their accuracy is limited. To overcome this limitation, ultrasonic probing has been proposed as a novel battery monitoring technique. This paper introduces the use of ultrasonic chirp signals for the transfer of ultrasound-based battery monitoring techniques without requiring prior knowledge of the architecture of the cell. To validate this technique, small, lightweight piezoelectric disc transducers that can be easily installed on off-the-shelf battery pouch cells were utilized for large cells with a capacity of 12.5 Ah. Furthermore, the dominant frequency of the response signal to a Hanning-windowed tone burst signal was identified as a quantitative state-of-charge indicator. A predictive model was developed to compare the performance of this indicator with that of previous ultrasound-based state-of-charge prediction methods. The influence of the cell temperature and cycle age on ultrasonic guided wave propagation was also investigated and isolated for analysis.

Transit time spectrum dependence upon ultrasound input wave types propagating through complex structures

Background: Ultrasound transit time spectroscopy (UTTS) has been introduced previously to characterize the propagation of ultrasound waves through complex structures such as cancellous bone to estimate bone quality and quantity. UTTS describes the propagation of ultrasonic waves through a medium with two components of differing sound speeds (e.g., bone and marrow) as a set of parallel sonic rays. The transit time spectrum (TTS) is derived via the digital deconvolution of the input and output signals. Aim: To investigate the dependence of TTS upon the type of ultrasound input wave, including four different 1 MHz ultrasound waves (pulse, chirp, tone-burst, and continuous). Methods: The presence of ischemic lesions was detected by the MDCT, transesophageal echocardiography (TEE), and non-contrast flat detector computed tomography (FDCT). The study selected the AIS patients with hyperacute stroke for less than 6 hours from July 2021 to August 2022. The CTA of cervical arteries was performed in order to determine stroke subtypes.Ten replica 3D- acrylic step-wedge models with different structure complexity were investigated. For each model and using the four types of input waves, TTS was derived and compared with calculated TTS based on the parallel sonic ray concept. Results: The results showed coefficients of determination (R2) of 0.994, 0.999, 0.90, and 1 for pulse, chirp, tone-burst and continuous signals respectively. Furthermore, solid volume fraction (SVF) was derived via TTS (TTS-SVF) and compared with the geometrically calculated SVF data of the models, yielding coefficients of determination (R2) of 0.941, 0.968, 0.489, and 0.981 for pulse, chirp, tone-burst and continuous waves, respectively. Therefore, the continuous wave provided a more accurate prediction of TTS and SVF, followed by chirp, then pulse waves. Conclusion: This study adds to the body of research supporting the validity and reliability of UTTS, as a potentially promising technique to provide a reliable in vivo estimate of bone mineral density.

A PhC-SOA based cancerous cell detection biosensor

In this paper, we present a novel method to design an ultra-small photonic integrated biosensor to detect cancerous cells. The proposed biosensor is based on the self-phase modulation in PhC-SOA, inducing a frequency shift on a pulse traveling through the device. The amount of the frequency chirp depends on the group velocity of the active medium waveguide being determined by the refractive index of the microfluidic infiltrating the holes around the waveguide. The refractive index of the microfluidic is also determined by the cell type that can be normal or cancerous. Since the refractive index of a cancerous cell is higher than that of a normal one, the group index of the waveguide and the output chirp will decrease. By measuring the amount of the output chirp, we can detect the cell type. The Simulation results showed that for a 0.02 change in the refractive index of the cell, a 3.71 nm central wavelength shift occurred for a 10-ps 7-mW gaussian pulse input with a central wavelength of 1533.53 nm. In terms of the wavelength shift, the sensitivity and figure of merit are 185.5 and 530, respectively. To detect the cell type, we integrated a PhC channel drop filter to drop the chirped signal due to the cancerous cell infiltration. Designing an appropriate PhC-CDF leads to achieving an ultra-small cancerous detection cell biosensor with more than 97% precision.

A computationally efficient algorithm to estimate the parameters of a two-dimensional chirp model with the product term

Chirp signal models and their generalizations have been used to model many natural and man-made phenomena in signal processing and time series literature. In recent times, several methods have been proposed for parameter estimation of these models. However, these methods are either statistically sub-optimal or computationally burdensome, especially for two dimensional chirp models. In this paper, we consider the problem of parameter estimation of two dimensional chirp models and propose a computationally efficient estimator and establish asymptotic theoretical properties of the proposed estimators. Moreover, the proposed estimators are observed to have the same rates of convergence as the least squares estimators. Further, the proposed estimators of chirp rate parameters are shown to be asymptotically optimal. Extensive and detailed numerical simulations are conducted, which support the theoretical results of the proposed estimators.

Pulse compression of guided wave by airborne ultrasound excitation for improving defect detection accuracy in concrete

Scanning airborne ultrasound source technique has been developed as a safe and simple non-contact non-destructive inspection method. This method enables non-contact excitation of guided waves by using high-intensity airborne ultrasound waves. However, the airborne ultrasound source that can generate high intensity airborne ultrasounds uses resonance drive, so the sound waves are emitted for a long time. As a result, the inspection results become complicated, and the inspection accuracy decreases. To solve this problem, we proposed a pulse compression using chirp signals of guided waves generated by airborne ultrasound. In this paper, we investigated the pulse compression of guided waves generated in mortar samples using an airborne ultrasound source driven by a chirp signal. As a result, it was confirmed that the visualization accuracy of defects was improved by pulse compression.

ISAR Imaging of Non-Stationary Moving Target Based on Parameter Estimation and Sparse Decomposition

This paper studies the inverse synthetic aperture radar imaging problem for a non-stationary moving target and proposes a non-search imaging method based on parameter estimation and sparse decomposition. The echoes received by radar can be thought of as consisting of chirp signals with varying chirp rates and center frequencies. Lv’s distribution (LVD) is introduced to accurately estimate these parameters. Considering their inherent sparsity, the signals are reconstructed via sparse representation using a redundant chirp dictionary. An efficient algorithm is developed to tackle the optimization problem for sparse decompositions. Then, by using the reconstructed data, adaptive joint time–frequency imaging techniques are employed to create high-quality images of the non-stationary moving target. Finally, the simulated experiments and measured data processing results confirm the proposed method’s validity.

Microlocal analysis for Gelfand–Shilov spaces

We introduce an anisotropic global wave front set of Gelfand–Shilov ultradistributions with different indices for regularity and decay at infinity. The concept is defined by the lack of super-exponential decay along power type curves in the phase space of the short-time Fourier transform. This wave front set captures the phase space behaviour of oscillations of power monomial type, a k a chirp signals. A microlocal result is proved with respect to pseudodifferential operators with symbol classes that give rise to continuous operators on Gelfand–Shilov spaces. We determine the wave front set of certain series of derivatives of the Dirac delta, and exponential functions.