Frequency Modulation Signal Research Articles

MVL-Tra: Multi-view LFM signal source classification using Transformer

Classifying the sources of linear frequency modulation (LFM) signals has practical significance, as these signals are widely applied in various scenarios. However, the signals emitted by the same configured sources exhibit insignificant differences and may suffer severe degradation in low signal-to-noise ratio (SNR) conditions. Previous research failed to achieve satisfactory classification results in these two conditions. To address such challenges, we propose a signal source classification method for LFM signals using multi-view representations, based on the Transformer network, named MVL-Tra. Multi-view learning improves robustness by utilizing multiple feature sets and multi-dimensional analysis on these features. Transformer, a emerging deep neural network, enhances the distinctiveness of features between signals through capturing long-range dependencies when dealing with large-scale time-series data. In the experiment, we conducted classification on a dataset comprising 15 sets of low-SNR LFM signals. Notably, Even under the challenging condition of SNR = −5, our method achieved an accuracy of 93.78%. Th results confirm the effectiveness of using multi-view representations and Transformer for LFM signal source classification.

USING ESP32 MICROCONTROLLER FOR PHYSICAL SIMULATION OF THE WIRELESS REMOTE CONTROL MODEM

Context. Due to the need for practical implementation of the theoretical provisions of the proposed method of the wireless transmission of the commands for controlling a moving object in conditions of intentional interference.
 Objective of the work is a practical verification of the possibility of using a phase-pulse modulation of the linear-frequencymodulated signal for transmission a control commands through physical modeling using microcontrollers.
 Method. Analytical calculations of the change in time of the voltage at the input and output of the device for optimal processing of the linear frequency-modulated signal were carried out exclusively using the computing capabilities of the microcontroller. The graphs of changes in time of the relevant parameters were built with the help of Excel using the data output to the monitor of the serial port of the Arduino IDE software environment. A digital oscilloscope with a USB host was used to monitor the operation of a wireless modem to transmit control commands to a moving object.
 Results. Analytical calculations and physical modeling using a modern microcontroller proved the operability of the lowfrequency part the wireless remote control modem with using phase-pulse modulation of the linear frequency-modulated signal.
 Conclusions. The possibility of using phase-pulse modulation of the linear-frequency modulated signal for the transmission of control commands is considered. This method of transmitting the information component, unlike the existing methods, does not require changing the parameters of the linear frequency modulated signal. The use in the receiver of optimal processing of a linearfrequency-modulated signal of sufficiently big base will allow of the wireless transmission of the commands for controlling a moving object in conditions of the intentional interference. The use of modern microcontrollers made it possible to conduct a practical test of the functionality of the low-frequency part the wireless remote control modem with phase-pulse modulation of the linear-frequency modulated signal through physical modeling.

Dual-loop fourier domain mode-locked optoelectronic oscillator based on three-section mutual-injection integrated semiconductor laser

A directly-modulated Fourier domain mode-locked optoelectronic oscillator (FDML_OEO) based on three-section mutual-injection integrated semiconductor laser (TS_MIISL) with dual-loop feedback structure is proposed and experimentally demonstrated in this paper. By driving the TS_MIISL to work under the period-one (P1) state and modulating the TS_MIISL with low-repetition-rate sawtooth drive signal, a linear frequency-modulated (LFM) signal can be generated. Through adjusting the delay time of the feedback loops to match with the time duration of drive signal, the LFM signal can be significantly optimized in terms of spectral purity. In such a proposed FDML_OEO, no external modulator, polarization controller (PC) and filter are utilized, leading to an outstanding advantage in terms of stable performance and compact structure. The high-purity LFM signal with center frequency and bandwidth of 14 GHz and 8 GHz is obtained. The maximum time-bandwidth product (TBWP) of generated LFM signal could reach up to 48800. Due to the introduction of dual feedback loop, the frequency comb contrast and linewidth could reach up to 45 dB and 5 kHz, respectively. The center frequency and bandwidth of the generated signals are both tunable. A demonstration is made to prove that the pre-compensation processing could improve the linearity of LFM signals.

Broadband linear frequency modulation signal compression based on a spectral Talbot effect.

Broadband linear frequency modulation (LFM) signals with a long duration are widely used in radar and broadband communication systems. The LFM signals are compressed to a Fourier-transform-limited pulse train after matched filtering, which effectively improves the signal-to-noise ratio (SNR) of detection. Quadratic phase response is the key component of matched filtering, which can be achieved by phase filters or dispersion elements. Suffering from the limited resolution of phase filters and complex equivalent large dispersion structures, pulse compression of broadband LFM signals with a long duration remains an open challenge. In this paper, LFM signal compression based on the spectral Talbot effect is proposed and experimentally demonstrated, where ultra-large equivalent dispersion (around 1.7 × 109 ps/nm) is realized by a simple optical filter ring. Experimentally, the LFM signal with a bandwidth of 12 GHz and a duration of 163 µs is compressed into a Fourier-transform-limited pulse train, which improves the SNR by 24 dB. Moreover, the proposed method also measures the delay difference between two LFM signals, ranging from 0 to 110 ns.

Photonics-assisted joint radar detection and frequency measurement system

A photonics-assisted joint radar detection and microwave frequency measurement system is proposed. A broadband dual-chirp linear frequency-modulated (LFM) signal is generated based on an optically injected semiconductor laser, which is later shared by two functional modules. Thanks to the photonics-assisted broadband signal generation method, both radar detection with high resolution and microwave frequency measurement with high accuracy can be realized without using high-speed electronic devices. In the experiment, a two-dimensional resolution of 1.25 cm × 1.33 cm and a measurement error within ±50 MHz are achieved in radar detection and frequency measurement, respectively.

Gate Controlled Photocurrent Generation Mechanism in Air-Grown Organic Single Crystals for High-Speed Multiband Imaging.

Organic semiconductors herald new opportunities for fabricating high-performance flexible and wearable optoelectronic devices owing to their intrinsic mechanical flexibility, excellent optical absorption, and cool-free operation. The photocurrent generation mechanisms are of multiple physical origins, including photoconductive, photovoltaic, and photogating effects, and the influence of individual effects on the device figures-of-merit is still not well understood. Here we fabricated a high-performance pentacene single-crystal transistor employing graphene electrodes and demonstrated the modulation from the photogating mechanism to the photoconduction effect by controlling gate bias. Control experiments indicate that the calculation based on transfer curves tends to overestimate the responsivity due to nearby trap states. Using a high frequency-modulated light signal to suppress the trapping process, we successfully measured its intrinsic -3 dB bandwidth of 75 kHz. Finally, high-resolution and UV-NIR high-speed imaging capability was demonstrated. Our work provides new guidelines for understanding the photophysical process and intrinsic performances of organic devices and also confirms the potential of organic single crystals in high-speed imaging applications.

Generation of Phase-Coded LFM Signals Based on Fourier Domain Mode-Locked Optoelectronic Oscillator

Phase-coded linearly frequency modulated (LFM) signals play essential roles in enhancing the performance of radar as well as exploring wireless communication. To generate phase-coded LFM signals, we propose to launch a phase-coded signal into an optoelectronic oscillator (OEO). When the OEO is Fourier domain mode-locked (FDML), a phase-coded LFM signal is generated. The center frequency, bandwidth, coding pattern, and bit rate of the generated signals can be flexibly adjusted. In the experiment, a phase-coded LFM microwave signal with a bandwidth of 5.0 GHz is generated, corresponding to a time bandwidth product (TBWP) of 2.8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> . The center frequency and bandwidth of the generated signals are adjusted from 9.7 to 10.7 GHz and from 5.0 to 3.0 GHz, respectively. Meanwhile, different coding patterns and rates are also implemented, indicating that the phase-coded LFM signal can be used in wireless communications. The proposed approach can potentially be applied to multifunctional integration in radar.

Sonar echo detection based on two-dimensional matched filtering and convolutional neural network

In underwater acoustics, the performance of sonar echo detection is limited when the echo-to-noise ratio or echo-to-reverberation ratio is low. As an attempt to improve the echo detection rate and maintain a low false alarm rate, a method based on two-dimensional matched filtering (2-D-MF) and convolutional neural network (CNN) is proposed. The 2-D-MF divides the replica signal into multiple sub-replicas, each with different frequency components, and utilizes the sub-replicas to perform the matched filtering individually, obtaining 2-D-MF features that better represent the amplitude-frequency characteristics of the echo signal. The CNN is utilized as an echo detector to extract echo information from the 2-D-MF features and determine the presence of an echo. The proposed method is tested using data collected in the South China Sea, 2021. During the experiment, a transducer transmitted linear frequency modulation (LFM) signals, and a transponder, acting as an analog target, forwarded the LFM signals as echoes. The detection results demonstrate that this method can improve the echo detection rate by approximately 7% while maintaining a constant false alarm rate of 1‰.

Photonics-enabled joint communication-radar system with improved detection performance and looser symbol length limitation based on resampling and phase compensation

A photonics-enabled joint communication-radar (JCR) system by employing a multiple phase-shift keying (MPSK)-sliced linearly frequency-modulated (LFM) signal for simultaneous range measurement, microwave imaging, and data transmission is proposed and experimentally demonstrated with improved detection performance and looser symbol length limitation. A two-stage modulation in conjunction with optical filtering is utilized at the radar transmitter for the generation of the frequency-and-bandwidth-multiplied MPSK-sliced LFM signal while resampling and phase compensation operations are introduced at the radar receiving end to break the detection performance limitation induced by the communication symbol length when MPSK-sliced LFM signal is used. We demonstrate the concept experimentally. BPSK-sliced and QPSK-sliced LFM signals centered at 12 GHz are generated for JCR systems. When the time difference between the radar echo and the de-chirping reference is close to or greater than one symbol length, range measurement and microwave imaging that are hard to be fulfilled due to the random phase jumps of the de-chirped signal can be successfully realized via resampling and phase compensation. Experiments show that the proposed resampling and phase compensation method is valid for improving radar detection performance and loosening the communication symbol length limitation. Data communication with a data rate of up to 400 Mbps and ISAR imaging with a radar signal bandwidth of 1 GHz are successfully realized.

Representation of frequency-modulated sweeps in the cochlear nucleus of the big brown bat.

The cochlear nucleus (CN) receives ipsilateral input from the auditory nerve and projects to other auditory brainstem nuclei. Little is known about CN processing of signals used for echolocation. This study recorded multiple unit activity in the CN of anesthetized big brown bats (Eptesicus fuscus) to ultrasonic frequency-modulated (FM) sweeps differing in sweep direction. FM up-sweeps evoke larger peak amplitudes at shorter onset latencies and with smaller amplitude-latency trading ratios than FM down-sweeps. Variability of onset latencies is in the tens of microsecond ranges, indicating sharp temporal precision in the CN for coding of FM signals.

Estimation of LFM signal parameters using RD compressed sampling and the DFRFT dictionary

In this paper, a method combining random demodulator (RD) and discrete fractional Fourier transform (DFRFT) dictionary is suggested to directly estimate the parameters of linear frequency modulation (LFM) signals from compressed sampling data. First, the RD system parameters are modified in accordance with the characteristics of the LFM signal to produce effective compressed sampling data. Next, a DFRFT dictionary is built using the fractional Fourier transform theory, and sparse representation coefficients are obtained by reconstructing the compressed sampling data using the recovery algorithm and DFRFT dictionary. The signal exhibits characteristics that make it pulse under the best fractional transform order, so the problem of signal parameter estimation can be reduced to searching for the location of the maximum value of sparse representation coefficients. The location is determined by a parameter optimization algorithm, and from there, the initial frequency and Chirp rate of the LFM signal can be estimated. Lastly, simulation and real data tests are performed to confirm that the suggested method can directly be utilized to estimate the parameter of LFM signals using compressed sampling data in addition to having high sparse representation ability for LFM signals.

An adaptive VNCMD and its application for fault diagnosis of industrial sewing machines

Due to the non-linearity and non-stationarity of sound signals from complex transmission structure and frequent start-stop of industrial equipment, such as sewing machine, its incipient faults cannot be accurately identified with classical fault diagnosis methods. Therefore, a new fault diagnosis method with an adaptive variational nonlinear chirp mode decomposition (AVNCMD) is proposed. Firstly, a pre-processing step of convex optimization with generalized minimax-concave penalty function and spline-kernelled chirplet transform is applied to obtain the time–frequency distribution (TFD) with energy concentration, and a peak frequency extension method is proposed to adaptively search initial instantaneous frequencies of AVNCMD on the TFD; then the Pearson correlation coefficient is introduced as the termination condition of the adaptive signal decomposition. Secondly, multi-domain features are extracted from the decomposed nonlinear chirp modes, and an optimal features set is constructed by the feature preference method of an improved ReliefF. Finally, the fault classification is realized by the extreme learning machine, whose input weights and biases are optimized via the salp swarm algorithm. The AVNCMD is testified to be accurate in simulation with nonlinear amplitude modulation–frequency modulation signals and be effective in actual sound signals of industrial sewing machines on four different states. Through the detailed analysis of the measured sound signals in factory, the proposed fault diagnosis method can identify four states of the industrial sewing machines with an overall identification accuracy of 95.0%.

Underwater Sound Detection Thresholds (0.031-80 kHz) of Two California Sea Lions (Zalophus californianus) and a Revised Generic Audiogram for the Species

Unmasked behavioral audiograms of two California sea lions (Zalophus californianus), an adult female (F01) and a subadult male (M02), were recorded using narrow-band frequency-modulated hearing test signals. Signals had a duration of 1 s and center frequencies ranging from 0.031 to 80 kHz. Hearing thresholds were measured by varying test signal amplitude according to the up-down staircase method. The resulting underwater audiograms (50% detection thresholds) of the two sea lions were similar and showed the typical mammalian U-shape. Maximum hearing sensitivity (58 and 57 dB re 1 mPa) occurred at 11.3 kHz for F01 and at 8 kHz for M02, respectively. The range of best hearing (defined as &lt; 10 dB from the maximum sensitivity) was from 1 to 16 kHz (four octaves). The detection thresholds for hearing test signal frequencies 0.031, 0.040, and 0.050 kHz were lower than expected, possibly caused by a shift in perceptional modality from auditory to vibrotactile, or due to the difficulty in measuring accurate SPLs of such low frequencies in a pool. Measurements of particle motion deemed detection of these very low frequencies via the vibrissae unlikely. The present study extends the frequency range for which the hearing of California sea lions has been tested. Based on the two audiograms of the present study and audiograms reported by Reichmuth et al. (2013) and Cunningham &amp; Reichmuth (2016), a revised generic audiogram for California sea lions is proposed.

Sliding-Window TD-FrFT Algorithm for High-Precision Ranging of LFM Signals in the Presence of Impulse Noise

To address the performance degradation of the conventional linear frequency modulation signal ranging method in the presence of impulse noise, this paper proposes a novel technique that integrates a sliding-window tracking differentiator (TD) with the fractional Fourier transform (FrFT) ranging method. First, the sliding-window TD filtering algorithm is used to suppress the noise in the echo. Subsequently, the filtered signal is subjected to FrFT to calculate the time delay based on the difference in the peak point positions in the fractional domain for realizing target ranging. The simulation results show that the proposed method can effectively suppress impulse noise of different intensities and achieve an accurate and robust ranging of the target.

Calcium messages in flagella are faster than messenger particles

Calcium is one of the most versatile messengers for intracellular signaling. In the case of cilia and flagella calcium has the central role in transfer of communications between extracellular stimuli and intracellular formation of frequency modulated signal and their deciphering by target proteins. In this paper, the diffusion of fluorescently or otherwise tagged and un-tagged Ca2＋ particles is analyzed by solving the system of pertaining reaction–diffusion equations. We used Fourier transform tools to get asymptotic eigenfunctions for tagged (un-tagged) free and buffered Ca2＋ ions. We made some numerical estimations for diffusion coefficients corroborating the fact that messages diffuse faster than Ca2＋ messengers. From the best of our knowledge, this is the first time that Ca2＋ signaling in living cells is biophysically elaborated within the framework of model presented here. We suggest the experimental assay on the basis of radioactive Ca2＋ as tagged probe.

Floquet engineering-based frequency demodulation method for wireless THz short-range communications

This study introduces a novel theoretical framework for detecting and decoding wireless communication signals in the nanoscale range operating at terahertz (THz) frequencies. Initially, we investigate the Floquet states in a dressed 2D semiconductor quantum well and derive an analytical expression to determine its longitudinal conductivity. The results indicate that the longitudinal conductivity of a dressed 2D semiconductor can be tailored to specific requirements by manipulating the frequency of the external dressing field. Furthermore, carefully selecting the intensity and polarization type of the external dressing field enables fine-tuning and optimization of the conductivity. To evaluate the effectiveness of each dressing field configuration, we present a figure of Merit (FoM) assessment that determines the maximum possible change in conductivity within the considered frequency range. The proposed theory introduces a mechanism capable of identifying frequency-modulated communication signals in the THz range and performing frequency demodulation. We comprehensively analyze of the demodulator’s transfer function in the receiver. Consequently, we establish that the transfer function exhibits linear behavior over a specific frequency range, rendering it suitable for frequency demodulation. Finally, we provide a numerical illustration of a frequency demodulation scenario. The breakthrough uncovered in this study opens up possibilities for the development of high-efficiency, lightweight, and cutting-edge chip-scale wireless communication devices, circuits, and components.

Quasi-maximum likelihood-based estimator of the hyperbolic frequency modulated signals

The quasi-maximum likelihood (QML) algorithm has been extended to estimate the phase parameters and the instantaneous frequency (IF) of the hyperbolic frequency modulated (HFM) signals. The Nelder-Mead simplex algorithm (NMSA) is adopted for a fine estimation. The obtained accuracy is excellent with the estimates achieving the Cramer-Rao lower bound (CRLB) above the signal-to-noise (SNR) threshold of 0 dB. The proposed technique is capable of functioning with signals that are sampled below the requirements of the sampling theorem, which is particularly important for HFM signals. Additionally, there are no limitations for signals with monotonic IF and/or group delay (GD) functions.

Smart Jamming Against SAR Based on Nonlinear Frequency-Modulated Signal

The traditional methods of jamming against synthetic aperture radar (SAR), which are implemented based on linear frequency-modulated (LFM) signals, are currently unable to meet the needs of electronic countermeasures. Compared with the LFM signal, the frequency of the nonlinear frequency-modulated (NLFM) signal varies nonlinearly with time. Because of this time-frequency structure, the NLFM signal is naturally mismatched with the linear matched filter of SAR; thus, a stronger and more flexible jamming effect is produced. In this paper, the NLFM signal is used in the SAR jamming field for the first time, and a smart jamming method against SAR based on the NLFM signal is proposed, which can produce the following two jamming effects: barrage and deceptive. First, the shaping factor is defined to generate the expected NLFM signal. The shaping factor controls the jamming range in the fast time direction for barrage jamming. For deceptive jamming, a jamming method involving piecewise weighting is proposed. The shaping factor is used to control the defocusing degree of false targets. Subsequently, the pulse compression results of the jamming signal are deduced, and the influence of different parameters on the jamming effect is theoretically analyzed. Experimental results based on simulation show that the method can control the jamming range and effect in the fast time direction while achieving a flexible deceptive jamming effect.

Noise analysis and modeling for a digital control architecture for Lissajous frequency-modulated MEMS gyroscope with amplitude-modulated readout

We report a digital control architecture that demodulates both amplitude-modulated (AM) and frequency-modulated (FM) rate information simultaneously from a gyroscope working in Lissajous frequency-modulated (LFM) mode. The angular rate information is derived from both quadrature (X and Y) resonance modes of the gyroscope simultaneously. A noise model for the AM signal processing channel of the LFM gyroscope is built, analyzed and compared with that of a conventional AM gyroscope, which shows that methods to improve the performance of the conventional AM gyroscope can also be applied to the AM signal processing channel of the LFM gyroscope. The angular rate output obtained from the AM information of the LFM gyroscope has better noise characteristics, which therefore supplements the low precision inadequacy of the FM signal channel of the LFM mode. Tests on the same gyroscope working in different control architectures are conducted. The angle random walk (ARW) and bias instability (BI) of the AM channel of the proposed architecture are 0.51 deg √h−1 and 1.8 deg h−1, respectively, which are better than the results obtained from the FM channel in the same architecture, with values of 0.99 deg √h−1 and 4.3 deg h−1, respectively. Also ARW amd BI of the same gyroscope working in conventional AM mode is 0.50 deg √h−1 and 5.2 deg h−1, respectively.

Active vibration control for reduction of interior noise caused by R-MDPS of electric power steering in electric vehicle

This paper presents a novel active vibration control (AVC) system for a motor driven power steering (MDPS) system to reduce interior noise in an electric vehicle. The novel control algorithm used for the AVC system is developed based on selection of two reference signals. One is the frequency modulation signal using the rotation speed of motor shaft of MDPS the other one is the band passed signal of acceleration measured on the major path structure identified by the blocked transfer path (BF-TPA). In addition, the piezo stack actuator is used for generation of control force of the AVC system in the frequency over 400 Hz. An MDPS system uses electronic power steering. An MDPS system attached to the rack gear of power steering system is called an R-MDPS. The vibration generated by the R-MDPS is transmitted to the car body through mounts attached onto the car subframe. Panel vibrations of car body are sources of vibroacoustic noise generated inside the car cabin. This vibracoustic noise is a structure-borne noise and causes passenger annoyance. The frequencies of the structure-borne noise measured inside the car cabin are 460 Hz and 920 Hz, which are the rotating frequency of the R-MDPS motor shaft and the second-order harmonic of the rotating speed of the motor shaft. To directly reduce the interior noise inside the car cabin, active noise control (ANC) has been used for the active cancellation of noises with frequencies less than 400 Hz. However, because the frequency of interior noise generated by the operation of the R-MDPS is higher than 400 Hz, AVC was employed in this study for the active cancellation of vibrations transmitted to the car body through the subframe mounts of the car. For application of AVC to the test car, the control force should be known. Therefore, the actuator for generating the control force should be inserted in the mount between the subframe and R-MDPS system. Installing the actuator in the test car is challenging because of the geometry limit of commercial cars. Hence, a test jig composed of an R-MDPS system and the subframe of the test car was developed and set up in the laboratory to study the applicability of AVC to R-MDPS. All investigations of AVC were performed using the test jig in the laboratory. The proposed method was successfully applied to the active cancellation of vibration at a target point on the subframe.