Multiple Frequency Signals Research Articles

Photonics-assisted simultaneous frequency and angle-of-arrival measurement using parameter mapping method

A photonics-assisted simultaneous frequency and angle of arrival (AOA) measurement system based on parameter mapping method is proposed and demonstrated by simulation and experiment. Using optical sideband sweeping and envelope detection, the frequencies of the signals under test (SUT) are mapped to the time domain of the output amplitude of the electrical pulses, and the AOA-dependent phase differences are mapped to the amplitudes of the output electrical pulses. The experiment achieved multiple-frequency signal measurements, and the absolute measurement error was between 1.8 MHz and 5.4 MHz in the range from 9.4 GHz to 13 GHz. The frequency range can be adjusted by modifying the bandwidth of the frequency-swept signal or the DC bias voltage. Furthermore, the unambiguous AOA measurement from −90° to 90° is successfully realized simultaneously, and the error of the AOA measurement ranging from −66.44° to 66.44° is confined to within ±1.4°. Due to its robustness and flexibility, this dual-function measurement system can find various applications in future electronic warfare systems.

Ultra-wideband instantaneous frequency measurement based on differential photonic time-stretch

A novel technique to perform ultra-wideband instantaneous frequency measurement in real-time based on differential photonic time-stretch is proposed and experimentally demonstrated. Wideband frequency measurement is enabled by time-stretching the RF input signal via the dispersion compensating fiber. Distortion of the measured frequency signal caused by the non-uniformity of the spectrum of the pulsed laser source, which can be found in most of traditional time-stretch systems, is eliminated here by implementing a dual-output Mach–Zehnder modulator (DOMZM) with complementary outputs and a balanced photodetector. Multi-tone tests with a 20 GHz frequency measurement range are conducted to verify the feasibility of the system of measuring multiple frequency signals. Followed by the proposed automated digital signal processing algorithms, our instantaneous frequency measurement system offers an ultra-fast sweep time of 10 ns, a frequency resolution of 660 MHz, and a measurement error within ±380 MHz. A larger frequency measurement range can be realized by implementing a DOMZM with a larger bandwidth.

A Novel Parameter Estimation Method of FHSS Signal with Low SNR

A novel parameter estimation method of frequency hopping spread spectrum (FHSS) signal is proposed. The observed signal is divided into multiple segments and forms an observed matrix, performing FFT on the observed matrix with different segment lengths to obtain the corresponding spectrum matrix. By analyzing the convergence characteristics of the spectrum matrix, the estimation of the symbol period is realized, on this basis, the symbol‐frequency distribution is obtained and its projected spectrum in Frequency‐Amplitude plane is further obtained to select the candidate frequencies. The matrix composed of multiple single frequency signals is constructed according to the candidate frequencies and multiplied with the observed matrix under the segment length of symbol period, then the number of symbols per hopping duration is estimated according to the matrix multiplication result, so as to realize the estimation of the hopping duration, and finally the real hopping frequencies and hopping sequence can be found out from the candidate frequencies. Simulation results are presented to indicate that the proposed method has good estimation performance especially under the condition of low SNR. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

An Adaptive Amplitude-Modulated Pseudo-Random Binary Sequence Excitation for Converter-Based Impedance Spectroscopy Characterization of Photovoltaic Modules

Pseudo-random binary sequence (PRBS) has been implemented through DC-DC converters for internal impedance identification and shown to be faster and easier to implement than analogue multiple frequency signals; this is because a PRBS is a digitally generated binary signal, thus has faster transients, and requires a few samples for excitation signal reconstruction. PRBS however, is strictly designed for linear excitation, but because both converter and PV module being non-linear and operated in their pseudo-linear range for system identification, presents linearity issues in induced excitation systems. As the excitation frequency and module operating point vary, the induced excitation signal also varies, which may push the system into its non-linear range of operation – this can cause significant inaccuracies in the impedance measurements. This study thus, demonstrates the use of an adaptive, two-level optimized APRBS parametric excitation signal, designed by defining an input space, for the signal design points, characterized by the dynamic system from the converter's APRBS modulating duty ratio signal to the induced APRBS excitation signal. This will mitigate frequency and variable operating point induced system non-linearities, while producing fast and accurate online impedance estimation. The results show that the APRBS achieves good tolerance for the induced system non-linearities – this is demonstrated by a small impedance error between the designed system and a Frequency Response Analyzer (FRA) at low frequencies compared to PRBS excitation.

Fairness-Aware Resource Allocation in Multi-Source WPCN in the Finite Blocklength Regime

In this work, we investigate a wireless powered communication network (WPCN) where multiple sources are jointly utilized for wireless power transfer (WPT). By consuming the energy harvested from the these WPT sources, a set of sensors are expected to accomplish reliable transmissions carried by finite blocklength (FBL) codes. This work proposes a fairness-aware resource allocation design with low-complexity in such a multi-source WPCN, where the practical nonlinear energy harvesting process is considered (including the effects of components nonlinearity in rectifier circuits and mutual interference between multiple radio frequency signals). In particular, a joint power and blocklength optimization problem minimizing the maximum reliability of all short packet transmissions is considered. To cope with the formulated extremely intractable nonconvex problem, we decompose it into two subproblems, i.e., a power allocation problem and a blocklength allocation problem, nevertheless, both of which are still nonconvex. To address the power allocation subproblem, auxiliary variables are introduced, subsequently variable substitutions are performed to convert the problem into one being analytically tractable, and an efficient iterative approach is provided via applying the successive convex approximation technique. For the blocklength allocation problem, we for the first time verify the convexity of error probability with respect to blocklength under a harvested energy constraint, which is of great theoretical value and can be extended to numerous applications with energy limitations. Finally, by alternatingly addressing the two subproblems, an efficient sub-optimal solution to the original problem is achieved. We provide numerical results to validate and evaluate the proposed design, and a set of guidelines are provided for practical system designs.

Multiple microwave frequency measurement system based on a sawtooth-wave-modulated non-flat optical frequency comb.

A photonic-assisted instantaneous microwave measurement system, capable of measuring multiple frequency signals, is demonstrated and analyzed. The principle lies in the combination of a channelizer and frequency-to-power mapping. An effective generation method of a non-flat optical frequency comb is proposed based on sawtooth wave modulation, which has more comb lines and adjustable comb spacing. Under this method, two low-speed post-processing devices are utilized to realize frequency measurements up to 32GHz. The scheme is verified by simulation, and factors affecting system performance are also studied.

Customized sea‐surface temperature indicators linking to streamflow at different timescales

AbstractInvestigation of SST–streamflow connectivity unravels the large‐scale climate influences that may have a potential role in modulating local hydrological components. Most studies exploring this relationship only focus on a single timescale; however, various atmospheric and oceanic phenomena occur at different temporal scales, which must be considered. This study examines the association of sea surface temperature (SST) and streamflow in Germany, divided into three regions, viz. Alpine, Atlantic and Continental, at timescales ranging from seasonal to interannual by integrating wavelet transform and complex network techniques. Wavelet transform is used to decompose the time series into multiple frequency signals. The network theory identifies the spatial connections for the 99 percentile correlation coefficient value based on these decomposed signals. The degree centrality metric is used to evaluate the characteristics of the spatially embedded networks. Our results re‐establish known SST regions that have a potential connection with the various streamflow regions of Germany. Spatial patterns that resemble the North Atlantic SST tripole‐like pattern is predominant for Alpine streamflow regions at finer timescale. Equatorial Atlantic Mode regions observed for Atlantic streamflow at interannual timescale and Vb weather system connected regions in the Mediterranean Sea have appeared for all the streamflow regions of Germany. Besides, continental streamflow regions exhibited combined characteristics of the Alpine and Atlantic streamflow spatial patterns. In addition to the above regions, we also identify the scale‐specific patterns in the Pacific, Indian and Southern Ocean regions at different timescales.

Highly Integrated Dual‐Modality Microwave Frequency Identification System

AbstractPhotonic‐assisted microwave frequency identification systems have been extensively explored and widely applied for civil and defense applications. Full integration of this system is a promising candidate in attempts to meet the requirements of reduction in size, weight, and power. Although many integrated photonic chips have been reported in different technologies, none has monolithically integrated all the main active and passive optoelectronic components. Furthermore, previous approaches could identify either a single frequency signal instantaneously or multiple frequency signals statistically, but not both, hindering the practical applications. Here, a highly integrated dual‐modality microwave frequency identification system on a single chip is reported. All critical components including a modulator, a sweeping‐frequency filter, a frequency‐selected filter, an amplitude comparison function, and parallel photodetectors, are monolithically integrated on the silicon‐on‐insulator platform. Thanks to the dual‐modality scheme, the chip is able to identify different types of microwave signals, including single‐frequency, multiple‐frequency, chirped, and frequency‐hopping microwave signals, as well as discriminate instantaneous frequency variation among the frequency‐modulated signals. This demonstration exhibits a highly integrated solution and fully functional microwave frequency identification, which can meet the requirements in reduction of size, weight, and power for future advanced microwave photonic processor.

Design of real-time data acquisition system for interferometer-based electron density diagnostics on EAST.

Laser-aided interferometers are employed as the common diagnostics for electron density measurements. On the EAST (Experimental Advanced Superconducting Tokamak), we have four main electron density diagnostics-the far-infrared hydrogen cyanide interferometer, polarimeter/interferometer, carbon dioxide (CO2) dispersion interferometer, and solid-state source interferometer. For interferometers, the phase difference brought by the change in electron density can be acquired via mixers. A real-time data acquisition (DAQ) system is needed to calculate the highly precise density values. In this paper, a field-programmable gate array is employed to implement the system with fast Fourier transform-based demodulation technology. A highly precise analog/digital converter is employed for readout and digitization of the waveform including multiple frequency signals from high-performance Schottky mixers. The system has been simulated, and the results show that it can meet the requirements of the accuracy of interferometers on the EAST. Furthermore, the framework of the DAQ system also offers a reference of the data processing method to the future laser-aided interferometers.

Acquisition sequences and reconstruction methods for fast chemical exchange saturation transfer imaging.

Chemical exchange saturation transfer (CEST) imaging is an emerging molecular magnetic resonance imaging (MRI) technique that has been developed and employed in numerous diseases. Based on the unique saturation transfer principle, a family of CEST-detectable biomolecules in vivo have been found capable of providing valuable diagnostic information. However, CEST MRI needs a relatively long scan time due to the common long saturation labeling module and typical acquisition of multiple frequency offsets and signal averages, limiting its widespread clinical applications. So far, a plethora of imaging schemes and techniques has been developed to accelerate CEST MRI. In this review, the key acquisition and reconstruction methods for fast CEST imaging are summarized from a practical and systematic point of view. The first acquisition sequence section describes the major development of saturation schemes, readout patterns, ultrafast z-spectroscopy, and saturation-editing techniques for rapid CEST imaging. The second reconstruction method section lists the important advances of parallel imaging, compressed sensing, sparsity in the z-spectrum, and algorithms beyond the Fourier transform for speeding up CEST MRI.

Phase-Stabilized Side-Branch RoF Link for Extensible Frequency Dissemination in Distributed Systems

Synchronization is a long-standing challenge in modern large-scale distributed systems, and newly deployed systems such as 5G and modern netted radars require more extensive synchronization. As the number of distributed stations increasing, new synchronization solution with much effort on extensibility is highly expected. In this paper we first analyze the requirements on extensibility of fiber-based sync systems, and then propose a phase-stabilized side-branch radio-over-fiber (RoF) link, which fully satisfies the extensibility requirements. The extensible side-branch link can be constructed at any intermediate point along the main link, without any reconfiguration at the central station, which is especially feasible when adding extra stations in system capacity expansion. The main link phase shift is first stabilized by tuning the optical carrier wavelength, while another phase-locked-loop constructed at the starting point of the branch link stabilizes the phase shift from the central station to the end of branch link, by phase locking two phase-varying signals. Moreover, the phase-stable side branch is inherently extensible to multiple frequency signals, which can be used in receivers requiring multiple local oscillators (LOs). Two frequency signals are simultaneously disseminated to the end of branch link in the experiment, with frequency stability optimization of two orders of magnitude on both LOs achieved. The proposed stable side-branch RoF link shows the potential of constructing a highly-extensible frequency dissemination network for the synchronization in modern distributed systems.

Multi-Frequency Multi-Amplitude Superposition Modulation Method With Phase Shift Optimization for Single Inverter of Wireless Power Transfer System

In wireless charging devices, different wireless charging standards have caused charging incompatibility, and the utilization rate of the DC voltage at the transmitter is not high, which brings challenges to the application of wireless charging. To solve these two problems, this paper proposes a multi-frequency multi-amplitude (MFMA) superimposition modulation method. This method superimposes multiple frequency signals, and then compares the synthesized signal with a high-frequency triangular carrier to output a square wave voltage signal containing information such as the frequency and amplitude of the pre-output signal. Furthermore, a phase-shifting optimization algorithm is proposed, i.e., based on the proposed MFMA superimposition modulation method, the utilization rate of the DC voltage of the system is improved by reasonably adjusting the initial phase of each frequency. Simulation and experimental results show that the proposed method can output at least four frequencies simultaneously by using a single inverter, effectively reducing the volume of the transmitter, and being compatible with the frequency range of several charging standards. The proposed phase-shifting optimization has a significant effect on improving the utilization of DC voltage with an increase of 44.88%.

Analysis of an all-in-plane spin-torque oscillator using injection locking to an external microwave magnetic field

We experimentally study the magnetization dynamics of an all-in-plane spin-torque oscillator (AIP-STO) by using injection locking to an external microwave magnetic field. The AIP-STO exhibits multiple frequency signals corresponding not only to the oscillation frequencies of the magnetic layers but also to the difference between these frequencies. The oscillation frequency is identified based on the principle that injection locking occurs only to the signal corresponding to the magnetization oscillation. We also analyze the magnetization dynamics during injection locking by micromagnetic simulations. The results demonstrate that injection locking is a powerful tool for elucidating the oscillation of the AIP-STO.

A Radio Over Fiber System Compatible With 3G/4G/5G for Full Spectrum Access and Handover With Multi-Scenarios

A Radio over Fiber system based on optical frequency multiplication and multiplexing compatible with 3G/4G/5G systems for full spectrum access and handover with multiple scenarios is proposed and analyzed theoretically as well as simulated numerically. By combining a dual-drive Mach-Zehnder Modulator in Push-Pull modulation-mode with optical frequency multiplication and multiplexing technology, the simultaneous transmission of multiple radio frequency signals in optical carrier is realized. It can be also switchable for full spectrum access of different scenarios and user terminals with Multi-Input Multi-Output wireless capability, based on frequency diversity technology. The BER and eye diagram for the transmission performances have been presented by the simulation experiment. Meanwhile, the feasibility of the scheme has been demonstrated by lots of numerical simulations and accurate theoretical analyses. The method could meet the requirements for communication capacity and transmission rate in both continuous-wide-area coverage and hot-spot high-capacity transmission of 5G system, and for full spectrum access and handover.

Improved empirical wavelet denoising algorithm with application to whirling detection in deep hole drilling process

This paper investigates the empirical wavelet denoising algorithm, to extract the high multiple frequency signals of rotation frequency from the spindle vibration signal in deep hole drilling. With the characteristic of adaptive frequency partition, empirical wavelet transform is introduced to decompose the vibration signal. Considering the influence of background noise on the vibration signal, an improved threshold denoising method is proposed to remove the noise of the spindle vibration signal. Thus, an improved empirical wavelet denoising algorithm is proposed for the high multiple frequency signals of rotation frequency extraction. The improved empirical wavelet denoising algorithm is combined with energy entropy to detect whirling in deep hole drilling process.

Multi-longitudinal mode fiber laser digital vibration-sensing system based on a multi-carrier modulation/demodulation technique.

A multi-longitudinal mode fiber laser sensor (MLMFLS) system based on a digital modulation/demodulation technique is proposed. To the best of the authors' knowledge, this is the first digital vibration-demodulation system ever reported by a MLMFLS system. Multiple beat frequency signals (BFS) generated by the MLMFLS work as signal carriers of applied vibration signals. The vibration signals modulated on several BFS at different frequencies are simultaneously demodulated based on a multi-channel digital down-conversion technique by utilizing the digital universal software radio peripheral (USRP). The demodulated vibration signals from different signal channels are superposed by the USRP. Signal-to-noise ratio (SNR) of output vibration signal is highly improved, which increases sensing stability and accuracy of the system. This is really important for sensing of vibration signals that have an extremely low frequency or weak energy. Measurement results demonstrate that the sensing system has an excellent low frequency vibration-sensing capability, simple structure, high SNR, stability and accuracy.

Vibration Signal Extraction Based on FFT and Least Square Method

Fast Fourier Transform (FFT), widely used in spectrum analysis, is a powerful processing vibration signal to obtain the signal amplitude, frequency, and phase. However, the discrepancy between the FFT derived values and the real values could be introduced due to spectral leakage and spectral interference. This inconsistency is prohibited in some applications, for example, the extraction of vibration characteristics for power machinery and failure diagnostics. Therefore, the methodology to obtain the frequency domain’s exact characteristics becomes one of the most concerning topics in vibration and signal processing. In this paper, a newly developed iterative method is presented in detail for high-accuracy characteristic extraction of multiple frequencies periodic vibration signals based on FFT and least square method. In the situation where the attenuation signal is superposed onto the periodic signal, the accurate characteristics of these two signals are also obtainable. Besides, simulation examples are provided, showing that the proposed method can be applied to the single-frequency signal, multiple frequency signals (including the signals of which the adjacent frequencies are close), and attenuation signal. The experimental results show that using the data processing method in this paper to extract the attenuation signals’ characteristics, and the fitted attenuation curves are in good agreement with the actual attenuation signals. The method shown in this paper can be used for precisely extracting the characteristics of the periodic signal and attenuation signals in engineering.

Design of multipath error correction algorithm of coarse and fine sparse decomposition based on compressed sensing in time-of-flight cameras

ABSTRACTA single pixel in time of flight cameras receives multiple reflected light from different scene points, resulting in erroneous depth information. In this paper, based on the proposed sparse decomposition, a coarse and fine sparse decomposition based on compressed sensing is applied to multipath separation. The applied method uses a linear combination of multiple frequency signals to modulate the source. The measured vector obtained through finite random measurements is subjected to two sparse decompositions – rough separation and detailed positioning, and finally the minimum direct path depth is accurately recovered. Under the premise of the same number of measurements, calculation amount, and storage space, the accuracy of the coarse and fine sparse decomposition based on compressed sensing is improved by nearly an order of magnitude compared to the sparse decomposition without compressed sensing. Moreover, our method can basically achieve multi-path separation accuracy to the sub-millimeter level.

Cascaded Kalman filter for target tracking in automotive radar

In automotive anti-collision radar system, the accuracy of velocity is one of the key indicators to measure radar performance. For frequency modulation continuous wave radar with chirp sequence, which is commonly used in automotive radar, there are two problems that are velocity ambiguity and measurement error. In order to address these problems, a cascaded Kalman filter algorithm is proposed in this article, which is able to overcome velocity ambiguity and improve the accuracy of measurements. In addition, the problem of velocity ambiguity can be solved just in the data processing and it avoids transmitting staggered or multiple pulse repetition frequency signal. The simulation results show that this algorithm can effectively improve the tracking performance.

Nonlinear Vibrations by Periodic Perturbation in a Murali–Lakshmanan–Chua Electronic Circuit Combined with Multiple Frequency Signal

In this paper, a detailed investigation of oscillation behaviors in the non-autonomous Murali–Lakshmanan–Chua (MLC) circuit is proposed. The determination of the bifurcation value in the MLC circuit is associated with the two switching boundaries leading to different types of nonlinearity in structures. The non-conventional bifurcations in the layer equations by switching manifolds are explored. The discontinuous Fold/Fold and Hopf/Hopf periodic vibration mechanisms can be well released. The influence of the addition of the second periodic force is also being discussed. We use Clarke’s concept of generalised differential to analyze the occurrence of discontinuous Hopf bifurcations. The DeMoivre expansion formula and the variable replacing method are used to express the relevant critical manifold. The validity for our study is also elucidated by numerical examples of application. Complex oscillation patterns under periodic perturbation with multiple-frequency signal as well as the underlying characteristic properties are demonstrated. The MLC circuit occurs the transitions through the sets of non-smooth bifurcation values leading to complicated wave forms. The addition of second periodic signal will provide the parameter condition to acquire more desired periodic vibrations.