Narrowband Interference Research Articles

ANALYSIS OF THE STRUCTURE OF INTERFERENCE COATINGS FOR THE OPTIMIZATION OF THE PARAMETERS OF NARROWBAND OPTICAL FILTERS

To monitor the parameters of semiconductor layers deposited from solid solutions of A3B5 compounds during the epitaxy, optical control methods are used. The choice of optical monitoring methods is determined by the reactor design, which requires non-contact, fast, and precise measuring of wafer surface parameters. During the growth of epitaxial layers, the deposition of semiconductor compounds causes changes in the optical parameters of the wafer surface. To ensure precise measurements, it is essential to monitor these parameters within a narrow spectral range. In electro-optical monitoring systems, narrowband interference filters are used to select the desired spectrum. However, this type of filters is sensitive to several factors, such as environmental conditions, aging of the coating, and the angle of incidence. As a result, the manufacturing of narrowband optical filters with stable and precisely controlled optical characteristics presents a complex challenge. This article analyzes the impact of various factors on the optical characteristics of interference coatings. Quantitative analysis of these shows that shift of the selected spectral band with central wavelength λmax can approach or even exceed the full width at half maximum (FWHM). These changes in the optical characteristics of narrowband filters lead to a decrease in the accuracy required for optical monitoring during epitaxial processes, which leads to inaccuracies in measurements. The results of this analysis will guide the optimization of thin-film structures used in narrowband optical filters. The study of the shift in the selected band also enables, within certain limits, controlled changes to λmax or the compensation of its shift its shift during regular factor variations. Ultimately, it enables to take these changes into account when designing electro-optical systems for monitoring the epitaxial growth of semiconductor heterostructures, which increases the accuracy and stability of optical measurements in the required accuracy range.

Method for determining the effect of destabilizing factors of digital filters on the multicriteria synthesis of radio communications of aviation robotic devices

The purpose of the research is development of a method for determining the influence of destabilizing factors, such as the unevenness of the amplitude-frequency response (AFC) and the nonlinearity of the phase-frequency response (FFC), in non-recursive digital frequency selection filters on the target function of multicriteria structural-parametric synthesis of radio communications from the payload of aviation robotic devices.Methods. In conducting scientific research, probability theory, mathematical statistics, statistical radio engineering and computational mathematics were used. The study obtained mathematical expressions of the dependence of the probability of error per bit (BER) on the average signal-to-noise ratio when signals pass through symmetrical non-recursive digital filters with quadrature amplitude modulation with a positivity of no more than 4096, signal constellation irregularities of no more than 5, which are the basis for the energy balance of radio lines with aviation robotic devices. The expressions obtained are one of the "foundations" for the implementation of a multi-criteria synthesis of radio systems adaptive to a cognitively formed flight task. In this paper, all the results of the probability of reliability of the received data by means of communication are reflected for the case of rigid decision-making (Gray coding).Results. In the course of the conducted research: 1) a mathematical model of the structural-parametric synthesis of radio communications with aviation robotic devices is demonstrated, which is based on the criteria for minimizing: electronic computing resources with a given noise immunity; radiation outside the operating frequency band; peak factor signals; the effects of narrowband, broadband and structural interference in the radio channel at a given bandwidth; the use of structural and functional nodes specific to the existing information and communication environment; 2) the analytical dependence of the influence of the parameters of one of several structural and functional nodes - digital filters of frequency selection, on the criteria for the synthesis of communication means has been revealed. The paper considers the most common approximating functions - Kaiser, Tukey, Barlett-Khan, Chebyshev, and also shows the influence of the filter order on the equivalent of energy loss in information communication lines of aviation robotic devices.Conclusion. The scientific article presents a method for determining the effect of the uneven frequency response of a symmetrical non-recursive digital filter in devices for receiving and processing radio signals of multicriteria means of communication with the payload of aviation robotic devices. The proposed approach increases the reliability of determining the values of criteria for minimizing electronic computing resources for a given noise immunity, radiation outside the operating frequency band, as well as the use of structural and functional nodes characteristic of the existing information and communication environment.

Research of the efficiency of Kravchenko weighting functions and combinations based on them in the problem of narrow band interference rejection

The influence of weight functions (WFs) of preliminary weighting on the quality of narrowband interference rejection based on direct and inverse discrete Fourier transforms has been studied. Classical and modern WFs are considered: Kravchenko, Kravchenko–Dolph–Chebyshev, Kravchenko–Gauss, Kravchenko–Bernstein–Rogozinsky. Quantitative estimates of efficiency were obtained – the coefficients of interference suppression and signal transmission, as well as their product – the total efficiency coefficient. Graphic examples of the behavior of the total efficiency coefficient depending on the interference frequency are shown. Estimates of the indicated quality indicators are presented when a fixed number of frequency samples are removed from the spectrum. The families of dependences of the probabilities of correctly performing a search for a spread spectrum signal on the “interference/signal” ratio when using modern WFs to weigh the implementations of an additive mixture of signal, interference and noise are presented. The significant advantage of modern WFs formed through combinations with Kravchenko functions in the problem of interference rejection has been demonstrated and confirmed.

Noise immunity of QAM-OFDM signal reception using soft-decision demodulation in the presence of narrowband interference

Noise immunity of QAM-OFDM signal reception using soft-decision demodulation in the presence of narrowband interference

Advances in optical coating uniformity of interference filters

We propose a method to obtain uniform multilayer coatings using vacuum assemblies with a linear ion source to manufacture narrow-band interference filters essential in astrophysical research for space object imaging in important spectral lines, and to provide multi-channel fiber-optic transmission of information. Interference filters and other optical systems, for example, high-reflective mirrors, steep-front beam splitters contain up to hundreds of film layers deposited onto a substrate. During the coating deposition, film thickness on the substrate must be strictly withstood and be uniform throughout the entire surface. This can be achieved by placing the linear source and target on the same platform and by conducting a test target sputtering on a fixed substrate. There is an inflection line on the coating thickness distribution on the substrate. By moving the platform, the inflection line midpoint is aligned with the center of the rotating working substrate, and in this position, the substrate is coated to a specified thickness, which is monitored during the deposition process.

Spectral redundancy for calibrating interferometers and suppressing the foreground wedge in 21 cm cosmology

ABSTRACT Observations of 21 cm line from neutral hydrogen promise to be an exciting new probe of astrophysics and cosmology during the Cosmic Dawn and through the Epoch of Reionization (EoR) to when dark energy accelerates the expansion of our Universe. At each of these epochs, separating bright foregrounds from the cosmological signal is a primary challenge that requires exquisite calibration. In this paper, we present a new calibration method called nucal that extends redundant-baseline calibration, allowing spectral variation in antenna responses to be solved for by using correlations between visibilities measuring the same angular Fourier modes at different frequencies. By modelling the chromaticity of the beam-weighted sky with a tunable set of discrete prolate spheroidal sequences, we develop a calibration loop that optimizes for spectrally smooth calibrated visibilities. Crucially, this technique does not require explicit models of the sky or the primary beam. With simulations that incorporate realistic source and beam chromaticity, we show that this method solves for unsmooth bandpass features, exposes narrow-band interference systematics, and suppresses smooth-spectrum foregrounds below the level of 21 cm reionization models, even within much of the so-called wedge region where current foreground mitigation techniques struggle. We show that this foreground subtraction can be performed with minimal cosmological signal loss for certain well-sampled angular Fourier modes, making spectral-redundant calibration a promising technique for current and next-generation 21 cm intensity mapping experiments.

OTFS narrowband interference suppression based on energy concentration

Orthogonal Time Frequency Space (OTFS) modulation has significant Doppler resistance in non-geostationary orbit (NGSO) satellite communications, but is extremely affected by single-tone interference (STI). In this paper, a Fast Harris Hawk Optimization-based Energy Concentration Interference Suppression (FHHO-ECIS) algorithm is proposed to remove STI. First, the algorithm designs the translation matrices in the Delay-Doppler (DD) domain based on the interference center. The STI energy is concentrated by the translation matrices to a single point in the OTFS data block and removed by a zero-setting operation. Subsequently, an interference center pre-estimation module is proposed to improve the accuracy and speed of the HHO algorithm for interference center estimation. Finally, the theoretical analysis of the algorithm's interference suppression gain and the effect of the zero-setting operation on the data is performed. Simulation results show that the FHHO-ECIS algorithm improves the signal to interference plus noise ratio (SINR) by more than 1.7 dB and the bit error rate (BER) performance is improved by more than 0.3 dB.

Interference Suppression Algorithm Based on Short Time Fractional Fourier Transform.

Narrowband interference and wideband interference are both common jamming signals against synthetic aperture radar, which can degrade the signal severely. To suppress interference effectively, an interference suppression method based on short-time fractional Fourier transform (STFrFT) is proposed. After transforming the signal into the time-frequency domain through STFrFT, an adaptive gain coefficient is determined for the instantaneous frequency spectrum at every certain time. The gain coefficient can be preserved while suppressing the interference. Finally, we obtain the useful signal by inverse STFrFT. The simulation and performance analysis show the effectiveness and validity of the proposed algorithm for measured data.

Enhanced Noise Suppression in Partial Discharge Signals via SVD and VMD with Wavelet Thresholding

Partial discharge evaluation is a principal method for assessing insulation conditions in power transformers. Traditional singular value decomposition (SVD) approaches, however, face issues like high residual noise and loss of signal details in white noise suppression. This article introduces an advanced denoising algorithm integrating SVD, variational mode decomposition (VMD), and wavelet thresholding to effectively address mixed noise in on-site power transformer assessments. The algorithm initially employs SVD to suppress mixed noise, specifically targeting narrowband interference by decomposing the noisy signal and nullifying the corresponding singular values. Post-SVD, the signal is further processed through VMD, with its modal components refined via wavelet thresholding. The final reconstruction of these denoised components effectively eliminates white noise. Applied to an input signal with a signal-to-noise ratio of -27.593 dB, the proposed method achieves a postdenoising ratio of 13.654 dB. Comparative analysis indicates its superiority over existing algorithms in mitigating white noise and narrowband interference and more accurately restoring the partial discharge signal.

Derivation of depolarization ratios of aerosol fluorescence and water vapor Raman backscatters from lidar measurements

Abstract. Polarization properties of the fluorescence induced by polarized laser radiation are widely considered in laboratory studies. In lidar observations, however, only the total backscattered power of fluorescence is analyzed. In this paper we present results obtained with a modified Mie–Raman–fluorescence lidar operated at the ATOLL observatory, Laboratoire d'Optique Atmosphérique, University of Lille, France, allowing us to measure depolarization ratios of fluorescence at 466 nm (δF) and of water vapor Raman backscatter. Measurements were performed in May–June 2023 during the Alberta forest fires season when smoke plumes were almost continuously transported over the Atlantic Ocean towards Europe. During the same period, smoke plumes from the same sources were also detected and analyzed in Moscow, at the General Physics Institute (GPI), with a five-channel fluorescence lidar able to measure fluorescence backscattering at 438, 472, 513, 560 and 614 nm. Results demonstrate that, inside the planetary boundary layer (PBL), the urban aerosol fluorescence is maximal at 438 nm, and then it gradually decreases with the increase in wavelength. The smoke layers observed within 4–6 km height present a maximum fluorescence at 513 nm, while in the upper troposphere, fluorescence maximum shifts to 560 nm. Regarding the fluorescence depolarization ratio, for smoke its value typically varies within the 45 %–55 % range. The depolarization ratio of the water vapor Raman backscattering at 408 nm is shown to be quite low (2±0.5 %) in the absence of fluorescence because the narrowband interference filter (0.3 nm) in the water vapor channel selects only the strongest vibrational lines of the Raman spectrum. As a result, the depolarization ratio at the water vapor Raman channel is sensitive to the presence of strongly depolarized fluorescence backscattering and can be used for the evaluation of the aerosol fluorescence contribution to measured water vapor mixing ratio.

Online Testing Method for the Fine Spectral Characteristics of Narrow-Band Interference Filters Based on a Narrow-Linewidth Tunable Laser.

The transmission spectrum of a narrow-band interference filter is crucial and highly influenced by factors such as the temperature and angle, thus requiring precise and online measurements. The traditional method of measuring the transmission spectrum of an interference filter involves the use of a spectrometer, but the accuracy of this method is limited. Moreover, placing a narrow-band interference filter inside a spectrometer hinders real-time online measurements. To address this issue, there is demand for high-precision online spectral testing methods. In response to this demand, we propose and experimentally validate a fine spectral characterization method for narrow-band interference filters. This method uses a narrow-linewidth tunable laser, achieving a spectral resolution in the MHz range for online testing. Two types of narrow-band interference filters were tested using the constructed laser spectroscopy experimental system, obtaining a transmission spectrum with a spectral resolution of 318 MHz. In comparison to spectrometer-based methods, our proposed method demonstrates higher spectral accuracy, enables online measurements, and provides more accurate measurements for special spectral interference filters. This approach has significant application value and promising development prospects.

Sparse Array Design for Optimum Beamforming Using Deep Learning

The paper considers sparse array design for receive beamforming achieving maximum signal-to-interference plus noise ratio (MaxSINR). We develop a design approach based on supervised neural network where class labels are generated using an efficient sparse beamformer spectral analysis (SBSA) approach. SBSA uses explicit information of the unknown narrowband interference environment for training the network and bears close performance to training using exhaustive search by enumerations which is computationally prohibitive for large arrays. The employed Deep Neural Network (DNN) effectively approximates the unknown mapping from the input received data spatial correlations to the output of sparse configuration with effective interference mitigation capability. The problem is posed as a classification problem where the sparse array configuration achieving MaxSINR is one-hot encoded, and indicated by the output layer of DNN. We evaluate the performance of the DNN in terms of the sparse array classification accuracy as well as in terms of the ability of the classified sparse array to mitigate interference and maximize signal power. It is shown that the DNN effectively learns the optimal sparse configuration which has desirable SINR characteristics, hence paving the way for efficient real-time implementation.

Active and passive sensors for diagnostics quasi-zenith ionospheric HF communication channels

Background. There is a growing need for active sensory diagnostics of partial HF channels to provide frequency support to quasi-zenith HF radio links in varying signal propagation conditions. Enhancing the efficiency of active sensor algorithms, particularly by reducing emission time, is topical. To address this, a transition from sequential to parallel (simultaneous) diagnostics is proposed. Another significant challenge in HF communication is narrowband interference, and overcoming this issue involves the method of passive sensory diagnostics. This method assesses the availability of partial channels by analyzing the spectral density of interference power within them.
 Aim. The goal of this study is to develop algorithms and software tools that implement spectral monitoring and parallel sensing of partial channels for sensory diagnostics of ionospheric channels in quasi-zenith HF communication.
 Methods. The proposed approach involves integrating dynamic diagnostic methods into the development of intelligent sensors for ionospheric HF radio links, along with the creation of data analysis methods. Specialized computer software is employed to address the defined tasks. Experimental studies are conducted using the developed devices, which include intelligent active and passive radio sensors for HF radio links, to assess the load on HF communication channels.
 Results. A sensor for orthogonal quasi-zenith ionospheric radio channels has been created, incorporating algorithms for synthesizing a group pulse with orthogonal subcarriers while minimizing the peak factor. Additionally, algorithms for separating subcarriers and calculating the correlation function at the reception have been developed. The sensor employs the OFDM-BPSK signal modulation method, enabling operation in simultaneous-sequential sounding mode across the potential frequency range for communication. This led to an 8-fold reduction in the total signal emission time.
 Conclusion. The scientific results obtained have broad practical applications, particularly in enhancing the efficiency of wideband HF communication systems using spread spectrum signals.

УСУНЕННЯ ЗАВАД У ДИНАМІЧНИХ СПЕКТРАХ ЗА НАЯВНОСТІ ПОТУЖНОГО СИГНАЛУ. Частина 2. ВУЗЬКОСМУГОВІ ЗАВАДИ УМОВНО-СТАЦІОНАРНОГО ХАРАКТЕРУ

Subject and Purpose. A new method for detecting narrow band interferences is discussed, with the use of an example record of Jovi- an Io-C decametric radio storm as obtained with the UTR-2 array on April 10, 2020. We aimed at developing an efficient and simple algorithm based on a detailed analysis of the effect the radio interference environment and the frequency response of the telescope may have on the efficiency of the interference mitigation procedure. Methods and Methodology. The ‘orthogonal detection’ method proposed for identifying linear interference patterns in dynamic spectra of powerful radio sources has been adapted for application to narrow band interferences of various spectral widths and variable brightness, which often happen to be located close to (or intersect with) the signal of interest. In order to minimize the impact of the telescope’s frequency response, a discretized frequency-scanning technique is used, which permits a steady approximation of the averaged spectrum by low order polynomials, as well as removal of the frequency trend which hinders distinguishing between the low-level interference signals and those coming from the source. Results. An efficient approach to the problem of detecting long lasting, narrowband interferences in dynamical spectra (con- ditionally stationary interferences) is proposed. The algorithm has been tested on the example of a powerful storm of Jovian radio emission. The proposed technique can be especially useful in situations where the signal of interest overlaps with the interference in the time-frequency domain. Conclusions. The new approach to the problem of interference mitigation, based on the development of combined algorithms of signal separation in the time-frequency domain, has been shown to offer an effective method of signal processing. In contrast to the previously used methods based on calculation of statistical moments for amplitudes, the new approach allows avoiding use of the same statistical indicators for both interference detection and subsequent steps of data analysis intended for building physical models and interpreting the observational data.

Enhanced IpD2FT-Based Synchrophasor Estimation for M Class PMUs Through Adaptive Narrowband Interferers Detection and Compensation

One of the most challenging problems in the design of next-generation Phasor Measurement Units (PMUs) is related to the need to minimize the impact of multiple harmonics and out-of-band interharmonics (OOBI) on the measurement of synchrophasors over short observation intervals. Most of the existing solutions aim at removing such narrowband disturbances before synchrophasor estimation. However, when data records are short, accurate OOBI filtering may be infeasible. The algorithm described in this paper tackles this problem through a prior estimation of the number and the frequency of the significant narrowband interferers emerging from the noise floor. This result is achieved using a non-parametric signal detector based on random matrix theory and hypothesis testing, followed by the application of the estimation of signal parameters via the rotational invariance technique (ESPRIT). Once the number and the frequency of the narrowband components are known, these parameters are used to augment the dimension of the frequency-domain linear system of equations employed by the Interpolated Dynamic Discrete Fourier Transform (IpD2FT) for synchrophasor estimation. The results of multiple simulations confirm not only that the proposed approach for narrowband components detection is robust and more accurate than other model-order estimation algorithms described in the scientific literature, but also that the synchrophasor estimation accuracy over two-cycle observation intervals is generally higher than using other for M Class PMUs algorithms when OOBIs or a mixture of OOBIs and harmonics are considered.

16-channel snapshot multispectral imaging based on integrated Fabry Perot microcavity array

<sec>By designing and fabricating a narrow-band Fabry-Perot multi-beam interference spectroscopic microcavity array, and integrating it with a visible light detector focal plane array, we demonstrate a small compact multispectral imaging detector. The micro-cavity filter array with 4×4 basic repeating units and a total of 2048×2048 pixels is obtained on a quartz substrate by the four-fractal combination lithograph-etching process. Then the micro miniatured multispectral imaging detector is formed by fitting with the detector chip. The depth and precision of the etching will determine the distribution and offset of the central wavelength of the narrowband spectral channel respectively. The results show that the etching rate of reactive ion is (3.6 ± 0.2) Å/s, and the process is stable and controllable. Due to the different etching depths, the basic repeating unit forms 16 different levels of steps, and the process achieves the design expectation well.</sec><sec>The results are obtained as follows: the response spectrum peak of the microcavity array sample varies from 520 to 680 nm, the free spectrum range is 160 nm, the full width at the half-peak is less than 10 nm, the transmittance is about 70%, the relative half-width of the transmittance peak at 590 nm is 1.19%, and the waveform coefficient is 2.78. A 16-channel multispectral camera is constructed by using the optical micro-precision assembly device to realize the precise alignment and the fitting of the micro-cavity filter array and the image sensor. Xenon lamp and monochromator are used as tunable wavelength monochromatic cooperative light source to detect the effect of 16-channel snapshot multispectral imaging on a pixel scale. The results show that the multispectral imaging detector has 16 different narrow-band response spectra. The characteristic spectrum of the target can be clearly distinguished by spectral channel.</sec><sec>When imaging the target with known spectral characteristics, for a certain frame of multi-spectral image, selecting a suitable spectral channel can eliminate the background in the field of view through image subtraction and improve the contrast of the target. In the dark room condition, we take the LED light source with center wavelength varying in a range between 528 and 589 nm as the target (the wavelength coincides with the working wavelength of the spectral channel), and effectively suppress the background through the spectral differential intensity subtraction, which can improve the accuracy and sensitivity of the target capture. The 16-channel snapshot multi-spectral imaging detector based on integrated Fabry-Perot microcavity array has the advantages of small size, high integration and strong environmental adaptability, and is expected to play a role in realizing the real-time detection of weak moving targets, auxiliary diagnosis of skin surface observation, and high dynamic range imaging of target observation under backlight conditions.</sec>

Design and FPGA Implementation of an Adaptive Narrowband Interference Suppression Filter

Design and FPGA Implementation of an Adaptive Narrowband Interference Suppression Filter

Dynamics of the plasma induced by laser on a cryogenically cooled aluminum target for application in space propulsion

In this work, we investigate the properties of the plasma induced by focusing a high-power laser beam on an aluminum target that was cooled by a helium refrigerator from room temperature down to 20 K. Fast, streak photographs of the plasma were taken at different temperatures and laser energies. From the images obtained, position-vs-time plots were made for each experiment, and from them, the speed was calculated. Additionally, narrowband interference filters were employed to image the dynamics of ions and neutrals separately. It was found that the plasma plume has two distinct speeds: that of its center and that of the outer edge. For unfiltered images, the former has values within the interval 6.2 to 9.1 km/s, while the latter can reach speeds of the order of hundreds of km/s. It was found that the plume of a target cooled to 20 K has a length that is 8%–12% less than the corresponding size at room temperature. Chilling the target did not seem to affect significantly either the plume's speed of expansion or the size of the crater produced. Lower bounds were estimated for the momentum imparted to the ejecta and the specific impulse. The latter can reach a 920-s level, nearly twice as much the amount obtained with chemical rocket fuel.

Performance Analysis of Multiple Interference Suppression of One Small Four Elements Array Antenna used in Satellite Navigation System

background: The anti-interference requirements of miniaturized satellite navigation arrays is increasing, the anti-interference ability reducing of small aperture arrays caused by large mutual coupling, large main lobe width, may be solved through adopting quad-arrays antenna. objective: Research of multiple interference suppression method is the aim of the paper, and it makes the research of small four element satellite navigation array antenna method: In the paper, it focuses on the structural design of low coupling polarized array antennas, and makes analysis of mutual coupling between array elements, the compensation technology based on auxiliary sources is proposed. result: Experimental analysis of antenna narrowband interference suppression are made. Relevant anti-interference results on four element antenna are also obtained. The anti-interference ability of four element antenna is summarized. conclusion: The anti-interference ability of four element antenna is analyzed and summarized in the paper, related results show that small four element satellite navigation array antenna can be used in the multiple interference suppression, in the satelliate navigation system.

Narrowband Interference Cancellation for OFDM Based on Deep Learning and Compressed Sensing

Narrowband Interference Cancellation for OFDM Based on Deep Learning and Compressed Sensing