Single Frequency Interference Research Articles

Generation Mechanism and Characteristic Analysis of Dual-Frequency Pseudo-Signal Interference of the Swept-Frequency Radar

In order to master the law of the pseudo-signal interference effect of dual-frequency electromagnetic radiation in typical radar equipment, a certain type of Ku-band swept-frequency ranging radar was used as the test object to carry out single-frequency continuous wave and dual-frequency continuous wave pseudo-signal interference effect experiments. Through experiments, it is found that dual-frequency electromagnetic radiation will cause “hill” and “spike” type pseudo-signal interference to the swept-frequency radar. Based on the frequency analysis of the radar receiving circuit, the interference mechanism of the dual-frequency pseudo-signal is revealed, and the morphological characteristics and distance law of the pseudo-signal are explained. The variation law of the pseudo-signal level with interference field strength is obtained. The results show that the in-band dual-frequency nonintermodulation interference is similar to the single-frequency interference, and the only difference is that the number of pseudo-signals increases; when the interference frequency difference is about 400∼600 MHz, the out-of-band dual-frequency second-order intermodulation signal will cause “hill” type pseudo-signal interference, and the pseudo-signal distance is random; when the interference frequency difference is less than 5 MHz, both the dual-frequency second-order intermodulation signal and the third-order intermodulation signal will cause “spike” pseudo-signal interference inside and outside the radar operating frequency band; the pseudo-signal distance is fixed.

Adaptive filtering of microseismic data for monitoring a water-conducting fractured zone in a mine

Water-conducting fractured zones in a rock mass can cause problems in mining. Attempts have been made to monitor their development using microseismic signals. However, due to the lack of prior information, it is difficult to filter out mixed low-frequency interference with traditional denoising methods. In this work, the proposed adaptive filtering algorithm is applied after the wavelet packets are decomposed. It is based on a cross-correlation analysis. The algorithm takes a high-quality signal in the common source waveform as prior information and applies the corresponding correlation coefficients between subbands as a threshold. The algorithm was verified with simulations. The results show that low-frequency interference can be effectively suppressed by filtering. For single-frequency interference, the signal-to-noise ratio increased from − 10.18 to 13.97, and the root-mean-square error was 43.88. For multi-frequency interference, it increased from − 10.01 and − 2.63 to 13.50 and 7.99. The root-mean-square errors were 46.31 and 138.07. The narrower the main frequency band of the interference signal and the less the overlap of the main frequency band of the interference signal and the effective signal, the better the filtering effect. When the algorithm was applied to microseismic data collected in the field, the number of effective channels increased and the accuracy improved. The development of a water-conducting fractured zone in the field was consistent with the microseismic location obtained after interference was removed by the algorithm, which indicates that it is feasible to monitor a water-conducting fractured zone by analyzing microseismic waveforms with the adaptive filtering algorithm.

Pseudo-Signal Interference Regularity of Single-Frequency Electromagnetic Radiation to Stepped-Frequency Radar

When typical radar equipment is subjected to single-frequency electromagnetic radiation, the radar display interface forms a pseudo-signal, resulting in the misjudgment of real targets. Based on the working principle of stepped-frequency radar ranging, the effect mechanism of radar equipment pseudo-signal interference is revealed. Taking a Ku band stepped-frequency ranging radar as the test object, the pseudo-signal interference effect test of single-frequency electromagnetic radiation is carried out in this study. The pseudo-signal level value of 6 dBmV is selected as the sensitive criterion of the pseudo-signal interference effect. Through experiments, the variation curves of the pseudo-signal level values of the sensitive frequency bands and the typical frequency points inside and outside the band with the field strength of the single-frequency interference are obtained. Based on the nonlinear distortion analysis of the receiving circuit, the variation laws of the pseudo-signal level values inside and outside the band are explained, respectively. The experimental results show that there are at least seven pseudo-signal interference-sensitive bands in the tested radar, and the first pseudo-signal strength is only related to the interference signal strength. The essence of the second type of pseudo-signal interference is intermodulation interference, and the pseudo-signal level is related to the interference signal and the useful signal strength.

Investigation on the Effect of the B1I Navigation Receiver Under Multifrequency Interference

At present, the research on the tracking performance of navigation receivers is based on the conditions of single-frequency interference, however, the space electromagnetic environment is complicated, and so it is necessary to study the effect of the navigation receiver under multifrequency interference. Through the analysis of the blocking interference mechanism of the navigation receiver and the mathematical model of the tracking loop, the effect model under in-band and out-of-band multifrequency interference is established, when the satellite tracking is missing. The Beidou navigation receiver is used as the experiment object to build a multifrequency interference effect experiment platform, and the carrier-to-noise ratio ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) threshold is used as the criterion for the satellite tracking missing, Finally, the model is verified with the experimental data, the error of the model under tri-frequency out-of-band interference exceeds 3 dB. For reducing the model error, the corrected model is proposed, and the corrected model errors are less than 1 dB. The model is helpful to predict the satellite signal status in the navigation receiver under complex electromagnetic environments.

A Model for Predicting Second-Order Intermodulation Low-Frequency Blocking Effects

To identify and improve the electromagnetic compatibility of a global navigation satellite system (GNSS) receiver under a complex electromagnetic environment, the blocking effects of single-frequency and out-of-band dual-frequency electromagnetic radiation (EMR) on a GNSS receiver were experimentally analyzed. This study is the first to investigate second-order intermodulation second-order intermodulation low-frequency blocking (SILB) interference which was newly discovered in our tests. The mechanism of the SILB effect was analyzed, and two key parameters were identified. The SILB interference factor and the relative value of the low-frequency interference level were introduced to establish a model predicting SILB effects. The method of determining the parameters, the modeling process, and the results are discussed in this article on the basis of both theoretical derivations and experimental measurements. A GNSS receiver was used as the equipment under test to verify the model. Notably, the results demonstrated that the threshold for SILB was approximately 30 dB lower than that for out-of-band single-frequency interference. The model proposed in this article accurately evaluated and predicted the SILB interference.

Adaptive Narrow-Band Interference Suppression and Performance Evaluation Based on Code-Aided in GNSS Inter-Satellite Links

In this paper an adaptive narrow-band interference (NBI) suppression scheme based on a code-aided technique in the global navigation satellite system inter-satellite links (ISLs) is proposed. Unlike the commonly used infinte impulse response (IIR) notch filter and frequency domain filtering, the code-aided technique does not require interference detection or fast Fourier transforms, and the adaptive performance is better. We introduce the principle and implementation of code-aided technique, and the concept of interference influence coefficient is proposed to evaluate the influence of residual interference on the carrier-to-noise ratio (CNR) at the receiving end. Through simulation and by combining the tracking CNR after antijamming, the optimal antijamming parameters and scheme are obtained. Meanwhile, we analyze the relationship between the loss of CNR caused by residual interference and the interference influence coefficient. The final results of the bit error rate (BER) and ranging error in ISLs indicate that the adaptive interference suppression scheme based on the code-aided technique can effectively suppress NBI and ensure the reliability of ISL communications. In the case where the pseudo code rate is 10.23 MHz and the BER does not exceed $1 \times {10^{ - 5}}$ , for the NBI with a bandwidth of 2 MHz, the maximum interference-to-signal ratio (ISR) that can be suppressed by the proposed scheme is 40 dB. For the NBI with a bandwidth of 1 MHz, the maximum ISR that can be suppressed is 55 dB, and for single frequency interference, the maximum ISR that can be suppressed is 75 dB.

Simultaneous wideband radio-frequency self-interference cancellation and frequency downconversion for in-band full-duplex radio-over-fiber systems.

A photonic approach for simultaneous wideband radio-frequency (RF) self-interference cancellation and frequency downconversion in an in-band full-duplex radio-over-fiber system is proposed based on a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator. The upper dual-parallel Mach-Zehnder modulator (DP-MZM) in the DP-QPSK modulator is used to cancel the self-interference directly in the optical domain and generate two sidebands of the desired RF signal, whereas the lower DP-MZM generates two sidebands of the local oscillator. After detecting the combined optical signal at a photodetector, the desired RF signal is downconverted to an intermediate frequency (IF) signal with the self-interference cancelled. The proposed approach can overcome the reappearance of the interference signal and the power fading effect of the received signal caused by fiber dispersion. An experiment is performed. The cancellation depth for single frequency interference cancellation is around 58dB, whereas that for the wideband interference cancellation is larger than 25dB. The fading effect of the proposed IF transmission system is also evaluated compared with the traditional RF transmission system.

FM sequence optimisation of chaotic‐based random stepped frequency signal in through‐the‐wall radar

Chaotic-based random stepped frequency signal is applied in the multiple-input-multiple-output through-the-wall detection radar (MIMO-TWDR)recently. When the frequency modulation (FM) sequence of transmission signal is controlled by the chaotic signal, the single-frequency interference such as the power harmonics sneaking into the phase detector becomes periodical and therefore can be filtered in frequency domain. However, the target echo signal becomes random after chaotic modulation, where the matched filter usually is unable to be realised by Fourier transform and consequently the envelope of direct wave after the phase detector varies stochastically and is difficult to be eliminated by an analogue filter. The FM sequence of random disorganising cannot meet the demand of filtering out the single-frequency interference and direct wave simultaneously. Therefore, a new method of FM sequence optimisation of chaotic-based random stepped frequency signal based on genetic algorithm is proposed to solve these problems in this study. Simulations show that the optimised stepped frequency signal possesses the advantages of both chaotic-based random and linear stepped frequency signal. The proposed scheme achieves excellent performance on direct wave and single-frequency interference suppression and target detection. Moreover, it can avoid the interference between transmission antennas of MIMO radar.

Improved robust T-wave alternans detectors.

New statistical and spectral detectors, the modified matched pairs t test, the extended spectral method and the modified spectral method, were proposed for T-wave alternans (TWA) detection gaining robustness according to trend and single-frequency interferences. They were compared to classic detectors such as matched pairs t test, unpaired t test, spectral method, generalized likelihood ratio test and estimated TWA amplitude within a simulation framework and applied to real data. The optimal detection threshold was selected by using a full Monte-Carlo simulation where signals, with and without alternans episodes, were corrupted by Gaussian noise with different power and single-frequency interferences with different tones. All the combinations of noise and frequency were selected and repeated 500 times in order to compute probability of detection ([Formula: see text]) and the false alarm probability ([Formula: see text]), providing ROC curves. The study group consisted of 50 patients with implantable cardioverter-defibrillator (age: [Formula: see text]; LVEF: [Formula: see text]), who were paced (ventricular pacing) at 100 bpm. Two-minute recordings were analyzed. The XYZ orthogonal lead system was used. The best performance was reached by using the modified matched pairs t test (in comparison with the spectral method and other reference methods).

Noise cancellation method for full-wave magnetic resonance sounding signal based on independent component analysis

Signal collected from magnetic resonance sounding (MRS) instrument is only a few tens of nano-volt and susceptible to environmental noise, leading to a low signal-to-noise ratio. In addition, the accuracy of characteristic parameter extraction from MRS signal is seriously affected, and the resulting error of the subsequent inversion interpretation increases. In this paper, a fast fixed-point algorithm for independent component analysis (FastICA) is utilized to enhance the performance in the high noisy environment. First, the applicability of FastICA algorithm to noise cancellation of MRS signal is analyzed. Whether the mixed signal can be separated completely depends on the appropriate choice of nonlinear function in FastICA algorithm, moreover, the choice of nonlinear function is closely related to the Gaussian type of signal. Thus, in this process, the kurtoses of noise and full-wave MRS signal are calculated, and then the Gaussian type of signal is determined. Therefore based on the Gaussian type of signal, we can choose the corresponding nonlinear function applied to the FastICA algorithm in order to realize the effective separation of the mixed signals. Secondly, undetermined blind source separation is one of common problems of ICA. To cope with this tough situation, a digital orthogonal method is adopted to construct some extra observed signals combined with the existing observed one as the input signal of this algorithm. Hence, the digital orthogonal method can satisfy the application condition of ICA, i.e., the number of observed signal must be greater than or equal to that of source signal. This means that it is able to remove the application limitation of ICA when there is only one observed signal. Owing to the problem of variable amplitude of separated signals after ICA, it is crucial to recover the initial amplitude of the separated MRS signal, because it represents the amount of water content in the aquifer. Aiming at this problem, a spectrum correcting method is proposed. In frequency domain, the spectrum of separated MRS signal is restored into the original value that is the spectrum of observed signal at Larmor frequency, then transformed into time domain by inversing fast Fourier transform to obtain the desired MRS signal. In the validation of the proposed algorithm, two tests are considered: simulation and field data processing. In the simulation case, the observed signal constructed by full-wave MRS signal and two power-line harmonics with different frequencies is the main processing object, and the proposed algorithm is utilized to realize the observed signal separated into ideal MRS signal and noise effectively. To verify the applicability of this proposed algorithm further, under the condition of different initial amplitudes and relaxation times, the characteristic parameters of separated MRS signal are extracted by this proposed algorithm and the corresponding relative fitting error is determined. The simulation results show that adopting this algorithm can effectively realize the separation of the noisy full-wave MRS signal. In addition, the relative errors of initial amplitude and relaxation time after data fitting are both within 5.00%. When compared with the denoising ability of some other classical algorithms, the performance of this proposed algorithm is superior. Finally, this algorithm is applied to the processing of the field data. The results indicate that power-line harmonics and other single-frequency interference contained in the MRS signal can be removed effectively.

Real-Time High-Precision Reading Algorithm for the Ironless Inductive Position Sensor

This paper presents a novel reading algorithm for an ironless inductive position sensor which exhibits immunity to single-frequency interference (both for high and low frequency signals). This algorithm is based on the three-parameter sine fitting, whose performances have been enhanced with proper windowing function design. The proposed algorithm exhibits high precision and suitability for real-time implementation. The performances of the new algorithm are tested on simulated and measured signals and the results are discussed in detail. The algorithm has been finally tested and validated on a real-time target.

Influence of Synchronous Jitter on GPS Receiving

Synchronous jitter is one of the factors that influence GPS receiving precision a lot. Jitter is the effective data offset off the ideal position in a data stream, which is divided into deterministic jitter and random jitter. A theoretical analysis was done to the influence of jitter. It can be seen that bit error rate gets larger due to the jitter of synchronous clock. By means of a simulation platform, a simulation was done to the synchronous jitter influence on bit error rate in the circumstance of white noise and single frequency interference. The result shows that as the synchronous jitter gets larger, the system bit error rate gets larger and the system function gets worse.

Adaptive filtering of 50 Hz line noise in ECG systems

In this paper a least mean square based adaptive algorithm for removing single frequency interference is analyzed. The possibility of using this algorithm to filtering 50 Hz line noise in the electrocardiographic signals (ECS) processing is checked. The comparison of the algorithm with classical digital filters is made. Modeling is carried out in the MATLAB. The results support the possibility to use considered algorithm for ECS preprocessing.References 4, figures 5.

Monochromatic Noise Removal via Sparsity-Enabled Signal Decomposition Method

Monochromatic noise always interferes with the interpretation of the seismic signals and degrades the quality of subsurface images obtained by further processes. Conventional methods suffer from several problems in detecting the monochromatic noise automatically, preserving seismic signals, etc. In this letter, we present an algorithm that can remove all major monochromatic noises from the seismic traces in a relatively harmless way. Our separation model is set up upon the assumption that input seismic data are composed of useful seismic signals and single-frequency interferences. Based on their diverse morphologies, two waveform dictionaries are chosen to represent each component sparsely, and the separation process is promoted by the sparsity of both components in their corresponding representing dictionaries. Both synthetic and field-shot data are employed to illustrate the effectiveness of our method.

The Research of Chaos-based M-ary Spreading Sequences

This paper is devoted to the generation and evaluation of the Chaos-based M-ary spreading sequences on communications systems. Sequences obtained by repeating a truncated and multi-ary quantized chaotic series are compared with classical m-sequences by means of the autocorrelation and cross-correlation properties and power-spectral features. Anti-noise performance of binary sequences and chaotic-based M-ary spreading sequences has been compared in the case of the same single-frequency interferences. Studies have shown that spectral features and anti-noise performance of chaotic-based M-ary spreading sequences which have great researching value are better than binary sequences. DOI: http://dx.doi.org/10.11591/telkomnika.v10i8.1654 Full Text: PDF

Application of Quantum Particle Swarm Optimization in Adaptive Notch Filter Design

Abstract: adaptive notch filter is a kind of apparatus which can eliminate single frequency or narrow-band interference, normal adaptive algorithm of notch filter is LMS algorithm, but the faster convergence velocity and the smaller steady error are difficult to gain simultaneously. Aimed at the weakness of LMS, the Particle Swarm Optimization (PSO) is studied deeply in the paper, based on the PSO; the quantum mechanic theory is added to improve it. Quantum Particle Swarm Optimization (QPSO) is researched and applied for adaptive notch filter which is proved more efficient in the noise control by MATLAB simulation. The new QPSO algorithm can balance the maladjustment and the searching ability of adaptive filter with a little calculation, the speed of convergence is faster than LMS and normal PSO algorithm.

Channel Equalization with Single Interference Technique based on FFT for efficient OFDM System

In today’s scenario the over sampled OFDM system performance is significantly improved if the deep faded symbols on the sub carriers of each over sampled OFDM signal are discarded and then reconstructed from the remaining OFDM signal by a time domain iterative algorithm. Base on the results of FFT in OFDM demodulation, one new single frequency interference estimation scheme is proposed, which can estimate accurately the parameters of single frequency interference by analyzing and comparing two spectrum lines having higher energy and power consumption ratio than others. The complexity of the scheme is very low and its accuracy is much higher than that of the conventional scheme which using only single spectra line possessing maximum energy to estimate interference parameters.

A frequency domain Hampel filter for blind rejection of sinusoidal interference from electromyograms

A frequency domain filtering method is presented for the removal of power-line and other sinusoidal interference from electromyograms. The presence of such interference results in spikes in the complex-valued fast Fourier transform which can be considered to be outliers. The filter uses the outlier-robust Hampel identifier to detect spikes and replaces them with the median value of local values. The performance of the filter was tested using a set of simulated electromyograms and on experimental data. It was shown that the filter is more effective at rejecting interference than multiple notch filtering and spectral interpolation. The main advantages of using this method are that the frequencies at which the interference occurs need not be known a priori and that signals are not distorted in the absence of interference. In the case of single-frequency interference added to simulated and experimental data, errors in root-mean-squared amplitude and median frequency of <5% are reported.

Edge location by use of optical phase variation

Traditional optical methods for locating an edge are based on light intensity variation with respect to a reference triggering level. Since the intensity variation is subject to stray light, the intensity variation of the light source, and the triggering level variation, the exact position of the edge cannot be determined. We describe a method for edge location that uses a phase variation in a modified differential interferometer. The maximal point of the slope of the phase variation across an edge is determined exactly by the relative position between the focused beam spot and the detected edge if the initial intensity ratio of the two single-frequency interference beams is kept unchanged. Therefore the phase variation can be used to locate the edge with high resolution and accuracy. To make practical use of the phase variation, the second derivative of the phase was used as a monotonic zero-crossing signal across the edge. The theoretical and the experimental verification have been conducted in detail. The results of the experiment show the feasibility of edge location when phase variation is used. The scheme is not affected by stray light and the intensity variation of the light source.

Stabilization of atoms in a strong laser field

The main mechanisms of atomic stabilization in a strong light field are surveyed. The main features and physics of Kramers-Henneberger and interference stabilization are discussed. Some experiments confirming existence of stabilization effects are briefly overviewed. Two-color interference stabilization is described in its connection with the single frequency interference stabilization and effects like the laser-induced continuum structures.