Cross Correlation In Frequency Domain Research Articles

Detection of GPS C/A Code Self-Interference: Monitor Overview and Applicability

<h3>Abstract</h3> Self-interference can cause large errors of up to tens of meters on the GPS C/A code pseudorange measurement. Although the probability of an occurrence of large self-interference errors is small, to enable the use of C/A code phase measurements in high accuracy or safety-of-life applications, a detection or mitigation method is needed. A stressful case of self-interference is modeled on a GPS hardware simulator to investigate monitor performance using real signal results. A summary of contributions in this paper follows. Self-interference pseudorange error characteristics within and mitigation requirements for the Ground Based Augmentation System (GBAS) Approach Service Type D (GAST-D) environment are identified. Existing monitors are evaluated for their response to self-interference and their ability to detect the error based on the GAST-D environment. This includes the potential for misidentification of the error. A novel Frequency Domain Cross-Correlation (FDCC) detector is proposed that can uniquely identify self-interference error with no siting constraints.

Frequency-Domain Q-Compensated Reverse Time Migration Using a Stabilization Scheme

Seismic attenuation occurs during seismic wave propagation in a viscous medium, which will result in a poor image of subsurface structures. The attenuation compensation by directly amplifying the extrapolated wavefields may suffer from numerical instability because of the exponential compensation for seismic wavefields. To alleviate this issue, we have developed a stabilized frequency-domain Q-compensated reverse time migration (FQ-RTM). In the algorithm, we use a stabilized attenuation compensation operator, which includes both the stabilized amplitude compensation operator and the dispersion correction operator, for the seismic wavefield extrapolation. The dispersion correction operator is calculated based on the frequency-domain dispersion-only viscoacoustic wave equation, while the amplitude compensation operator is derived via a stabilized division of two propagation wavefields (the dispersion-only wavefield and the viscoacoustic wavefield). Benefiting from the stabilization scheme in the amplitude compensation, the amplification of the seismic noises is suppressed. The frequency-domain cross-correlation imaging condition is exploited to obtain the compensated image. The layered model experiments demonstrate the effectiveness and great compensation performance of our method. The BP gas model examples further verify its feasibility and stability. The field data applications indicate the practicability of the proposed method. The comparison between the acoustic and compensated results confirms that the proposed method is able to compensate for the seismic attenuation while suppressing the amplification of the high-frequency seismic noise.

Calculation Methods and Comparison for Lightning Optical Return-Stroke Speed

The optical return-stroke speed calculation is vital to analyze the lightning development process. The traditional calculation methods of lightning optical return-stroke speed, including the slope-intercept and percentage-of-peak methods, usually have considerable calculation errors in noise cases. In this article, we generate the simulated optical return-stroke signal within 100 m above the starting point along the lightning channel and use four cross-correlation methods and six traditional methods to calculate the return-stroke speed at different observation points along the channel. We optimize the cross-correlation method and reduce the calculation error to within ±10% by selecting a part of the waveform to participate in the cross-correlation operation and performing the exponential operation on the frequency-domain cross-correlation sequence. The calculation results of the quadratic-correlation method and two optimized cross-correlation methods do not change significantly at different observation points along the channel. Different channel-base waveforms affect the return-stroke speed variation trend. The smaller the dispersion factor <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_p</i> is, the more pronounced the variation of the calculation result is, and the greater the calculation error is. The optical waveform with generated Gaussian noise will significantly affect the traditional calculation method. In contrast, the cross-correlation calculation method with noise has only a tiny calculation error.

Marine heatwaves and marine cold-spells on the Yucatan Shelf-break upwelling region

Since the historic marine temperature has been changing and consequently the ecological processes, this work studies the presence and magnitude of anomalous events at the sea surface temperature (SST) from a climate change perspective in a Non-eastern upwelling system. Concepts and metrics for Marine Heatwaves (MHW) and Marine Cold–Spell (MCS) were applied over the marine region of the Yucatan continental shelf and Yucatan Channel. To calculate the MHW/MCS and climatology between 1982 and 2019, a remote historic dataset of SST was used. Temporal differences of MHW/MCS events were calculated to assess the increase of MHW reported at a global scale in the last 10–20 years, splitting the resulting metrics of the study period. Furthermore, a frequency-domain cross-correlation analysis between SST and Chlorophyll-a was conducted to analyze a temporal relationship among those anomalies and the Red tide that struck the coastal region, in the year 2011. Results indicate that MHW/MCS have varied spatially and temporarily over the marine region of the Yucatan shelf, and have become more frequent and longer in the last twenty-years, tending to keep increasing in some sub-regions. MCS events are of equal or greater significance than MHW, mainly in the inner–shelf sub-region, where more than 110 days of MCS were recorded in 2011. The extreme biological event reported that year could be explained by MCS. Variability of the Yucatan current and upwelling, as well as large-scale synoptic atmospheric events are discussed as possible drivers for MHW/MCS.

An Adaptive ICA-Based Cross-Correlation Techniques for Water Pipeline Leakage Localization Utilizing Acousto-Optic Sensors

This paper describes the implementation of an adaptive ICA (Independent Component Analysis) based cross-correlation technique to process the noisy output from Acoustic optic sensor to locate the leaks in water pipes. In Digital Signal Processing methods, cross-correlation technique plays a prominent role in detecting the leak signals. In a real-time scenario, the leak signals get convolved with the impulse response of the pipe. In such cases, the conventional cross-correlation technique fails to detect the leak. This paper implements the maximization of non-gaussianity of ICA techniques along with wavelet decomposition as a preprocessing stage of frequency domain cross-correlation. The decomposition of the sensor data using wavelet reduces the computational complexity of the ICA. The adaptiveness of ICA in the proposed technique is more suitable for real-time water leak detection system. The probable benefit of using adaptive ICA is to enforce strong decorrelation and separation of the real-time leak signal from the convoluted impulse response of the pipe with noise. The above algorithm is validated using different experiments. The experimental result shows that the proposed method offers high accuracy of detecting the leak location compared to the conventional methods.

Coherency spectral analysis of interfacial water at TiO2 surfaces

ABSTRACT Classical molecular dynamic studies of anatase <101> and rutile <110> surfaces immersed in bulk SPC/fw water were performed to investigate the dynamic properties of the semi-mobile water layers formed thereon. Spectral analysis techniques were used to characterise and interpret the observed dynamical behaviour, including the use of frequency domain cross-correlation measures. Both surfaces exhibit distinct layering patterns, wherein molecular motion is inhibited and certain molecular vibrational modes are augmented or diminished. There is evidence that this effect is mediated by coupling of vibrational modes between the observed layers and under-coordinated surface oxygen (Obr) atoms and may play a role in the fascinating behaviour of water at TiO2 interfaces.

An Efficient Analytical Evaluation of the Electromagnetic Cross Correlation Green’s Function in MIMO Systems

In this paper, we completely eliminate all numerical integrations needed to compute the far-field envelope cross-correlation (ECC) in multiple-input-multiple-output (MIMO) systems by deriving accurate and efficient analytical expressions for the frequency-domain cross-correlation Green's functions (CGF), the most fundamental electromagnetic kernel needed for understanding and estimating spatial correlation metrics in multiple-antenna configurations. The analytical CGF is derived for the most general three-dimensional case, which can be used for fast CGF-based correlation matrix calculations in MIMO systems valid for arbitrary locations and relative polarizations of the constituent elements.

Deep characterization of the Santiago Basin using HVSR and cross-correlation of ambient seismic noise

Continuously recorded seismic ambient noise is used to investigate the intermediate and deep structure of the Santiago Basin for seismic site-response evaluation. Single-station H/V spectral ratios (HVSR) were used as a proxy to identify zones with high stiffness soils and low impedance contrast with the underlying bedrock, as a complement of available surface geology information. Frequency-domain cross-correlation of the vertical components of ambient noise were calculated and used to estimate phase velocity dispersion curves associated to station pairs over different soil deposits. In addition, noise correlation functions (NCFs) calculated from time-domain cross-correlation of the vertical seismic noise records were used to estimate group velocity dispersion curves and to verify results from the spectral method. Data processing from both methods resolves a frequency band between 0.1 and 8.0Hz, a critical band for civil infrastructure that is difficult to determine with traditional local-scale passive surface wave methods. Station pairs with high signal correlation over stiff soils in the center, south, and east part of the basin, mainly associated to flat HVSR response, yielded robust phase velocity dispersion curves that vary approximately from 3.5km/s at 0.1Hz to 1km/s at 4Hz. Shear wave velocity profiles inverted from the dispersion curves show high average shear wave velocities that also have a pronounced increase rate with depth and a lack of clear soil-bedrock interface at depths predicted by available gravimetric data.

Novel Spectrum Sensing Algorithms for OFDM Cognitive Radio Networks.

Spectrum sensing technology plays an increasingly important role in cognitive radio networks. Consequently, several spectrum sensing algorithms have been proposed in the literature. In this paper, we present a new spectrum sensing algorithm “Differential Characteristics-Based OFDM (DC-OFDM)” for detecting OFDM signal on account of differential characteristics. We put the primary value on channel gain θ around zero to detect the presence of primary user. Furthermore, utilizing the same method of differential operation, we improve two traditional OFDM sensing algorithms (cyclic prefix and pilot tones detecting algorithms), and propose a “Differential Characteristics-Based Cyclic Prefix (DC-CP)” detector and a “Differential Characteristics-Based Pilot Tones (DC-PT)” detector, respectively. DC-CP detector is based on auto-correlation vector to sense the spectrum, while the DC-PT detector takes the frequency-domain cross-correlation of PT as the test statistic to detect the primary user. Moreover, the distributions of the test statistics of the three proposed methods have been derived. Simulation results illustrate that all of the three proposed methods can achieve good performance under low signal to noise ratio (SNR) with the presence of timing delay. Specifically, the DC-OFDM detector gets the best performance among the presented detectors. Moreover, both of the DC-CP and DC-PT detector achieve significant improvements compared with their corresponding original detectors.

An Effective Time Delay Estimation Method Based on Frequency Difference Compensation for Narrowband RF Signals

This paper addresses a novel time delay estimation (TDE) method for narrowband RF signals with intermediate frequency difference (IFD). Since IFD is the main factor which affects the TDE precision, we present the frequency detection TDE model with IFD and discuss the effects of the IFD on the TDE. Then, a frequency detection TDE method based on IFD compensation is proposed. Especially, an improved frequency-domain cross-correlation method is adopted to estimate the IFD. The effectiveness of the algorithm is verified by MATLAB simulation. Simulation results demonstrate that the proposed TDE method shows a significant performance improvement over the classical TDE method based on Hilbert transform. Furthermore, the proposed method is also used in the actual system, and its estimation value is very close to the true value, which presents an enormous engineering practicality.

Rapid Location of LED Die Array Based on Cross Correlation in Frequency Domain

A rapid template matching algorithm is used to locate l-emitting d (LED) die array on wafer planes in vision-based LED sorting or die-bonding system, the image of LED die array is first converted to binary image and is pre-processed through morphological operations such as dilation and erosion, and the cross correlation operation between LED die templatae and wafer image in frequency domain is implemented by using fast Fourier transform (FFT), and the pixel coordinates of all LED dies on the wafer plane can be determined at one time using the cross correlation in frequency domain (CCFD) instead of in spacial domain. Experimental results of LED die array measurement to a large-diameter LED wafer show that detection efficiency is far higher than conventional normalized cross-correlation (NCC) algorithm, and is only half of consumed time to compare with the sequential similarity detection algorithm (SSDA), the proposed CCFD algorithm can be used for rapid LED die array location in vision-baesd LED sorting or die-bonding machines.

Low-Complexity Carrier Frequency Offset Estimation Algorithm in TD-LTE

Frequency offset estimation is an important module in the downlink synchronization process of orthogonal frequency division multiplexing (OFDM) system. Research on frequency synchronization of OFDM, a low-complexity and efficient method is proposed to evaluate frequency offset in this paper. In general, maximum likelihood (ML) based on cyclic prefix (CP) and primary synchronization signal (PSS) frequency-domain cross-correlation algorithm are applied for fractional carrier frequency offset estimation. PSS time-domain cross-correlation algorithm is used to estimate integral carrier frequency offset. However, for fractional carrier frequency estimation, the performance of ML based on CP degrades in fading channel. The complexity of the other algorithm is high. Also, the conventional integral carrier frequency estimation requires cross-correlation between the received PSS and local PSS or auto-correlation of received PSS, so they also have great complexity. In this paper, relying on the PSS time center-symmetric property, we perform PSS auto-correlation method twice in the time domain. Hence fractional carrier frequency offset is obtained and compensated. Next, relying on the PSS frequency center-symmetric property, we perform energy difference computations to estimate the integral carrier frequency offset, which is equal to the distance between the calculated minimum and the central frequency in frequency domain. Simulation results demonstrate that the proposed algorithm can estimate frequency offset accurately, guarantee the reliance and reduce complexity in comparison with the normal methods

Suppression of narrowband interference using frequency-domain cross-correlation

Suppression of narrowband interference using frequency-domain cross-correlation

On measuring surface wave phase velocity from station–station cross-correlation of ambient signal

We apply two different algorithms to measure surface wave phase velocity, as a function of frequency, from seismic ambient noise recorded at pairs of stations from a large European network. The two methods are based on consistent theoretical formulations, but differ in the implementation: one method involves the time-domain cross-correlation of signal recorded at different stations; the other is based on frequency-domain cross-correlation, and requires finding the zero-crossings of the real part of the cross-correlation spectrum. Furthermore, the time-domain method, as implemented here and in the literature, practically involves the important approximation that interstation distance be large compared to seismic wavelength. In both cases, cross-correlations are ensemble-averaged over a relatively long period of time (1 yr). We verify that the two algorithms give consistent results, and infer that phase velocity can be successfully measured through ensemble-averaging of seismic ambient noise, further validating earlier studies that had followed either approach. The description of our experiment and its results is accompanied by a detailed though simplifed derivation of ambient-noise theory, writing out explicitly the relationships between the surface wave Green's function, ambient-noise cross-correlation and phase and group velocities.

Failure of normal development of central drive to ankle dorsiflexors relates to gait deficits in children with cerebral palsy

Neurophysiological markers of the central control of gait in children with cerebral palsy (CP) are used to assess developmental response to therapy. We measured the central common drive to a leg muscle in children with CP. We recorded electromyograms (EMGs) from the tibialis anterior (TA) muscle of 40 children with hemiplegic CP and 42 typically developing age-matched controls during static dorsiflexion of the ankle and during the swing phase of treadmill walking. The common drive to TA motoneurons was identified through time- and frequency-domain cross-correlation methods. In control subjects, the common drive consists of frequencies between 1 and 60 Hz with peaks at beta (15-25 Hz) and gamma (30-45 Hz) frequencies known to be caused by activity within sensorimotor cortex networks: this drive to motoneurons strengthens during childhood. Similar to this drive in control subjects, this drive to the least affected TA in the CP children tended to strengthen with age, although compared with that in the control subjects, it was slightly weaker. For CP subjects of all ages, the most affected TA muscle common drive was markedly reduced compared with that of their least affected muscle as well as that of controls. These differences between the least and most affected TA muscles were unrelated to differences in the magnitude of EMG in the two muscles but positively correlated with ankle dorsiflexion velocity and joint angle during gait. Time- and frequency-domain analysis of ongoing EMG recruited during behaviorally relevant lower limb tasks provides a noninvasive and important measure of the central drive to motoneurons in subjects with CP.

Evidence for magmatic underplating and partial melt beneath the Canary Islands derived using teleseismic receiver functions

In recent years, an increasing number of studies have focussed on resolving the internal structure of ocean island volcanoes. Traditionally, active source seismic experiments have been used to image the volcano edifice. Here we present results using the analysis of compressional to shear (P to S) converted seismic phases from teleseismic events, recorded by stations involved in an active source experiment “TOM-TEIDEVS” (Ibáñez et al., 2008), on the island of Tenerife, Canary Islands. We supplement this data with receiver function (RF) analysis of seismograms from the Canary Islands of Lanzarote and La Palma, applying the extended-time multitaper frequency domain cross-correlation estimation method (Helffrich, 2006). We use the neighbourhood inversion approach of Sambridge (1999a,b) to model the RFs and our results indicate magmatic underplating exists beneath all three islands, ranging from 2 to 8km, but showing no clear correlation with the age of the island. Beneath both La Palma and Tenerife, we find localized low velocity zones (LVZs), which we interpret as due to partial melt, supported by their correlation with the location of historical earthquakes (La Palma) and recent earthquakes (Tenerife). For Lanzarote, we do not sample the most recently volcanically active region and find no evidence for a LVZ. Instead, we find a simple gradational velocity structure, with discontinuities at ∼4, 10 and 18km depth, in line with previous studies.

Sensing orthogonal frequency division multiplexing systems for cognitive radio with cyclic prefix and pilot tones

The detection of orthogonal frequency division multiplexing (OFDM) for cognitive radio is considered in this paper. A frequency-selective fading channel is considered and the receiving process is modeled with timing and frequency offsets. Firstly, the authors propose a new decision statistic based on time-domain cross-correlation of the cyclic prefix (CP) embedded in OFDM signals. The probability distribution functions (PDFs) of the statistics under both hypotheses of primary signal absence and presence are derived. Estimation of the timing and frequency offset is obtained through the maximum likelihood method and the received signals are modified. Then another new decision statistic based on frequency-domain cross-correlation of the pilot tones (PTs) is proposed whose PDF is also analyzed. Then, through the likelihood ratio test, the authors utilize CP and PT jointly and propose a global test statistic. The theoretical probabilities of false alarm (PFA) and detection are derived, and the theoretical threshold for any given PFA is proposed. The simulation results show that the proposed spectrum-sensing scheme has excellent performance, especially under very low signal-to-noise ratio (SNR).

Optical periodic code matching by single-shot broadband frequency-domain cross-correlation

We introduce and experimentally demonstrate a simple and reliable optical technique for matching between two periodic numerical sequences based on optical single-shot measurement of their broadband cross-correlation function in the frequency domain. Each sequence is optically encoded into the shape of the different broadband femtosecond pulse using pulse-shaping techniques. The two corresponding shaped pulses are mixed in a nonlinear medium together with an additional (amplitude-shaped) narrowband pulse. The spectrum of the resulting four-wave mixing signal is measured to provide the cross-correlation function of the two encoded sequences. For identical sequences it is the auto-correlation function that is being measured, allowing also the identification of the sequence period. The high contrast achieved here between cross-correlation and auto-correlation functions allows to determine with a very high reliability whether the two encoded sequences are identical or not. The demonstrated technique might be employed in an optical implementation of CDMA communication protocol.

Frequency-Domain Double-Talk Detection Based on the Gaussian Mixture Model

In this letter, we propose a novel frequency-domain approach to double-talk detection (DTD) based on the Gaussian mixture model (GMM). In contrast to a previous approach based on a simple and heuristic decision rule utilizing time-domain cross-correlations, GMM is applied to a set of feature vectors extracted from the frequency-domain cross-correlation coefficients. Performance of the proposed approach is evaluated through objective tests under various environments, and better results are obtained as compared to the time-domain method.

Erratum to Extended-Time Multitaper Frequency Domain Cross-Correlation Receiver-Function Estimation

In my article, “Extended-Time Multitaper Frequency Domain Cross-Correlation Receiver-Function Estimation” (Helffrich, 2006), I discovered an error transcribing the algorithm from code to its English-language description. The window overlap is …