Time Difference Measurement Research Articles

Data Fusion of Time Stamps and Transmitted Data for Unsynchronized Beacons

Unsynchronized localization systems based on the measurement of time (difference) of arrival require reliable time stamps of the received signal. Noise, frequency shifts, and echoes disturb the signal and induce measurement errors of the time stamp, which leads to localization errors. Furthermore, the line of sight (LOS) signal has to be distinguished from the echoes to avoid false signal tracking. The proposed method combines the information of an ultrasound transmission with the measured time stamp and estimates the identifier. In our approach, the ultrasound transmission system uses phase-shift keying to modulate the signal. The received symbols and the time stamps are tracked and fused by the Kalman filter to increase the signal-to-noise ratio of the fused symbols and improve the validity of the decoding. Hence, the bias of the received symbols is tracked and the tracking allows to distinguish between the LOS signal and the echoes. As a result, the data fusion reduces the packet error rate from 70% at a distance of 21 m to 4.5%. Moreover, the median error of the localization is reduced from 7 to 4.6 cm.

Spectral domain optical coherence tomography with balanced detection using single line-scan camera and optical delay line.

We propose a spectral domain optical coherence tomography (SD-OCT) system that uses a single line-scan detection scheme for balanced detection. Two phase-opposed spectra, generated by two optical fiber couplers, were detected by using a spectrometer with fast optical switching. A 2.69 km optical fiber was introduced to provide a proper time delay to prevent phase errors caused by the difference in measurement time between the two opposing spectra and unstable output voltages for controlling the galvano-scanner. Hence, a phase difference of π was obtained between the spectra over the sample depth without a phase error, which improved sensitivity by approximately 6 dB compared to that of conventional SD-OCT. We directly showed and compared the OCT images before and after applying the proposed balanced detection method in a phantom and in vivo sample.

Improvement of time difference of arrival measurements resolution by using fractional delay filters in a direct sequence‐code division multiple access radionavigation system

This study presents a method of improving time measurements resolution in a direct sequence-code division multiple access receiver by using a fine code tracking loop based on fractional delay filtering of a despreading sequence. It briefly describes the structure of a generic digital code tracking loop and the proposed modification which allows to measure time difference of arrival values with the subsample resolution, together with suggestions to reduce computational complexity by storing the set of samples of fractionally-delayed signals in memory. The proposed solution was tested in a laboratory and in real environment in a radionavigation system built in Gdansk University of Technology.

다중 요소를 가지는 SVM을 이용한 이블 트윈 탐지 방법

Widespread use of smart devices accompanies increase of use of access point (AP), which enables the connection to the wireless network. If the appropriate security is not served when a user tries to connect the wireless network through an AP, various security problems can arise due to the rogue APs. In this paper, we are going to examine the threat by evil-twin, which is a kind of rogue APs. Most of recent researches for detecting rogue APs utilize the measured time difference, such as round trip time (RTT), between the evil-twin and authorized APs. These methods, however, suffer from the low detection rate in the network congestion. Due to these reasons, in this paper, we suggest a new factor, packet inter-arrival time (PIAT), in order to detect evil-twins. By using both RTT and PIAT as the learning factors for the support vector machine (SVM), we determine the non-linear metric to classify evil-twins and authorized APs. As a result, we can detect evil-twins with the probability of up to 96.5% and at least 89.75% even when the network is congested.

Composite leading search index: a preprocessing method of internet search data for stock trends prediction

Previous studies have revealed that Internet search data is a new source of data that can be used to predict the stock market. In this new, data-driven research field, choosing a method for preprocessing data is crucial to achieving accurate prediction performance. This paper proposes a preprocessing method of Internet search data: composite leading search index (CLSI), which is composed of three steps: (a) keyword selection, (b) time difference measurement, and (c) leading index composition. We demonstrate the validity of CLSI by comparing this method’s results with the results from search volume index (SVI), which is most commonly used in previous literatures. We build a time series model (TS) with error correction and support vector regression (SVR) for stock trend prediction, and combine into four models for comparison: SVI–TS, CLSI–TS, SVI–SVR, and CLSI–SVR. We test these four models in the context of the Chinese stock market, which interests more and more investors nowadays, and analyzed results in nine datasets: stable periods, peak periods and trough periods of Shanghai Composite Index, Shenzhen Composite Index, and Hushen 300 index respectively. The results show that using TS and SVR as forecasting models, CLSI performs better than SVI on majority of the test dataset while has almost the same performance with that of SVI on the remaining test dataset. It is to some extent convincing that CLSI is a more efficient preprocessing method of Internet search data for stock trend prediction.

Study on the Time-grating Displacement Sensor of the Static Light Field Type Based on Linear Charge-coupled Device

According to the design ideology of time-grating sensor, continuing with the research foundation of the magnetic field type and electronic field type in the past, a time-grating sensor of light field type is put forward and analyzed. In addition, the principle and implementation plans are proposed. On the basis of measurement principle of time-grating, exploratory presented a method of uniform scanning by using photoelectric detector of timing driven, to convert the displacement detection of the object into measured time difference. To verify the validity of the scheme, a charge-coupled device(CCD) time-grating prototype is designed by a circular array which is constituted by multiple linear CCD of the same type. After multiplied the time difference variation of the output electric signal on the adjacent CCD and the uniform scanning speed value, through proper transformation, size and direction of the relative shaft angular displacement would be got. By measuring compare with circular grating which measurement accuracy reach within ±1″, measuring errors with a developed prototype are controlled within ±6° in the range of entire circumference. A reliable basis of theoretic and practical is provided for the further study on the time-grating of light field type.

Design and Evaluation of an Open-Loop Receiver for TWSTFT Applications

The two-way satellite time and frequency transfer (TWSTFT) technique provides uncertainty at the nanosecond level for time differences measured over an intercontinental baseline. The time-difference results occasionally reveal daily variations of a few nanoseconds due to multiple effects. These daily variations are called diurnals, and they increase the uncertainty of the time-difference measurements. Since a time difference is obtained by combining two time-of-arrival (TOA) measurements of two receivers, the receivers may contribute the diurnals if they are not reciprocal. To improve reciprocities, a TWSTFT receiver based on the open-loop (OL) method was proposed and implemented on a software-defined radio receiver (SDR). For evaluation, the OL-based SDR was compared with a conventional receiver in a short-baseline TWSTFT experiment. The experimental results indicate that the diurnals disappeared with the OL-based SDRs while a diurnal of ±0.2 ns could be observed with conventional receivers. These results imply that the diurnals partially depend on TOA measurement methods used in the TWSTFT receiver.

A Bayesian Approach for Localization of Acoustic Emission Source in Plate-Like Structures

This paper presents a Bayesian approach for localizing acoustic emission (AE) source in plate-like structures with consideration of uncertainties from modeling error and measurement noise. A PZT sensor network is deployed to monitor and acquire AE wave signals released by possible damage. By using continuous wavelet transform (CWT), the time-of-flight (TOF) information of the AE wave signals is extracted and measured. With a theoretical TOF model, a Bayesian parameter identification procedure is developed to obtain the AE source location and the wave velocity at a specific frequency simultaneously and meanwhile quantify their uncertainties. It is based on Bayes’ theorem that the posterior distributions of the parameters about the AE source location and the wave velocity are obtained by relating their priors and the likelihood of the measured time difference data. A Markov chain Monte Carlo (MCMC) algorithm is employed to draw samples to approximate the posteriors. Also, a data fusion scheme is performed to fuse results identified at multiple frequencies to increase accuracy and reduce uncertainty of the final localization results. Experimental studies on a stiffened aluminum panel with simulated AE events by pensile lead breaks (PLBs) are conducted to validate the proposed Bayesian AE source localization approach.

A 3D approximate maximum likelihood solver for localization of fish implanted with acoustic transmitters.

Better understanding of fish behavior is vital for recovery of many endangered species including salmon. The Juvenile Salmon Acoustic Telemetry System (JSATS) was developed to observe the out-migratory behavior of juvenile salmonids tagged by surgical implantation of acoustic micro-transmitters and to estimate the survival when passing through dams on the Snake and Columbia Rivers. A robust three-dimensional solver was needed to accurately and efficiently estimate the time sequence of locations of fish tagged with JSATS acoustic transmitters, to describe in sufficient detail the information needed to assess the function of dam-passage design alternatives. An approximate maximum likelihood solver was developed using measurements of time difference of arrival from all hydrophones in receiving arrays on which a transmission was detected. Field experiments demonstrated that the developed solver performed significantly better in tracking efficiency and accuracy than other solvers described in the literature.

Asynchronous time difference of arrival (ATDOA) method

A new method for a location service in the asynchronous wireless sensor networks is outlined. This method, which is called asynchronous time difference of arrival (ATDOA), enables calculation of the position of a mobile node without knowledge of relative time differences (RTDs) between measuring sensors. The ATDOA method is based on the measurement of time difference of arrival between the node and the same sensor at the discrete time n and n+1, and the solution of a nonlinear system of equations. The paper concentrates on the description of the method, solving the nonlinear system of equations and simulation results.

Artifacts in digital coincidence timing

Digital methods are becoming increasingly popular for measuring time differences, and are the de facto standard in PET cameras. These methods usually include a master system clock and a (digital) arrival time estimate for each detector that is obtained by comparing the detector output signal to some reference portion of this clock (such as the rising edge). Time differences between detector signals are then obtained by subtracting the digitized estimates from a detector pair. A number of different methods can be used to generate the digitized arrival time of the detector output, such as sending a discriminator output into a time to digital converter (TDC) or digitizing the waveform and applying a more sophisticated algorithm to extract a timing estimator.All measurement methods are subject to error, and one generally wants to minimize these errors and so optimize the timing resolution. A common method for optimizing timing methods is to measure the coincidence timing resolution between two timing signals whose time difference should be constant (such as detecting gammas from positron annihilation) and selecting the method that minimizes the width of the distribution (i.e. the timing resolution). Unfortunately, a common form of error (a nonlinear transfer function) leads to artifacts that artificially narrow this resolution, which can lead to erroneous selection of the ‘optimal’ method. The purpose of this note is to demonstrate the origin of this artifact and suggest that caution should be used when optimizing time digitization systems solely on timing resolution minimization.

Diurnal pattern in canopy light interception for tree fruit orchard trained to an upright fruiting offshoots (UFO) architecture

Fractional interception of photosynthetically active radiation (FIPAR) (i.e. light interception) by tree fruit canopies determines, in large part, fruit quantity and quality, and thus profitability. This study aimed to elucidate the diurnal pattern in FIPAR and determine the optimum time at which the measured FIPAR best represents mean daily FIPAR in sweet cherry trees trained to the planar UFO (Upright Fruiting Offshoots) architecture. Two experiments were conducted to assess the influence of canopy development stages and of canopy height to row spacing ratios (H/S ratio) on diurnal FIPAR pattern and optimum measurement time. For different canopy development stages, three adjacent north-to-south sample blocks were selected. For different H/S ratios, three levels of 0.75, 1.00, and 1.25 were used, and 9 north-to-south sample block for each level were selected. Daily FIPAR was determined from measurements taken within ±6 h of solar noon. Gaussian process regression with four parameters was applied to obtain the diurnal pattern with coefficients of determination (R2) ranging from 0.97 to 1.00. The diurnal pattern was symmetric with the lowest point around solar noon. Mean daily FIPAR increased during the season, as well as with increasing H/S ratio. For both experiments, there was no substantial difference in optimum measurement time among stages and among H/S ratios, with maximum difference of 0.3 h and 0.4 h respectively. We recommend an optimal measurement time window of −2.5 h to −2.0 h with reference to solar noon for the planar UFO architecture to estimate mean daily FIPAR with ±10% tolerance interval.

Study on the Time-Grating Sensor Method of the Static Light Field Type Based on Timing-Driven

In order to time grating measurement principle application to the field of optical measurement, a uniform scan coordinate system by using photosensitive element of timing driven is presented to convert the displacement detection of the object into measured time difference. According to the conversion principle of relative motion coordinate systems of time grating, when view the photosensitive element of linear CCD as a uniform scanning coordinate system, view the spatial side by side and timing of mutually staggered on the two linear CCD as a stationary coordinate system, after measured the time difference variation of the output electric signal on the different CCD for the same object, size and direction of the relative displacement of the object would be made by multiplying time difference variation and scanning speed. With the calibration of the Renishaw laser interferometer for the developed linear CCD displacement sensor, the measuring errors are controlled within after error correction in the effective measuring range of 600.05mm. This realizes the idea of time measuring space in the field of optical.

A Study on Impact of Alcohol Among Young Indian Population Using HRV Analysis

Heart Rate Variability (HRV) is the measure of time difference between two successive heart beats and its variation occurring due to internal and external stimulation causes. HRV is a non-invasive tool for indirect investigation of both cardiac and autonomic system function in both healthy and diseased condition. It has been speculated that HRV analysis by nonlinear method might bring potentially useful prognosis information into light which will be helpful for assessment of cardiac condition. In this study, HRV from two types of data sets are analyzed which are collected from different subjects in the age group of 18 to 22. Then parameters of linear methods and three nonlinear methods, approximate entropy (ApEn), detrended fluctuation analysis (DFA) and Poincare plot have been applied to analyze HRV among 158 subjects of which 79 are control study and 79 are alcoholics. It has been clearly shown that the linear and nonlinear parameters obtained from these two methods reflect the opposite heart condition of the two types of data under study among alcoholics non-alcoholic’s by HRV measures. Poincare plot clearly distinguishes between the alcoholics by analysing the location of points in the ellipse of the Poincare plot. In alcoholics the points of the Poincare plot will be concentrated at the centre of the ellipse and in nonalchoholics the points will be much concentrated along the periphery of the ellipse. The Approximate Entropy value will be lesser than one in alcoholics and in nonalcoholics the entropy shows values greater than one. The increased LF/HF value in alcoholics denotes the increase in sympathetic nervous system activities and decrease of the parasympathetic activity which will be lesser in alcoholics subjects.

Improving accuracy of acoustic source localization in anisotropic plates

The acoustic source localization technique for anisotropic plates proposed by the authors in an earlier publication ([1] Kundu et al., 2012) is improved in this paper by adopting some modifications. The improvements are experimentally verified on anisotropic flat and curved composite plates. Difficulties associated with the original technique were first investigated before making any modification. It was noted that the accuracy of this technique depends strongly on the accuracy of the measured time difference of arrivals (TDOA) at different receiving sensors placed in close proximity in a sensor cluster. The sensor cluster is needed to obtain the direction of the acoustic source without knowing the material properties of the plate. Two modifications are proposed to obtain the accurate TDOA. The first one is to replace the recorded full time histories by only their initial parts – the first dip and peak – for the subsequent signal processing. The second modification is to place the sensors in the sensor cluster as close as possible. It is shown that the predictions are improved significantly with these modifications. These modifications are then applied to another sensor cluster based technique called the beamforming technique, to see if similar improvements are achieved for that technique also with these modifications.

Location of PDs inside transformer windings using UHF methods

Diffraction of Ultra-High-Frequency (UHF) electromagnetic waves generated by partial discharges (PDs) inside a transformer will decrease the amplitude when passing through the winding and delay the arrival time of initial wave at the UHF sensors installed on the internal wall of the tank. It may be difficult to locate PDs inside the winding based on detection of UHF signals. To study the feasibility of locating PDs inside the winding using UHF methods, the propagation of UHF wave through windings was simulated by the XFDTD software and the cause of arrival time delay was analyzed by a geometric model. Experiments were carried out on a 220 kV oil-immersed transformer to test the measurement sensitivity and the location accuracy of UHF method for PDs inside windings. The theoretical research results indicated that the UHF wave passed through windings along broken lines, and the propagation time from the PD source to UHF sensors was compared to the time of wave travelling along a straight line. It was found that the arrival time delay caused by diffraction was less than 1ns. The experimental results showed that PDs about 500 pC inside the windings could be detected and located. The amplitude of the UHF signal decreased by about 18 dB, the errors of time difference measurements were less than 0.5 ns, and the location errors were less than 0.1 m.

Delay and Doppler Induced Direct Tracking by Particle Filter

The geolocation and tracking of a moving transmitter using receivers mounted on stationary or moving platforms is considered. Two-step conventional methods measure time difference of arrivals (TDOA) and differential Doppler in the first step, and in the second step use these measurements for geolocation and tracking. We explore a particle filter that uses the received radio signal directly in order to determine the location and velocity of the transmitter. Two algorithms are derived for the case of unknown deterministic signals and for the case of unknown Gaussian signals. In addition we derive recursive performance bounds for the two cases. The proposed methods show better performance than two-step methods at low signal-to-noise ratio (SNR) values and achieve the performance bound at high SNR values.

Self-sensing time domain reflectometry method for damage monitoring of a CFRP plate using a narrow-strip transmission line

Time domain reflectometry (TDR) measures the time difference between the pulse signals reflected from the end of a transmission line and from damage, and it obtains the location of the damaged point in the target transmission line from the measured time difference. In previous studies, authors of the present paper proposed a self-sensing TDR method for a carbon fiber reinforced polymer (CFRP) plate. The results of a previous paper revealed the applicability of the self-sensing TDR method for the CFRP plate. In this study, a new self-sensing TDR method is proposed: a narrow-strip line is used for a transmission line. The narrow-strip transmission line allows us to determine the location of damage in the transverse direction. The present study experimentally investigates impedance matching using the narrow-copper-strip transmission line. The results of the damage detections show the applicability of the new method to damage monitoring of CFRP plates.

Meridional-Flow Measurements from Global Oscillation Network Group Data

We present measurements of the solar meridional flow using time-distance analysis based on Global Oscillation Network Group (GONG) data. In an attempt to detect the deep equatorward flow, which is believed to be a very small amplitude motion, we averaged time-difference measurements over a 15-year period and utilized both phase-velocity and high-m filtering techniques. These method seem to be capable of extending the meridional-flow measurements to the deep layers of the convection zone, down to 0.7 R⊙. Typical uncertainties for most depths within ± 35∘ latitude are less than 0.03 s. At higher latitudes, the uncertainties are about 0.06 s. There is a significant abrupt decrease in the nature of the travel-time differences for measurements that probe the bottom of the convection zone.

Sonographic evaluation of intravascular volume status in the surgical intensive care unit: a prospective comparison of subclavian vein and inferior vena cava collapsibility index

BackgroundTraditional methods for intravascular volume status assessment are invasive and are associated significant complications. While focused bedside sonography of the inferior vena cava (IVC) has been shown to be useful in estimating intravascular volume status, it may be technically difficult and limited by patient factors such as obesity, bowel gas, or postoperative surgical dressings. The goal of this investigation is to determine the feasibility of subclavian vein (SCV) collapsibility as an adjunct to IVC collapsibility in intravascular volume status assessment. MethodsA prospective study was conducted on a convenience sample of surgical intensive care unit patients to evaluate interchangeability of IVC collapsibility index (IVC-CI) and SCV-CI. After demographic and acuity of illness information was collected, all patients underwent serial, paired assessments of IVC-CI and SCV-CI using portable ultrasound device (M-Turbo; Sonosite, Bothell, WA). Vein collapsibility was calculated using the formula [collapsibility (%) = (max diameter – min diameter)/max diameter × 100%]. Paired measurements from each method were compared using correlation coefficient and Bland–Altman measurement bias analysis. ResultsThirty-four patients (mean age 56 y, 38% female) underwent a total of 94 paired SCV-CI and IVC-CI sonographic measurements. Mean acute physiology and chronic health evaluation II score was 12. Paired SCV- and IVC-CI showed acceptable correlation (R2 = 0.61, P < 0.01) with acceptable overall measurement bias [Bland–Altman mean collapsibility difference (IVC-CI minus SCV-CI) of −3.2%]. In addition, time needed to acquire and measure venous diameters was shorter for the SCV-CI (70 s) when compared to IVC-CI (99 s, P < 0.02). ConclusionsSCV collapsibility assessment appears to be a reasonable adjunct to IVC-CI in the surgical intensive care unit patient population. The correlation between the two techniques is acceptable and the overall measurement bias is low. In addition, SCV-CI measurements took less time to acquire than IVC-CI measurements, although the clinical relevance of the measured time difference is unclear.