Accurate Time Delay Research Articles

Decoding microwave modulation transfer: The impact of dissipation through stochastic processes

AbstractAn anomalous transfer of modulation from a modulated microwave beam () to an unmodulated one () has been experimentally demonstrated through accurate delay time measurements. These results are analyzed according to two possible interpretations: one based on an electromagnetic approach as reported elsewhere, and the other based on a purely stochastic model. This latter model, made up of random zig‐zag paths, is the focus of the current paper. It is demonstrated that it is possible to obtain a plausible description of the experimental data.

Guided Lamb Wave Array Time-Delay-Based MUSIC Algorithm for Impact Imaging.

Composite materials, valued in aerospace for their stiffness, strength and lightness, require impact monitoring for structural health, especially against low-velocity impacts. The MUSIC algorithm, known for efficient directional scanning and easy sensor deployment, is gaining prominence in this area. However, in practical engineering applications, the broadband characteristics of impact response signals and the time delay errors in array elements' signal reception lead to inconsistencies between the steering vector and the actual signal subspace, affecting the precision of the MUSIC impact localization method. Furthermore, the anisotropy of composite materials results in time delay differences between array elements in different directions. If the MUSIC algorithm uses a fixed velocity value, this also introduces time delay errors, further reducing the accuracy of localization. Addressing these challenges, this paper proposes an innovative MUSIC algorithm for impact imaging using a guided Lamb wave array, with an emphasis on time delay management. This approach focuses on the extraction of high-energy, single-frequency components from impact response signals, ensuring accurate time delay measurement across array elements and enhancing noise resistance. It also calculates the average velocity of single-frequency components in varying directions for an initial impact angle estimation. This estimated angle then guides the selection of a specific single-frequency velocity, culminating in precise impact position localization. The experimental evaluation, employing equidistantly spaced array elements to capture impact response signals, assessed the effectiveness of the proposed method in accurately determining array time delays. Furthermore, impact localization tests on reinforced composite structures were conducted, with the results indicating high precision in pinpointing impact locations.

Adaptive contrastive learning based network latency prediction in 5G URLLC scenarios

With the increasing demand for 5G Ultra-Reliable Low Latency Communication (URLLC), accurate network time delay analysis is crucial. However, current network latency prediction models designed for 5G URLLC scenarios overlook the multiple downstream tasks case, such as network intrusion detection, recognition of network operational states, and decision-making for network resource scheduling.Furthermore, the robustness of the models needs to be enhanced. In this paper, we propose a Contrastive Convolutional Structure for Network Delay (CCSND), an adaptive contrastive learning framework that utilizes a temporal representation extraction module for capturing temporal periodicity and statistical features. To improve robustness and adaptability in time-series representation, CCSND designs strategic data augmentation methods, including temporal segmentation and delay obscuration. Experiment results on several real-world 5G URLLC scenario datasets demonstrate the superior performance of the proposed CCSND. It outperforms the current state-of-the-art Informer model by 38.7% and the traditional LSTM model by 64.5% in terms of mean squared error (MSE). Our code can be accessed at https://github.com/MerelyBreeze/CCSND.

Attosecond delay locking of large arm pump-probe system

With the development of ultrafast science and attosecond laser technology, the pump-probe system based on isolated attosecond laser pulses is a key to attosecond science, which will be used to study electronic dynamics on an attosecond time-scale. To obtain stable and reliable signals, it is necessary to ensure ultra-stable and ultra-accurate synchronization. Any timing jitter can cause signal to disperse or get buryied in noise, making it impossible to obtain the true physical mechanism. Based on the above, the delay between pump laser pulse and probe laser pulse must be controlled with an attosecond time resolution. In this work, a dual-layer system is developed to achieve high-precision synchronization locking. To ensure that both layers have the same time jitter, we design an adapter to secure the elements placed during installation. Timing jitter is obtained by shaking interference fringes through fast Fourier transformation, and can be calculated in several ms. Then error signals are fed back to the PZT stage in order to compensate for real-time optical path drift. Through such a design, a time-delay accuracy of 7.64 as to 15.53 as is realized, which is linearly related to the interferometer arm length ranging from 1 m to 5 m, with an <i>R</i><sup>2</sup> of 0.96. Moreover, the error between the experimental result of arm length of 8 m and 10 m and the result fitted with the above data is less than 3 as. These results show that using a small interferometer can achieve the fast detection of the time-delay accuracy of long-arm attosecond pump-probe detection system in large scientific instrument, which is of great significance in guiding ther applications such as in non-collinear attosecond streaking spectroscopy, time-resolved photoelectron spectroscopy, and coherent synthesis.

Transcranial Ultrasonic Focusing by a Phased Array Based on Micro-CT Images.

In this paper, we utilize micro-computed tomography (micro-CT) to obtain micro-CT images with a resolution of 60 μm and establish a micro-CT model based on the k-wave toolbox, which can visualize the microstructures in trabecular bone, including pores and bone layers. The transcranial ultrasound phased array focusing field characteristics in the micro-CT model are investigated. The ultrasonic waves are multiply scattered in skull and time delays calculations from the transducer to the focusing point are difficult. For this reason, we adopt the pulse compression method and the linear frequency modulation Barker code to compute the time delay and implement phased array focusing in the micro-CT model. It is shown by the simulation results that ultrasonic loss is mainly caused by scattering from the microstructures of the trabecular bone. The ratio of main and side lobes of the cross-correlation calculation is improved by 5.53 dB using the pulse compression method. The focusing quality and the calculation accuracy of time delay are improved. Meanwhile, the beamwidth at the focal point and the sound pressure amplitude decrease with the increase in the signal frequency. Focusing at different depths indicates that the beamwidth broadens with the increase in the focusing depth, and beam deflection focusing maintains good consistency in the focusing effect at a distance of 9 mm from the focal point. This indicates that the phased-array method has good focusing results and focus tunability in deep cranial brain. In addition, the sound pressure at the focal point can be increased by 8.2% through amplitude regulation, thereby enhancing focusing efficiency. The preliminary experiment verification is conducted with an ex vivo skull. It is shown by the experimental results that the phased array focusing method using pulse compression to calculate the time delay can significantly improve the sound field focusing effect and is a very effective transcranial ultrasound focusing method.

Optimized Design of a Variable Fractional Delay Filter With Delay Error Constraints

A novel algorithm for designing variable fractional delay (VFD) filter coefficients is proposed to improve time delay accuracy. The principle of this method is to model the coefficient design as an optimization problem with fractional delay error constraints (FDECs) and use a linear approach to derive a new FDEC expression for solving the problem. The solution of the FDEC expression can be efficiently obtained through linear programming (LP). Compared with existing algorithms, the design examples show the proposed method achieves a 100-fold improvement in delay accuracy while maintaining the frequency response (FR) error at an acceptable level, and yields a 5 dB reduction in FR error with the same level of delay accuracy.

An Improved Time Delay Measurement Method for the Long-Distance Underwater Environment.

With the development of underwater navigation and underwater communication, it remains difficult to obtain time delay measurements after propagating long distance. This paper proposes an improved high-accuracy time delay measuring method for long distance underwater channel propagation. First, by sending an encoded signal, the signal acquisition is carried out at the receiving end. Then, to improve signal to noise ratio (SNR), bandpass filtering is carried out on the receiving end. Next, considering the random changes in the underwater sound propagation channel, a strategy is proposed to select the optimal time window for cross-correlation. Then, new regulations are proposed to calculate the cross-correlation results. To verify the effectiveness of the algorithm, we compared it with other algorithms under low SNR conditions using Bellhop simulation data. Finally, the accurate time delay is obtained. With underwater experiments over different distances, the method proposed by the paper achieves high accuracy. The error is about 10-3 s. The proposed method makes a contribution to underwater navigation and communication.

Providing a simple and efficient algorithm for passive sound localization

The sound source localization (SSL) system is one of the main approaches for detecting targets. This kind of localization method is carried out in a passive way, without the emission of any signals, and cannot be detected easily. This paper investigates the two-dimensional SSL of stationary targets using only three receivers. Given that, flow-induced noise of the bluff-bodies in viscous fluids is one of the most important noise generation sources, firstly, this noise is simulated numerically. Due to the distance between the receivers in an array, the sound reaches the receiver with time delay. High accuracy SSL needs highly accurate time delays measurement. In the following, time delays are obtained by calculating the cross-correlation in a time domain of sound signals arriving at the receiver array, and next, the bearing angle of the sound source is estimated. Later, using a new, simple (easy installation), fast (real-time), and accurate pure geometric algorithm, the source candidate locations are obtained. Then, using an elimination algorithm, the ambiguity of the noise source location is removed, and source imaginary locations are removed. Finally, this process is validated by a physical algorithm. Numerical results verify the effectiveness of this geometric algorithm.

A Low Temperature Coefficient Time-to-Digital Converter with 1.3 ps Resolution Implemented in a 28 nm FPGA.

Time-to-digital converter (TDC) is the key technology to realize accurate time delay measurement in high-precision optical fiber time-frequency transmission and synchronization, optical sensing and many scientific applications. The performance of FPGA-TDC based on the carry chain is sensitive to the operating temperature. This paper presents a parallel multichain cross segmentation method, without multitime measurements, which merges multichain into an equivalent chain, achieving low temperature coefficient and maintaining high precision. The equivalent chain breaks the limit of the intrinsic cell delay of a single carry chain, improves the precision and reduces the impact of temperature variation significantly. A two-channel TDC based on parallel multichain cross segmentation method is implemented in a 28 nm fabrication process Kintex-7 FPGA. The results show that the performance of TDC is improved with the increase of the number of chains. The 10-chain TDC with 1.3 ps resolution, 4.6 ps single-shot precision performs much better than the plain TDC with 11.4 ps resolution, 8.7 ps single-shot precision. The resolution is stable with 0.0002 ps/°C temperature coefficient under an operating temperature range from 25 °C to 70 °C. Moreover, the proposed method reduces the complexity of the circuit and the resource usage.

Cramér–Rao Lower Bounds for Estimating Time Delay and Doppler Stretch for Monostatic and Bistatic Impulse Radar Systems Using Ultrawideband-Throb Signal

In this article, the wideband ambiguity function (WBAF) of monostatic radar and that of bistatic radar, both operating with ultrawideband (UWB)-throb signals, are presented and used to calculate Cramér–Rao lower bounds (CRLBs) on the estimation accuracy of time delay and Doppler stretch in the case of monostatic radar and CRLBs on the estimation accuracy of receiver-to-target range and relative-velocity of a moving point target in the case of bistatic radar. Performance analysis is carried out to investigate the effects of the parameters that characterize the UWB-throb signal, i.e., pulse scaling factor, initial pulse repetition frequency (PRF), throb rate, and signal duration, and the parameters defining the bistatic-radar geometry, i.e., receiver-to-target range, baseline distance, and elevation angle, on the estimation accuracy of the monostatic-CRLBs and on that of the bistatic-CRLBs. Computer plots demonstrate that the estimation accuracy of the monostatic-CRLBs and the bistatic-CRLBs is influenced by the aforementioned radar parameters. It is also shown that target relative velocity has no major effects on the estimation performance of monostatic-CRLBs and bistatic-CRLBs.

Large-Scale 3D Baseline Measurement Based on Phase-Stabilized GNSS-Over-Fiber System

Multi-antenna GNSS-over-fiber system is considered an effective solution for three-dimension (3D) baseline measurement. By precisely determining the transmission time delays between the antennas and the receiver, the vertical precision can be improved based on the single difference (SD) model. This method, however, would encounter problems if the baseline is too long, since a high precision measurement of the time delay of a long fiber link is usually time-consuming. Here, we propose and demonstrate a high-speed phase-stabilized GNSS-over-fiber system for large-scale 3D baseline measurement. A relatively slow but accurate time delay measurement module is used to calibrate the link delay, then a fast active compensation device is employed to keep the time delay constant. If the delay variation exceeds the compensation range, the time delay measurement module would measure the link delay again and bias the active compensation device at a new operating state. In a proof-of-concept experiment, the precision of the 3D baseline measurement obtained by the proposed system with a 20-km optical fiber is around 2.82 mm thanks to the rigid active compensation and the high-precision time delay measurement. If the active compensation device is disabled, the vertical precision of the baseline measurement obtained would be degraded from 2.82 mm to 16.46 mm in 10 minutes.

Enhanced Localization of Transients Based on a Novel Cross-correlation Method

Abstract Locating gamma-ray transients including gamma-ray bursts (GRBs) and soft gamma repeater (SGR) bursts is of great importance in multi-messenger and multi-wavelength astronomy, such as guiding optical and radio follow-up observations and evaluating the association of a GRB with a gravitational wave or an SGR with a galaxy or fast radio burst (FRB). A time delay (or triangulation) method with multiple missions has been utilized to localize GRBs since their discovery in the 1970s. In this paper, we propose to use the Modified Cross-correlation Function (called Li-CCF hereafter) to derive the accurate time delay from the high time resolution light curves recorded by GRB detectors. This method has been extensively verified with simulation and a sample of GRBs and SGRs with precise positions, using event-by-event data (TTE or Evt data) of Insight-HXMT/HE, Fermi/GBM, Swift/BAT, and GECAM. We find that the 1σ uncertainty (annulus half-width) can be less than 0.3 degrees despite the relatively short distance between these satellites. We note that the localization error given by Li-CCF can be reduced by several times compared with the traditional CCF method or the Fermi/GBM-alone localization, depending on the timing, spectral lag and direction of the GRB, and the distance and number of satellites used. Finally, systematic errors of this time delay method, including the effect of GRB spectral lags and background variation in light curves, have been studied in detail and several improvements have been proposed to deal with those effects.

A Novel Synchronization Method in Terahertz Large‐Scale Antenna Array System

We focus on the problems of the accurate time delay estimation, the design of training pilots, and hybrid matrix optimization within the large-scale antenna array Terahertz (THz) broadband communication system. In contrast to the existing researches based on narrow-band arrays, we hereby shed light on the time delay estimation of broadband arrays. In THz broadband communication systems, the data symbol duration is relatively short when comparing with the dimension of the antenna array. In large-scale antenna systems, signals received in each antenna are no longer different phase-shifted copies of the same symbol, but completely different symbols in which occasion traditional narrow-band structure is no longer suitable. Based on the above conclusion, firstly, we put forward a system model based on large-scale antenna arrays and Time delay line (TDL) structure. Secondly, we deduce the Cramer-Rao lower bound (CRLB) of the time delay estimation, and present a time delay estimation algorithm that could reach the CRLB. Thirdly, by minimizing the CRLB, we address the design of the training pilot and optimized TDL structure under the condition of constant envelope training pilot and modulus TDL structure. Finally, we disclose the numerical simulation results. According to the simulation results, the aforementioned method is workable in reaching the CRLB, the TDL structure can significantly surpass that of the traditional model, and the optimal pilot design method outperforms the pseudo-random pilot structure.

Design of Sparse Multiband Signal for Precise Positioning With Joint Low-Complexity Time Delay and Carrier Phase Estimation

This paper presents a methodology to design a sparse multiband ranging signal with a large virtual bandwidth, from which time delay and carrier phase are estimated by a low complexity multivariate maximum likelihood (ML) method. In the estimation model for a multipath channel, not all reflected paths are considered, and time delay and carrier phase are estimated in a step-wise manner to further reduce the computational load. By introducing a measure of dependence and a measure of bias for a multipath reflection, we analyse the bias, precision and accuracy of time delay and carrier phase estimation. Since these two indicators are determined by the signal spectrum pattern, they are used to formulate an optimization for signal design. By solving the optimization problem, only a few bands from the available signal spectrum are selected for ranging. Consequently, the designed signal only occupies a small amount of signal spectrum but has a large virtual bandwidth and can thereby still offer a high ranging precision with only a small bias, based on the low-complexity simplified ML method. Numerical and laboratory experiments are carried out to evaluate the ranging performance of the proposed estimation method based on sparsely selected signal bands. Relative positioning, in which we only measure a change in position, based on either the time delay estimates or the carrier phase estimates, is presented as a proof-of-concept for precise positioning. The results show that positioning based on only 7 out of 16 signal bands, sparsely placed in the available spectrum, achieves a decimeter level accuracy when using time delay estimates, and a millimeter level accuracy when using carrier phase estimates. Compared with the case of using all available bands, and without largely decreasing the positioning performance, the computational complexity when using the sparse multiband signal can be reduced by about 80%.

Временные корреляционные методы оценки задержки комплексных сигналов, некратной периоду дискретизации, на основе полиномиальной интерполяции.

This paper deals with the problem of subsample time delay estimation of complex signal based on polynomial interpolation. Time delay estimation is performed by cross-correlation time approach. Three polynomial interpolation techniques applied to the discrete complex cross-correlation function in the neighborhood of its maximum are proposed. These methods show high processing speed and allow obtaining accurate real-valued time delay estimation when digital complex signals are processed. The comparative analysis between these methods is performed. A rigorous analytical solution for the correction of time delay estimation for one of the proposed methods is obtained for the case of the third-order polynomial interpolation. This solution is applied for an equidistant grid of discrete cross-correlation function samples. One can improve the accuracy of time delay estimates by using aforementioned correction. A numerical simulation is performed to quantify the accuracy of the time delay estimates when using the proposed methods for the case where a stationary random process described by the first-order autoregressive mode is chosen as a model of original signal. The main results were presented and discussed at XIV All-Russian conference “Radar and telecommunication”.

Abstract 14786: Women Wait Longer Than Men for First EKG When Self-Presenting With Suspected Acute Coronary Syndrome, A Review of the Irish National ACS Registry

Introduction: Women suffer longer delay times until diagnosis and treatment when presenting with ACS, despite cardiovascular disease being the biggest cause of death amongst women. European guidelines recommend that women and men with suspected ACS are managed according to a common protocol. We aimed to investigate whether differential system delay existed for women versus men due to longer wait time for initial EKG testing in patients who self-presented to the emergency room with suspected ACS, bypassing the pre-hospital diagnosis and warning system Methods: We retrospectively reviewed the Irish national ACS registry and identified all cases of patients who self-presented to the emergency room between 2013-2018. Those patients for whom accurate time delays were not recorded were excluded. Baseline characteristics were compared for both groups. We determined the wait time from presentation to first EKG for both groups and performed a Mann-Whitney U test to test the difference between the groups. Results: Total number of self-presenters was 714 (women 154, men 560), representing 13.2% of all patients in the registry. We excluded 54 due to inaccurate time recordings; 14 were excluded due to first EKG performed by a family doctor in the community. Women were older than men (mean age 66.3 vs. 59.2yrs, P=0.0000012) and had similar rates of diabetes mellitus (10.4% vs. 11.9%, P=0.63). More women were current smokers (45.4% vs. 37.3%, P=0.11), more likely to be hypertensive (58.5% vs 44.5%, P=0.002) and have a diagnosis of hyperlipidaemia (56.7% vs. 46.8%, P=0.048). Median wait times were longer for women compared with men: 25.0 min (IQ 13-74) vs. 18.0 min (IQ 8-42)( P=0.002)(see Figure). Conclusion: Women self-referring with suspected ACS to the emergency room had longer wait times for their first EKG compared with men despite being more likely to have an elevated cardiovascular risk factor profile. Differential wait times for EKG is an important contributor to system delay.

Multi-Resolution Generalized S-Transform Denoising for Precise Localization of Partial Discharge in Substations

Denoising is a crucial step in the localization of partial discharge (PD) in a substation. In this paper, a novel multi-resolution generalized S-transform (GST) denoising algorithm for precise localization of PD in substations is proposed. The algorithm denoises the PD signal received by the ultra-high frequency (UHF) sensor in two steps. First, the GST with the high frequency resolution is used to analyze the PD signal, and a GST filter is designed to filter out periodic narrowband noises. Then, the S-transform (a particular case of GST) is applied to analyze the PD signal, and the white Gaussian noise is suppressed according to the statistical characteristic difference between the noise and effective signal. Finally, the denoised PD signal is obtained and applied to PD localization. The simulations results show that the proposed algorithm can effectively suppress noise and can extract accurate time delay data from the denoised PD signal. The experiment results show that, compared with the wavelet transform, the localization error of the proposed algorithm is the smallest, which is 1.59m. The proposed algorithm can realize the precise localization of PD.

Efficient Mass Estimate at the Core of Strong Lensing Galaxy Clusters Using the Einstein Radius

Abstract In the era of large surveys, yielding thousands of galaxy clusters, efficient mass proxies at all scales are necessary in order to fully utilize clusters as cosmological probes. At the cores of strong lensing clusters, the Einstein radius can be turned into a mass estimate. This efficient method has been routinely used in literature, in lieu of detailed mass models; however, its scatter, assumed to be , has not yet been quantified. Here, we assess this method by testing it against ray-traced images of cluster-scale halos from the Outer Rim N-body cosmological simulation. We measure a scatter of 13.9% and a positive bias of 8.8% in , with no systematic correlation with total cluster mass, concentration, or lens or source redshifts. We find that increased deviation from spherical symmetry increases the scatter; conversely, where the lens produces arcs that cover a large fraction of its Einstein circle, both the scatter and the bias decrease. While spectroscopic redshifts of the lensed sources are critical for accurate magnifications and time delays, we show that for the purpose of estimating the total enclosed mass, the scatter introduced by source redshift uncertainty is negligible compared to other sources of error. Finally, we derive and apply an empirical correction that eliminates the bias, and reduces the scatter to 10.1% without introducing new correlations with mass, redshifts, or concentration. Our analysis provides the first quantitative assessment of the uncertainties in , and enables its effective use as a core mass estimator of strong lensing galaxy clusters.

LNOI waveguide grating based true time delay line for tunable bandpass microwave photonic filter

A precisely tunable true time delay line (TTDL) based on lithium niobate on insulator waveguide grating is proposed. Utilizing the electro-optic effect of lithium niobate, active tuning of reflected wavelength and time delay can be realized. The numerical simulation results show that, with the optimized grating structure and flexible electrode distribution, wide tuning range and high tuning accuracy of time delay can be achieved by simply controlling the charging position of the electrodes. This TTDL is applied to a tunable bandpass microwave photonic filter (TBMPF), which using PM-IM conversion to suppressed dc signal to achieve bandpass. In the TBMPF, the TTDL plays the role of introducing the dispersion for PM-IM conversion, time delay between the taps and tuning of central frequency. This TTDL can reduce the system complexity and cost of microwave photonic filter.

Phase Wrap Error Correction by Random Sample Consensus With Application to Synthetic Aperture Sonar Micronavigation

Accurate time delay estimation between signals is crucial for coherent imaging systems such as synthetic aperture sonar (SAS) and synthetic aperture radar (SAR). In such systems, time delay estimates resulting from the cross-correlation of complex signals are commonly used to generate navigation and scene height measurements. In the presence of noise, the time delay estimates can be ambiguous, containing errors corresponding to an integer number of phase wraps. These ambiguities cause navigation and bathymetry errors and reduce the quality of synthetic aperture imagery. In this article, an algorithm is introduced for the detection and correction of phase wrap errors. The random sample consensus (RANSAC) algorithm is used to fit 1-D and 2-D models to the ambiguous time delay estimates made in the time delay estimation step of redundant phase center (RPC) micronavigation. Phase wrap errors are then corrected by recalculating the phase wrap number using the best-fitting model. The approach is demonstrated using the data collected by the 270–330 kHz SAS of the NATO Centre for Maritime Research and Experimentation Minehunting unmanned underwater vehicle for Shallow water Covert Littoral Expeditions. Systems with lower fractional bandwidth were emulated by windowing the bandwidth of the signals to increase the occurrence of phase wrap errors. The time delay estimates were refined using both the RANSAC algorithms using 1-D and 2-D models and the commonly used branch-cuts method. Following qualitative assessment of the smoothness of the full-bandwidth time delay estimates after application of these three methods, the results from the 2-D RANSAC method were chosen as the reference time delay estimates. Comparison with the reference estimates shows that the 1-D and 2-D RANSAC methods outperform the branch-cuts method, with improvements of 29%–125% and 30%–150%, respectively, compared to 16%–134% for the branch-cuts method for this data set.