Precise Delay Research Articles

Global Ionosphere Estimation Based on Data Fusion From Multisource: Multi‐GNSS, IRI Model, and Satellite Altimetry

AbstractTraditionally, the ionosphere determination just uses American Global Positioning System and Russian GLObal NAvigation Satellite System dual‐frequency data and has a low precision particularly on oceans. With the rapid development of Chinese BeiDou and European Galileo systems, they are playing an increasingly important role for modeling global ionosphere. Meanwhile, satellite altimetry provides valuable and precise ionosphere delay over the oceans. Through introducing priori ionosphere values from an advanced empirical ionosphere model, combining the advantages of Global Navigation Satellite System (GNSS) and satellite altimetry technologies, the precision of global ionosphere estimation can be further improved. To assess the improvement, we collect satellite altimetry data from Jason‐2/3 and more than 300 global GNSS stations, the data are processed in 2014 and 2018 when the Sun is in a high and a low activity conditions. The results suggest that the ionosphere determination based on multitechnique fusion in a solar‐geomagnetic reference frame is well suitable to represent the ionosphere and its structure. The determined ionosphere achieves a better global consistency, and its formal accuracy is significantly reduced. By comparing with the International GNSS Service products, evaluating by satellite altimetry measurements, and independently validating with ionosonde techniques, it is proved that the ionosphere results are further improved through employing additional available data, especially for the ionosphere over the oceans.

High-Speed RF Switch Electronics for Picking Up of Electron–Positron Beam Bunches

Beam diagnostics is important to guarantee good quality of beam in particle accelerator. Both the electron and positron run in the tunnel in some modern electron positron colliders such as Circular Electron Positron Collider (CEPC) to be built and Beijing Electron Positron Collider II (BEPC II). To measure the electron and positron beams, picking up of these two different bunches in real time is of notable concern. Because the time interval between adjacent electron and positron bunches is quite small, for example, 6 ns in CEPC, high-speed switch electronics is required. This paper presents the prototype design of a high-speed radio frequency (RF) electronics that can pick up nanosecond positron-electron beam bunches with a switching time of less than 6 ns. Fast separation of electron and positron is achieved based on RF switches and precise delay adjustment of the controlling signals (~10 ps). Initial tests have been conducted in the laboratory to evaluate the performance of electronics, the results indicate that this circuit can successfully pick up the bunch signal within a time interval of 6 ns, which makes it possible to further measure the electron and position beams simultaneously.

Precise Power Delay Profiling with Commodity Wi-Fi

Power delay profiles characterize multipath channel features, which are widely used in motion- or localization-based applications. The performance of power delay profile obtained using commodity Wi-Fi devices is limited by two dominating factors. The resolution of the derived power delay profile is determined by the channel bandwidth, which is however limited on commodity WiFi. The collected CSI reflects the signal distortions due to both the channel attenuation and the hardware imperfection. A direct derivation of power delay profiles using raw CSI measures, as has been done in the literature, results in significant inaccuracy. In this paper, we present Splicer, a software-based system that derives high-resolution power delay profiles by splicing the CSI measurements from multiple WiFi frequency bands. We propose a set of key techniques to separate the mixed hardware errors from the collected CSI measurements. Splicer adapts its computations within stringent channel coherence time and thus can perform well in the presence of mobility. Our experiments with commodity WiFi NICs show that Splicer substantially improves the accuracy in profiling multipath characteristics, reducing the errors of multipath distance estimation to be less than $2\;\mathrm{m}$2m. Splicer can immediately benefit upper-layer applications. Our case study with recent single-AP localization achieves a median localization error of $0.95\;\mathrm{m}$0.95m.

Turning Gravitationally Lensed Supernovae into Cosmological Probes

Abstract Recently, there have been two landmark discoveries of gravitationally lensed supernovae: the first multiply imaged SN, “Refsdal”, and the first Type Ia SN resolved into multiple images, SN iPTF16geu. Fitting the multiple light curves of such objects can deliver measurements of the lensing time delays, which are the difference in arrival times for the separate images. These measurements provide precise tests of lens models or constraints on the Hubble constant and other cosmological parameters that are independent of the local distance ladder. Over the next decade, accurate time delay measurements will be needed for the tens to hundreds of lensed SNe to be found by wide-field time-domain surveys such as LSST and WFIRST. We have developed an open-source software package for simulations and time delay measurements of multiply imaged SNe, including an improved characterization of the uncertainty caused by microlensing. Using this package, we describe simulations that suggest that a before-peak detection of the leading image enables a more accurate and precise time delay measurement (by ∼1 and ∼2 days, respectively), when compared to an after-peak detection. We also conclude that fitting the effects of microlensing without an accurate prior often leads to biases in the time delay measurement and over-fitting to the data, but that employing a Gaussian Process Regression technique is sufficient for determining the uncertainty due to microlensing.

Precise excitation-inhibition balance controls gain and timing in the hippocampus.

Excitation-inhibition (EI) balance controls excitability, dynamic range, and input gating in many brain circuits. Subsets of synaptic input can be selected or 'gated' by precise modulation of finely tuned EI balance, but assessing the granularity of EI balance requires combinatorial analysis of excitatory and inhibitory inputs. Using patterned optogenetic stimulation of mouse hippocampal CA3 neurons, we show that hundreds of unique CA3 input combinations recruit excitation and inhibition with a nearly identical ratio, demonstrating precise EI balance at the hippocampus. Crucially, the delay between excitation and inhibition decreases as excitatory input increases from a few synapses to tens of synapses. This creates a dynamic millisecond-range window for postsynaptic excitation, controlling membrane depolarization amplitude and timing via subthreshold divisive normalization. We suggest that this combination of precise EI balance and dynamic EI delays forms a general mechanism for millisecond-range input gating and subthreshold gain control in feedforward networks.

Timing Analysis of Precedence Constraint Messages Scheduled With Slot Multiplexing Over Dynamic Segment of FlexRay

FlexRay offers high-speed reliable transmission in the vehicle domain. Thus, it is one of the most popular in-vehicle communication protocols for the applications that are safety-critical or applications with very low transmission time requirement. Due to the real-time constraint, the worst case end-to-end delay (EED) for such applications transmitting over a shared bus must be known. This paper addresses the problem of computation of EED for a given set of tasks with precedence constraint and corresponding messages, which are scheduled with slot multiplexing for event-triggered communication over the dynamic segment of FlexRay. First, computing precise delay has been shown to be an intractable problem. Subsequently, motivated by the intractability, an efficient estimation technique has been proposed to compute approximate EED. Unlike the common practice of considering the network in isolation, we present a comprehensive timing analysis, which considers the effects of task execution as well. Moreover, EED is allowed to be greater than interactivation time of task graph. The extensive simulation has been performed on the test cases generated with uniform as well as normal distribution. Note to Practitioners —In the past few decades, due to the large-scale use and sophistication of automotive electronic systems, various in-vehicle communication networks and protocols are also evolving. FlexRay is one such in-vehicle communication protocol, which provides the mechanism for the fault-tolerant high-speed communication over FlexRay bus. FlexRay is widely being employed for safety-critical applications in the automotive domain. For such applications, often the timing constraint is imposed with a bound on the worst case EED. Thus, timing properties of the designed network must be verified before applying it on the real domain such that the worst case EED for the propagation of an event at sensor end to actuator end is known. The proposed estimation technique can be used to compute approximate EED for an application scheduled with other applications over the dynamic segment of FlexRay. In addition, various guidelines for designing the network in order to reduce overestimation have also been presented.

Constraining Cosmological Parameters in the FLRW Metric with Lensed GW+EM Signals

Abstract We proposed a model-independent method to constrain cosmological parameters using the Distance Sum Rule of the Friedmann–Lemaître–Robertson–Walker metric by combining the time delay distances and the comoving distances through a multi-messenger approach. The time delay distances are measured from lensed gravitational wave (GW) signals together with their corresponding electromagnetic wave (EM) counterparts, while the comoving distances are obtained from a parameterized fitting approach with independent supernova observations. With a series of simulations based on the Einstein Telescope, Large Synoptic Survey Telescope, and The Dark Energy Survey, we find that only 10 lensed GW+EM systems can achieve the constraining power comparable to and even stronger than 300 lensed quasar systems due to the more precise time delay from lensed GW signals. Specifically, the cosmological parameters can be constrained to and (1σ).5 Our results show that more precise time delay measurements could provide more stringent cosmological parameter values, and lensed GW+EM systems therefore can be applied as a powerful tool in the future precision cosmology.

Interferometric delay tracking for low-noise Mach-Zehnder-type scanning measurements.

Precise delay control is of paramount importance in optical pump-probe measurements. Here, we report on a high-precision delay tracking technique for mechanical scanning measurements in a Mach-Zehnder interferometer configuration. The setup employs a 1.55-µm continuous-wave laser beam propagating along the interferometer arms. Sinusoidal phase modulation at 30 MHz, and demodulation of the interference signal at the fundamental frequency and its second harmonic, enables delay tracking with sampling rates of up to 10 MHz. At an interferometer arm length of 1 m, root-mean-square error values of the relative delay tracking below 10 attoseconds for both stationary and mechanically scanned (0.2 mm/s) operation are demonstrated. By averaging several scans, a precision of the delay determination better than 1 as is reached. We demonstrate this performance with a mechanical chopper periodically interrupting one of the interferometer arms, which opens the door to the combination of high-sensitivity lock-in detection with (sub-)attosecond-precision relative delay determination.

A new model for reduction of Azimuth asymmetry biases of tropospheric delay

ABSTRACTNowadays, a GNSS application is one of the main backbones of lifestyle. The GNSS signal that comes from space satellites to receivers on Earth suffers some delays. The troposphere layer is one of the basic sources of delay to signals. To detect the delay, many models have been produced taking into account the receiver location and satellite zenith angle. Most of these models give vertically perfect representation without accounting the horizontal asymmetry effect. The horizontally graded difference “azimuth asymmetry” is negligible at high elevation angles up to 10°. At low elevation angles, the asymmetry is significant. At 2° elevation angle, the asymmetry is about 72 mm for east and west and about 66 mm for south. Using the Precise Tropospheric Delay Database (PTD), the difference in horizontal plane delays is studied. A new model is proposed and compared to PTD calculations. The model has three coefficients obtained for high zenith angles (70° to 88°). These coefficients are modelled as a function of zenith angle and used to give a horizontal gradient factor which is multiplied by the northern mapping function to map it to any azimuth. The proposed model makes significant improvement. For east and west directions, the model decreases the bias from around 72 mm to be about 1.0 mm. For the southern direction, the produced model needs an improvement to get closer to the true asymmetry.Abbreviations: GNSS: Global Navigation Satellite Systems; HG: Horizontal Gradient; MF: Mapping Function; PTD: Precise Tropospheric Delay Database; Z: Zenith Angle; ZHD: Zenith Hydrostatic Delay; ZTD: Zenith Total Delay; ZWD: Zenith Wet Delay

Measurement of femtosecond pulses based on transient grating frequency-resolved optical gating

Femtosecond pulse measurement of ultrafast spectrum is one of the important research directions in the ultrafast laser field. The conventional femtosecond pulse autocorrelation method is implemented by measuring the autocorrelated frequency-doubling signal, and the frequency-doubling signal has wavelength selectivity, so the femtosecond pulse measurement for the case of different central wavelengths needs to replace different frequency-doubling crystals, which is very inconvenient. This paper reports a kind of modified transient grating frequency resolution optical gating for measuring the femtosecond pulses. The method combines frequency-resolved optical gating (FROG) method with four-wave mixing. Its basic process is to divide the pulse to be measured into three beams. Two of the pulses can reach spatiotemporal coincidence on optical medium through precise delay control and focus. The other pulse interacts with the transient grating, and serves as the detection light to produce signal light. The spectrum and delay time of the signal light are measured by a spectrometer, and the spectrum and electric field information of the femtosecond pulse to be measured are obtained through the inversion iterative algorithm. Because this method only needs the power density of the measured light to reach the third-order nonlinear effect, it can be applied to the femtosecond pulse measurement of any central wavelength. We use this method to measure the femtosecond pulses with the central wavelengths of 800 nm and 400 nm respectively, and the ultra-wide spectrum femtosecond pulses with the period magnitude of sub-10 fs, and compare the measurement results with the results obtained with the conventional interferometric autocorrelation instrument. They are basically consistent. The experimental results show that our frequency-resolved optical switching method based on transient grating is very effective for measuring the femtosecond pulses with different central wavelengths and pulse widths.

Design of precise delay system for streak tube imaging lidar

A precise delay system for a streak tube imaging lidar (STIL) is developed. Two delay schemes are designed that are suitable for long- and short-distance lidar imaging. The digital scheme delay can reach 100 μs, and its precision is <6 ns; the analog scheme delay can reach 1200 ns and its precision is <1 ns. Using the STIL system, three-dimensional (3-D) imaging experiments are carried out on land targets at about 2.3-km range and underwater targets at about 25-m range. The experimental results show that the designed delay device can produce precise delay times and effectively verify the 3-D imaging quality of the STIL. This device also has the advantages of stable operation, being more compact, and requiring less power than existing instruments.

Regional Egypt tropospheric mapping function model

It’s essential to find out the delay caused by the troposphere layer to be able to get more accurate results. The precise positioning is very essential for accurate geodetic applications e.g., Crustal deformation and military purposes. The delay is usually modeled as a zenith value and a mapping function to map it to the observed angle. The current research develops a new mapping function model for Egypt through a least square analysis using ten radiosonde stations. The proposed model is a development of Herring continued fraction equation for dry case and wet case separately. The developed model coefficients depend on latitude and day of year. The produced model as well as Niell, Vienna and Chao models are all evaluated using Precise Tropospheric Delay database (PTD). The test data are 36 days over the year 2015 representing winter, spring, summer and fall. The obtained results clearly showed the proposed model is more accurate for Egypt than other models for both dry and wet cases.

Why we should use Min Max DEVS for modeling and simulation of digital circuits

The delay is a very important element in modeling hardware behavior, and is realized in many hardware description languages such as ADLIB-SABLE, Verilog, and VHDL. The state of the art on hardware delay identifies four classes. In the first class, mean values are used as a precise delay element in the simulation; we found it in VHDL (VHSIC (very high speed integrated circuit) Hardware Description Language), where a single value is utilized to characterize the transport delay. In the second class, the delay is represented by an interval min max, meaning that the delay value is precisely unknown and every value in the interval can represent a possible value for the actual delay. In the third class, a delay is expressed in the form of a stochastic distribution. Fuzzy models of delay constitute the last class. In reality, it is very difficult, if not impossible, to obtain a precise value of the delay; there are many reasons for that: temperature, voltage, variation in the manufacturing process, and other environment parameters. The Min Max DEVS formalism allows an efficient design of the min max delay by proposing a definition of the lifetime function based on time interval. Moreover, its simulation semantics allows the simulation of Min Max DEVS models with only one replication, allowing us to conclude whether the min max delay is too large or exact simulations cannot be obtained. In this paper, we propose to highlight the Min Max DEVS formalism through examples from digital circuits, after having recalled its basic definitions and its simulation semantics. Then, we compare the simulation results obtained with those provided by the well-known tool in the field of digital circuits, Verilog, using the same examples.

Design of Low Delay Ring Oscillator Using CMOS

In the Era of digital World, low power applications are the needs of the market to save the resources. Delay elements (e.g. digital clock) are essential parts of such digital applications. Ring oscillators have been used because of their ease of implementation, wide tuning ranges, operating at low voltages and existing possibility of complete integration in standard CMOS processes. It desires at identifying the best possible configuration for the hoop oscillators having the least strength intake and precise delay with lesser sensitivity to the variations inside the temperature and deliver voltage for frequencies of few KHz. while N = 7, for 0.18 µm generation , put off is 0.07ns simplest. Compare with N = 3, 14.2 % delay time reduced and 12.6 % lower when N= 7 taken into account.

Design and testing of a bunch-by-bunch beam position transverse feedback processor

Shanghai Synchrotron Radiation Facility (SSRF) is a 3.5 GeV storage ring with a bunch rate of 499.654 MHz, harmonic number of 720, and circumference of 432 meters. SSRF injection works at 3.5 GeV, where the multi-bunch instabilities limit the maximum stored current. In order to suppress multi-bunch instabilities caused by transverse impedance, a bunch-by-bunch transverse feedback system is indispensable for SSRF. The key component of that system is the bunch-by-bunch transverse feedback electronics. An important task in the electronics is precise time synchronization. In this paper, a novel clock synchronization and precise delay adjustment method based on the PLLs and delay lines are proposed. Test results indicate that the ENOB (Effective Number Of Bits) of the analog-to-digital conversion circuit is better than 9 bits in the input signal frequency range from 100 kHz to 700 MHz, and the closed loop attenuation at the critical frequency points is better than 40 dB. The initial commissioning tests with the beam in SSRF are also conducted, and the results are consistent with the expectations.

A New Method to Test the Einstein’s Weak Equivalence Principle

Abstract The Einstein’s weak equivalence principle (WEP) is one of the foundational assumptions of general relativity and some other gravity theories. In the theory of parametrized post-Newtonian (PPN), the difference between the PPN parameters γ of different particles or the same type of particle with different energies, Δγ, represents the violation of WEP. Current constraints on Δγ are derived from the observed time delay between correlated particles of astronomical sources. However, the observed time delay is contaminated by other effects, such as the time delays due to different particle emission times, the potential Lorentz invariance violation, and none-zero photon rest mass. Therefore, current constraints are only upper limits. Here, we propose a new method to test WEP based on the fact that the gravitational time delay is direction-dependent while others are not. This is the first method that can naturally correct other time-delay effects. Using the time-delay measurements of BASTE gamma-ray burst sample and the gravitational potential of local super galaxy cluster Laniakea, we find that the constraint on Δγ of different energy photons can be as low as 10−14. In the future, if more gravitational wave events and fast radio bursts with much more precise time-delay measurements are observed, this method can give a reliable and tight constraint on WEP.

Adaptive SMF Coupling Based on Precise-Delayed SPGD Algorithm and Its Application in Free Space Optical Communication

The adaptive coupling of laser beam from space into single-mode fiber (SMF) plays an important role in the fiber-based free space optical communication technology. This paper investigates a kind of adaptive SMF coupling system based on a novel corrector named adaptive fiber coupler, and an improved control algorithm named precise-delayed stochastic parallel gradient descent (PD-SPGD). Compared to the SPGD algorithm used previously, PD-SPGD can compensate for the inherent response delay of the controlled system by setting a precise time delay between the disturbed voltages and the performance metrics. The experimental results show that this new algorithm increases the iteration rate from 3 to 8 kHz and decreases the convergence time from 6.3 to 2.5 ms when the static angular errors was corrected. As a result, the control bandwidth of the sinusoidal angular jitters is more than doubled. At the end, a preliminary atmospheric compensation experiment over a 520 m near-ground propagation path is conducted to verify the effectiveness of the method mentioned above.

Real-time precise point positioning-based zenith tropospheric delay for precipitation forecasting

GPS-based Zenith Tropospheric Delay (ZTD) estimation should be easily obtained in a cost-effective way, however, the most previous studies focus on post-processed ZTD estimates using satellite orbit and clock products with at least 3–9 hours latency provided by International GNSS Service (IGS), which limits the GNSS meteorological application for nowcasting. With the development of IGS’s real-time pilot project (RTPP), this limitation was removed by April, 2013 as real-time satellite orbit and clock products can be obtained on-line. In this paper, on the one hand, the GPS-derived ZTD estimation was evaluated using the IGS final and real-time satellite products based on independently developed PPP software. On the other hand, the analysis of the time series of GPS-derived ZTD by least-square fitting of a broken line tendency for a full year of observations, and a forecasting method for precipitation is proposed based on the ZTD slope in the ascending period. The agreement between ZTD slope and the ground rainfall records suggested that the proposed method is useful for the assisted forecasting, especially for short-term alarms.

Digital Self-Interference Cancellation With Variable Fractional Delay FIR Filter for Full-Duplex Radios

In full-duplex radios, delay alignment errors result in random mismatch between the self-interference (SI) signal and the reconstructed cancellation signal, leading to the performance degradation of the SI cancellation. In this letter, a variable fractional delay (VFD) FIR filter with more precise delay alignment is exploited to suppress the SI in digital domain. The closed-form expressions of the VFD FIR filter coefficients are reformulated by minimizing the residual SI power. Based on the obtained SI cancellation capability, the influence of the filter order on the SI cancellation is then characterized. Simulations show that the deployment of the VFD FIR filter significantly enhances the SI cancellation performance. Specifically, when the SI signal bandwidths are 0.5 and 10 MHz, the cancellation capability of employing the VFD FIR filter based on the proposed coefficients outperforms the VFD FIR filter under the LS criterion by 6.5 and 3.7 dB, respectively, which presents a potential contribution to enhance the SI cancellation performance.

Input Time Delay Margin in Event-Triggered Consensus of Multiagent Systems.

In this paper, the event-triggered consensus problem of multiagent systems with input time delay is investigated. First, the normal event-triggered control scheme containing the input time delay is introduced to reduce the number of communication. Then the following results are achieved: 1) the procedure of setting parameters is carefully formulated for the event-triggered control scheme; 2) the precise input time delay margin is calculated for the event-triggered consensus of the multiagent systems; 3) a more general condition of constructing event-triggered functions is derived to exclude the Zeno behavior; 4) the self-triggered control scheme is further applied to avoid the continuous measurement; and 5) the observer-based control scheme is also utilized to tackle the problem of unmeasurable state. Finally, the correctness and the effectiveness of these results are demonstrated by numerical simulations.