Measurement Of Propagation Delay Research Articles

ELoran Propagation Delay Prediction Model Based on a BP Neural Network for a Complex Meteorological Environment.

The core of eLoran ground-based timing navigation systems is the accurate measurement of groundwave propagation delay. However, meteorological changes will disturb the conductive characteristic factors along the groundwave propagation path, especially for a complex terrestrial propagation environment, and may even lead to microsecond-level propagation delay fluctuation, seriously affecting the timing accuracy of the system. Aiming at this problem, this paper proposes a propagation delay prediction model based on a Back-Propagation neural network (BPNN) for a complex meteorological environment, which realizes the function of directly mapping propagation delay fluctuation through meteorological factors. First, the theoretical influence of meteorological factors on each component of propagation delay is analyzed based on calculation parameters. Then, through the correlation analysis of the measured data, the complex relationship between the seven main meteorological factors and the propagation delay, as well as their regional differences, are demonstrated. Finally, a BPNN prediction model considering regional changes of multiple meteorological factors is proposed, and the validity of the model is verified by long-term collected data. Experimental results show that the proposed model can effectively predict the propagation delay fluctuation in the next few days, and its overall performance is significantly improved compared with that of the existing linear model and simple neural network model.

Propagation Delay Measurement and Evaluation for SV Based on HSR Networks

Propagation Delay Measurement and Evaluation for SV Based on HSR Networks

Differential Propagation Delay Measurement of RSFQ Library Cells Using Ring Oscillators

Performing comprehensive timing characterization of library cells and establishing their model-to-hardware correlation are essential for building robust integrated circuits and scaling circuit complexity. To measure the propagation delay of fabricated library cells, we have designed a differential delay measurement scheme using SFQ ring oscillators. The reference and design-under-test (DUT) rings are designed using circuit elements that are either common to both rings or are of nominally similar design, except for the DUT. By inserting a single pulse in the ring, the oscillation period is measured using two methods: (1) direct voltage measurement, and (2) frequency measurement using a frequency divider followed by an SFQ-to-DC converter. Subtracting delay of the two rings gives us the propagation delay of the DUT. A 1 cm by 1 cm chip and another 5 mm by 5 mm chip, incorporating stand-alone ring oscillator test structures for different library cells, have been fabricated in the MIT-LL SFQ5ee process. The chips also contain test circuits to validate two variants of the input/output multiplexing scheme that facilitate reducing the pads requirement. Two copies of a chip with fifteen DUTs were tested. The measured and simulated results for the voltage and frequency of the ring are compared. The simulations account for critical current density ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> ) and sheet resistance (Rs) fabrication parameters. In addition, we have used the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> as a single free parameter to get a better matching with measurement results. For one of the chips, a 15% higher <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> in simulations results in better matching with measured frequency results for all the DUTs. For example, the discrepancy between simulated and measured DUT ring frequency for the NOT cell was reduced from 19% to 1% when the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> was changed from nominal to 15% higher in simulations. Detailed measurement and simulation results for several DUTs are presented.

Accurate Single-Ended Measurement of Propagation Delay in Fiber Using Correlation Optical Time Domain Reflectometry

A correlation optical time-domain reflectometry (COTDR) method is presented, which measures the propagation delay with an accuracy of a few picoseconds. This accuracy is achieved using a test signal data rate of 10 Gbit/s and employing cross-correlation and pulse fitting techniques. In this paper we introduce and evaluate the basic signal processing steps, investigate the measurement accuracy, and discuss applications for monitoring link delay and chromatic dispersion of long fiber spans as well as temperature sensing applications.

High-Accuracy Positioning Based on Pseudo-Ranges: Integrated Difference and Performance Analysis of the Loran System.

The Long Range Navigation (Loran) system as a backup of the Global Navigation Satellite System (GNSS) is a good choice. The dominant deterioration factors of position accuracy are the pseudo-range measurement errors and the geometric dilution of precision (GDOP). This paper focuses on the algorithm integrated difference with pseudo-ranges to improve the position accuracy. Firstly, the theoretical prediction of propagation delay and raw measurement are compared. The results show that the measured pseudo-range consists of a constant term and a temporal term, which reflect the propagation situation along the true path. Secondly, a position solution algorithm based on a pseudo-range and difference is presented, exceeding the limit of a single chain. Finally, some simulation tests are implemented utilizing the new proposed position algorithm to verify the differential performance. This method can reduce the GDOP conveniently through increasing the number of transmitters. In view of the amplitude and characteristics of errors in measurement, systematic error and random noise are distinguished and discussed. The absolute accuracy responds to the pseudo-range bias that is different from geometric distance and repeatable accuracy is mainly influenced by random noise. The difference method can improve the absolute accuracy via the correction degree without changing the geometry of the transmitters.

Reducing the measurement error of signal propagation delays using an optical reflectometer with picosecond resolution

The problems requiring high-precision measurements of signal propagation delays in optical fibers are considered. Design features of a pulsed optical reflectometer with a picosecond resolution designed for measuring propagation delays of a signal are considered. It is shown that the error of such a reflectometer includes the additive and multiplicative components. A method for determining the additive component of the optical reflectometer error based on measurements of signal delays introduced by individual optical fiber coils and the total delay introduced by series-connected coils is proposed. The requirements to the measurement conditions are formulated and the results of the error estimation of the proposed method are presented. To exclude the multiplicative component of the reflectometer error, a method for determining corrections to the reflectometer readings is proposed. The method is based on measuring the propagation delays of the signal in the coils of the optical fiber, first using reference equipment (installation for measuring the propagation delay of the signal), and then using an optical reflectometer, and then calculating the differences of the obtained measurement results. The scheme of installation for measurements of a propagation delay of signal in a coil of optical fiber is presented, the principle of operation of measuring installation is described. The results of the estimation of the error in determining the corrections to the reflectometer readings by the proposed method are presented. It is shown that the exclusion of the additive and multiplicative components of the error will reduce the error of optical reflectometers to values less than ± 100 ps.

Horizontal Atmospheric Delay Measurement Using Wireless Two‐Way Interferometry (Wi‐Wi)

AbstractA method of estimating the propagation delay between two remote sites using a wireless communication module that is compatible with IEEE 802.15.4g is proposed. In our previous paper, we reported that propagation delay due to water vapor can be estimated using digital terrestrial broadcasting waves, which is a passive method from the user's view point. In this paper, we propose an active method that allows the propagation delay between two remote sites of the user's choice to be monitored, as long as a line of sight exists. A real‐time propagation delay monitoring system with wireless communication modules, (wireless two‐way interferometry [Wi‐Wi] modules,) is developed and tested. The data obtained using Wi‐Wi modules separated by 4.25 km show about 14‐cm variation of propagation delay in 1 day, in good agreement with values obtained by ground‐based meteorological observation. This study shows that this technique enables measurement of the surface propagation delay in the horizontal direction with millimeter precision and high spatial and temporal resolution at a low cost.

Measurement of Dielectric Constant and Cross-Sectional Variations of a Wire

A new measurement method is proposed for identifying small differences between the relative permittivity of data wires of a twisted pair used in high-data-rate USB cables with <1% uncertainty. This method can also detect small variations in the cross section of the insulated wires. Both the variations are the root causes of the differential mode to common-mode conversion, skew, and possibly electromagnetic interference. The method is based on forming a coaxial structure around the insulated wire under test using metals with low melting points, such as Field’s metal or mercury. Using time-domain reflectometry and knowing the exact length of the structure, the dielectric constant can be derived from the propagation delay measurement. The local cross-sectional variations are detected by observing local impedance variations. Two examples are provided to verify the method and illustrate how to use the method to determine the dominant sources of skew.

Research on the Additional Secondary Phase Factor for Automatic Identification System Signals Transmitted over a Rough Sea Surface.

This paper investigates the Additional Secondary Phase Factor (ASF) characteristics of Automatic Identification System (AIS) signals spreading over a rough sea surface. According to the change of the ASFs for AIS signals in different signal form, the influences of the different propagation conditions on the ASFs are analyzed. The expression, numerical calculation, and simulation analysis of the ASFs of AIS signal are performed in the rough sea surface. The results contribute to the high-accuracy propagation delay measurement of AIS signals spreading over the rough sea surface as, well as providing a reference for reliable communication link design in marine engineering for Very High Frequency (VHF) signals.

Relativistic Gravitational Experiment in the Earth Orbit: Concept, Technology, and Configuration of Satellite Constellation

An arrangement of the orbital experiment on the measurement of the light propagation delay in the gravitational field of the Earth (Shapiro effect) using laser interferometry based on a cluster of small spacecraft (SC) is proposed. SC layouts, launch technology, and high-precision measurements of their orbital parameters are considered.

Evaluation of multipath signal loss for AIS signals transmitted on the sea surface

This paper investigates the losses of AIS signals received in different transmission modes based on a fading algorithm for multipath AIS signals transmitted on the sea surface and analyzes the influence of different sea conditions on AIS signals. A numerical study and simulation analysis of multipath fading signals for AIS signals transmitted on the sea surface are performed. This study provides a reference for the positioning process of several multipath signals using the propagation delay measurement of AIS signals as well as for reliable VHF communication link design in offshore engineering. In addition, the results of this research provide evaluation results for using the measured transmission delay of AIS signals in the positioning process of several multipath signals and provide a reference for reliable communication link design in marine engineering for VHF signals.

Propagation delay measurement and compensation for sampled value synchronization in a smart substation

Reliable sampled value (SV) synchronization is used to ensure the reliability of protective relaying in a smart substation based on IEC 61850. In this paper, an SV synchronization method based on SV propagation delay measurement and compensation is proposed. The method does not depend on an external reference clock and has higher reliability than existing ones. The core issue in the proposed method is to measure the switching delay. The following steps are undertaken in this work: First, the composition of SV propagation delay in a smart substation is analyzed. Second, a new switch with the capability of switching delay measuring and recording is presented. Third, two laboratory tests are conducted to study the measurement accuracy of the switching delay. Finally, an SV synchronization method is presented and its application is tested on a busbar protection system to demonstrate that the proposed method can achieve SV synchronization effectively. Test results show that the measurement is sufficiently accurate for the SV propagation delay compensation. The proposed method also shows that the reliability of the protective relaying in a smart substation is significantly improved.

A Flexible Millimeter-Wave Channel Sounder With Absolute Timing

This paper presents a novel ultrawideband wireless spread spectrum millimeter-wave (mmWave) channel sounder that supports both a wideband sliding correlator mode and a realtime spread spectrum mode, also known as wideband correlation or direct correlation. Both channel sounder modes are capable of absolute propagation delay (time of flight) measurements with up to 1 GHz of radio frequency null-to-null bandwidth, and can measure multipath with a 2-ns time resolution. The sliding correlator configuration facilitates long-distance measurements with angular spread and delay spread for up to 185 dB of maximum measurable path loss. The real-time spread spectrum mode is shown to support short-range, small-scale temporal, and Doppler measurements (minimum snapshot sampling interval of 32.753 μs) with a substantial dynamic fading range of 40 dB for human blockage and dynamic urban scenarios. The channel sounder uses field programmable gate arrays, analog-to-digital converters, digital-to-analog converters, and low-phase-noise rubidium standard references for frequency/time synchronization and absolute time delay measurements. Using propagation theory, several methods are presented here to calibrate and verify the accuracy of the channel sounder, and an improved diffraction model for human blockage, based on the METIS model but now including directional antenna gains, is developed from measurements using the channel sounder. The mmWave channel sounder described here may be used for accurate spatial and temporal raytracing calibration, to identify individual multipath components, to measure antenna patterns, for constructing spatial profiles of mmWave channels, and for developing statistical channel impulse response models in time and space.

Direction-of-Arrival Estimation of VHF Signals Recorded on the International Space Station and Simultaneous Observations of Optical Lightning

We report an initial investigation of the new location method of a very high frequency (VHF) radiation source, using signals recorded at the International Space Station. A VHF interferometer (VITF) has two VHF sensors. Locating lightning with VHF bands is useful to locate the position of the charge distribution in the thunderstorm. The location method of a radio source proposed used two direction-of-arrival estimation techniques. One is the interferometric technique, and another is based on the ionospheric propagation delay measurement of received signals. The combination of the two techniques provides two angular positions of the radiation source. When an altitude of a radiation source is assumed, we can determine two possible positions. One of the two positions was associated with the radiation source, while the other was not. In this paper, we compared the position of lightning and sprite imager (LSI) data, which are simultaneously captured during a lightning emission, with the locating position near the emission. The data set of the VITF within 100 ms of the optical lightning emission captured with the LSI was used. The temporally simultaneous event seems to be associated with the same lightning event. The estimated radiation positions were spatially in close agreement with the optical lightning positions captured with LSI, under nighttime ionosphere conditions. From statistical analysis, the spatial difference of the standard deviation changed from 15.3 to 30.8 km depending on the installation direction of the VHF sensors. The usefulness and limitations of the method are also discussed.

Assimilative model for ionospheric dynamics employing delay, Doppler, and direction of arrival measurements from multiple HF channels

AbstractWe describe the development of new HF data assimilation capabilities for our ionospheric inversion algorithm called GPSII (GPS Ionospheric Inversion). Previously existing capabilities of this algorithm included assimilation of GPS total electron content data as well as assimilation of backscatter ionograms. In the present effort we concentrated on developing assimilation tools for data related to HF propagation channels. Measurements of propagation delay, angle of arrival, and the ionosphere‐induced Doppler from any number of known propagation links can now be utilized by GPSII. The resulting ionospheric model is consistent with all assimilated measurements. This means that ray tracing simulations of the assimilated propagation links are guaranteed to be in agreement with measured data within the errors of measurement. The key theoretical element for assimilating HF data is the raypath response operator (RPRO) which describes response of raypath parameters to infinitesimal variations of electron density in the ionosphere. We construct the RPRO out of the fundamental solution of linearized ray tracing equations for a dynamic magnetoactive plasma. We demonstrate performance and internal consistency of the algorithm using propagation delay data from multiple oblique ionograms (courtesy of Defence Science and Technology Organisation, Australia) as well as with time series of near‐vertical incidence sky wave data (courtesy of the Intelligence Advanced Research Projects Activity HFGeo Program Government team). In all cases GPSII produces electron density distributions which are smooth in space and in time. We simulate the assimilated propagation links by performing ray tracing through GPSII‐produced ionosphere and observe that simulated data are indeed in agreement with assimilated measurements.

Estimating Multiple Target Locations in Multi-Path Environments

This paper addresses the problem of multi-target localization with distributed multiple-input-multiple-output (MIMO) radar systems without angular resolution capability-i.e., only based on the measurements of the signal propagation delays. In particular, we address the case that multiple targets cannot be distinguished by their “signatures” or other unique characteristics. Further complications in realistic settings arise from the following factors: 1) the direct path (DP) between transmitter/receiver and target might be blocked, and 2) indirect paths (IPs) arising from multi path propagation might be present. We present in this paper a novel algorithm that can accurately localize multiple targets even under these difficult circumstances. This algorithm is based on an iterative approximation to an exhaustive maximum likelihood (EML) estimation of the target locations, yet avoiding the exponential complexity that an EML requires. It utilizes a clustering technique that gives the number and locations of targets, and incorporates an IP detection mechanism based on the likelihood of several propagation delay measurement (PDM) correspond to DPs from the same target. Despite its lower complexity, our algorithm achieves almost the same performance as the EML in a variety of simulation settings. We finally study the choice of algorithm parameters and the configurations of the MIMO system nodes to achieve the best localization performance.

An accurate model for dynamic crosstalk analysis of CMOS gate driven on-chip interconnects using FDTD method

An accurate and time efficient model of CMOS gate driven coupled-multiple interconnects is presented in this paper for crosstalk induced propagation delay and peak voltage measurements. The proposed model is developed using the finite difference time domain (FDTD) technique for coupled RLC interconnects, whereas the alpha power law model is used to represent the transistors in a CMOS driver. As verified by the HSPICE simulation results, the transient response of the proposed model demonstrates high accuracy. Over the random number of test cases, crosstalk induced peak voltage and propagation delay show average errors of 1.1% and 4.3%, respectively, with respect to HSPICE results.

LOS and NLOS Classification for Underwater Acoustic Localization

The low sound speed in water makes propagation delay (PD)-based range estimation attractive for underwater acoustic localization (UWAL). However, due to the long channel impulse response and the existence of reflectors, PD-based UWAL suffers from significant degradation when PD measurements of nonline-of-sight (NLOS) communication links are falsely identified as line-of-sight (LOS). In this paper, we utilize expected variation of PD measurements due to mobility of nodes and present an algorithm to classify the former into LOS and NLOS links. First, by comparing signal strength-based and PD-based range measurements, we identify object-related NLOS (ONLOS) links, where signals are reflected from objects with high reflection loss, for example, ships hull, docks, rocks and so on. In the second step, excluding PD measurements related to ONLOS links, we use a constrained expectation-maximization algorithm to classify PD measurements into two classes: LOS and sea-related NLOS (SNLOS), and to estimate the statistical parameters of each class. Since our classifier relies on models for the underwater acoustic channel, which are often simplified, alongside simulation results, we validate the performance of our classifier based on measurements from three sea trials. Both our simulation and sea trial results demonstrate a high detection rate of ONLOS links, and accurate classification of PD measurements into LOS and SNLOS.

Low-cost, high-precision propagation delay measurement of 12-fibre MPO cables for the CMS DT electronics upgrade

CMS DT electronics upgrade involves laying down 3500 optical links from the CMS experimental cavern to the service cavern, whose lengths must be matched to minimize skew, so that the present upstream electronics can be reused at an initial stage. In order to assess the cables' compliance, a high resolution and cost-effective system has been developed to measure the length uniformity of these fibres. Transit-time oscillation method has been implemented with matched MTP 12-channel fibre optic transmitter and receiver and a Spartan-6 FPGA. After proper corrections and averaging, millimetre-range accuracy has been achieved.

Soil Moisture Sensing via Swept Frequency Based Microwave Sensors

There is a need for low-cost, high-accuracy measurement of water content in various materials. This study assesses the performance of a new microwave swept frequency domain instrument (SFI) that has promise to provide a low-cost, high-accuracy alternative to the traditional and more expensive time domain reflectometry (TDR). The technique obtains permittivity measurements of soils in the frequency domain utilizing a through transmission configuration, transmissometry, which provides a frequency domain transmissometry measurement (FDT). The measurement is comparable to time domain transmissometry (TDT) with the added advantage of also being able to separately quantify the real and imaginary portions of the complex permittivity so that the measured bulk permittivity is more accurate that the measurement TDR provides where the apparent permittivity is impacted by the signal loss, which can be significant in heavier soils. The experimental SFI was compared with a high-end 12 GHz TDR/TDT system across a range of soils at varying soil water contents and densities. As propagation delay is the fundamental measurement of interest to the well-established TDR or TDT technique; the first set of tests utilized precision propagation delay lines to test the accuracy of the SFI instrument’s ability to resolve propagation delays across the expected range of delays that a soil probe would present when subjected to the expected range of soil types and soil moisture typical to an agronomic cropping system. The results of the precision-delay line testing suggests the instrument is capable of predicting propagation delays with a RMSE of +/−105 ps across the range of delays ranging from 0 to 12,000 ps with a coefficient of determination of r2 = 0.998. The second phase of tests noted the rich history of TDR for prediction of soil moisture and leveraged this history by utilizing TDT measured with a high-end Hewlett Packard TDR/TDT instrument to directly benchmark the SFI instrument over a range of soil types, at varying levels of moisture. This testing protocol was developed to provide the best possible comparison between SFI to TDT than would otherwise be possible by using soil moisture as the bench mark, due to variations in soil density between soil water content levels which are known to impact the calibration between TDR’s estimate of soil water content from the measured propagation delay which is converted to an apparent permittivity measurement. This experimental decision, to compare propagation delay of TDT to FDT, effectively removes the errors due to variations in packing density from the evaluation and provides a direct comparison between the SFI instrument and the time domain technique of TDT. The tests utilized three soils (a sand, an Acuff loam and an Olton clay-loam) that were packed to varying bulk densities and prepared to provide a range of water contents and electrical conductivities by which to compare the performance of the SFI technology to TDT measurements of propagation delay. For each sample tested, the SFI instrument and the TDT both performed the measurements on the exact same probe, thereby both instruments were measuring the exact same soil/soil-probe response to ensure the most accurate means to compare the SFI instrument to a high-end TDT instrument. Test results provided an estimated instrumental accuracy for the SFI of +/−0.98% of full scale, RMSE basis, for the precision delay lines and +/−1.32% when the SFI was evaluated on loam and clay loam soils, in comparison to TDT as the bench-mark. Results from both experiments provide evidence that the low-cost SFI approach is a viable alternative to conventional TDR/TDT for high accuracy applications.