Analysis of Time of Arrival Estimation Using Wideband Measurements of Indoor Radio Propagations

Using time of arrival (TOA) to determine the distance between the transmitter and the receiver is the most popular technique for accurate indoor positioning. The accuracy of measuring the distance using this method is sensitive to the bandwidth of the system and the multipath condition between the wireless terminal and the access point. In general, as the bandwidth increases beyond a certain value, it is expected that the measured TOA error approaches zero. However, for the so-called undetected direct path (UDP) conditions, the system exhibits substantially high distance measurement errors that cannot be eliminated with the increase in the bandwidth of the system. In this paper, we provide an analysis of the behavior of superresolution and traditional TOA estimation algorithms in line-of-sight (LOS), non-LOS, and UDP conditions in indoor areas. The analysis is based on wideband frequency- domain measurements of the indoor radio channel propagations in several indoor areas, with special attention to the UDP conditions.     

High Accuracy Ultraviolet Index of Refraction Measurements Using a Fourier Transform Spectrometer

We have constructed a new facility at the National Institute of Standards and Technology (NIST) to measure the index of refraction of transmissive materials in the wavelength range from the visible to the vacuum ultraviolet. An etalon of the material is illuminated with synchrotron radiation, and the interference fringes in the transmittance spectrum are measured using a Fourier transform spectrometer. The refractive index of calcium fluoride, CaF₂, has been measured from 600 nm to 175 nm and the resulting values agree with a traditional goniometric measurement to within 1 × 10⁻⁵. The uncertainty in the index values is currently limited by the uncertainty in the thickness measurement of the etalon.     

Millimeter- and Submillimeter-Wave Dielectric Measurements of Household Powders Using Fourier Transform Spectroscopy

This paper presents the first step in characterizing and detecting common household powders as hoax materials by investigating their broadband dielectric characteristics. Pesticide is also studied due to its similarities to anthrax. A modified two-beam polarizing interferometer and custom-made sample holders were utilized to obtain the refractive index (RFI), absorption coefficient, complex real and imaginary permittivity, and loss tangent of flour, dry milk, cornstarch, pesticide, baking soda, and talc as a continuous function of frequency in the range of 400-1200 GHz. Dispersive Fourier transform spectroscopy was employed to provide phase and amplitude information, leading to the accurate and direct acquisition of the complex RFI and complex dielectric permittivity spectra. It is the first time that such measurements were carried out over such an extended frequency range for common powders to reveal marked variation in absorption and RFI values for different powders. The powders exhibit high-absorption characteristics, and the RFI values lie between 2.4 and 3.4 in this spectral range. A unique resonance signature for talc was detected at 1135 GHz with an associated anomalous dispersion. Parameters such as grain size and orientation were analyzed for their effect on the dielectric properties of powders. Relationships between density, permittivity, and RFI are explored to provide the ability to extrapolate results for other densities. The RFI and the real part of the dielectric permittivity were found to be the most reliable for identification and detection purposes.     

Telstar Time Synchronization

A broad-band completely reciprocal transmission path across the Atlantic was made available for the first time by the Telstar I satellite. In August, 1962, the U. S. Naval Observatory (USNO) and the National Physical Laboratory (NPL) cooperated in an experiment using the satellite to relate the master clocks at the USNO, and the Royal Greenwich Observatory (RGO) at Herstmonceux, U. K. Pulsed signals, 5 ?s long, at the rate of ten per second were transmitted simultaneously over the satellite circuit from the ground stations at Andover, Me. and Goonhilly Downs, Cornwall, U. K. The time difference between received and transmitted pulses was measured at each station and from these results the relative setting of the station clocks was obtained directly. In the final experiment on August 27th, the Goonhilly clock was found to be 72.6±0.8 ?s ahead of Andover. The internal consistency of the results was checked by comparing the measured time delays of the signals over whole or part of the path with the value calculated from the satellite ephemeris, based entirely on Minitrack observations. The measured time delays were consistent to ±1 ?s and did not differ from the ephemeris by more than 6 ?s, equivalent to 1 km error in range. The time synchronization between the ground stations was extended to the observatory clocks by low-frequency ground-wave signals propagating with known velocities.     

Time Synchronization by Television

A simple technique for clock synchronization uses signals included in normal television transmissions as time markers. By use of automatic equipment built in the laboratory, it has been possible to make regular comparisons of time scales. Remote time laboratories can also be intercompared by this process. Accuracy of a fraction of a microsecond can be obtained easily. Numerical results of different experiments and comparisons with other methods are presented.     

Ferroelectric Switching Time Measurements

A simple method is described for determining field-induced polarization reversal times in ferroelectrics ranging from seconds to nanoseconds without the use of an oscilloscope. The procedure consists of 1) setting some selected reference state of polarization, preferably by recording a hysteresis loop which is terminated at the reference state, 2) applying a pulse field of known amplitude and duration to reverse a portion or all of the polarization, and 3) tracing a new hysteresis loop. The difference in polarization state between the starting point of the second loop and the termination point of the first is the amount of polarization switched by the pulse field. Data consist of charge densities ?Pr switched by the pulse fields of various amplitudes E and durations t. From ?Pr versus E plots, the field corresponding to half-switching of the polarization is read for each pulse length applied and a log/log plot of the half-switching time t1/2 versus E is constructed. These log/log plots for lead zirconate-titanate ferroelectrics generally yield, each, three linear segments in which, with increasing field, t1/2 is proportional to E-?, E-?, and E-? and ?>?>?.     

High-Accuracy Settling Time Measurements

Methods are described for measuring the settling times and other dynamic characteristics of voltage and current output D/A converters (DAC's), operational amplifiers, and precision voltage step generators. Circuits are described for measuring voltage-output device settling times as short as 1?s to within a settling error of ±2 ppm, and current-output device settling times as short as 40 ns to within a settling error of ±0.012 percent.     

Short-Term Wind Speed Forecast Using Measurements From Multiple Turbines in A Wind Farm

Turbine operations in a wind farm benefit from an understanding of the near-ground behavior of wind speeds. This article describes a probabilistic spatial-temporal model for analyzing local wind fields. Our model is constructed based on measurements taken from a large number of turbines in a wind farm, as opposed to aggregating the data into a single time-series. The model incorporates both temporal and spatial characteristics of wind speed data: in addition to using a time epoch mechanism to model temporal nonstationarity, our model identifies an informative neighborhood of turbines that are spatially related, and consequently, constructs an ensemble-like predictor using the data associated with the neighboring turbines. Using actual wind data measured at 200 wind turbines in a wind farm, we found that the two modeling elements benefit short-term wind speed forecasts. We also investigate the use of regime switching to account for the effect of wind direction and the use of geostrophic wind to account for the effects of meteorologic factors other than wind. These at best provide a small performance boost to speed forecast.     

Time Domain Reflectometer Return Loss Measurements

Equations are derived for the exact identification of a transmission line discontinuity that can be represented by an equivalent circuit consisting of one or more cascaded, series-inductive, parallel-capacitive, and series-transmission-line elements. Equations are presented for determining frequency domain return loss from time domain reflectometer data and the frequency limitations for this method of discontinuity evaluation are discussed.     

Fourier Analysis of Time-Stamped Signals Using a Small Number of Samples

This paper concerns the Fourier analysis of measurements taken at times that are not at all uniformly spaced yet are accurately known. Such can be the case when measurements are obtained by networked sensors with accurate or synchronized clocks using common Internet Protocol networks or other networks that do not guarantee timely data delivery. Such can also be the case when the object being measured is only sporadically available for measurement. A method for computing a complex spectrum from a minimal number of samples taken at nonuniform time intervals is described. The novelty of this paper lies in the method's ability to minimize the number of samples required to ensure a desired accuracy. A practical application of the method lies in doing spectral analysis of signals obtained from networked sensors where acquiring each sample is expensive in time, power, or money, and so, the number of samples taken is to be minimized. The method has been tested on two rather different sets of actual measurements: one taken via smart sensors connected to the Internet and the other taken by a number of observational astronomers using a variety of apparatus over decades.     

Crack-Tip Toughness From Wide-Range COD Measurements

An evaluation of crack opening displacement measurements is presented, which enables the determination of the crack tip toughness K ₁₀ from the whole database. The procedure is applied to results from literature for coarse-grained and fine-grained alumina.     

时钟指示时间同步误差的测量

时间同步对我们越来越重要,同步时钟应用越来越广泛,同步时钟不可避免会存在同步误差,同步时钟指示时间大于1s的同步误差和PPS脉冲间同步误差测量非常简单,但是时钟指示时间在1s以内的同步误差测量有些棘手,现有资料没有这类同步误差的测量方法,研究探索这类同步误差测量方法,对同步时钟使用和评估有非常积极的意义.     

Uncertainty and Worst-Case Analysis in Electrical Measurements Using Polynomial Chaos Theory

In this paper, the authors propose an analytical method for estimating the possible worst-case measurement due to the propagation of uncertainty. This analytical method uses polynomial chaos theory (PCT) to formally include the effects of uncertainty as it propagates through an indirect measurement. The main assumption is that an analytical model of the measurement process is available. To demonstrate the use of PCT to assess a worst-case measurement, the authors present two examples. The first one involves the use of PCT to estimate the possible worst case of a measurement due to the propagation of parametric uncertainty of a low-pass filter. This case study concerns the analysis of nonlinear effects on the propagation of uncertainty of a signal-conditioning stage used in power measurement. In this paper, the PCT method is applied to determine the probability density function (pdf) of magnitude and phase of the frequency response of the filter and their impact on the power measurement. Of particular interest is the use of PCT to determine the worst-case, expected-case, and best-case effects of the filter, avoiding the reconstruction of the complete pdf of the filter output. The results illustrate the potential of this method to determine the significant boundary of measurement uncertainty, even when the uncertainty propagates through a nonlinear nonpolynomial function. In the second example, the authors use PCT to perform a worst-case analysis for an indirect measurement of a loop impedance. For both examples, the PCT method is compared with the numerical Monte Carlo analysis and the analytical method described in the guide on uncertainty on measurements (GUM).      

Uncertainty Analysis of Thermophysical Property Measurements of Solids Using Dynamic Methods

This work reports on an analysis of thermophysical properties (thermal conductivity, thermal diffusivity, and specific heat capacity) measurements of solids using dynamic methods. The influence of temperature measurement uncertainty on the parameter estimation uncertainty is studied using a least-squares procedure. The standard and difference analyses are used for optimizing the experiment with respect to the data window or time interval of measurements. The analysis is applied to the extended dynamic plane source method, and the results of numerical computations are illustrated in the form of contour plots.     

在时、频测量中的倍增器

本文阐述了倍增原理，详细分析了多级倍增器的噪声门限以及确定它们的测量上限，还介绍有关倍增器里的关键电路－倍频器及其影响和倍增器在时、频测量中的应用．     

Relaxation Time Measurements by an Electronic Method

In many experiments, one is faced with the problem of measuring the time constant of decaying signals. The paper describes a simple electronic system that permits the direct measurement of time constants. The system was used in connection with relaxation experiments on hydrogen and rubidium masers and was found to operate well. The use of a computing counter in the systems gives the possibility of making averages on several experiments and obtaining the standard deviation of the results from the mean. The program for the computing counter is given.