Delay Estimation Method Research Articles

Estimation of Incident Delay and Its Uncertainty on Freeway Networks

Estimating incident-induced delay on freeways is important for measuring the impacts of incidents. Information regarding delay can be used for transportation planning or the assessment of traffic improvement projects. Traditional delay estimation methods cannot account for the stochastic attributes of dynamic traffic networks. Introducing the incident duration model and the reduced capacity model into the traditional deterministic queuing model allows researchers to understand better the stochastic characteristics of dynamic networks and to develop a new stochastic incident-induced delay model. The mean delay, the variance of delay, and the expected total delay are estimated on the basis of the proposed model. The analysis shows that the deterministic queuing model can estimate the mean delay as well as the stochastic delay model, but it seriously underestimates the variance of delay and the expected total delay in dynamic networks, which are found to be dominated by incident duration. In addition, depending on the parameter values in the probability distribution of incident duration and reduced capacity, the standard deviation of delay can be higher than the mean delay.

Estimation of Incident Delay and Its Uncertainty on Freeway Networks

Estimating incident-induced delay on freeways is important for measuring the impacts of incidents. Information regarding delay can be used for transportation planning or the assessment of traffic improvement projects. Traditional delay estimation methods cannot account for the stochastic attributes of dynamic traffic networks. Introducing the incident duration model and the reduced capacity model into the traditional deterministic queuing model allows researchers to understand better the stochastic characteristics of dynamic networks and to develop a new stochastic incident-induced delay model. The mean delay, the variance of delay, and the expected total delay are estimated on the basis of the proposed model. The analysis shows that the deterministic queuing model can estimate the mean delay as well as the stochastic delay model, but it seriously underestimates the variance of delay and the expected total delay in dynamic networks, which are found to be dominated by incident duration. In addition, depending on the parameter values in the probability distribution of incident duration and reduced capacity, the standard deviation of delay can be higher than the mean delay.

A Method for the Ionospheric Delay Estimation and Interpolation in a Local GPS Network

To estimate ionospheric delays from the Global Positioning System (GPS) measurements, satellite and receiver equipment biases have to be modeled. This paper presents a procedure based on the least squares (LS) approach, which implicitly takes into account these equipment biases in the estimation of the ionospheric effect. The second part of this work deals with the interpolation of the ionospheric correction from a permanent GPS network to a single frequency GPS user. The results obtained show that for 10-cm position accuracy the ionospheric delay can be successfully interpolated when the GPS user is within 40 km of the GPS permanent network.

APPROXIMATE REALIZATION OF VALVE DYNAMICS WITH TIME DELAY

This paper describes the model identification of control valve dynamics with a time delay. An experimental set-up is used to perform both frequency response and step response measurements on the control valve. An approximate realization algorithm and a new time delay estimation method are applied on the experimental data. The results illustrate that the suggested approach provides a good time delay estimate and a reasonable state space description for the valve dynamics.

Delay Estimation in Long-Code Asynchronous DS/CDMA Systems Using Multiple Antennas

The problem of propagation delay estimation in asynchronous long-code DS-CDMA multiuser systems is addressed. Almost all the methods proposed so far in the literature for propagation delay estimation are derived for short codes and the knowledge of the codes is exploited by the estimators. In long-code CDMA, the spreading code is aperiodic and the methods developed for short codes may not be used or may increase the complexity significantly. For example, in the subspace-based estimators, the aperiodic nature of the code may require subspace tracking. In this paper we propose a novel method for simultaneous estimation of the propagation delays of several active users. A specific multiple-input multiple-output (MIMO) system model is constructed in a multiuser scenario. In such model the channel matrix contains information about both the users propagation delays and channel impulse responses. Consequently, estimates of the delays are obtained as a by-product of the channel estimation task. The channel matrix has a special structure that is exploited in estimating the delays. The proposed delay estimation method lends itself to an adaptive implementation. Thus, it may be applied to joint channel and delay estimation in uplink DS-CDMA analogously to the method presented by the authors in 2003. The performance of the proposed method is studied in simulation using realistic time-varying channel model and different SNR levels in the face of near-far effects, and using low spreading factor (high data rates).

Closed-Loop Time Delay Estimation of SISO Processes for Control Performance Monitoring

A novel time delay estimation method for SISO control loop monitoring has been introduced. The proposed method requires a process regulated by a SISO controller during routine operation to be temporarily switched to relay control. The input and output data gathered from the process under relay control can be used to produce a time delay estimate.

A novel method for worst-case interconnect delay estimation

This brief presents a novel low-complexity crosstalk-aware method to estimate the worst-case interconnect delay. By regarding the RC network as a modified two-pole linear time-invariant system and taking the skew of aggressive signals into consideration, the worst-case delay estimated by the proposed method is approximately 5% different from the results by HSPICE.

Simulation analysis of the ability to estimate motor unit propagation velocity non-invasively by different two-channel methods and types of multi-electrodes

Ability to estimate motor unit propagation velocity correctly using different two-channel methods for delay estimation and different non-invasive spatial filters was analysed by simulation. It was established that longitudinal double difference electrodes could be not a better choice than simple bipolar parallel electrodes. Spatial filtration with a new multi-electrode (performing difference between signals detected by two transversal double difference electrodes positioned along the muscle fibres) promises to give the best estimate. Delay estimation between reference points is more preferable than that based on the cross-correlation technique, which is considerably sensitive to the fundamental properties of the muscle fibre extracellular fields. Preliminary averaging and approximation of the appropriate parts of the signals around chosen reference points could reduce the larger noise sensitivity and the effects of local tissue inhomogeneities as well as eliminate the sampling problem. A correct estimate of the propagation velocity could be impossible, even in the case of not very deep motor units (15 or 10 mm, depending on the spatial filter used) with relatively long (about 120 mm) muscle fibres. In the case of fibres with asymmetrical location of the end-plates in respect to the fibre ends, the propagation velocity estimates could be additionally biased above the longer semilength of the motor unit fibres.

Bias and consistency in time delay estimation methods: Case of the double quasar HE 1104–1805

We present a short re-evaluation of a recently published time delay estimate for the gravitational lens system HE 1104-1805 with emphasis on important methodological aspects: bias of the statistics, inconsistency of the methods and use of the purposeful selection of data points (or so-called cleaning ) at the preprocessing stage. We show how the inadequate use of simple analysis methods can lead to too strong conclusions. Our analysis shows that there are indications for the time delay in HE 1104-1805 to be between -0.9 and -0.7 years, but still with a large uncertainty.

Comparison of independent integrated water vapour estimates from GPS and sun photometer measurements and a meteorological model

Measurements using the Global Positioning System (GPS) are affected by the so-called tropospheric delay. Of this, the so-called wet delay is related mainly to the amount of water vapour along the path of the GPS signal through the troposphere. Precise knowledge of the abundance of water vapour, in space and time, is important for meteorology, both in forecasting and now-casting as well as in climate studies. Both because water vapour is the predecessor of precipitation, which is a forecast product, and because a very significant fraction of the energy released to the atmosphere comes from latent heat via water vapour. Despite the high variability of water vapour compared to other meteorological fields, like pressure and wind, water vapour observations are scarce; wherefore additional measurements of water vapour are expected to benefit meteorology. Water vapour is crucial for the development of the small scale, but sometimes very severe,precipitation events which are often seen at mid latitudes, and which are very hard to predict. In this work a comparison between radiometric (sun photometer) and GPS integrated water vapour (IWV) is presented. A sun photometer has been installed at the ENEA (Ente per le Nuove tecnologie, l'Energia e l'Ambiente) base of Lampedusa Island. The sun photometer is quite close (less then 4 km) to an ASI (Agenzia Spaziale Italiana) GPS permanent receiver. In Venezia an ASI GPS permanent receiver is collocated with another sun photometer. Both sun photometers are installed as part of the AERONET (AErosol and RObotic NETwork) program. A long record of sun photometric measurements, GPS data, and meteorological data is available for the Venezia site. A shorter record (summer period of the year 2000) is available for the station at Lampedusa. The comparison among the three different methods for water vapour delay estimation is presented. We find that the GPS and sun photometric data are better correlated (S.D. about 10 mm for the wet delay) than are the measurements with the NWP model predictions. This is an indication that GPS delay data may contain information useful for weather prediction.

Logic simulation methods for longest path delay estimation

Two original methods are proposed for digital circuit delay estimation with logic simulation: direct circuit simulation (DCS) and inverse circuit simulation (ICS). With only one run of the logic simulator the DCS method evaluates the longest path delay for each signal in the circuit for both rising and falling edges. If the delay to some primary output is too long to meet with required circuit operating frequency, the ICS method can be applied to extract that portion of the circuit that is subject to redesign and delay minimisation. Both methods are very fast and suitable for interactive use during the logic verification phase of the design process. While the ICS method can be easily implemented in modern hardware description languages such as VHDL or VERILOG, for the implementation of the DCS method a simple, yet effective, general signal attribute modelling mechanism is proposed. Both methods are implemented in AleC++, the input language of the simulator ALECSIS, and their efficiency is shown on a set of ISCAS'85 benchmark circuits.

Performance of a new digital baseband predistorter using calibration memory

Digital predistortion of a baseband signal is a well-known method of power amplifier (PA) linearization used to reduce adjacent channel interference (ACI) in a nonconstant envelope modulation system. This paper proposes a specific predistorter configuration based on the estimation of the PA characteristics extracting its linear behavior and comparing with a linear model by means of a calibrating signal. The effects of quadrature modulator and demodulator imbalances are included in our analysis. The effects and requirements of the reconstruction filters are stated and a new method for the loop delay estimation is presented. We also focus our attention in some design considerations and simulation results related to the use of a fixed point digital signal processor (DSP). Simulations show that out-of-band skirts lower than -60 dBc can be obtained for a narrow bandwidth system.

Timing recovery for OFDM transmission

Orthogonal frequency division multiplexing (OFDM) is an effective modulation technique for high-rate and high-speed transmission over frequency selective fading channels. However, OFDM systems can be extremely sensitive and vulnerable to synchronization errors. In this paper, we present a scheme for performing timing recovery that includes symbol synchronization and sampling clock synchronization in OFDM systems. The scheme is based on pilot subcarriers. In the scheme, we use a path time delay estimation method to improve the accuracy of the correlation-based symbol synchronization methods, and use a delay-locked loop (DLL) to do the sampling clock synchronization. It is shown that by using this scheme, the mean square values of the symbol timing estimation error can be decreased by several orders of magnitude compared to the common correlation methods in both the AWGN and multipath fading channels. In addition, the scheme can track the symbol timing drift caused by the sampling clock frequency offsets.

An iterative quadratic method for high resolution delay estimation with known waveform

The iterative delay estimation method is based on its analogy with parameter estimation of sinusoids in correlated noise. It assumes a-priori knowledge of echo waveform, their number, and the structure of the covariance matrix of noise. The advantages of this method are improved resolution as compared to the conventional matched filter approach and convergence, in a few iterations, to maximum likelihood estimate.

Application of the continuous wavelet transform to the angular location of jet aircraft

For a fast moving source and widely spaced sensors, the passive wideband cross-correlation method for time delay estimation requires compensation for the relative time scaling between the received signals, otherwise the time delay estimates will be in error. Passive wideband cross correlation with differential Doppler compensation is equivalent to evaluating the continuous wavelet transform, which is an operation that transforms a function (represented by the output waveform of one sensor) by integrating it with time-scaled and time-delayed versions of some kernel function (represented by the output waveform of the other sensor). When the signal-to-noise ratio is high, the coordinates of the wavelet transformed global maximum provide reliable estimates of both the time delay and the ratio of the time scales of the signals received by the two sensors. The wavelet transform is used to process real acoustic data recorded from an orthogonal configuration of three microphones during the low altitude transit of a jet aircraft. The resulting time delay estimates are used to calculate the variation with time of the azimuth and elevation angles of the aircraft during its transit.

A new blind identification method for DS-CDMA systems with antenna array under multipath fading

In recent years, some blind adaptive multiuser detectors have been presented to implement multiuser detection with only the knowledge of the desired user's spreading code and propagation delay. We find, in this paper, that with the aid of the antenna array, multiuser detection can be achieved even without the desired user's spreading code and propagation delay, provided that the direction of arrival of every user is different from each other. Propagation delay and array response estimation methods are also proposed in this paper.

Super resolution time delay estimation via MODE-WRELAX

We consider estimating time delays and amplitudes (real- or complex-valued) from the superposition of very closely spaced signals with known shapes. The well-known high resolution MODE (Method Of Direction Estimation) algorithm, which was originally proposed for angle estimation in array processing, is modified and used with our efficient time delay estimation method WRELAX (Weighted Fourier transform and RELAXation based) algorithm to deal with this problem. The proposed method is referred to as MODE-WRELAX. MODE-WRELAX provides better accuracy than MODE and higher resolution than WRELAX. Moreover, it can be used for both complex- and real-valued signals (including those with highly oscillatory correlation functions). Numerical results show that the MODE-WRELAX estimates can approach the corresponding Cramer-Rao bound. Efficient implementation of the algorithm is also discussed.

Latency change estimation for evoked potentials via frequency selective adaptive phase spectrum analyzer.

This paper addresses the problem of detecting and estimating latency changes in evoked potentials (EP's). EP's have been widely used to quantify neurological system properties. Transient and time-varying changes in latency may indicate impending neurological injury. Traditional time averaging and correlation methods for EP latency estimation are inefficient under low signal-to-noise ratio (SNR) and/or strong periodic interference conditions. This paper proposes an adaptive phase spectral time delay estimation method to detect and estimate the time-varying latency changes when both the SNR and the signal-to-interference ratio (SIR) are low. A theoretical analysis and computer simulation demonstrate that the proposed method can track the time-varying latency changes effectively and accurately when both the SNR and the SIR are as low as -5 dB. The method is also suitable for real time detection and estimation of the latency changes.

Comparison of discrete subsample time delay estimation methods applied to narrowband signals

The problem of estimating the subsample time delay between two noise-corrupted narrowband signals is considered. Significant improvements to two previously proposed estimators, the MXS and MSX, are made. The performance of the revised estimators is assessed through simulation over a range from -10 to 20 dB, with four well known estimators, two of which are asymptotically maximum likelihood (the direct correlator and the average square difference function) and the other two are windowed versions of them (the generalized cross-correlator and generalized least squares). Also, the estimators are applied to ultrasonic experimental data at three different SNRs. At low SNR, the MXS/MSX estimators are shown to exhibit a significant reduction in the variance of the estimates.

Blind beamforming on a randomly distributed sensor array system

We consider a digital signal processing sensor array system, based on randomly distributed sensor nodes, for surveillance and source localization applications. In most array processing the sensor array geometry is fixed and known and the steering array vector/manifold information is used in beamformation. In this system, array calibration may be impractical due to unknown placement and orientation of the sensors with unknown frequency/spatial responses. This paper proposes a blind beamforming technique, using only the measured sensor data, to form either a sample data or a sample correlation matrix. The maximum power collection criterion is used to obtain array weights from the dominant eigenvector associated with the largest eigenvalue of a matrix eigenvalue problem. Theoretical justification of this approach uses a generalization of Szego's (1958) theory of the asymptotic distribution of eigenvalues of the Toeplitz form. An efficient blind beamforming time delay estimate of the dominant source is proposed. Source localization based on a least squares (LS) method for time delay estimation is also given. Results based on analysis, simulation, and measured acoustical sensor data show the effectiveness of this beamforming technique for signal enhancement and space-time filtering.