Jitter Estimation Research Articles

Shape Variability of Potentials Recorded by a Single-Fiber Electrode and its Effect on Jitter Estimation

Technical problems accompanying the recording of fiber pair potentials introduce certain instability in the peak-to-peak interval (rise-time, RT) of these potentials. This study aims (1) to measure the variability observed in RT of a large number of sets of consecutive potentials recorded by a single-fiber (SF) electrode and (2) to evaluate the effect of such variability on the jitter estimation. Using a SF electrode, 140 sets of consecutive potentials were recorded from the m. tibialis anterior of four healthy subjects. For each set, the rise-time variability (RTV) was calculated as the standard deviation of the RTs of the discharges within that set. The effect of RTV in the estimation of jitter from simulated fiber pairs with controlled values of neuromuscular jitter was analyzed. The RTVs of sets visually assessed as produced by a "single-fiber" were always less than 20μs, whereas those of "composite" sets were normally higher than 20μs. We found that the RTV always increased the estimated jitter of fiber pairs. Such increment depended on the amount of neuromuscular jitter. The RTV provides an estimate of the possible error introduced in jitter assessment. This could be important for the diagnosis of mild clinical manifestations of myasthenia gravis, myopathies, and Duchenne dystrophies.

In-orbit measurements of spacecraft microvibrations for satellite laser communication links

Angular microvibrations of platform jitter on the optical inter-orbit communications engineering test satellite are measured in space during ground-to-satellite laser communication links. The microaccelerations are measured by the onboard accelerometers at a sampling rate of 2048 Hz. The angular microvibrations are estimated from the measured microaccelerations using the tracking characteristics of the laser communications terminal and the conversion factor on the basis of microvibration data obtained from ground-based tests. The power spectral density (PSD) of the satellite microvibrations is analyzed by using the fast Fourier transform analysis and the data length is examined according to the frequency resolution of the PSD. The in-orbit measurements of the PSDs are compared with those obtained from the ground test. The angular microvibrational base motion is estimated and a PSD up to 1024 Hz is additionally provided as a database of the real measurement results with previously obtained in-orbit measurements. The measured results will contribute to the angular jitter estimation and the design of a tracking control loop for space laser communication systems in the future.

Timing Jitter and Modulation Profile Extraction for Spread-Spectrum Clocks

This paper presents a built-in jitter measurement approach for measuring the timing jitter of spread-spectrum clocks (SSCs) and a jitter estimation method for validating the approach. Because of the lack of dedicated measurement instruments for SSC timing jitter measurement, the jitter estimation method is proposed to correlate SSC and non-SSC jitter. A 1.2-GHz eight-phase SSC generator with the jitter measurement circuit is designed and fabricated using the 0.18-?m complementary metal-oxide-semiconductor technology. The measured results are validated by the proposed estimation method, which is the key contribution of this paper. The experimental results show that the proposed built-in measurement approach has an error of less than 0.0026 UI.

Jitter Estimation Algorithms for Detection of Pathological Voices

This work is focused on the evaluation of different methods to estimate the amount of jitter present in speech signals. The jitter value is a measure of the irregularity of a quasiperiodic signal and is a good indicator of the presence of pathologies in the larynx such as vocal fold nodules or a vocal fold polyp. Given the irregular nature of the speech signal, each jitter estimation algorithm relies on its own model making a direct comparison of the results very difficult. For this reason, the evaluation of the different jitter estimation methods was target on their ability to detect pathological voices. Two databases were used for this evaluation: a subset of the MEEI database and a smaller database acquired in the scope of this work. The results showed that there were significant differences in the performance of the algorithms being evaluated. Surprisingly, in the largest database the best results were not achieved with the commonly used relative jitter, measured as a percentage of the glottal cycle, but with absolute jitter values measured in microseconds. Also, the new proposed measure for jitter, LocJitt, performed in general is equal to or better than the commonly used tools of MDVP and Praat.

Spectral jitter modeling and estimation

This paper suggests a new method for short-time jitter estimation based on a mathematical model that describes the coupling of two periodical phenomena. Specifically, jitter is modeled as the movement of one of the two periodic phenomena with respect to the other. The proposed method measures this movement indirectly by taking into account the spectral properties of the suggested model. Experiments with synthetic jitter signals showed that the suggested method produces accurate local estimates of jitter. Further evaluation was conducted on actual normal and pathological voice signals using two databases and jitter estimations from the Multi-Dimension Voice Program (MDVP) and the Praat system. Compared with the corresponding parameters from these two systems, the proposed method outperformed both in normal vs. pathological voice discrimination accuracy by at least 4%. Furthermore, it was shown that these methods actually rely on low-pass information, while the proposed method takes into account the full spectrum. The study of the short-time statistics of the jitter measurements provided by the suggested method indicates that there is a higher correlation with voice pathology compared to that obtained by the other two systems.

Objective characterization of oesophageal voice supporting medical diagnosis, rehabilitation and monitoring

Otolaryngologists use computational tools in the objective diagnosis of vocal folds pathologies by means of a set of acoustic parameters among others. This can be achieved in the cases of slight pathologies, but it does not exist any commercial software suitable for severe degradations of speech, as they are the oesophageal voice of laryngectomees. The present article shows a high-accuracy algorithm for the detection of the periodicity cycles of both oesophageal and laryngeal voices with low quality which allows the accurate and automatic estimation of pitch, jitter and shimmer. As the proposed algorithm works also with slighter pathologies, it is a useful contribution which allows doctors to perform an objective control during rehabilitation and monitoring stages. Thus, a patient can be controlled during oesophageal voice learning stage and it can also be saved a medical record with the results of the acoustic parameters’ measurements in order to detect possible relapses.

Estimation of laser beam pointing parameters in the presence of atmospheric turbulence

The problem of estimating mechanical boresight and jitter performance of a laser pointing system in the presence of atmospheric turbulence is considered. A novel estimator based on maximizing an average probability density function (pdf) of the received signal is presented. The proposed estimator uses a Gaussian far-field mean irradiance profile, and the irradiance pdf is assumed to be lognormal. The estimates are obtained using a sequence of return signal values from the intended target. Alternatively, one can think of the estimates being made by a cooperative target using the received signal samples directly. The estimator does not require sample-to-sample atmospheric turbulence parameter information. The approach is evaluated using wave optics simulation for both weak and strong turbulence conditions. Our results show that very good boresight and jitter estimation performance can be obtained under the weak turbulence regime. We also propose a novel technique to include the effect of very low received intensity values that cannot be measured well by the receiving device. The proposed technique provides significant improvement over a conventional approach where such samples are simply ignored. Since our method is derived from the lognormal irradiance pdf, the performance under strong turbulence is degraded. However, the ideas can be extended with appropriate pdf models to obtain more accurate results under strong turbulence conditions.

A MAP-Based Algorithm for Joint Estimation of Transition Jitter and Timing Error

To improve the robustness to timing errors in future high-density perpendicular recording channels where the dominant noise source is transition jitter, this paper proposes a scheme that jointly estimates transition jitter and timing error along with the data recovery. This estimation is based on the intuition that timing error is independent from transition jitter, while both can be quantized and characterized in an extended trellis together with the bit sequence. Simulation results demonstrate significant performance improvement using this scheme, where the cycle-slip dominant bit error rate (BER) is lowered to the same order of magnitude as the detection performance in the absence of timing errors

Fast Methods to Estimate Clock Jitter due to Power Supply Noise

In this paper, we propose two methods to estimate clock jitter caused by power supply noise in a LSI (Large-Scale Integrated circuit). One of the methods enables estimation of clock jitter at the initial design stage before floor-planning. The other method reduces simulation time of clock distribution network to analyze clock jitter at the design verification stage after place-and-route of the chip. For an example design, the relative difference between clock jitter estimated at the initial design stage and that of the design verification stage is 23%. The example result also shows that the proposed method for the verification stage is about 24 times faster than the conventional one to analyze clock jitter.

Maximum-likelihood estimation of a laser system pointing parameters by use of return photon counts

A maximum-likelihood estimator used to determine boresight and jitter performance of a laser pointing system has been derived. The estimator is based on a Gaussian jitter model and uses a Gaussian far-field irradiance profile. The estimates are obtained using a set of return shots from the intended target. An experimental setup with a He-Ne laser and steering mirrors is used to study the performance of the proposed method. Both Monte Carlo simulations and experimental results demonstrate excellent performance of the estimator. Our study shows that boresight estimation is more challenging than jitter estimation when both quantities are estimated. Furthermore, their estimation performance improves with an increase in the number of shots. The experimental results are found to agree well with the simulation results.

Towards generic charge-pump phase-locked loop, jitter estimation techniques using indirect on chip methods

Due to desirable operational and implementation characteristics, charge-pump phase locked loop (CP-PLL) systems are the architecture of choice for a variety of embedded frequency synthesis applications. A key performance metric of these systems is the spectral purity of the output signal. Spectral purity is difficult to measure directly, especially within a production test environment. This situation is not likely to improve as on-chip system frequencies increase. This paper focuses on specific aspects of a new framework including techniques and methodologies that can detect significant block level errors that lead to spectral degradation. The final crux of the work is to focus towards measurement techniques that can be mapped directly to spectral degradation, and thus prove unambiguously that the CP-PLL system is ‘right by design’ and free from errors without resorting to difficult direct measurements. This paper provides an overview of typical non-idealities and the associated effects on spectral degradation and also provides explanations of suitable detection methods. It is expected that with ever increasing system frequencies, thorough analysis of the relationship between system non-idealities and jitter/phase noise may be the only option available for rapid production testing of fully embedded CP-PLLs.

Adaptive Delay and Synchronization Control for Wi-Fi Based Mobile AV Conferencing

The tremendous success of the IEEE 802.11b technology and the popularity of portable computing units (e.g., PDAs) have led to a surge of Wi-Fi based real-time multimedia applications. However, due to the unpredictable and often fluctuating channel behavior, it is rather difficult to configure an appropriate de-jitter buffer to maintain a satisfactory perceived quality for end users. Motivated by this problem, we propose in this paper an adaptive delay and synchronization control scheme for Wi-Fi based AV conferencing applications. We target at campus-wide IEEE802.11b WLANs that are generally capable of supporting low-latency multimedia applications. The proposed scheme employs a distributed timing mechanism and performs localized control at the receiver side. The scheme can also be configiured flexibly with either one of the two inter-stream synchronization control options. Based on real-time monitored synchronization errors, Media Data Unit (MDU) loss, and real-time statistical estimation of the delay jitter among adjacent MDUs, the scheme is able to piece-wisely adjust the equalization delay to compensate for the delay jitter and control the MDU loss effectively. We investigate the performance of the proposed scheme using trace-driven approach. Through simulations, we show that the proposed scheme is capable of dynamically balancing between synchronization and latency requirements and effectively control the MDU loss as well. In particular, compared to the solutions using a static setting, the proposed scheme is able to provide the same MDU loss performance with a significant reduction in resultant latency.

A Study on Jitter of Thermal Printer (Estimation of Jitter from Carriage's Velocity Fluctuation)

A printer may generate striped patterns in the printing images. This is known as jitter, and the jitter is one of most important themes for high quality printing. In a serial printer, jitter is mainly caused by velocity fluctuation of the print-head carriage system. The purpose of this paper is to find out a method for estimating the jitter. An image scanner is used to digitize the print image and a density fluctuation ratio is introduced to valuate the jitter level. It is found that the jitter level depends not only on the carriage's velocity fluctuation but also on the density of printing image, and it can be estimated by using density velocity curve. The printing experiments in the study have been carried out by way of dye-sublimation transfer, which is usually used for high quality photo printing.

Methods for alignment of multi-class signal sets

The paper treats jitter estimation for alignment of a set of signals which contains several unknown classes of waveforms. The motivating application is epileptic EEG spikes, where alignment prior to clustering and averaging is desired. The assumption that the signal waveforms are unknown precludes the use of classical techniques, notably matched filtering. Instead we treat two other classes of methods. In the first class the jitter of each signal is estimated with aid of the whole data set, using the Rayleigh quotient of the sample correlation matrix. The main idea of the paper is the suggestion of two such methods, consisting respectively of mean value computation and maximization of the Rayleigh quotient as a function of translation of a given signal. In the second class of methods each signal is processed individually, and one such method is estimation of the jitter of a signal by its centre of gravity. By means of deduction, simulations and evaluation on real life epileptic EEG signals, we show that the first class of methods is preferable to the second. Simulations also show that the method of maximization of the Rayleigh quotient seems to be a generally good method, which gives small estimation error and is applicable in a wide range of circumstances. For seven investigated sets of real life EEG data, the maximization algorithm turned out to give the best results, and improved alignment in the majority of signal clusters.

P3 latency jitter assessed using 2 techniques. I. Simulated data and surface recordings in normal subjects

Latency variability measurement using cross-correlational techniques has the drawback of alignment to background noise not related to ERP activity. We compared latency jitter estimation in simulated and real P3 recordings using Woody's algorithm and a non-cross-correlational technique, the maximum likelihood technique (MLT). Simulated ERPs (with introduced latency jitter) were generated using either a 1/2 cycle 2 Hz sine wave or an averaged P3 ERP with 1 of 3 added noise types in 5 signal to noise ratios (SNRs): (i) white noise; (ii) a 10 Hz sine wave; (iii) a 7.5 Hz sine wave. Jitter measurement accuracy was assessed using mean square error (MSE) for 1 iteration of the Woody method and each of 4 iterations of the MLT. Lowest MSEs occurred for higher SNRs and 1 iteration of the MLT. The MLT and Woody method were applied to P3 ERPs of 13 subjects with SNRs greater than 0.4. P3 latency jitter was significantly lower for the MLT. Latency jitter (both methods) did not differ between homologous electrodes and was highest in posterior electrodes. In the latency corrected ERP data of subjects with persistent alpha activity periodic components occurred in the Woody corrected average (not seen in the conventional or the MLT corrected averages). Our data indicate that the MLT is the more accurate method for determining latency jitter.

P3 latency jitter assessed using 2 techniques. I. Simulated data and surface recordings in normal subjects

Latency variability measurement using cross-correlational techniques has the drawback of alignment to background noise not related to ERP activity. We compared latency jitter estimation in simulated and real P3 recordings using Woody's algorithm and a non-cross-correlational technique, the maximum likelihood technique (MLT). Simulated ERPs (with introduced latency jitter) were generated using either a 1/2 cycle 2 Hz sine wave or an averaged P3 ERP with 1 of 3 added noise types in 5 signal to noise ratios (SNRs): (i) white noise; (ii) a 10 Hz sine wave; (iii) a 7.5 Hz sine wave. Jitter measurement accuracy was assessed using mean square error (MSE) for 1 iteration of the Woody method and each of 4 iterations of the MLT. Lowest MSEs occurred for higher SNRs and 1 iteration of the MLT. The MLT and Woody method were applied to P3 ERPs of 13 subjects with SNRs greater than 0.4. P3 latency jitter was significantly lower for the MLT. Latency jitter (both methods) did not differ between homologous electrodes and was highest in posterior electrodes. In the latency corrected ERP data of subjects with persistent alpha activity periodic components occurred in the Woody corrected average (not seen in the conventional or the MLT corrected averages). Our data indicate that the MLT is the more accurate method for determining latency jitter.

A model for timing jitter estimation in optical‐fiber PPM

AbstractAn original model for timing jitter estimation in optical‐fiber PPM is developed and used to examine the performance impairment due to imperfect slot synchronization. An original expression that predicts the spectral properties in the presence of jitter is presented. The extracted slot clock timing variance is evaluated in terms of the PPM parameters such as the number of slots and the modulation index, and the effects of the other parameters such as the phase‐locked loop (PLL) bandwidth and the fiber bandwidth are examined and used to optimize the slot clock timing variance. Original results are presented for the system wrong slot error (WSE) probability due to imperfect synchronization. The results indicate that this probability can be maintained well below the 10−9 system operating error rate. The model enables the identification of the set of optimum PPM, PLL, and fiber parameters for a given required performance. © 1994 John Wiley & Sons, Inc.

Axonal stimulation for end-plate jitter studies.

This single fibre EMG study compares the standard method of neuromuscular jitter measurement in voluntarily activated muscle to that by intramuscular electrical stimulation of motor axons in a group of normal subjects. The latter method avoids the interdischarge interval-dependent jitter, as well as a possible failure to recognise split muscle fibres. The mean MCD on axonal stimulation was only 5.2 microseconds less than in the voluntary activation study and was thus 8% more than theoretically expected for single motor end plates. The difference could be due to an axonal jitter and some other factors. Axonal stimulation has proved to be a relatively easy and reliable method for routine estimation of neuromuscular jitter, provided that the resolution of time measurement is better than 2 microseconds, so that low jitter due to occasional direct muscle fibre stimulation is not mistaken for a normal reading. The upper normal limits for the extensor digitorum communis muscle suggested by the present study are 40 microseconds (individual muscle fibres) and 25 microseconds (mean of 30 muscle fibres).