Presence Of Jitter Research Articles

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.

The Bispectrum of Sampled Data: Part 1-Detection of the Sampling Jitter

The effect of timing error (jitter) on the power spectrum (second-order spectrum) of sampled data has been investigated previously. The current increasing interest in higher-order spectra calls for investigation of the effect of sam- pling jitter on the discrete higher-than-order-two spectra. In this paper, we present results concerning the bispectrum (third- order spectrum). We derive expressions for the bispectrum of sampled data under the assumption that the timing errors are independently identically distributed (i.i.d.) random variables. It is shown that, while the discrete bispectrum of a uniformly sampled third-order stationary signal is zero in a triangle that is a proper subset of the principal domain, it differs from zero in the presence of jitter. Exploiting this effect, we propose a test for detection of sampling jitter, using the bispectrum. Namely, given estimates of the discrete bispectrum of an un- known band-limited signal, we can decide whether jitter is present or not. The performance of the proposed detector is analyzed, and its dependence on the jitter variance, signal skewness, and observation time is shown.

Communication architectures and algorithms for media mixing in multimedia conferences

The problem of media mixing that arises in teleconferencing applications such as teleorchestra is addressed. The mixing algorithm presented minimizes the difference between generation times of the media packets that are being mixed together in the absence of globally synchronized clocks, but in the presence of jitter in communication delays on packet switched networks. In order to support applications, such as teleorchestra, that involve a large number of participants, hierarchical mixing architectures are proposed, and it is shown that they are an order of magnitude more scalable than purely centralized or distributed architectures. Furthermore, mechanisms for minimizing the delays incurred by mixing in various communication architectures are presented. The mixing algorithms are implemented on a network of workstations connected by Ethernets, and the performance of various mixing architectures is experimentally evaluated. The results reveal the maximum number of participants that can be supported in a conference. >

Distribution free bound on the performance of optical communication systems in the presence of jitter

For very high data rate optical communication systems, jitter is an impairment which may seriously degrade system performance. Assuming knowledge of the jitter statistics to be restricted to just the range and RMS value, the authors determine a new upper bound on the performance. For a certain class of signals, they derive a worst-case distribution (WCD) which consists of three Dirac impulses, located at the centre and at the extremes of the range. The usefulness of the WCD is demonstrated by means of examples which show that for many practical cases the new bound is tight. They show how the WCD may be combined with a modified Chernoff bound to obtain an overall upper bound on system performance which encompasses a comprehensive set of impairments including jitter.

Changes in voice fundamental frequency following discharge of single motor units in cricothyroid and thyroarytenoid muscles.

This investigation was designed to measure voice Fo changes related to single motor unit (SMU) contractions in the cricothyroid and thyroarytenoid muscles. Four subjects (3 men and 1 woman) were recorded producing a prolonged vowel at modal pitch and loudness levels while simultaneous recordings of electromyograms (EMG) from the muscles were obtained. Voice Fo changes unrelated to SMU firings in the muscles were eliminated using an averaging method previously described by Baer (1979). Results indicate that the time between discharge of the SMU and the peak in Fo change ("Fo Latency") was variable and ranged from 5 to 20 ms for the thyroarytenoid and 6 to 75 ms for the cricothyroid muscle. Distinct oscillations in Fo were always present in recordings from the woman subject and from the men when they phonated at higher-than-modal pitch levels. The findings are discussed in relation to SMU contraction times, biomechanics of the vocal folds, and the presence of jitter in normal voices.

Influence of timing errors on the performance of direct-detection optical-fibre communication systems

Upper and lower bounds are derived on error probability for direct-detection binary optical communication in the presence of jitter. Symbol-conditioned moment generating functions are employed, enabling the various stochastic impairments encountered, signal dependent compound Poisson statistics, coloured additive Gaussian noise and intersymbol interference, as well as timing errors in the signal elements or sampling instants, to be accommodated. The bounds are shown to be tight for a wide range of parameter values encompassing and extending significantly beyond those encountered in practical systems. They are then used to examine the influence of jitter on system performance.

Effect of Sampling Time Jitter on Array Performance

The effect on array SNR of errors in sampling times (jitter) isan analyzed for the processor. Jitter is modeled as a discrete-paramter er random process, and expressions for array SNR are determined as a function of signal and noise spectra and jitter characteristics. For a plane wave signal, it is found that jitter in the data used to design the processor has no effect on output SNR if the noise is independent between channels. However, jitter in the input (evaluation) n) data can cause a substantial loss in peak array SNR and in the array's frequency selectivity. These losses can be expected to increase as the high-frequency content of the data increases. The Bryn processor also loses its interpretation as a likelihood ratio processor in the presence of jitter. The effect of jitter can be reduced in many cases by increasing the sampling rate.

Timing jitter in digital filtering of analog signals

Effects of timing jitter in digital filtering of analog signals are analyzed. Jitter may be introduced into the system when the incoming analog signal is being sampled and when the samples of the output of the digital filter are being read out for reconstruction back into an analog signal. These two jitters are called readin and readout jitters, respectively. General expressions are derived for the spectrum of the analog output in the presence of jitter and for the mean-square error introduced by the jitter. Four specific cases are then considered. They are readin jitter only, readout jitter only, independent jitter, and locked jitter. In each case, the general expression for the spectrum of the analog output is reduced to a more explicit form, and a simple upper bound on the mean-square error is derived. An example is included to illustrate the effect of high-frequency jitter and the effect of jitter due to 60-cycle pickup.

Sampling with periodically varying rates

This paper considers a number of problems arising from the reconstruction of a continuous stochastic signal from its samples taken at periodically nonuniformly spaced intervals. The optimum mean-square error time varying reconstruction filter in the presence of jitter for the periodically varying sampling rate is determined. Expressions for the error arising from the use of a common class of simple but nonoptimum reconstruction filters are derived. The results may be useful when the relative merits of uniform and nonuniform sampling schemes are compared.