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	Allan variance - Wikipedia, the free encyclopedia
		The Allan variance, named after David W. Allan, is a measurement of accuracy in clocks.
		For most real-world systems, the Allan variance depends on the time period used between samples: therefore it is a function of the sample period, as well as the distribution being measured.
		A low Allan variance is a characteristic of a clock with good stability over the measured period.
	en.wikipedia.org /wiki/Allan_variance (152 words)

	Allan variance: Definition and Links by Encyclopedian.com - All about Allan variance
		The Allan variance is a measurement of accuracy in clocks.
		For most real-world systems, the Allen variance depends on the time period used between samples: therefore it is a function of the sample period, as well as the distribution being measured.
		Note: a low Allan variance is a characteristic of a clock with good stability over the measured period.
	www.encyclopedian.com /al/Allan-variance.html (139 words)

	Hadamard Variance
		The Hadamard [1] variance is based on the Hadamard transform [2], which was adapted by Baugh as the basis of a time-domain measure of frequency stability [3].
		The Hadamard variance is a 3-sample variance that is similar to the 2-sample Allan variance.
		Analytical methods are available for calculating the number of degrees of freedom for an overlapping Allan variance estimation, and that same theory can be used to establish reasonable single or double-sided confidence intervals for an overlapping Hadamard variance estimate with a certain confidence factor, based on Chi-squared statistics.
	www.wriley.com /paper4ht.htm (1409 words)

	Astron. Astrophys. 336, 697-720 (1998) (Site not responding. Last check: 2007-09-18)
		For a random time series, the Allan variance on a given time scale T is basically the variance of the differences of subsequent averages over time T.
		Varying T thus allows to trace the average behavior of the power spectrum with frequency, which determines the drift characteristics of the signal.
		As the literature on the Allan variance is rather sparse, Appendix A summarizes the definition of the Allan-variance for 1-dimensional random functions, discusses its relation to Fourier-analysis and in particular to the power spectrum in a consistent notation, and lists its characteristic properties with various types of drift behavior.
	aa.springer.de /papers/8336002/2300697/sc2.htm (1799 words)

	Allan Variance Definition (Site not responding. Last check: 2007-09-18)
		The Allan Variance was introduced to solve the problem of characterizing the frequency stability of oscillators.
		The confidence interval of an overlapping Allan deviation estimate is better than that of a normal Allan variance estimation.
		The time variance, TVAR, is a measure of time stability based on the modified Allan variance.
	yazdiet.club.fr /av_help/definitions.html (263 words)

	Allan Variance and Deviation (Site not responding. Last check: 2007-09-18)
		VARIANCE We recall from descriptive statistics that a "variance" statistic attempts to capture (or "model") -- in one value -- the extent to which data vary from some basis.
		A log-log plot of Allan variance versus sample period produces approximate straight line values of different slopes in four of the five possible cases.
		There is a lot of mention of Allan variance in the literature surrounding precision frequency measurement, e.g., in the yearly proceedings of the annual IEEE International Frequency Control Symposium.
	www.ciphersbyritter.com /NEWS6/ALLANVAR.HTM (1226 words)

	The periodogram and Allan variance reveal fractal exponents greater than unity in auditory-nerve spike trains - Lowen, ... (Site not responding. Last check: 2007-09-18)
		Two estimates of the fractal exponent are considered which do not suffer from this limit: one derived from the Allan variance, which was developed by the authors, and one based on the periodogram.
		The AV IDC, which is based on the Allen variance (as opposed to the ordinary variance) is de ned in terms of the variability of...
		1 Variability and long-duration correlation in the sequence of..
	citeseer.ist.psu.edu /lowen96periodogram.html (655 words)

	ALMA Memo #310 - Measurements of Allan Variance and short term phase noise of millimeter Local Oscillators (Site not responding. Last check: 2007-09-18)
		Measurements of Allan Variance and short term phase noise of millimeter Local Oscillators
		The SSB phase noise and the Allan Variance are the physical quantities usually measured, with different techniques, to represent the two spectral regions of phase stability, with a crossover around one second.
		Here we propose a new data acquisition system, essentially dedicated to the measurement of the Allan Variance, which is built around two programs, written in the LabView environment.
	www.alma.nrao.edu /memos/html-memos/abstracts/abs310.html (400 words)

	The Wavelet Digest :: View topic - Preprint: The relation of the Allan- and Delta-variance...
		Preprint: The relation of the Allan- and Delta-variance...
		Subject: Preprint: The relation of the Allan- and Delta-variance...
		that the Allan- and Delta-variances are the variances of wavelet
	www.wavelet.org /phpBB2/viewtopic.php?t=4070 (129 words)

	Journal of Vision - Discriminating isotrigon textures, by Maddess & Nagai (Site not responding. Last check: 2007-09-18)
		The input to the discriminant models was 5 variance measures derived from the mini-textures.
		The variance measures included 2D oriented and unoriented versions of the Allan Variance, and these are shown to be related to physiologically plausible mechanisms for calculating forth-order spatial correlations.
		Our quadratic discriminant models behaved similarly to humans suggesting that humans discriminate these textures as if they were using quadratic comparisons between the variance of the output of oriented filters, where the variance is either computed either over quite large parts of the image or more locally with an orientation bias.
	www.journalofvision.org /1/3/151 (278 words)

	Micro-g LaCoste, Inc.
		Shown below are two Allan Variances of the laser frequency when the ML1 is "beat" with an iodine-stabilized laser (primary standard frequency source).
		Allan Variance when room temperature cycles over 2 degC.
		Allan Variance when room temperature cycles over 0.4 degC.
	www.microgsolutions.com /ml1.htm (446 words)

	Allan Variance -- Overview by David W. Allan
		The divide by two causes this variance to be equal to the classical variance if the ys are taken from a random and uncorrelated set; i.e.
		The advantage of this variance over the classical variance is that it converges for most of the commonly encountered kinds of noise, whereas the classical variance does not always converge to a finite value.
		Appendix A and B (pages 66-71) in HP application note 1289: "The Science of Timekeeping" are excellent tutorials for those who are beginning in their understanding of clock statistics and why the Allan variance.
	www.allanstime.com /AllanVariance (709 words)

	Terme (Site not responding. Last check: 2007-09-18)
		One half of the time average over the sum of the squares of the differences between successive readings of the frequency deviation sampled over the sampling period.
		The Allan variance is conventionally expressed by σy 2(ζ).
		The term is used interchangeably with Allen deviation, which is the rigorously correct term since it is the square root of a variance type statistical term.
	doc-telecom.enst-bretagne.fr /doc-telecom/terme.jsp?715 (98 words)

	Information Bridge: DOE Scientific and Technical Information (Site not responding. Last check: 2007-09-18)
		Allan variance, a time domain analysis technique, is an accepted IEEE standard for gyro specifications.
		The method was initially developed by David Allan of the National Bureau of Standards to quantify the error statistics of a Cesium beam frequency standard employed as the US Frequency Standards in 1960`s.
		This report presents an overview of the method, explains the relationship between Allan variance and power spectral density distribution of underlying noise sources, describes the batch and recursive implementation approaches, validates the Allan variance computation with a simulation model, and illustrates the Allan variance method using data collected from several Honeywell LIMU units.
	www.osti.gov /bridge/product.biblio.jsp?osti_id=10196087 (301 words)

	Sect_1.3.2
		This two-sample variance of the fractional frequency error is the standard measure of clock stability.
		The Allan Variance is a measure of the performance of a clock.
		The Allan Variance is, however, not based on any physical model of the oscillator, but rather the stability graphs are produced from the results of testing actual oscillators.
	www.gmat.unsw.edu.au /snap/gps/gps_survey/chap1/132.htm (1045 words)

	Hadamard Variance
		It reviews the classical Hadamard variance, describes an overlapping version of the Hadamard variance that offers better estimates for this statistic, and introduces the new Hadamard total variance that offers improved confidence at large averaging factors.
		For best consistency, the overlapping Hadamard variance is used instead of the Hadamard total variance at m=1.
		It is identical to the Hadamard variance except for a factor of 2/3 [12, 13].
	www.stable32.com /paper4ht.htm (1409 words)

	Allan variance - Encyclopedia, History, Geography and Biography
		Allan variance - Encyclopedia, History, Geography and Biography
		This page was last modified 04:46, 29 Apr 2005.
		This encyclopedia, history, geography and biography article about Allan variance contains research on
	www.arikah.com /encyclopedia/Allan_variance (174 words)

	The Calculation of Time Domain Frequency
		It is most efficiently calculated by a reflection method [22], and has the same expected value as the normal Allan variance for white and flicker PM noise and white FM noise.
		Noise recognition can generally be accomplished by using the B1 bias function (the ratio of the standard variance to the Allan variance) and the R(n) ratio function (the ratio of the modified Allan variance to the normal Allan variance).
		The normal and modified Allan variances and total variance should be identical for an averaging factor of 1.
	www.ieee-uffc.org /freqcontrol/paper1ht.html (3604 words)

	Time and Frequency from A to Z (Site not responding. Last check: 2007-09-18)
		This statistic is sometimes called the Allan variance, but since it is the square root of the variance, its proper name is the Allan deviation.
		The Allan deviation is also used to identify types of oscillator and measurement system noise.
		Note that the Allan deviation does not distinguish between white phase noise and flicker phase noise.
	www.boulder.nist.gov /timefreq/general/glossary.htm (838 words)

	Independent References to the Allan Variance
		Definition: Allan Variance: One half of the time average over the sum of the squares of the differences between successive readings of the frequency deviation sampled over the sampling period.
		Frequency Stability and Root Allan Variance The frequency stability of signal sources (oscillators) depends on any active device employed within the oscillator package and the frequency-determining element (crystal, LC, RC, transmission line, etc..
		Allan Variance from Phase Noise - This spreadsheet calculates the Allan Variance from supplied phase noise intercepts.
	www.allanstime.com /AllanVariance/references.htm (819 words)

	Definition: allan variance (Site not responding. Last check: 2007-09-18)
		Allan variance: One half of the time average over the sum of the squares of the differences between successive readings of the frequency deviation sampled over the sampling period.
		Note: The Allan variance is conventionally expressed by
		This HTML version of Telecom Glossary 2K was last generated on Wed May 8 15:36:48 MDT 2002.
	www.its.bldrdoc.gov /projects/devglossary/_allan_variance.html (63 words)

	Building a better clock predictor (March 1997) - News - optics.org
		One recommended method hasbeen to use the two-sample frequency variance known as the Allan variance statistic.
		Recent NIST analysis has shown that the Allan vairiance statistic does not adequately characterize certain types of oscillator behavior and measurement protocols.
		Use of the "total variance" method results in more accurate predictions of the time errors that evolve after a precision clock is synchronized, researchers say.
	optics.org /articles/news/3/3/2/1 (212 words)

	Network Time Protocol - Wikipedia, the free encyclopedia
		NTP uses UDP port 123 as its transport layer.
		It is designed particularly to resist the effects of variable latency.
		NTP uses Marzullo's algorithm with the UTC time scale, including support for features such as leap seconds.
	en.wikipedia.org /wiki/Network_time_protocol (735 words)

	Allan Variance
		The plots do not reflect the variances of the quarz oscillators of the computers since the frequency of the kernel clock is corrected using an optimized value for
		When looking at packet traces generated with disciplined local clocks it is not easy to decide if variances in delay times are caused by the system or the measurement process (i.e.
		The well-known separation of variance technique is not applicable here since the datasets are correlated and the variances estimated with this method are even negative in our example.
	www7.informatik.uni-erlangen.de /~ksjh/research/cluster/timesync/avar.html (315 words)

	Fractal properties of human muscle sympathetic nerve activity -- Fadel et al. 286 (3): 1076 -- AJP - Heart and ...
		is the variability of cardiac-related burst amplitude and interburst
		The Allan factor curve for MSNA is shown in Fig.
		Slope of power law in Allan factor curve for original time series was 0.66, yielding a persistent H of 0.83.
	ajpheart.physiology.org /cgi/content/full/286/3/H1076 (6140 words)

	Astron. Astrophys. 336, 697-720 (1998) (Site not responding. Last check: 2007-09-18)
		Another useful quantity, now commonly called Allan variance, was introduced by Allan (1966) in order to characterize the drift behavior.
		The Allan variance in particular is the filtered average of the power spectrum, the filter function being
		The definition of the variance of the double difference as given in the preceding appendix can be straightforwardly extended to higher dimension.
	aa.springer.de /papers/8336002/2300697/appa.htm (2498 words)

	Summary for `Wavelet Variance, Allan Variance, and Leakage' (Site not responding. Last check: 2007-09-18)
		The properties of a time series at different scales can then be summarized by the wavelet variance, which decomposes the variance of a time series on a scale by scale basis.
		The wavelet variance corresponding to some of the recently discovered wavelets can provide a more accurate conversion between the time and frequency domains than can be accomplished using the Allan variance.
		This increase in accuracy is due to the fat that these wavelet variances give better protection against leakage than does the Allan variance.
	faculty.washington.edu /dbp/ABSTRACTS/wvavleak.html (178 words)

	Crystals
		If you look at how the frequency varies as a function of how far from the carrier you test the parameter is called phase noise.
		If you look at how the time varies as a function of the time interval the variation is called Allan Variance or modified Allan Variance.
		A low cost unit oscillator may have a frequency variation of a few Hz when measured using a 1 second integration time counter whereas a high quality oscillator will have a one second frequency stable to a small fraction of a cycle.
	www.pacificsites.com /~brooke/Xtal.shtml (1205 words)

	DC&LF Club (Site not responding. Last check: 2007-09-18)
		The resolution can be adjusted by varying the number of integrators, the number of bits of the DAC and the oversampling ratio.
		Analysis of Noise in DC Resistance Measurements Using the Allan Variance".
		Noise Simulation and evaluation were also discussed, and the evaluation of a CCC system using Allan variance.
	www.npl.co.uk /electromagnetic/clubs/dclfclub/meeting1 (691 words)

	IDC 99: On-Line Estimation of Allan Variance Parameters (Site not responding. Last check: 2007-09-18)
		A new on-line method is presented for estimation of the angular random walk and rate random walk coefficients of IMU (Inertial Measurement Unit) gyros and accelerometers.
		The on-line method proposes a state space model and proposes parameter estimators for quantities previously measured from off-line data techniques such as the Allan variance graph.
		Allan variance graphs have large off-line computational effort and data storage requirements.
	www.eleceng.adelaide.edu.au /ieee/idc99/abstracts/ford1.html (110 words)

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