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Time Deviation
Time deviation (TDEV), also known as \sigma_x(\tau), measures the time stability of a clock source's phase over an observation interval, expressed as a standard deviation of the time variations. This indicates the time instability of the signal source. This is a scaled variant of frequency stability of Allan deviation. It is commonly defined from the modified Allan deviation, but other estimators may be used. Time variance (TVAR), symbolised as \sigma_x^2(\tau), is the time stability of phase versus observation interval tau. It is a scaled variant of modified Allan variance. TDEV is a metric often used to determine an aspect of the quality of timing signals in telecommunication applications and is a statistical analysis of the phase stability of a signal over a given period. Measurements of a reference timing signal will refer to its TDEV and maximum time interval error (MTIE) values, comparing them to specified masks or goals. Definition The most common estimator uses the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Allan Deviation
The Allan variance (AVAR), also known as two-sample variance, is a measure of frequency stability in clocks, oscillators and amplifiers. It is named after David W. Allan and expressed mathematically as \sigma_y^2(\tau). The Allan deviation (ADEV), also known as sigma-tau, is the square root of the Allan variance, \sigma_y(\tau). The ''M-sample variance'' is a measure of frequency stability using ''M'' samples, time ''T'' between measurements and observation time \tau. ''M''-sample variance is expressed as :\sigma_y^2(M, T, \tau). The Allan variance is intended to estimate stability due to noise processes and not that of systematic errors or imperfections such as frequency drift or temperature effects. The Allan variance and Allan deviation describe frequency stability. See also the section Interpretation of value below. There are also different adaptations or alterations of Allan variance, notably the modified Allan variance MAVAR or MVAR, the total variance, and the Had ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modified Allan Deviation
The modified Allan variance (MVAR), also known as mod ''σy''2(''τ''), is a variable bandwidth modified variant of Allan variance, a measurement of frequency stability in clocks, oscillators and amplifiers. Its main advantage relative to Allan variance is its ability to separate white noise, white phase noise from flicker noise, flicker phase noise. The modified Allan deviation (MDEV), also known as mod ''σy''(''τ''), is the deviation variant of the modified Allan variance. Background The Allan variance has a drawback in that it is unable to separate the white phase modulation (WPM) from the flicker phase modulation (FPM). Looking at their response to Allan variance#Power-law noise, Power-law noise it is clearly seen that WPM and FPM have almost the same response to tau, but WPM is linearly sensitive to the system bandwidth ''fH'' whereas FPM is only weakly dependent on it. Thus, by varying the system bandwidth the WPM and FPM noise forms may be separ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synchronization In Telecommunications
Many services running on modern digital telecommunications networks require accurate synchronization for correct operation. For example, if telephone exchanges are not synchronized, then bit slips will occur and degrade performance. Telecommunication networks rely on the use of highly accurate primary reference clocks which are distributed network-wide using synchronization links and synchronization supply units. Ideally, clocks in a telecommunications network are synchronous, controlled to run at identical rates, or at the same mean rate with a fixed relative phase displacement, within a specified limited range. However, they may be mesochronous in practice. In common usage, mesochronous networks are often described as ''synchronous''. History Synchronization in communications was a hard problem for Alexander Bain in the development of the teleprinter. Thomas Edison achieved synchronization in his stock ticker with a clunky but effective ''unison mechanism'' to resynchron ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Maximum Time Interval Error
Maximum time interval error (MTIE) is the maximum error committed by a clock under test in measuring a time interval for a given period of time. It is used to specify clock stability requirements in telecommunications standards. MTIE measurements can be used to detect clock instability that can cause data loss on a communications channel. Measurement A given dataset (clock waveform) is first compared to some reference. Phase error (usually measured in nanoseconds) is calculated for an observation interval. This phase shift is known as time interval error (TIE). MTIE is a function of the observation interval. An observation interval window moved across the dataset. Each time the peak-to-peak distance between the largest and smallest TIE in that window is noted. This distance varies as the window moves, being maximal for some window position. This maximal distance is known as MTIE for the given observation interval. Plotting MTIE vs. different observation interval duration gives a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Signal Processing Metrics
A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing'' includes audio, video, speech, image, sonar, and radar as examples of signals. A signal may also be defined as observable change in a quantity over space or time (a time series), even if it does not carry information. In nature, signals can be actions done by an organism to alert other organisms, ranging from the release of plant chemicals to warn nearby plants of a predator, to sounds or motions made by animals to alert other animals of food. Signaling occurs in all organisms even at cellular levels, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
