The unit interval (UI), also known as pulse time or symbol duration, is the shortest time between changes in a
data
Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...
transmission signal
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 ...
. In a data stream, each pulse (or symbol) takes one UI, representing the time to send a single piece of information.
When used to measure a time interval, the UI gives a relative value without units, showing the interval as a multiple of the UI. Often, but not always, the UI equals the time to send one bit (a single binary digit), known as the bit time. For example, in
NRZ transmission, the UI matches the bit time, but in
2B1Q transmission, one pulse covers the time of two bits. In a system with a
baud rate of 2.5 Gbit/s, the UI is 1/(2.5 Gbit/s) = 0.4 nanoseconds per symbol.
Jitter measurement
Jitter
In electronics and telecommunications, jitter is the deviation from true periodicity of a presumably periodic signal, often in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a signifi ...
, the deviation from true periodicity in signal timing, is often expressed as a fraction of the UI. For instance, jitter of 0.01 UI means the signal's timing shifts by 1% of the UI duration.
Using UI for jitter measurements allows consistent comparisons across systems with different symbol rates, as jitter often depends on the symbol duration. This works when jitter is closely linked to the timing of each symbol. This approach is common in serial communications and on-chip clock systems.
This measurement unit is extensively used in jitter literature. Examples can be found in various ITU-T Recommendations, or in the tutorial from Ransom Stephens.
[Tektronix Jitter 360° Knowledge Series rom http://www.tek.com/learning/]
See also
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Baud
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Symbol rate
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Frequency
Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...
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Telecommunications
Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...
References
Data transmission
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