A set of elements onto which another set of elements has been mapped according to a code.
Note: Examples of coded sets include the list of names of airports that is mapped onto a set of corresponding three-letter representations of airport names, the list of classes of emission that is mapped onto a set of corresponding standard symbols, and the… (Read More →)

1. In communications systems, the altering of the characteristics of a signal to make the signal more suitable for an intended application, such as optimizing the signal for transmission, improving transmission quality and fidelity, modifying the signal spectrum, increasing the information content, providing error detection and/or correction, and providing data security.
Note: A single coding scheme usually does not provide… (Read More →)

Synonym code.

In military communications systems, a message in which the entire address is encrypted with the message text.

Abbreviation for centralized ordering group.

Pertaining to an electromagnetic wave, the area of a surface perpendicular to the direction of propagation, over which the electromagnetic wave maintains a specified degree of coherence.
Note: The specified degree of coherence is usually taken to be
0. 88 or greater.

See degree of coherence.

The propagation distance from a coherent source to a point where an electromagnetic wave maintains a specified degree of coherence.
Note 1: In long-distance transmission systems, the coherence length may be reduced by propagation factors such as dispersion, scattering, and diffraction.
Note 2: In optical communications, the coherence length, L, is given approximately by L = 2/(n), where is the… (Read More →)

For an electromagnetic wave, the time over which a propagating wave may be considered coherent.
Note 1: In long-distance transmission systems, the coherence time may be reduced by propagation factors such as dispersion, scattering, and diffraction.
Note 2: In optical communications, coherence time, , is calculated by dividing the coherence length by the phase velocity of light in a medium;… (Read More →)

Pertaining to a fixed phase relationship between corresponding points on an electromagnetic wave.
Note: A truly coherent wave would be perfectly coherent at all points in space. In practice, however, the region of high coherence may extend over only a finite distance.