The modulation order of a digital communication scheme is determined by the number of the different symbols that can be transmitted using it.
Modulation order can only be defined for
digital modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the '' carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informa ...
s. The simplest forms of digital modulation are of second order because they can transmit only two symbols (usually denoted as "0" and "1" or as "-1" and "1"). They are called ''binary shift keying'' (BSK).
Modulations which have an order of 4 and above usually are termed as
higher-order modulation
Higher-order modulation is a type of digital modulation usually with an order of 4 or higher. Examples: quadrature phase-shift keying (QPSK), and m-ary quadrature amplitude modulation ( m-QAM).
See also
* phase-shift keying
Phase-shift keyin ...
s. Examples of these are ''quadrature phase shift keying'' (
QPSK
Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs ...
) and its generalisation as
m-ary ''quadrature amplitude modulation'' (m-
QAM
Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. It conveys two analog message signa ...
).
Because existing computers and automation systems are based on binary logic most of the modulations have an order which is a power of two: 2, 4, 8, 16, etc. In principle, however, the order of a modulation can be any integer greater than one.
When the order of a digital modulation approaches infinity its properties approach those of the respective analog modulation. Thus the analogue modulations can be viewed as extreme cases of higher-order digital modulations for which the order is equal to infinity.
Telecommunication theory
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