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Modulation

From Academic Kids

For the musical use of "modulation", see modulation (music).

Modulation is the process of varying a carrier signal, typically a sinusoidal signal, in order to use that signal to convey information. One of the three key characteristics of a signal are usually modulated: its phase, frequency or amplitude. A device that performs modulation is known as a modulator and a device that performs demodulation is known as a demodulator. A device that can do both operations is a modem, a contraction of the two.

In digital modulation, the changes in the signal are chosen from a fixed list (the modulation alphabet) each entry of which conveys a different possible piece of information (a symbol). The alphabet is often conveniently represnted on a constellation diagram.

In analogue modulation, the change is applied continuously in response to the data signal. The modulation may be applied to various aspects of the signal as the lists below indicate.

Contents

Analogue Modulation Techniques

Digital Modulation Techniques

Often incorrectly referred to as a modulation scheme, orthogonal frequency division multiplexing (OFDM) usually takes advantage of one of the digital techniques. It is also known as discrete multitone (DMT). When OFDM is used in conjunction with channel coding techniques, it is described as Coded orthogonal frequency division multiplexing (COFDM). OFDM is strictly a channel access method and not a modulation scheme.

Pulse modulation

These are hybrid digital and analogue techniques.

Miscellaneous Techniques

See also

External links

cs:Modulace

da:Modulation de:Modulation (Technik) es:Modulación id:Modulasi it:Modulazione nl:Modulatie ja:変調方式 pl:Modulacja pt:Modulação fi:Modulointi

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