Modulation

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

Modulation describes a range of techniques for encoding information on a carrier signal, typically a sine-wave signal. A device that performs modulation is known as a modulator.

Modulation techniques include:

Amplitude modulation (AM)
Phase modulation (PM, includes BPSK, QPSK, etc.)
Frequency modulation (FM)
Single-sideband modulation (SSB)
Vestigial-sideband modulation (VSB, or VSB-AM)
Quadrature amplitude modulation (QAM)
Orthogonal frequency division modulation (OFDM), also known as 'Discrete multitone modulation' (DMT)
Wavelet modulation
Trellis modulation
Adaptive modulation
Sigma-delta modulation (∑Δ)

When OFDM is used in conjunction with channel coding techniques, it is described as 'Coded orthogonal frequency division modulation' (COFDM).

Pulse modulation techniques include:

Where the signal is a simple low speed on-off indication, as in morse code or radioteletype (RTTY) transmission, modulation is often known as 'keying' as in the terms

Frequency-shift keying (FSK) see Frequency modulation
Phase-shift keying (PSK) see Phase modulation
Gaussian Minimum Shift Keying (GMSK)

RTTY can also be regarded as a simple kind of pulse code modulation.

Where Morse code is used to turn the carrier wave on and off, the term used is not 'amplitude keying', but 'continuous wave' (CW) operation.

Modulation is frequently used in conjunction with various channel access methods.

External links

"Data Encoding Techniques" and "Specifications for Data Encoding" discuss the various encoding techniques that have been used with various types of Ethernet.

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