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

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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:

• Pulse-code modulation (PCM)
• Pulse-width modulation (PWM)
• Pulse-amplitude modulation (PAM)
• Pulse-position modulation (PPM)
• Pulse-density modulation (PDM)

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.

See also:

• Types of radio emissions
• Communications channel
• Channel coding
• Telecommunication
• Modem
• RF modulator
• Codec

External links

• "Data Encoding Techniques" http://www.rhyshaden.com/encoding.htm and "Specifications for Data Encoding" http://www.wildpackets.com/compendium/FE/FE-Encod.html discuss the various encoding techniques that have been used with various types of Ethernet.