Modulation

In music, the term "modulation" means a key change. This article is about the concept of signal modulation in communications engineering.

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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)
• 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
• Ring modulation

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)

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

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:

• Communications channel
• Channel coding
• Telecommunication
• Modem
• RF modulator
• Codec