Modulation

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

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:

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.