Modulation

Modulation describes a range of techniques for encoding information on a carrier signal, typically a sine-wave signal.

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'

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 (FSK) see Phase modulation

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

Modulation is frequently used in conjunction with various channel access methods, such as

• [Frequency division multiple access]? (FDMA)
• [Time division multiple access]? (TDMA)
• [Code division multiple access]? (CDMA)
• [Space division multiple access]? (SDMA)

Where these methods are used for dividing forward and reverse communication channels, they are known as duplexing methods, such as:

• [Time division duplex]? (TDD)
• [Frequency division duplex]? (FDD)

See also:

• [Channel coding]?
• Telecommunication