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' (DMT)
Pulse modulation techniques include:
- Pulse code modulation (PCM)
- Pulse width modulation (PWM)
- Pulse amplitude modulation (PAM)
- Pulse position modulation (PPM)
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, such as
- Frequency division multiple access (FDMA)
- Time division multiple access (TDMA)
- Code division multiple access (CDMA)
- Frequency hopping spread spectrum (FHSS)
- Space division multiple access (SDMA)
- Carrier sensing multiple access with collision detection (CSMA/CD)
Where these methods are used for dividing forward and reverse communication channels, they are known as duplexing methods, such as: