Editing Signal modulation (section)

===List of common digital modulation techniques===
The most common digital modulation techniques are:
* [[Phase-shift keying]] (PSK)
** Binary PSK (BPSK), using M=2 symbols
** Quadrature PSK (QPSK), using M=4 symbols
** 8PSK, using M=8 symbols
** 16PSK, using M=16 symbols
** Differential PSK (DPSK)
** Differential QPSK (DQPSK)
** Offset QPSK ([[OQPSK]])
** π/4–QPSK
* [[Frequency-shift keying]] (FSK)
** [[Audio frequency-shift keying]] (AFSK)
** [[Multi-frequency shift keying]] (M-ary FSK or MFSK)
** [[Dual-tone multi-frequency signaling]] (DTMF)
* [[Amplitude-shift keying]] (ASK)
* [[On-off keying]] (OOK), the most common ASK form
** M-ary [[vestigial sideband modulation]], for example [[8VSB]]
* [[Quadrature amplitude modulation]] (QAM), a combination of PSK and ASK
** [[Polar modulation]] like QAM a combination of PSK and ASK{{Citation needed|date=October 2008}}
* [[Continuous phase modulation]] (CPM) methods
** [[Minimum-shift keying]] (MSK)
** [[Gaussian minimum-shift keying]] (GMSK)
** [[Continuous-phase frequency-shift keying]] (CPFSK)
* [[Orthogonal frequency-division multiplexing]] (OFDM) modulation
** [[Discrete multitone]] (DMT), including adaptive modulation and bit-loading
* [[Wavelet modulation]]
* [[Trellis coded modulation]] (TCM), also known as [[Trellis modulation]]
* [[Spread spectrum]] techniques
** [[Direct-sequence spread spectrum]] (DSSS)
** [[Chirp spread spectrum]] (CSS) according to IEEE 802.15.4a CSS uses pseudo-stochastic coding
** [[Frequency-hopping spread spectrum]] (FHSS) applies a special scheme for channel release

[[Minimum-shift keying|MSK]] and [[GMSK]] are particular cases of continuous phase modulation. Indeed, MSK is a particular case of the sub-family of CPM known as [[continuous-phase frequency-shift keying]] (CPFSK) which is defined by a rectangular frequency pulse (i.e. a linearly increasing phase pulse) of one-symbol-time duration (total response signaling).

[[OFDM]] is based on the idea of [[frequency-division multiplexing]] (FDM), but the multiplexed streams are all parts of a single original stream. The bit stream is split into several parallel data streams, each transferred over its own sub-carrier using some conventional digital modulation scheme. The modulated sub-carriers are summed to form an OFDM signal. This dividing and recombining help with handling channel impairments. OFDM is considered as a modulation technique rather than a multiplex technique since it transfers one bit stream over one communication channel using one sequence of so-called OFDM symbols. OFDM can be extended to multi-user [[channel access method]] in the [[orthogonal frequency-division multiple access]] (OFDMA) and [[multi-carrier code-division multiple access]] (MC-CDMA) schemes, allowing several users to share the same physical medium by giving different sub-carriers or [[spreading code]]s to different users.

Of the two kinds of [[RF power amplifier]], [[switching amplifier]]s ([[Class D amplifier]]s) cost less and use less battery power than [[linear amplifier]]s of the same output power. However, they only work with relatively constant-amplitude-modulation signals such as angle modulation (FSK or PSK) and [[CDMA]], but not with QAM and OFDM. Nevertheless, even though switching amplifiers are completely unsuitable for normal QAM constellations, often the QAM modulation principle are used to drive switching amplifiers with these FM and other waveforms, and sometimes QAM demodulators are used to receive the signals put out by these switching amplifiers.