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Phase modulation (analog PM) and phase-shift keying (digital PSK) can be regarded as a special case of QAM, where the amplitude of the transmitted signal is a constant, but its phase varies. This can also be extended to frequency modulation (FM) and frequency-shift keying (FSK), for these can be regarded as a special case of phase modulation ...
An M-ary transmission is a type of digital modulation where instead of transmitting one bit at a time, two or more bits are transmitted simultaneously. This type of transmission results in reduced channel bandwidth. However, sometimes, two or more quadrature carriers are used for modulation. This process is known as quadrature modulation.
Examples of these are quadrature phase shift keying and its generalisation as m-ary quadrature amplitude modulation (m-QAM). Because existing computers and automation systems are based on binary logic most of the modulations have an order which is a power of two: 2, 4, 8, 16, etc.
Multi-frequency shift keying (M-ary FSK or MFSK) Dual-tone multi-frequency (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 ...
Quadrature amplitude modulation (QAM) can be considered a subset of APSK because all QAM schemes modulate both the amplitude and phase of the carrier. Conventionally, QAM constellations are rectangular and APSK constellations are circular, however this is not always the case.
Higher-order modulation is a type of digital modulation usually with an order of 4 or higher. Examples: quadrature phase-shift keying (QPSK), and m-ary quadrature amplitude modulation ( m-QAM ). See also
Such a representation on perpendicular axes lends itself to straightforward implementation. The amplitude of each point along the in-phase axis is used to modulate a cosine (or sine) wave and the amplitude along the quadrature axis to modulate a sine (or cosine) wave. By convention, in-phase modulates cosine and quadrature modulates sine.
QAM is a digital television standard using quadrature amplitude modulation. It is the format by which digital cable channels are encoded and transmitted via cable television providers. QAM is used in a variety of communications systems such as Dial-up modems and WiFi.