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Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information.
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.
The two amplitude-modulated components are known as the in-phase component (I, thin blue, decreasing) and the quadrature component (Q, thin red, increasing). A sinusoid with modulation can be decomposed into, or synthesized from, two amplitude-modulated sinusoids that are in quadrature phase , i.e., with a phase offset of one-quarter cycle (90 ...
Orbital angular momentum multiplexing is a relatively new and experimental technique for multiplexing multiple channels of signals carried using electromagnetic radiation over a single path. [7] It can potentially be used in addition to other physical multiplexing methods to greatly expand the transmission capacity of such systems.
Some coherent optical modules can fall back to older, simpler modulation techniques such as on-off keying (NRZ) and/or Pulse-amplitude modulation with 4 levels (PAM-4) when appropriate. This is used, for example, when it is discovered that the module on the other end of the link does not support coherent modulation.
Once correctly aligned/recovered, the quadrature signals also successfully demodulate the signal. Costas loop carrier recovery may be used for any M-ary PSK modulation scheme. [ 5 ] One of the Costas Loop's inherent shortcomings is a 360/M degree phase ambiguity present on the demodulated output.
Spatial modulation is a technique that enables modulation over space, across different antennas (radio) at a transmitter. [1] [2] Unlike multiple-input and multiple-output (MIMO) wireless (where all the transmitting antennas are active and transmitting digital modulated symbols such as phase-shift keying and quadrature amplitude modulation), in spatial modulation, only a single antenna among ...
Amplitude-shift keying (ASK) is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. [1] In an ASK system, a symbol, representing one or more bits, is sent by transmitting a fixed-amplitude carrier wave at a fixed frequency for a specific time duration.