"QAM" redirects here. For the digital television standard, see QAM (television). For other uses, see QAM (disambiguation).
This article may be too technical for most readers to understand. Please help improve it to make it understandable to non-experts, without removing the technical details.(June 2020) (Learn how and when to remove this message)
Passband modulation
Analog modulation
AM
FM
PM
QAM
SM
SSB
Digital modulation
ASK
APSK
CPM
FSK
MFSK
MSK
OOK
PPM
PSK
QAM
SC-FDE
TCM
WDM
Hierarchical modulation
QAM
WDM
Spread spectrum
CSS
DSSS
FHSS
THSS
See also
Capacity-approaching codes
Demodulation
Line coding
Modem
AnM
PoM
PAM
PCM
PDM
PWM
ΔΣM
OFDM
FDM
Multiplexing
v
t
e
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. It conveys two analog message signals, or two digital bit streams, by changing (modulating) the amplitudes of two carrier waves, using the amplitude-shift keying (ASK) digital modulation scheme or amplitude modulation (AM) analog modulation scheme. The two carrier waves are of the same frequency and are out of phase with each other by 90°, a condition known as orthogonality or quadrature. The transmitted signal is created by adding the two carrier waves together. At the receiver, the two waves can be coherently separated (demodulated) because of their orthogonality. Another key property is that the modulations are low-frequency/low-bandwidth waveforms compared to the carrier frequency, which is known as the narrowband assumption.
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.
QAM is used extensively as a modulation scheme for digital telecommunication systems, such as in 802.11 Wi-Fi standards. Arbitrarily high spectral efficiencies can be achieved with QAM by setting a suitable constellation size, limited only by the noise level and linearity of the communications channel.[1] QAM is being used in optical fiber systems as bit rates increase; QAM16 and QAM64 can be optically emulated with a three-path interferometer.[2][3]
^"Digital Modulation Efficiencies". Barnard Microsystems. Archived from the original on 2011-04-30.
^"Ciena tests 200G via 16-QAM with Japan-U.S. Cable Network". lightwave. April 17, 2014. Retrieved 7 November 2016.
^Kylia products Archived July 13, 2011, at the Wayback Machine, dwdm mux demux, 90 degree optical hybrid, d(q) psk demodulatorssingle polarization
and 21 Related for: Quadrature amplitude modulation information
Quadratureamplitudemodulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used...
Amplitudemodulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude...
sideband modulation (VSB, or VSB-AM) Quadratureamplitudemodulation (QAM) Angle modulation, which is approximately constant envelope Frequency modulation (FM)...
real-valued filter Quadratureamplitudemodulation (QAM), a modulation method of using both an (in-phase) carrier wave and a 'quadrature' carrier wave that...
representation of a signal modulated by a digital modulation scheme such as quadratureamplitudemodulation or phase-shift keying. It displays the signal...
Carrierless amplitude phase modulation (CAP) is a variant of quadratureamplitudemodulation (QAM). Instead of modulating the amplitude of two carrier...
phase modulation[citation needed], but the results end up being equivalent mathematically as both are essentially a special case of quadratureamplitude modulation[citation...
of phase-shift keying and amplitude-shift keying which is called (in the jargon of the field) "quadratureamplitudemodulation" (QAM) that are used in high-capacity...
RF systems are not uncommon: see mechanical filter and RF MEMS. Amplitudemodulation (AM) Bandwidth (signal processing) Electromagnetic interference Electromagnetic...
principally by American broadcast engineer Leonard R. Kahn; and quadratureamplitudemodulation (QAM) multiplexing systems (conceptually closer to FM stereo)...
the propagation path. Amplitude distortion is distortion occurring in a system, subsystem, or device when the output amplitude is not a linear function...
each other, then phase modulation (PM) of the carrier occurs. AM and PM together then create quadratureamplitudemodulation (QAM). ISB may or may not...
on the video standard, the chrominance subcarrier may be either quadrature-amplitude-modulated (NTSC and PAL) or frequency-modulated (SECAM). In the PAL...
typical optical modulations that are used include Dual Polarization Quadrature Phase Shift Keying (DP-QPSK) and QuadratureAmplitudeModulation QAM-16. These...
transmits 2400 bit/s using 1200 Bd (1200 symbol/s), where each quadratureamplitudemodulation symbol carries two bits of information. The modem can generate...
Under quadratureamplitudemodulation the modulated chrominance signal changes phase as compared to its subcarrier and also changes amplitude. The chrominance...
common types of modulation that may be used with differential coding include phase-shift keying and quadratureamplitudemodulation. When data is transmitted...
relation to the modulating signal amplitude. Digital data can be encoded and transmitted with a type of frequency modulation known as frequency-shift keying...
m-ary quadratureamplitudemodulation (m-QAM). Because existing computers and automation systems are based on binary logic most of the modulations have...
reflected signals. Additional improvements were introduced by quadratureamplitudemodulation (QAM) encoding, which increased the number of bits per symbol...
and downlink throughput is improved by using 16 or 32 QAM (quadratureamplitudemodulation), along with turbo codes and higher symbol rates. The Global...