Back تضمين مطالي متعامد Arabic Modulació d'amplitud en quadratura Catalan Kvadraturní amplitudová modulace Czech Quadraturamplitudenmodulation German Modulación de amplitud en cuadratura Spanish Kvadratuur-amplituudmodulatsioon ET مدولاسیون کیوآام FA QAM Finnish Modulation d'amplitude en quadrature French Modulación de amplitude en cuadratura GL
 | This article may be too technical for most readers to understand. (June 2020) |
| Passband modulation |
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| Analog modulation |
| Digital modulation |
| Hierarchical modulation |
| Spread spectrum |
| See also |
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[citation needed].
QAM is used extensively as a modulation scheme for digital communications 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