QAM - définition. Qu'est-ce que QAM
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Qu'est-ce (qui) est QAM - définition

FAMILY OF DIGITAL MODULATON METHODS OF TELEVISION SIGNALS
QAM-modulated; Quadrature Amplitude Modulation; QAM; 256QAM; 256-QAM; 16-QAM; 16QAM; 64-QAM; 64QAM; 2-QAM; 2QAM; 4-QAM; 4QAM; 8-QAM; 8QAM; 32QAM; 32-QAM; 128-QAM; 128QAM; 512-QAM; 512QAM; 1024QAM; 1024-QAM; 2048QAM; 2048-QAM; 4096-QAM; 4096QAM; IQ Modulation; Qam
  • Bit-loading (bits per QAM constellation) on an ADSL line
  • Analog QAM: measured PAL color bar signal on a vector analyzer screen.
  • Digital 16-QAM with example constellation points
  • Constellation points for 4-QAM, 16-QAM, 32-QAM, and 64-QAM overlapped
  • The graphs of the sine (solid red) and [[cosine]] (dotted blue) functions are sinusoids of different phases.

QAM         
Quadrature Amplitude Modulation (Reference: HiperLAN/2, 802.11a)
QAM (television)         
TELEVISION ENCODING
QAM Tuner; ClearQAM; Clear QAM; QAM tuner
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.

Wikipédia

Quadrature amplitude modulation

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 property. 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.  QAM is being used in optical fiber systems as bit rates increase; QAM16 and QAM64 can be optically emulated with a 3-path interferometer.