Quadrature Amplitude Modulation

May 5th, 2015
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Quadrature amplitude modulation (QAM) ([pic] /ˈkwɑːm/ or /ˈkæm/ or simply "Q-A-M") is both an analog and a digital modulation scheme. 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.

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Quadrature Amplitude ModulationQuadrature amplitude modulation(QAM) ([pic]/kwm/or/km/or simply "Q-A-M") is both an analog and a digitalmodulationscheme. It conveys two analog message signals, or two digitalbit streams, by changing (modulating) theamplitudesof twocarrier waves, using theamplitude-shift keying(ASK) digital modulation scheme oramplitude modulation(AM) analog modulation scheme. The two carrier waves, usuallysinusoids, areout of phasewith each other by 90and are thus calledquadraturecarriers or quadrature components hence the name of the scheme. The modulated waves are summed, and the resulting waveform is a combination of bothphase-shift keying(PSK) andamplitude-shift keying(ASK), or (in the analog case) of phase modulation (PM) and amplitude modulation. In the digital QAM case, a finite number of at least two phases and at least two amplitudes are used. PSK modulators are often designed using the QAM principle, but are not considered as QAM since the amplitude of the modulated carrier signal is constant. QAM is used extensively as a modulation scheme for digitaltelecommunicationsystems.Spectral efficienciesof 6 bits/s/Hz can be achieved with QAM.[1]QAM modulation is being used in optical fiber systems as bit rates increase QAM16 and QAM64 can be optically emulated with a 3-pathinterferometer.[2]|Contents ||[hide] ||1Digital QAM ||2Analog QAM ||2.1Fourier

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