Quadrature amplitude modulation

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Quadrature amplitude modulation (QAM) is the name of a family of signal modulation methods widely used in modern telecommunications to transmit information. At its core, it conveys two independent analog signals by changing (modulating) the amplitudes of two differently phased versions of a single carrier wave using amplitude modulation. These paired analog signal channels may then be used either directly or to encode digital bit streams using joint amplitude-shift keying across the synchronized channels. 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...

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