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Quadrature Modulation is a technique for encoding 2-dimensional signals as the sum of in-phase and quadrature (90 degrees out of phase) signals.
This communication scheme involves the modulation of a carrier by two different signals. One signal modulates the carrier (I) and the other signal modulates the carrier shifted by 90° (Q). The two modulated carriers are then summed and transmitted as a single I&Q modulated carrier. The receiver decodes the I&Q channels and demodulates them 90° apart. QAM lends itself to the transmission of data in a digital format by assigning discrete levels to the two signal inputs which creates a "constellation" of possible digital word combinations on the I&Q graph. The following illustrates a 16-QAM constellation (4 levels of input on the I channel/4 levels of input on the Q channel).
Quadrature Phase Error represents the amount to which that ideal phase deviates from 90 degrees, and will degrade the ability of the channel to transmit information.
The mathematical operation of truncating a decimal value of arbitrary precision to a fixed binary resolution.
Noise generated in a DAC output due to errors created by the quantization process.