technoguy

Do you know the real and imaginary axes are often called the in phase, or I-axis and the quadrature, or Q-axis. By choosing a set of complex numbers to represent the modulation symbols in this way, they may be physically transmitted by varying the amplitude of a cos wave and a sin wave since these are naturally 90° out-of-phase with one another and are a convenient representation of the two axes. The amplitude of the cos wave (or sin wave) is set to the absolute value of the imaginary part of the symbol to be transmitted and the amplitude of the sin wave (or cos wave) to the absolute value of the real part. The example shown here is for 8-PSK, which has also been given a Gray coded bit assignment.