In digital quadrature amplitude modulation QAM any number of points arranged in grid-form can be reached in the signal space using a mapper.
(a) Describe its fundamental structure
(b) How many signal states (points in the signal space) are needed for a 4 bit signal at the input?
(c) How can this be realized in terms of circuits in mapper?
(d) How many discrete amplitude levels are required by the real and imaginary part of a signal?