Distortion Reduction in Phase Modulation

When a phase-modulated carrier of the form sin (wt+?) is multiplied by cos (wt), the recovered phase modulation is sin (?), which is a distorted version of . For small ?, the error is small, but is appreciable as A approaches unity or more. When ? is complicated (several subcarriers for example), the intermodulation can seriously degrade the system. This paper discusses distortion reduction by means of predistortion and postdistortion.