Chapter 6 / 6.7 / 6.7.4

6.7.4 Amplitude Phase Shift Keying (APSK)

As illustrated in Figure 6.31, amplitude phase-shift keying (APSK) combines elements of both MPSK and QAM. Like QAM, APSK conveys information through variations in both amplitude and phase, but its constellation points are arranged in concentric rings rather than in a rectangular grid.

This structure provides many of the advantages of MPSK and QAM while maintaining wider spacing between symbols in both amplitude and phase. The increased symbol separation improves resistance to additive noise and reduces sensitivity to nonlinear distortion from high-efficiency power amplifiers.

Because of these properties, APSK can achieve improved performance relative to rectangular QAM constellations under nonlinear amplification, making it particularly well suited to satellite systems operating near saturation.