Fig. 13

Goodness of fit. The true PDF (left), bivariate Gaussian fit (middle), and circularly symmetric Gaussian fit (right). A constellation point from the third ring (bottom) and fourth ring (top) of a 64-APSK constellation under nonlinear amplification with an input power of -3 dB relative to amplifier saturation. Corresponding values of Akaike information criterion (AIC) are displayed for each model (scaled by 10⁻⁷), where lower values represent a preferred model