Fig. 2
From: Improved demapping for channels with data-dependent noise
Visualization of data-dependent noise. Scatter diagram of the received symbols (I/Q components) illustrating a nonlinear effects from imprecise amplifier compensation for 64-APSK modulation and b phase noise from receiver oscillator instabilities for 64-QAM constellation. The estimated covariance for each constellation point is depicted in c and d as ellipsoids at the 99% confidence level. Ideal symbol locations are marked with a circle and estimated symbol centroids with a cross