# How exactly do I plot a constellation Diagram?

I am relatively new to signal processing and I would like to correctly draw a constellation diagram to check the results of a study. I need my signal processing to be as close as them to make sure I am doing it correctly.

I am trying to use constellation diagrams to fingerprint ADS-B signals which use a PPM (pulse position modulation) scheme. Considering I got some IQ data, it is sufficient to do a scatter plot of the IQ data to call it a constellation diagram ? Or do I need to collect only samples from IQ data that are in special positions(like the position of the pulses)? I am also asking this question because I do not get exactly the plot that the study shows for constellation diagram. I would be very thankful if someone can point why there is a difference or something I missed/misunderstood.

Here is the link of the study You can find the plots on page 4, FIGURE 8. (What they call contour stellar image is just a constellation diagram but with colors based on density of points nearby from what I understood (FIGURE 7)).

And Using the following python code:

from scipy.stats import gaussian_kde
import matplotlib.pyplot as plt

fig = plt.figure()

z = gaussian_kde(xy)(xy) #This is just to get colors to see better

ax.set_xlabel("in_phase")



I get the following images (2 exemple):

• Can you elaborate on “IQ” data? Is it baseband data? Dec 29 '20 at 20:34