# 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 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, is it 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 position s(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 the 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.)

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? Commented Dec 29, 2020 at 20:34
• Use plt.plot(np.real(samples), np.imag(samples), '.') Commented Feb 17, 2023 at 0:54