Identification of line code from amplitude, phase and PSD plots
What you need is to plot the I and Q values out to decide what kind of encoding scheme the transmitter used.  

This can be done by using plot(I,Q) or scatter(I,Q) for whatever data you have. You should get a plot kind of like the ones below, but with noise added.


Source: https://www.researchgate.net/publication/228380492_conceptual_background_to_radio/figures?lo=1