I was wondering how a diagram like this is generated.
I am generating a QPSK signal using MATLAB by taking a cos and sin wave, multiplying each one by either 1 or -1 and adding them together to form a real valued QPSK signal. I then simulate an AWGN channel and send it to my demodulator. I mix it down using another cos and sin wave plus Low Pass Filter to get my recovered I and Q data. At this point I am left with the baseband which I can recover my data from by taking the angle of the I and Q components.
I am wondering at what point in that chain I could generate a the plot I post above.