I am looking at the frequency correction burst of a GSM signal.
According to spec the original data defines 148 bits of 0 that are
differentially encoded and GMSK modulated. After the data goes
through the differential encoder it ends up as [-1,1,1, (142 1s),
1,1,1]. I have taken this burst and plotted I vs Q (which is
attached). I was expecting to see the amplitude ramp up followed by a
negative pi/2 phase shift, followed by 147 positive pi/2 phase shifts,
and a ramp down. I never see the initial negative phase shift though.
Am I missing something in my sanity? Any thoughts or ideas?
Thank you for your time