Re: [Discuss-gnuradio] How to determine phase shifts

[Marcus Müller]

Also note that FM is an analog modulation, whereas PSK is a linear digital one. The difference between digital and analog is that digital means discrete symbols at discrete times – and thus, a digital signal always tends to have autocorrelation functions with peaks at the center frequency and multiples of the symbol rate away from that. Thus, you can often infer whether something is digital or analog from the autocorrelation function.

Best regards,
Marcus

On 23.11.2016 14:10, Roman wrote:

I would like to recognize and distinguish between FM and QPSK signal by analyzing its properties. 

I have a general idea about their main distinguishing feature: 

- FM has continuous phase; 

- PSK has phase disruptions (gaps). 

I can get phase for every sample since they are complex. 

But I am lost in the implementation because I have many ideas how to find the phase differences but not so much practice with gnuradio blocks. 

I tried to implement some kind of phase derivative function by measuring the phase difference between consecutive samples. But the problem is the following - I do no know exactly symbol rate. Can I do this by trying variable delay between samples or are there any other better alternatives in Gnuradio?

Thank you in advance for any suggestions! Of course, some channel noise exists and impairs phase measurements.

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