Re: [Discuss-gnuradio] some results about D8PSK (problems)

[Stefan Brüns]

On Monday 23 March 2009 16:35:45 you wrote:
> We've got the patch in the queue for testing.  It looks correct,
> though I wonder how the block even worked at all given this issue.
>
> Tom--could you comment?

Although I am not Tom ...

Obviously, if there is no carrier offset, freq (IMHO misnamed, should be 
something like phase_increment ...) is 0, and adding 0 twice is no problem. 
As long as freq is smaller than pi/M, it gives some additional noise, but it 
should still work. The costas loop sets freq so that the average value is 
correct.

Example:
3 Samples per symbol
carrier offset of 0.2 (radians)
freq should be 0.2/3
As freq is added 4 times instead of instead of 3 times (once per sample), freq 
is set to 0.05
this gives an phase error of -0.016 for the first sample, 0 for the second and 
+0.016 for the 3rd.

Stefan

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