Re: [Discuss-gnuradio] A little DQPSK demodulation progress and a question

[Eric Blossom]

On Mon, Mar 31, 2003 at 08:30:11AM +0100, Ian Wraith wrote:
> 
>  At the moment though all the class does is take in the I & Q data then
> filter them with a root raised cosine filter. For debugging purposes it
> also writes the raw and filtered I/Q values to a CSV file for later
> analysis. You can see a little of this data in graphical form by looking
> here ..
> 
> http://borg.shef.ac.uk/~ianw/dqpsk.html
> 
>  My next stage is to recover the symbol timing which isn't as easy as I
> first thought. My original idea was to sum the I squared and Q squared
> through a band pass filter at the symbol rate and the resulting waveform
> peaks would be the symbol timing. However if you look at this document ..
>
> http://www-s.ti.com/sc/psheets/spra341/spra341.pdf

What's your sample rate and the nominal symbol rate?  
These two rates have a lot to do with what will actually work.

> then go to figure 30 on page 38 you will see the author uses a much more
> complex method of symobol timing recovery using a PLL. Can anyone tell me
> why my original idea for timing recovery wouldn't work ? or suggest
> another method of doing this ?

Eric