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[Discuss-gnuradio] Re: FSK now (really) working at 100kbit/sec

From: Eric Blossom
Subject: [Discuss-gnuradio] Re: FSK now (really) working at 100kbit/sec
Date: Fri, 15 Apr 2005 10:41:42 -0700
User-agent: Mutt/1.5.6i

On Fri, Apr 15, 2005 at 03:37:27PM +0000, Deqiang chen wrote:
> hello, Eric,
> I remembered there is an annoucement that FSK can work at 100kbps.
> So I dig it out and take a look at the source code for the FSK ( 
> fsk_rx.py) . I am a little surprised
> that there are no time recovery there.

> My understanding is that for fsk, if you use noncoherent
> demodulation, you would not need the phase information.  However,
> you still need to know the timing in order to correctly sampling the
> output of correlator or matched filter.  Could you give a hint of
> what is going on here ?

> david

The output rate of gr.quadrature_demod_cf is 8 times the symbol rate.
The selection of the center of the bit is done in gr.simple_correlator.
It watches for a pseudo random sync pattern at the beginning of
each packet and uses this to figure out which of the possible alignments
is best.  A similar technique is used in Bluetooth.


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