Re: [Discuss-gnuradio] Help using simple_framer and simple_correlator

[address@hidden]

On Thu, 17 Nov 2005 15:41:15 -0800, Eric Blossom address@hidden



>>On Thu, Nov 17, 2005 at 04:16:55PM -0500, address@hidden
wrote:
>> I am also in the process of studying this part of the software to see if
I
>> can use it to recreate my data from the demodulated signal.

> Let me start by saying that you'd be *much* better off studying the
> packet framing / deframing and clock recovery code that is used in the
> new gmsk2.py and gmsk2_pkt.py files in
gnuradio-core/src/python/gnuradio/blksimpl
> and the corresponding examples in gnuradio-examples/python/gmsk2

> The new code is much cleaner and faster, and since it tracks symbol
> timing, works for long packets.

> As Bob pointed out, the so called GMSK receiver will receive pretty
> much any kind of FSK data.

It is brand spanking new code, I had to get a new cvs.

I did a very quick look and it is very different than the frame/correlate
code.

Will this work for very low data rate?  I saw in on of the files,
digital_voice.py.real, that the frame adds 10 bytes of overhead.  In my
application I am need to keep it to 1 byte.  Is this possible with this
code? 

> With the new code you specify the nominal samples/baud (spb), which
> needn't be an integer, and it recovers the clock, resamples the
> incoming data so that we're sampling in the middle of a bit, and then
> passes the properly timed data off to the packet sink.  The packet
> sink correlates for the sync pattern in a similar fashion to
> gr_simple_correlator, but is simpler, since it's not dealing with
> oversampled data.  The clock recovery code take a parameter that
> specifies the maximum relative frequency error that it will track out.
> The default value is 200 parts per million (ppm), which should be
> plenty loose for anything with a xtal oscillator in it.

> Trust me, you really want to be studying the new code...

I do trust you and this code sound real good.  Any reference material that
this was based on?

>Eric

Thanks a bunch,
Mike
PS: Back to some heavy studying of this new code.


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