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

[Eric Blossom]

On Fri, Nov 18, 2005 at 11:21:56AM -0500, address@hidden wrote:
> 
> On Thu, 17 Nov 2005 15:41:15 -0800, Eric Blossom address@hidden
> 
> > 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? 

Perhaps.  The code is split into two basic pieces: the actual GMSK
mod/demod and the build-a-packet/recognize-a-packet code.  The
mod/demod should be usable as-is.

Without knowing more about your application, it's hard to comment.  Is
your data sent continuously, or is it broken up into possibly variable
length packets? How to you propose to "find the start of the data" at
the receiver?

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

The clock synchronization algorithm and MMSE FIR interpolator are
described in "Digital Communication Receivers: Synchronization,
Channel Estimation and Signal Processing", by Meyr, Moeneclaey and
Fechtel, ISBN 0-471-50275-8.  It's a very thorough book, but can be
pretty heavy going at times.  The Meuller & Müller (M&M) Synchronizer
is described on page 86.  See chaper 9 for info on the interpolator
and control structure.  The interpolater taps were designed by
optimizing equation (9-7).  The code that does that lives in
gnuradio-core/src/gen_interpolator_taps.

Eric