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RE: [Discuss-gnuradio] M&M impl, its parameters, and why does itwork for


From: Long, Jeffrey P.
Subject: RE: [Discuss-gnuradio] M&M impl, its parameters, and why does itwork for GMSK?
Date: Fri, 11 Apr 2008 14:11:14 -0400

Thanks I will take a look.

Jeff 

-----Original Message-----
From: Bob McGwier [mailto:address@hidden 
Sent: Friday, April 11, 2008 2:09 PM
To: Long, Jeffrey P.
Cc: George Nychis; gnuradio mailing list
Subject: Re: [Discuss-gnuradio] M&M impl, its parameters, and why does
itwork for GMSK?

Long, Jeffrey P. wrote:
> While we are on the topic of clock recovery and someone more
> knowledgeable than me is reading :) I would like to pose a question
to
> Bob. How might one do clock recovery on a M-ary CPM signal? It sounds
> like a ML sequence technique might be an option but is there a
simpler
> ad-hoc technique that works as well? My "superiors" tell me to just
do
> clock recovery on a 2-ary modulated preamble and then hold it for the
> rest of the packet when it switches to your M-ary mode. I suppose
this
> would work but I think it might be a little too much work in GNU
right
> now until the meta data extra channel thing is ready, right? For
> simplicity I would prefer a technique that could run on streaming
data
> like the M&M.
>
> thanks
> Jeff
>
>   
Jeff:

The answer is between the two.

;-)

Use the 2-ary modulated symbols for timing acquisition and also for 
initial carrier recovery.  Then since you will be close switch to a 
tracking mode:  Mengali's joint timing and recovery algorithm for CPM 
signals

Search for "Joint Timing and Phase Recovery for CPM signals" by Umberto

Mengali, et. al.  The joint estimator helps significantly as you can
read.

Bob


-- 
AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are, by
definition, not smart enough to debug it." - Brian W. Kernighan 





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