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[Discuss-gnuradio] extending gr-trellis for general coherent CPM demodul
From: |
Achilleas Anastasopoulos |
Subject: |
[Discuss-gnuradio] extending gr-trellis for general coherent CPM demodulation |
Date: |
Wed, 25 Feb 2009 19:57:31 -0500 |
User-agent: |
Thunderbird 2.0.0.19 (Windows/20081209) |
Hi all,
I just committed an update to gr-trellis that can handle coherent
demodulation of an arbitrary CPM signal (CPFSK, RC-CPFSK, GMSK, etc)
It consists of an additional fsm constructor that provides the FSM
description and a couple of helper utilities (in fsm_utilities.py)
that can help construct the appropriate matched filters etc.
The remaining functions can be used verbatim (ie, all the viterbi/siso
blocks in gr-trellis)
I have also added a test_cpm.py file with an example case.
The theory behind the decomposition is all detailed in a
classic paper by Bixio Rimoldi "A decomposition approach to CPM"
IEEE Trans. Information Theory, March 1988.
A summary of this can be found in
http://www.eecs.umich.edu/~anastas/docs/cpm.pdf
I didn't have the time to make an xml file out of my latex file, so for
the time being this summary is not committed to the trunk.
***********************************
Careful: this is a "coherent" demodulator, so it will not
work with real data from the USRP. It does neither
symbol timing tracking nor phase tracking.
The focus was to demonstrate the generality of the decomposition.
If you want to make a practical CPM demod based on this approach, you
need to either
(i) do timing/phase estimation OUTSIDE the Viterbi decoding (either
using a non-data aided scheme or a coded-data aided scheme) and use the
rest of the demodulator as provided, or (better)
(ii) modify the viterbi block in gr-trellis to add timing/phase
estimation based on tentative decisions (with some delay "d") from the
decoder.
If anyone wants to take up this task I can help. I'll probably won't
have time to do it myself before the summer...
***********************************
Achilleas
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