Shizheng Li wrote:
Thank you for your reply!
I think the generic receiver for CPM you mentioned is the optimal
receiver for CPM and the projection onto basis functions (correlation
with basis functions) is equivalent to the matched filters, am I right?
yes; however see the comment i made about the colored noise and the
detection vs detection/estimation in my earlier post
Go back to the GMSK transceiver I mentioned in the file
http://gnuradio.org/trac/browser/gnuradio/branches/releases/3.2/gnuradio-core/src/python/gnuradio/blks2impl/gmsk.py
The modulator structure is NRZ mapping --> Gaussian filter --> FM modulator
And the demodulator structure is FM demodulator --> Timing recovery -->
detector
I think after the FM demodulator the signal can be viewed as a PAM
modulated signal and what if I add a matched filter before the timing
recovery? Can I improve the BER performance? I think the matched filter
can maximize the output SNR. Will it make the detector work better?
you are already suboptimal when you do FM demodulation...
Best regards,
Shizheng Li
On Thu, Jul 30, 2009 at 2:07 PM, Achilleas Anastasopoulos
<anas...@umich.edu <mailto:anas...@umich.edu>> wrote:
There is no reason why you should not use a matched filter.
However make sure you understand that a symbol-spaced MF
generates sufficient statistics only for detection,
ie, not for (epoch) synchronization.
Also note that in the case of GMSK (CPM in general) a bank of MFs
will generate colored noise.
Another appropriate implementation of a front end projects the
entire oversampled signal to a set of orthonormal basis functions
which has the advantage of generating white noise samples for
(simpler) further processing.
Take a look at how a generic receiver for an arbitrary CPM
is developed in
http://gnuradio.org/svn/gnuradio/trunk/gr-trellis/src/examples/test_cpm.py
There, the signal is first projected to its basis functions (which
is calculated by a helper python application in "fsm_utils.py")
to generate a sufficient statistic which is then used in conjunction
with trellis decoding to do soft-decision sequence detection.
What is missing though is epoch and phase syncronization (to do at
some point...)
Achilleas
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Best Regards,
Shizheng Li
Ph.D. Student and Research Assistant
Department of Electrical and Computer Engineering
Iowa State University
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