Any suggestions on my problem guys?
On Tue, Apr 2, 2013 at 3:45 PM, Nemanja Savic <[email protected]> wrote: > Hi all again, > > I basically did what Martin suggested, after demodulation I lowered > sampling rate from 500k to 100k. Just to make brief reminding, I am working > on a > FSK receiver, working in 434MHz ISM band, symbol rate is 19.2kbps and used > modulation is FSK. > After making decimation, the number of samples per symbol within M&M sync > block changed, from previous 26 to 5. When I made this change M&M stoped > working properly, and packed demod is unable to detect preamble. I would > like to ask if somebody can explain me the way to tune this block, I don't > think > making 5 sliders and just changing values would be the solution, and there > must be some logical way to do that. > > Best > Nemanja > > > On Thu, Feb 21, 2013 at 4:19 PM, Nemanja Savic <[email protected]> wrote: > >> Hi, >> >> thaks again Martin, I will take a look at the block you suggested. >> >> What I meant before, is that I was expecting that M&M block will >> tune it's internall coefficients ,or whatever, based on preamble that >> comes, >> since that should be the purpose of the preamble (like in hardware >> receivers). >> >> The structure of my receiver is more or less copied one from >> gfsk_loopback. >> But in that block, output of demodulator is connected to the M&M. In my >> case >> I provide M&M with pure digital signal, which should make things better >> in the meaning of finding correct edges. >> >> A the moment, M&M has 100% successful preamble detection, but then it >> starts to stuff some bits which make >> message incorrect. >> >> Best >> Nemanja >> >> >> >> On Thu, Feb 21, 2013 at 2:36 PM, Martin Braun (CEL) <[email protected] >> > wrote: >> >>> On Thu, Feb 21, 2013 at 02:10:24PM +0100, Nemanja Savic wrote: >>> > Preamble is indeed long. On the figure I attached in my first post it >>> can be >>> > seen the input and output od >>> > synchronization M&M block. I am expecting this block to do >>> synchronization >>> > based on preamble. >>> >>> Your packet sync, but not your clock sync (how would the M&M even know >>> about your preamble?). >>> >>> > Not quite sure that I understand, but I am sampling signal with ca. >>> 500k, and >>> > symbol rate is 19.2k, so if you were thinking about oversampling after >>> bit >>> > slicer, yes i have oversampling of ca. 25. >>> >>> Yeah, that's probably over the top. Filter and decimate, that saves >>> clock cycles and possibly improves your SNR. >>> >>> > In my receiver, after a bit filtered demodulated signal from >>> quadrature FM >>> > demodulator, I have a block, designed by myself, that does bit >>> slicing. It is >>> > basically simulation of a circuit that is used in >>> > >>> > some receivers with min and max diode detector circuits. Since I am >>> quite sure >>> > this is not the usual way of doing this, how am I supposed to get >>> digital >>> > pulses from demodulated signal. >>> >>> I recommend parsing gr-digital/python/gmsk.py for an idea how this could >>> be done (though, granted, that doesn't work perfect either, but also >>> doesn't sync via preamble). >>> >>> MB >>> >>> -- >>> Karlsruhe Institute of Technology (KIT) >>> Communications Engineering Lab (CEL) >>> >>> Dipl.-Ing. Martin Braun >>> Research Associate >>> >>> Kaiserstraße 12 >>> Building 05.01 >>> 76131 Karlsruhe >>> >>> Phone: +49 721 608-43790 >>> Fax: +49 721 608-46071 >>> www.cel.kit.edu >>> >>> KIT -- University of the State of Baden-Württemberg and >>> National Laboratory of the Helmholtz Association >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> [email protected] >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> >> >> >> -- >> Nemanja Savić >> > > > > -- > Nemanja Savić > -- Nemanja Savić
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