Hi Nemanja, I remember having some trouble with this, as well, but I can't quite remember the details.
However, since you're using a pretty long preamble, have you tried using that for sync? The problem with M&M is that the output of the phase demodulator is quite 'soft', so accurate syncing is difficult in any case. Using the preamble makes it much easier; if you start with an oversampling rate of 4 you don't even need to do any polyphase-stuff. MB On Mon, Feb 18, 2013 at 05:23:04PM +0100, Nemanja Savic wrote: > Hi guys, > > > I am trying for quite some time to tweak M&M synchronizationi block, but the > problem is I have a lot of single bit errors, and I suppose it shouldn't be > like that because signal I am providing is almost ideal. Here are some > important features of the communication itself: > > > - data is encoded using differential manchester code > > - modulation scheme is FSK with frequency deviation of arround 75KHz > > - symbol rate is 19200 KBaud > > > I suppose for this simple communication protocol, I should have much better > results. Frame starts with preamble, followed by 160 symbols, which is 10 > bytes > of data at the end. Preamble has following structure > 10011001100110011001100110011010. The percentage of sucesfully received > preamble is 1005, but then comes trouble. > > > Setup is following: usrp1 with sample rate od 507937 Sps (I set 512KSps but > device doesn't support this rate), then comes bandpass filter, followed by > quadrature demodulator and bit slicer. Bit slicer is connected to correlate > access code block which is connected to modified framer sink block. > > > Here I provide output of my bit slicer (which I am proud of :)), and hope > somebody of you guys can provide me advices based on your experience. > > > Many regardsInline image 1 > > > -- > Nemanja Savić > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio -- 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
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