Re: [Discuss-gnuradio] Setting up clock synchronization blocks

[Martin Braun (CEL)]

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
> 



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-- 
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

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KIT -- University of the State of Baden-Württemberg and
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