Re: [Discuss-gnuradio] Problem with USRP!

[John Malsbury]

A few more things:

1)  You have both the receive and transmit portions assigned to TX/RX.  
This only works if you run in half-duplex mode and stop streaming to the 
USRP.  This is not the case.
2)  Note the difference between sample rate, symbol rate, and bit rate.

    symbol_rate = sample_rate / samples_per_symbol
    bit_rate = sample_rate/bits_per_symbol

I think there are issues with packing/unpacking of bits.  The 
requirements for packing and unpacking aren't completely consistent 
across the mod/demods within GNU Radio.  Let me experiment real quick 
and get back to you.

-John


On 04/08/2012 02:34 PM, huzaifazafar108 wrote:
> Dear Marcus,
>
> I truly appreciate your prompt reply. However, I am not sure what should I
> put in the 'modulus' field of the block. By hit and trial, wrong outputs are
> emerging. Please guide.
>
> Best Regards,
> Huzaifa
>
>
>
> Marcus D. Leech wrote:
> > > We just removed the throttle blocks and the same problem remains. Please
> > > let
> > > us know how to achieve symbol synchronization.
> > Well, you're using DPSK, but not using a differential encoder on the TX
> > side, nor a differential decoder on the RX side.
> >
> > > huzaifazafar108 wrote:
> > > > Dear John,
> > > >
> > > > Thank you for such a prompt reply. Okay, we will remove the throttle
> > > > blocks just now. But can you guide us how to achieve symbol
> > > > synchronization then?
> > > >
> > > > Best Regards,
> > > > Huzaifa
> > > >
> > > >
> > > >
> > > > John Malsbury wrote:
> > > > > You do not need to use throttles when using a UHD sink/source, because
> > > > > the device provides timing for the flowgraph.
> > > > >
> > > > > Remove the throttles and try again.  If you still see the failure I'd
> > > > > say you are not achieving symbol sync.
> > > > >
> > > > > -John
> > > > >
> > > > >
> > > > >
> > > > > On 04/08/2012 01:58 PM, Huzaifa Zafar wrote:
> > > > > > Dear all,
> > > > > >
> > > > > > I am working with 3 people on a project involving GNU Radio and USRP1.
> > > > > > We have tried to implement a simple point to point digital
> > > > > > communication system in GRC involving DQPSK modulation. Using a vector
> > > > > > source we are sending a finite stream of zeros and ones (the vector
> > > > > > source has Repeat set to yes). On the receiver side, what we receive
> > > > > > is really very strange: The same stream of zeros and ones, but with
> > > > > > extra zeros in between our actual data. For example, we send three
> > > > > > ones and three zeros, but what we receive is a one followed by seven
> > > > > > zeros, another one followed by seven zeros, another one followed by
> > > > > > seven zeros, and then a zero followed by seven zeros e.t.c. We tried
> > > > > > to experiment more by using the 'KEEP 1 in N' block and the
> > > > > > 'DECIMATING FIR FILTER', but things are not working out the way they
> > > > > > should.
> > > > > >
> > > > > > I am also attaching a snapshot of the .grc file for your reference.
> > > > > > Please tell us the reason why these extra zeros are present between
> > > > > > our data bits, and the way to combat this effect (remember that the
> > > > > > decimating fir filter and keep 1 in N block are not showing the
> > > > > > desired output). Any kind of help is appreciated in advance.
> > > > > >
> > > > > > --
> > > > > > Huzaifa Zafar
> > > > > >
> > > > > >
> > > > > > _______________________________________________
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> >
> > --
> > Marcus Leech
> > Principal Investigator
> > Shirleys Bay Radio Astronomy Consortium
> > http://www.sbrac.org
> >
> >
> >
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