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Re: [Discuss-gnuradio] Problem with USRP!

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] Problem with USRP!
Date: Sun, 08 Apr 2012 17:29:59 -0400
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20111108 Fedora/3.1.16-1.fc14 Thunderbird/3.1.16

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,

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.


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

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

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