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Re: [Discuss-gnuradio] dbpsk on gnuradio-3.5 and Ubuntu 11.10

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] dbpsk on gnuradio-3.5 and Ubuntu 11.10
Date: Sat, 31 Mar 2012 10:34:56 -0400

On Thu, Mar 29, 2012 at 10:04 AM, Jon Watson <address@hidden> wrote:
> All,
> I have been playing with two simple flow-graphs in gnuradio-companion, one
> for dbpsk transmitter and other for dbpsk receiver. The transmitter
> flow-graph is:
> vector source -- > packet encoder -- > dpsk modulator -- > uhd: usrp sink
> The receiver flow-graph is:
> uhd: usrp source --> low-pass filter --> dpsk demodulator --> packet decoder
> --> file sink
> The vector source is given a vector {10,20,30} as input, repeat is set to
> "yes"; in the packet encoder, samples/symbols is set to 8,  bits/symbols is
> set to 1 (because dbpsk scheme is to be used), pad for usrp is set to "yes"
> and payload is set to "0"; in the dpsk modulator, samples/symbols is set to
> 8 and all other parameters are left unchanged.
> At the receiver, I use matching/appropriate parameters inside the dpsk
> demodulator and low-pass filter blocks. And the sampling rate is set to be
> 1M Sps on both transmitter and receiver.
> Now, the issue is that I do not receive any decoded symbols in the file
> sink. Previously, when I was running the two flow-graphs on two computers
> with Ubuntu 11.04 and gnuradio-3.4 on them, everything was just fine, but as
> soon as I have upgraded the OS and gnuradio to 11.10 and 3.5 versions, I do
> not get anything in the file sink.
> Could someone provide a suggestion in this regard?
> Thanks.
> Jon


I'm not sure why this would change between 3.4 and 3.5, but my guess
is that it's something to do with the frequency offset, which tends to
be the biggest problem with these things. I've attached a GRC example
that runs what you want in a loopback simulation (you need gr-qtgui
installed for this). It looks good here, but I haven't tried going
over the air. This was just to make sure the data and everything were
passing through the algorithm blocks correctly.

Try figuring out what the frequency difference is between your two
USRPs (to about 100 Hz or so) and correct either the transmitter or
receiver to more closely match them up.

Also, when you were using 3.4, were you using UHD or libusrp(2)?


Attachment: test_packet_encoder.grc
Description: Binary data

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