[USRP-users] USRP under run when when trying to send messages in a low rate

Damindra Bandara damindra.bandara at gmail.com
Tue Mar 22 11:22:10 EDT 2016

Hi Marcus,

Thank you for getting back to me. Here is the description of my application.

I want to get the user messages and transmit it via USRP. Since the
messages are infrequent I am use a beacon message to keep the message
stream  alive. I use QPSK as the modulation scheme. A beacon message is
transmitted in every second. At the receiving end I extract the application
level message and output it. I am using Etuss USRP N200 to test the setup.

The problem is that I do not receive the message at the other end. When I
observe the constellations at the receiver  it shows that the QPSK
demodulator does not remain synchronized. Also I observed  'UUUUUU'  at the
transmitter end.(which is due to an under run at the USRP).

 If I transmit a file using this setup it works fine. But when I transmit
messages it is not transmitting.

The transmitter end: application-->packet encoder --> QPSK modulator -->
USRP sink

Receiver end: USRP source --> Synchronization blocks --> QPSK demodulator
--> Packet decoder --> application

Let me know if you need further information. I really appreciate if you
could help me to solve this issue.

Thank you

On Tue, Mar 22, 2016 at 4:05 AM, Marcus Müller <usrp-users at lists.ettus.com>

> Hi Damindra,
> it's a bit too much guesswork involved if you don't share *what* kind of
> application in GNU Radio you're designing. And a few parameters would be
> helpful too: something like sampling rate of the USRP, which USRP type
> you're using.
> Generally, an underrun means your computer wasn't fast enough at providing
> samples to your USRP.
> Best regards,
> Marcus
> On 22.03.2016 04:06, Damindra Bandara via USRP-users wrote:
> Hi,
> I am creating an application using GNURadio that transmits a message every
> second. When I try to do this the transmit USRP indicates that is is under
> run and I was not able to recover the message at the receiving end.
> When I use the same setup to transmit a file it works fine and able to
> recover it.
> Is there any procedure that should be followed when transmitting
> infrequent messages? I appreciate if I could get any help.
> Thank you
> Damindra
> --
> Damindra Savithri Bandara,
> PhD in Information Technology (Candidate)
> George Mason University,
> Fairfax,
> Virginia
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Damindra Savithri Bandara,
PhD in Information Technology (Candidate)
George Mason University,
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