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

Martin Braun martin.braun at ettus.com
Wed Mar 23 13:46:28 EDT 2016


Damindra,

this looks like bursty transmission, are you sending end-of-burst packets?


M

On 03/22/2016 08:22 AM, Damindra Bandara via USRP-users wrote:
> 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
> Damindra
> 
> On Tue, Mar 22, 2016 at 4:05 AM, Marcus Müller
> <usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>> wrote:
> 
>     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
>>
>>
>>     _______________________________________________
>>     USRP-users mailing list
>>     USRP-users at lists.ettus.com <mailto:USRP-users at lists.ettus.com>
>>     http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
> 
> 
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> 
> 
> 
> 
> -- 
> Damindra Savithri Bandara,
> PhD in Information Technology (Candidate)
> George Mason University,
> Fairfax,
> Virginia
> 
> 
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