Why does increased Samples per Symbol result in underruns?

GNU Radio
#1

Hi,
I used benchmark_tx.py with dbpsk modulation with Samples per symbol=7
and
higher. I found that this resulted in lots of USRP underruns(uU). Why is
it
so?

Thanks,
Ali

#2

On Mon, Jul 20, 2009 at 05:29:02PM -0500, Mir M. Ali wrote:

Hi,
I used benchmark_tx.py with dbpsk modulation with Samples per symbol=7 and
higher. I found that this resulted in lots of USRP underruns(uU). Why is it
so?

You’re doing more work per symbol. The uU indicates that the host is
not sending data to the USRP fast enough.

Eric

#3

Does that mean that the data being sent is lost or is it just that USRP
is
waiting for it to arrive?

#4

On Mon, Jul 20, 2009 at 09:10:07PM -0500, Mir M. Ali wrote:

Does that mean that the data being sent is lost or is it just that USRP is
waiting for it to arrive?

uU means that there’s a discontinuity in the transmitted burst. The
USRP needed to transmit some data, but there was none to send. The
receiver will not be able to demodulate the malformed burst.