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Re: [Discuss-gnuradio] High packet loss problem (samples dropped?) and f

From: Hsin-mu Tsai
Subject: Re: [Discuss-gnuradio] High packet loss problem (samples dropped?) and fusb parameters
Date: Wed, 25 Jul 2007 16:34:32 -0400

Sorry I reread your original email, ... you're now using settings where
the there are no more (or very few) USRP overruns? Is that correct?

Yes. When using smaller fusb_nblock and fusb_block_size parameters, I
don't see any 'uO' when running the script.

In that case it's not the overruns, it's the detector. I suspect there
is too much noise or the gain is set wrong. What reason do you have to
believe that 20% packet loss is not expected? What's the SNR?

I was under the impression that when using a cable to connect TX and
RX boards, the SNR should be very high and the BER or PER should be
close to 0. Could it be that the SNR is too high and the signal is

I tried using antennas instead. The packet loss ratio is about the
same as as when I'm using a direct antenna cable. That's why I
believed the loss is not due to the physical channel. (can't be 100%
sure with this kind of logic though)

I don't know how to measure the SNR with existing GNU Radio blocks. Is
there any fast ways to do this?

Especially at large symbol rates (like 2MHz), there is no reason to
expect that the error performance would be 0% packet loss without
actually knowing the SNR.

That's usually due to insufficient channel coherence bandwidth. That
shouldn't be the case for the antenna cable.

Many thanks,

Hsin-Mu (Michael) Tsai
Ph.D. Student
Electrical and Computer Engineering Department
Carnegie Mellon University
E-Mail: address@hidden
Web: http://www.ece.cmu.edu/~hsinmut/
Office: +1-412-268-4639

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