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Re: [Discuss-gnuradio] continuous data collection?

From: Clark Pope
Subject: Re: [Discuss-gnuradio] continuous data collection?
Date: Mon, 27 Feb 2006 10:37:46 -0500

----Original Message Follows----
From: Matt Ettus <address@hidden>
To: Clark Pope <address@hidden>
CC: address@hidden
Subject: Re: [Discuss-gnuradio] continuous data collection?
Date: Sun, 26 Feb 2006 18:31:49 -0800

Clark Pope wrote:
> I've been collecting snapshots through my DBS and USRP to do DBPSK and
> DQPSK bit error rate testing. I'm not able to get the BER below about
> 1e-5. It seems that slips are occuring spontaneously in the data even
> though no over/underflow is reported during the collection.
> Questions:
> 1. Has anyone successfully done long term collections without any slips?
> 2. Are the O/U flags sticky?, i.e. if I don't see an under or overflow
> reported then I can be sure the fifos were okay?
> I've done BERs from 1 Mbaud to 11 Mbaud all with the same frequency of
> slips so it does not appear to be speed related.

Do the errors occur at uniform intervals?

This may actually be internal to GNU Radio.  Can you try demodulating a
signal which is generated in GNU Radio?  You should have no hardware in
the chain at all.  This will help tell us where the problem is.


It's sort of regular. I was starting to think that it may be the wrap point of the PN15 code I am using because 1/32767 ~= 3e-5 which is about the BER I'm getting. However, I just switched to a PN9 code and I still get the same BER. If it were the wrap point, by the way, I would expect to see a bit error at the wrap not a whole slip in the PN sequence.

I thought I was gaining ground and then I tried an 11-chip barker code spread signal. Turns out I get the same BER on the despread signal as a raw DBPSK signal. This is very strange since the spread signal is 11 times as long as the non-spread signal. So if there were regular glitches in the file I would expect the bers to occur 11 times more frequently in the despread data. To the contrary the BERs are exactly the same!?

I am starting to suspect my bit error measurement code in matlab, since that is the only common element between the two cases...

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