Re: [Discuss-gnuradio] continuous data collection?

[Clark Pope]

----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.

Thanks,
Matt

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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