Forum: GNU Radio "Error rate" block with USRP

A74013616c499f1549018208364ef324?d=identicon&s=25 Azza (Guest)
on 2014-04-16 16:32
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Hi All,

I am working with GNU Radio Companion 3.6 on CentOS. I want to calculate
the
BER, so I have been using the "Error rate" block.
First, I send a random QPSK-modulated signal through a simulated noisy
channel (AWGN). I calculate the BER using the function error:
BER=0.5*erfc(sqrt(snr)) and compare it to the output of the "Error rate"
block. I find almost same results.
Second, I send a random QPSK-modulated signal through one USRP and
receive
it with another USRP. Here is the problem: contrary to expections, the
output of "Error rate" block is always 0.5, and it does not vary with
the
variation of SNR.
You find attached the flowgraph of this second scenario.
<http://gnuradio.4.n7.nabble.com/file/n47625/gnu-ber.png>
I am wondering if this block should not be used with USRPs to calculate
the
BER. If not, any suggestions?
Any help is appreciated. Thank you.

Regards,
Azza



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C539637020fd56193dd6daec746c4a84?d=identicon&s=25 Tom Rondeau (Guest)
on 2014-04-16 16:45
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On Wed, Apr 16, 2014 at 10:31 AM, Azza <azza.ben.mosbah@gmail.com>
wrote:

> it with another USRP. Here is the problem: contrary to expections, the
>
Azza,

First, you should take out the throttle. With the USRPs in the loop,
you're
going to have conflicts with the rates that will cause problems.

Second, at the very least, you need to synchronize everything through
the
hardware. The constellation decoder doesn't do any timing, phase, or
frequency synchronization. You'll also need an AGC block to scale the
received samples before anything else.

Tom
A74013616c499f1549018208364ef324?d=identicon&s=25 Azza (Guest)
on 2014-04-16 16:58
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Thank you.
I have taken out the throttle block and add an AGC block at the
receiver.
To proceed with the synchronization, should I use a Constellation
Receiver
block or a Polyphase Clock Sync block ?

Kind regards,
Azza



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C539637020fd56193dd6daec746c4a84?d=identicon&s=25 Tom Rondeau (Guest)
on 2014-04-16 17:06
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On Wed, Apr 16, 2014 at 10:57 AM, Azza <azza.ben.mosbah@gmail.com>
wrote:

> Thank you.
> I have taken out the throttle block and add an AGC block at the receiver.
> To proceed with the synchronization, should I use a Constellation Receiver
> block or a Polyphase Clock Sync block ?
>
> Kind regards,
> Azza
>


You'll actually need both. AGC -> clock sync -> constellation receiver
(phase/freq recovery and decoding).

Also, please reply in-line with the rest of the message. By cutting off
the
other part of our conversation makes it difficult for others to follow
the
thread.

Tom
A74013616c499f1549018208364ef324?d=identicon&s=25 Azza (Guest)
on 2014-04-16 20:08
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Tom Rondeau-2 wrote
> On Wed, Apr 16, 2014 at 10:57 AM, Azza &lt;

> azza.ben.mosbah@

>>
> Tom
>
> _______________________________________________
> Discuss-gnuradio mailing list

> Discuss-gnuradio@

> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

Thank you.
I have added modifications to my flowgraph:
<http://gnuradio.4.n7.nabble.com/file/n47630/gnu-be...
But, I am still confused about minimum/maximum frequency deviation in
the
Constellation Receiver block. How should it be set?

Regards,
Azza



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C539637020fd56193dd6daec746c4a84?d=identicon&s=25 Tom Rondeau (Guest)
on 2014-04-16 20:56
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On Wed, Apr 16, 2014 at 2:06 PM, Azza <azza.ben.mosbah@gmail.com> wrote:

> >> To proceed with the synchronization, should I use a Constellation
> >
> <http://gnuradio.4.n7.nabble.com/file/n47630/gnu-be...
> But, I am still confused about minimum/maximum frequency deviation in the
> Constellation Receiver block. How should it be set?
>
> Regards,
> Azza
>

 Those are settings to keep the frequency sync from walking away, in
normalized frequency. +1 and -1 should work fine.

Tom
A74013616c499f1549018208364ef324?d=identicon&s=25 Azza (Guest)
on 2014-04-16 21:39
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Tom Rondeau-2 wrote
> On Wed, Apr 16, 2014 at 2:06 PM, Azza &lt;

> azza.ben.mosbah@

>> >> I have taken out the throttle block and add an AGC block at the
>> > You'll actually need both. AGC -> clock sync -> constellation receiver
>> Thank you.
> normalized frequency. +1 and -1 should work fine.
> Azza
> _______________________________________________
> Discuss-gnuradio mailing list

> Discuss-gnuradio@

> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio





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A74013616c499f1549018208364ef324?d=identicon&s=25 Azza (Guest)
on 2014-04-16 21:40
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Tom Rondeau-2 wrote
> On Wed, Apr 16, 2014 at 2:06 PM, Azza &lt;

> azza.ben.mosbah@

>> >> I have taken out the throttle block and add an AGC block at the
>> > You'll actually need both. AGC -> clock sync -> constellation receiver
>> Thank you.
> normalized frequency. +1 and -1 should work fine.
>
> Tom
>
> _______________________________________________
> Discuss-gnuradio mailing list

> Discuss-gnuradio@

> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio


Tom,

I still found BER=0.5, however the error output of the Constellation
Receiver block gives 0.

Regards,
Azza



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C539637020fd56193dd6daec746c4a84?d=identicon&s=25 Tom Rondeau (Guest)
on 2014-04-17 17:10
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On Wed, Apr 16, 2014 at 3:38 PM, Azza <azza.ben.mosbah@gmail.com> wrote:

> >> > azza.ben.mosbah@
> >> >> Kind regards,
> >> > other part of our conversation makes it difficult for others to follow
> the
> >
> I still found BER=0.5, however the error output of the Constellation
> Receiver block gives 0.
>
> Regards,
> Azza
>

Azza,

Maybe take a step back from trying to calculate the BER. Make sure you
have
a transmitting system and receiver system that are working correctly. At
the receiver, the first thing to do is make sure you're getting a proper
constellation. If so, you should be able to extract the bits to compare
them. And by this, I mean make two flowgraphs for the tx and rx sides so
you're not confusing yourself by trying to tie everything together.

Also, make sure you are either using differential modulation encoding to
correct for unknown phase offsets or that you are somehow correcting for
this possibility. Then, you need to make sure you're getting your frames
through. There will be a delay between what you transmit over the air
and
when you receive it. You'll have to account for this, too.

Tom
3297f492e9d0f62696428b52277d0b29?d=identicon&s=25 sivakumar r. (sivakumar_r)
on 2014-04-24 08:34
Dear TOM,
Is it needed to use AGC/Clock Sync/Constellation Receiver blocks for
every receiver section. For my flow graph I am using phase lock loop,
frequency locked loop blocks instead of those?. Then, may I use all
these blocks in the receiver section?
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