Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Martin Braun]

On 22.07.2015 16:49, Jose Perez wrote:
> Thanks again Marcus.
> 
> Now I am using the "Head" block... I don't know which number I have to put
> in "Num Items" to get out my file with no repeated information. 
> I can understand this number to a Sin/Cosine function or a random source
> that I can limit how many samples I want ... but for a file I don't know and
> how calculate this number.
> Can you help me with this?

Jose,

I suggest you start a new thread for other, specific questions. Also,
you seem to be struggling with some of the basics, may I suggest you
take a look at our guided tutorials:
http://gnuradio.org/redmine/projects/gnuradio/wiki/Guided_Tutorials

Cheers,
Martin


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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Marcus Müller]

Jose,

If you set your file source to "repeat" it will produce an infinite 
amount of samples, just like a sine would.
If you know you want to produce 10,000 packets (and see how many are 
received), you only need to 96*10,000 samples.
Hence, you'll use the head block after the file source and set it to 
960,000.


Best regards,
Marcus

On 23.07.2015 01:49, Jose Perez wrote:

Thanks again Marcus.

Now I am using the "Head" block... I don't know which number I have to put
in "Num Items" to get out my file with no repeated information.
I can understand this number to a Sin/Cosine function or a random source
that I can limit how many samples I want ... but for a file I don't know and
how calculate this number.
Can you help me with this?

My size's file: 120 bytes ; packet length: 96

Thanks so much

Cheers,
José

On 16.07.2015 18:52, Marcus Müller-3 wrote:


As I mentioned, use the "head" block.
BR,
Marcus



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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Marcus Müller]

Jose,

If you set your file source to "repeat" it will produce an infinite 
amount of samples, just like a sine would.
If you know you want to produce 10,000 packets (and see how many are 
received), you only need to 96*10,000 samples.
Hence, you'll use the head block after the file source and set it to 
960,000.


Best regards,
Marcus

On 23.07.2015 01:49, Jose Perez wrote:

Thanks again Marcus.

Now I am using the "Head" block... I don't know which number I have to put
in "Num Items" to get out my file with no repeated information.
I can understand this number to a Sin/Cosine function or a random source
that I can limit how many samples I want ... but for a file I don't know and
how calculate this number.
Can you help me with this?

My size's file: 120 bytes ; packet length: 96

Thanks so much

Cheers,
José

On 16.07.2015 18:52, Marcus Müller-3 wrote:


As I mentioned, use the "head" block.
BR,
Marcus



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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Jose Perez]

Thanks again Marcus.

Now I am using the "Head" block... I don't know which number I have to put
in "Num Items" to get out my file with no repeated information. 
I can understand this number to a Sin/Cosine function or a random source
that I can limit how many samples I want ... but for a file I don't know and
how calculate this number.
Can you help me with this?

My size's file: 120 bytes ; packet length: 96

Thanks so much

Cheers,
José

On 16.07.2015 18:52, Marcus Müller-3 wrote: 

>As I mentioned, use the "head" block.
>BR,
>Marcus 



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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Marcus Müller]

As I mentioned, use the "head" block.
BR,
Marcus

On 16.07.2015 14:33, Jose Perez wrote:

Marcus and Martin, you are helping me to much! Sorry for this guys.
I just have this forum to ask because my partners here don't know nothing
about GNU Radio.

So, I have the number of packets that I received but how I know how many
packets my original file have?
(I have: packet_len Value: 96 and my file have 176 bytes ... 96 means 96
bits? so I have (176*8)/96=14,67 packets, it is right?)

As Marcus said, if I divide received file's size to original file's size I
will have a number that how good it is.. but, for example, in a simulation I
just can obtain success with the FILE SOURCE block with Repeat = Yes and I
obtain a file as big as my simulation runs... if I put in "Repeat =No", I
could not obtain nothing... How can I obtain a single file as the original
size with the FILE SOURCE block in Repeat = No? (i.e., just transmit the
file one time).


Thanks a lot...
P.S.: Sorry guys to extend this topic. Should I open a new one?



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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Jose Perez]

Marcus and Martin, you are helping me to much! Sorry for this guys.
I just have this forum to ask because my partners here don't know nothing
about GNU Radio.

So, I have the number of packets that I received but how I know how many
packets my original file have?
(I have: packet_len Value: 96 and my file have 176 bytes ... 96 means 96
bits? so I have (176*8)/96=14,67 packets, it is right?)

As Marcus said, if I divide received file's size to original file's size I
will have a number that how good it is.. but, for example, in a simulation I
just can obtain success with the FILE SOURCE block with Repeat = Yes and I
obtain a file as big as my simulation runs... if I put in "Repeat =No", I
could not obtain nothing... How can I obtain a single file as the original
size with the FILE SOURCE block in Repeat = No? (i.e., just transmit the
file one time).


Thanks a lot...
P.S.: Sorry guys to extend this topic. Should I open a new one?



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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Martin Braun]

On 15.07.2015 07:23, Jose Perez wrote:
> Hi Marcus!
> 
> Yes, Percentage of successful packets would be great for me. But I don't
> have idea how blocks I need use in the flowgraph to obtain a number for
> this.

Run the ofdm_loopback example, and you'll see the receiver block outputs
a sequence number. You can use that to check, but don't forget that the
sequence numbers wrap around (check the OFDM packet header to see how
many bits the sequence number has).

That leaves the question how many packets you *sent*, but that depends
on your app (and you can probably easily control that in your setup).


M


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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Marcus Müller]

Well, that depends, but couldn't you simply save the successfully 
decoded packets to a file (assuming that no broken packages pass the 
checksums) and divide that file's size by the payload size of a packet?

You'd limit the amount of payload being sent using the good ol' head block.

Best regards,
Marcus

On 15.07.2015 16:23, Jose Perez wrote:

Hi Marcus!

Yes, Percentage of successful packets would be great for me. But I don't
have idea how blocks I need use in the flowgraph to obtain a number for
this.




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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Jose Perez]

Hi Marcus!

Yes, Percentage of successful packets would be great for me. But I don't
have idea how blocks I need use in the flowgraph to obtain a number for
this.




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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Marcus Müller]

Kind of what Martin hinted at:
Percentage of successful packets? Net throughput?

On 15.07.2015 02:10, Jose Perez wrote:

Ok, Martin.
But do you have any suggest to measure how good is the
transmission/reception?

Thaks.
Cheers,
José



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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Jose Perez]

Ok, Martin.
But do you have any suggest to measure how good is the
transmission/reception?

Thaks.
Cheers,
José



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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Martin Braun]

On 13.07.2015 17:49, Jose Perez wrote:
> Another question... to use the block "Error Rate" to calculate the
> BER of the system, I just need put the File Source block in the
> Reference in Error Rate block and the output of Repack Bits block on
> RX side?

That won't be as helpful as you might think, because the CRC check drops
packets with bit errors. So the output of the OFDM Rx will most likely
be a-OK in terms of bit errors, but you will miss packets.

A different metric might be more appropriate here.

Cheers,
Martin

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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Jose Perez]

Thanks for all, Martin and Marcus!

I changed the Random Source block to a File Source block and put a File Sink
block on the receiver side ... It is working well ;) (I am transmitting a
.txt file)


Another question... to use the block "Error Rate" to calculate the BER of
the system, I just need put the File Source block in the Reference in Error
Rate block and the output of Repack Bits block on RX side?

Thanks a lot!



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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Martin Braun]

On 30.06.2015 12:12, Jose Perez wrote:
> 
> So ... Is it possible to see the Constellation points like QPSK in this
> flowgraph?
> Sorry for so many questions!

On TX, you can plot the complex symbols before they go into the carrier
allocator. On the receive side, you can do the same after the carrier
serializer. This won't exactly plot 1 OFDM symbol at a time, if that is
what you want.

Also, in both cases, the output will be pretty boring. On TX, it's just
your constellation; on RX, it's already equalized, so it's also just the
constellation.

M


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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Marcus Müller]

Jose,

we're talking about this flow graph, right?
http://gnuradio.4.n7.nabble.com/file/n54534/ofdm_tx.png

In this flow graph, you're trying to find the individual symbols in time
domain; that's not possible, they only exist clearly distinguishable in
frequency. That is why there is an DFT (in this implementation, the FFT)
in OFDM!

Best regards,
Marcus

On 06/30/2015 09:12 PM, Jose Perez wrote:
> So ... Is it possible to see the Constellation points like QPSK in this
> flowgraph?
> Sorry for so many questions!
>
> Thanks Martin!
>
>
>
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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Jose Perez]

So ... Is it possible to see the Constellation points like QPSK in this
flowgraph?
Sorry for so many questions!

Thanks Martin!



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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Martin Braun]

On 30.06.2015 11:06, Jose Perez wrote:
> I am plotting the signal after the Multiply Const Block ... the signal that I
> will transmitt with USRP.
> Isn't correct? 
> 

If what you want to plot is your constellation, then no, it's not. This
is all modulated, pulse shaped and all.

Cheers,
M

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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Jose Perez]

I am plotting the signal after the Multiply Const Block ... the signal that I
will transmitt with USRP.
Isn't correct? 

 



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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Martin Braun]

On 30.06.2015 10:41, Jose Perez wrote:
> Hi Marcus,
> 
> Thanks so much for the answer. But like in the screenshots of Gabriele, the
> blocks OFDM Transmitter e OFDM Receiver are off. And I can't visualize four
> symbols (QPSK) or 2 symbols (BPSK) in the output of QT Constellation just a
> big one (see the screenshot), is this correct?

Are you plotting the output of the IFFT by any chance?

M


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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Jose Perez]

Hi Marcus,

Thanks so much for the answer. But like in the screenshots of Gabriele, the
blocks OFDM Transmitter e OFDM Receiver are off. And I can't visualize four
symbols (QPSK) or 2 symbols (BPSK) in the output of QT Constellation just a
big one (see the screenshot), is this correct?

Thanks again.


 



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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Marcus Müller]

Hi Jose,
> And I have another question (if Marcus can help) ... what is the modulation
> in this example (QPSK, QAM)?
You can set that yourself in the OFDM Transmitter Block, separately for
header and payload.

> Sorry for my bad english
Your English is really fine, don't worry. If we don't understand
something, we will just ask :)

Best regards,
Marcus

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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Jose Perez]

Hi,


Gabriele, do you have news about this? I am trying to do the same.


And I have another question (if Marcus can help) ... what is the modulation
in this example (QPSK, QAM)?


Sorry for my bad english

Thanks



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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Marcus Müller]

Hi Gabriele,
if there is no output, chances are the receiver side packet detector
doesn't see any valid packets.
Make sure tx and rx parameters match, and adjust the RX gain. Make sure
no under/overflows happen. There's quite a lot of things that can go
wrong in a real-world transceiver, but these are the most likely to
happen in my experience.

Greetings,
Marcus

On 06/26/2015 12:54 PM, Gabriele Galiero wrote:
> Thanks Marcus and Martin. I finally increased the sample rate up to 1
> Msps and decreased the amplitude multiplier. Now I can see a clear ofdm
> spectrum with no distortion at all.
>
> Did some of you tried file transmission from one end to the other? I did
> it for GMSK before. Now when it comes ofdm and I open the receiving file
> while transmitting there is no printed information in the received file.
>
> In that configuration I replaced the random source by a file source and
> a file sink after constellation decoder.
>
> Again thanks for your help. It was so useful
>


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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Gabriele Galiero]

Thanks Marcus and Martin. I finally increased the sample rate up to 1
Msps and decreased the amplitude multiplier. Now I can see a clear ofdm
spectrum with no distortion at all.

Did some of you tried file transmission from one end to the other? I did
it for GMSK before. Now when it comes ofdm and I open the receiving file
while transmitting there is no printed information in the received file.

In that configuration I replaced the random source by a file source and
a file sink after constellation decoder.

Again thanks for your help. It was so useful

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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Martin Braun]

On 25.06.2015 06:07, Marcus Müller wrote:
> Hi Gabriele,
> 
> have you tried adding more gain on the TX side?

...or less gain?

> Also, you will need to increase sampling rate. Right now, you're using
> 100kHz, which is 1/1000 of the master clock rate of the N200. If I'm not
> mistaken, the maximum decimation for the N200 is 512, and hence the
> minimum rate would be 100MHz/512 = 195.3125kHz. You probably just want
> to use 200kHz or something similarly practical.

Or even more, like 1-2 Msps.

I haven't tried a combo of N-Series specifically with this example, but
I've tried X-Series + B-Series, so I'm confident it's all OK. However,
OFDM is sensitive to distortions, so you need to play around with the
amplitude multiplier before tx'ing as well as the gain for your specific
setup to get a good transmit spectrum.

Since you have a spectrum analyzer, that's pretty useful for getting
those settings right.

You might also try playing with the rolloff length and/or adding more
empty carriers left and right of your tx spectrum while experimenting
with settings.

Cheers,
Martin

> 
> I hope that helps!
> 
> Best regards,
> Marcus
> 
> On 06/25/2015 02:23 PM, Gabriele Galiero wrote:
>> Hello, I was interested to test tx_ofdm.grc and rx_ofdm.grc from
>> gr-digital, at the same time using USRP N200 devices.
>>
>> TX OFDM:
>>
>> The changes that I did were, removing throttle block and adding an UHD
>> Sink instead, with center frequency 430 MHz, which is the frequency band
>> for which my department has license to transmit.
>>
>> RX OFDM:
>>
>> In this case I removed all blocks before throttle (included), and placed
>> there an UHD Source at the same center frequency.
>>
>> Flow graphs attached in the files.
>>
>> I monitored the output signal and the received signal. I also used a
>> spectrum analyzer to check the actual signal that is being transmitted.
>> Pics are attached.
>>
>> In the tx signal measured by a spectrum analyzer, we can see that the
>> spectrum is not that we desire. I would like to ask if I am doing
>> something wrong with the configuration. Before transmission there was no
>> signal at that frequency and tx and rx antennas are suitable for the
>> carrier frequency.
>>
>> In addition I tried to transmit a file instead of just random bits. In
>> reception I was not receiving the file. The config was just adding a
>> file sink at the end of the rx block and a file source at the beginning
>> of the tx block. Could you please help me with some tip?
>>
>> Attachments:
>> http://www.ruby-forum.com/attachment/10886/tx_ofdm.jpg
>> http://www.ruby-forum.com/attachment/10887/rx_ofdm.png
>> http://www.ruby-forum.com/attachment/10888/tx_signal.jpg
>> http://www.ruby-forum.com/attachment/10889/rx_signal.jpg
>> http://www.ruby-forum.com/attachment/10890/tx_sig_spectrum.jpg
>>
>>
> 
> 
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Re: [Discuss-gnuradio] OFDM example from gr-digital with UHD

[Marcus Müller]

Hi Gabriele,

have you tried adding more gain on the TX side?
Also, you will need to increase sampling rate. Right now, you're using
100kHz, which is 1/1000 of the master clock rate of the N200. If I'm not
mistaken, the maximum decimation for the N200 is 512, and hence the
minimum rate would be 100MHz/512 = 195.3125kHz. You probably just want
to use 200kHz or something similarly practical.

I hope that helps!

Best regards,
Marcus

On 06/25/2015 02:23 PM, Gabriele Galiero wrote:
> Hello, I was interested to test tx_ofdm.grc and rx_ofdm.grc from
> gr-digital, at the same time using USRP N200 devices.
>
> TX OFDM:
>
> The changes that I did were, removing throttle block and adding an UHD
> Sink instead, with center frequency 430 MHz, which is the frequency band
> for which my department has license to transmit.
>
> RX OFDM:
>
> In this case I removed all blocks before throttle (included), and placed
> there an UHD Source at the same center frequency.
>
> Flow graphs attached in the files.
>
> I monitored the output signal and the received signal. I also used a
> spectrum analyzer to check the actual signal that is being transmitted.
> Pics are attached.
>
> In the tx signal measured by a spectrum analyzer, we can see that the
> spectrum is not that we desire. I would like to ask if I am doing
> something wrong with the configuration. Before transmission there was no
> signal at that frequency and tx and rx antennas are suitable for the
> carrier frequency.
>
> In addition I tried to transmit a file instead of just random bits. In
> reception I was not receiving the file. The config was just adding a
> file sink at the end of the rx block and a file source at the beginning
> of the tx block. Could you please help me with some tip?
>
> Attachments:
> http://www.ruby-forum.com/attachment/10886/tx_ofdm.jpg
> http://www.ruby-forum.com/attachment/10887/rx_ofdm.png
> http://www.ruby-forum.com/attachment/10888/tx_signal.jpg
> http://www.ruby-forum.com/attachment/10889/rx_signal.jpg
> http://www.ruby-forum.com/attachment/10890/tx_sig_spectrum.jpg
>
>


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[Discuss-gnuradio] OFDM example from gr-digital with UHD

[Gabriele Galiero]

Hello, I was interested to test tx_ofdm.grc and rx_ofdm.grc from
gr-digital, at the same time using USRP N200 devices.

TX OFDM:

The changes that I did were, removing throttle block and adding an UHD
Sink instead, with center frequency 430 MHz, which is the frequency band
for which my department has license to transmit.

RX OFDM:

In this case I removed all blocks before throttle (included), and placed
there an UHD Source at the same center frequency.

Flow graphs attached in the files.

I monitored the output signal and the received signal. I also used a
spectrum analyzer to check the actual signal that is being transmitted.
Pics are attached.

In the tx signal measured by a spectrum analyzer, we can see that the
spectrum is not that we desire. I would like to ask if I am doing
something wrong with the configuration. Before transmission there was no
signal at that frequency and tx and rx antennas are suitable for the
carrier frequency.

In addition I tried to transmit a file instead of just random bits. In
reception I was not receiving the file. The config was just adding a
file sink at the end of the rx block and a file source at the beginning
of the tx block. Could you please help me with some tip?

Attachments:
http://www.ruby-forum.com/attachment/10886/tx_ofdm.jpg
http://www.ruby-forum.com/attachment/10887/rx_ofdm.png
http://www.ruby-forum.com/attachment/10888/tx_signal.jpg
http://www.ruby-forum.com/attachment/10889/rx_signal.jpg
http://www.ruby-forum.com/attachment/10890/tx_sig_spectrum.jpg


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