Re: [Discuss-gnuradio] Help with GNU Radio Companion

[Marcus Müller]

Hi Antonio,

During the last two months I've been trying to contact to the helpdesk GNU Radio (address@hidden) to solve the problems in the design of a communications system using gnuradio companion. As no one answer my messages I think it may be because you think that they are spam. Please, could you help me to solve the problems that I have? The message I wrote last week is as follows:
 

that is not the "helpdesk"; everyone on the list tries to be as helpful as we can, but it's a mailing list for people of a common interest, GNU Radio in that case, not something that can guarantee a certain reaction. I love to help, though, so here's me, in the middle of the night, answering you.

Your mail from ten days ago definitely reached the mailing list.
I don't currently have time to discuss it in detail, but considering it hasn't gotten a reply in more than a week, I think it's fair to say you should send another one, but this time improving your questions a little bit:
* the GNU Radio companion has a function to save an image of your flowgraph, instead of sending a screenshot of your screen. Use that.
* Your flowgraph is not not tidy, and contains a lot of stuff that you don't seem to use. Tidy it up. Remember: the easier you make it for other people to understand your problem, the more likely you'll get good responses.
* Don't repeat previous emails without adding information. Seriously, you've sent me the same email personally that you sent to the mailing ten days ago; aside from me having a constant urge to help people, why should the situation have changed since then? Note that I really don't want to scare you away, but increase your chance of getting a good solution.
* You're not using the default values in the OFDM mod and demod blocks, if I'm not mistaken. Why are you using exactly those?
* You say "the BER is the same"; well, what is "the same"? If I go back and look into one of your screenshots, it's very close to 0.5, right? That's crucial information, and including that in your mail text would make a lot of sense.
* You're not really trying to investigate the situation; for example, a BER of 0.5 has a special meaning, which you should know if you're doing your final project on BER curves.
* You ask for "correct settings". Well, obviously, "correct" depends on what you're trying to do; it's not like there's one universially correct way to do digital communications (otherwise, the research on that would be pretty dead!).
* You have a 32kS/s throttle block in there, but your BER rate block has a window of 20 million samples -- which means that the BER sink accumulates over more than 10 minutes worth of samples; you should explain why you chose that.
* There should be the ofdm_loopback.grc example, installed with the other GNU Radio examples. It achieves a 0 BER after the first few samples. Have you compared that to your flow graph?

I think if you answer all of the above questions, you can make a pretty good mailing list post. Right now, you're asking "I don't know what goes wrong!"; maybe if you start asking yourself "how does one diagnose this?", you can come up with a way to understand what's going wrong. Maybe start with a data source that is simpler than an image -- what about sending a sawtooth signal? It would be much easier to see in a graphical sink when you display the received signal.

Mostly, don't use the old OFDM mod/demod blocks, but the new OFDM transmitter/receiver blocks.

Best regards,
Marcus

On 19.11.2015 23:19, ANTONIO TAMAYO wrote:

Hello Marcus,

During the last two months I've been trying to contact to the helpdesk GNU Radio (address@hidden) to solve the problems in the design of a communications system using gnuradio companion. As no one answer my messages I think it may be because you think that they are spam. Please, could you help me to solve the problems that I have? The message I wrote last week is as follows:
 
[Hi all,

Two months ago I shared with you the following message:

"I'm doing my College final project about gnuradio companion. Specifically I have to calculate the BER with OFDM using different modulations to the subcarriers. After that, I have to do a graphic with the BER numbers. The configuration I use is in the image attached.

When I'm using GRC to calculate BER I always have the same problem. First I try to simulate without introducing any noise and get a BER data. Then I try to introduce AWGN noise and the BER data is the same. Clearly I'm making a mistake, but I'm not able to identify what is it. In view of the configuration used, someone could tell me which are my mistakes?

Also, I would like to know how to configure the block Channel Model correctly."

In that moment I was using an old version of GNURadio Companion, 3.2.2, now I'm using 3.7.1.2 version and I still have the same problem. Please, could someone tell me which are my mistakes? I would like to be informed of how to set the parameters of the blocks I used.

Also I share with you the gnuradio Companion configuration file I've used in which the block diagram is displayed, the image I've used to calculate the BER and the results I get when I run the diagram.

Thank you all,

Antonio.]

Your help will be very useful for me. Thank you.

Regards,

Antonio