# How to calculate BER in different modulations with OFDM using GNURadio Companion

**URL:** <https://www.ruby-forum.com/t/how-to-calculate-ber-in-different-modulations-with-ofdm-using-gnuradio-companion/243270>\
**Category:** GNU Radio\
**Created:** [September 6, 2015, 12:57pm UTC](https://www.ruby-forum.com/t/how-to-calculate-ber-in-different-modulations-with-ofdm-using-gnuradio-companion/243270 "2015-09-06T12:57:01Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Rafa\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/958977/32.png) [@Rafa\_F](https://www.ruby-forum.com/u/Rafa_F)\
**Post date:** [September 6, 2015, 12:57pm UTC](https://www.ruby-forum.com/t/how-to-calculate-ber-in-different-modulations-with-ofdm-using-gnuradio-companion/243270/1 "2015-09-06T12:57:01Z")

</div>

Hello Jawad,

Today I send the same message that I sent a few days ago because I  
realized  
I did not include GRC code files. Those files are necessary to detect  
errors.

I’ve made the changes you said. As you say, when I assign the Payload  
parameter to the number of samples of the block Random Source without  
introducing Delay, I get a BER value equal to 0. But what I need to  
introduce a noise source so that when I increase the power noise, also  
increase the BER. This doesn’t happen making the changes that you say,  
when  
I introduce a noise source and the noise power is increasing the value  
of  
BER remains 0. This is incorrect. As you can see in the spectrum  
received,  
the signal contains errors that they aren’t appreciated by the block  
Error  
Rate. (SistemasOFDM\_prueba.grc)  
Also, I need to send an image and calculate the BER in the same way as  
with  
the random vector. When I use the block File Source and calculate the  
BER,  
I have the same problem, the BER remains constant at 0.51 and although  
the  
noise power increases, the BER remains unchanged.  
(SistemaOFDM\_Pruebas1.grc)  
The image that I send in the previos example is called “imagen”  
Thank you.

Regards,  
Antonio

Date: Tue, 1 Sep 2015 15:04:26 +0200  
From: Jawad S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
To: gnuradio mailing list [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
Cc: ANTONIO TAMAYO [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
Subject: Re: [Discuss-gnuradio] How to calculate BER in different  
modulations with OFDM using GNURadio Companion  
Message-ID:  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
Content-Type: text/plain; charset=“utf-8”

Hello Antonio,

Please take the habit of replying to the list. People might get into the  
same problems or someone might have some knowledge to share.

Also, try to provide a flowgraph (.grc file) to make testing easier for  
the  
people helping you out.

That said, I did some testing and it looks like I was wrong. The delay  
isn’t the problem here (at least not on my machine).  
But I think I figured out the problem. It looks like you provided a  
Payload  
length of 0 in your OFDM modulator block.  
If I set the payload length to 100 and then the random source Num.  
samples  
to the same value, the BER goes to 0 without adding delay. And you can  
see  
the BER moving when you change the delay.

There is one problem though, it doesn’t seem to work when the payload  
length and the Num. samples are not set to the same value.

Regards,  
Jawad

2015-09-01 13:50 GMT+02:00 ANTONIO TAMAYO [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> Hello Jawad,
> 
> I have tried to use the delay block but I keep having the same problem. I  
> have attached an image of how I used the block. I also attached an image  
> of  
> the value of BER obtained, whenever I make changes to the delay block I  
> get  
> the value of 0.1251. So the problem is not resolved. Also, I tried change  
> the paremeter simbol per bit in the Error Rate block, but the problem  
> persists. What is the optimal value for this parameter? Regarding the use  
> of the throttle block I tried to run this diagram without him and the  
> value  
> BER is the same.  
> Thank you for answering my emails, your answers are very useful.  
> I’ve included our previous emails in the end of this email. Thank you.
> 
> Regards,  
> Antonio
> 
> * * *

* * *

> > Hello,
> > 
> > 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 it is. In view of  
> > the  
> > Subject: Re: [Discuss-gnuradio] How to calculate BER in different  
> > some time to do their processing and forward their outputs to the next  
> > block in line. Therefore, there is a delay between the output of the OFDM  
> > demod block and the original signal.  
> > What you need to do is add a delay block between your Random source and  
> > the