# Problem in simulation on GRC at the measure of BER in digital modulations with Chunks to Symbol in r

**URL:** <https://www.ruby-forum.com/t/problem-in-simulation-on-grc-at-the-measure-of-ber-in-digital-modulations-with-chunks-to-symbol-in-r/241126>\
**Category:** GNU Radio\
**Created:** [May 14, 2014, 5:26am UTC](https://www.ruby-forum.com/t/problem-in-simulation-on-grc-at-the-measure-of-ber-in-digital-modulations-with-chunks-to-symbol-in-r/241126 "2014-05-14T05:26:17Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\
**Post date:** [May 14, 2014, 5:26am UTC](https://www.ruby-forum.com/t/problem-in-simulation-on-grc-at-the-measure-of-ber-in-digital-modulations-with-chunks-to-symbol-in-r/241126/1 "2014-05-14T05:26:17Z")

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Good Evening,

I am a student of eletronic engineer in Brazil and I am using GNURadio  
Companion as a research.  
I have attached some pictures of my model on GRC and the problems.  
In this case, I made a circuit with PSK modulation, using the block  
Chunks to Symbol.  
Before and after the the Channel Model, I used the root raised cosine  
filter to get a better signal of FFT at the WX GUI FFT Sink.  
Using the software called octave I could measure the power at the output  
of filters, First I read the file saved from the block file sink and  
after I could measure the power using the equation.  
mean(abs(in).^2).  
After this process i could see that the power at the output of Chuns to  
Symbol was equal the number 1 and in the output of the first filter was  
very small number, different of 1 and the factor that made this happen  
was the interpolation factor in the properties of the root raised cosine  
filter.  
I couldn’t find a relation of the interpolation factor of the filter to  
get the number of power equal the value at the output of Chunks to  
symbol.  
After some tests i get a result equal the number 1 in the output of the  
two filters, but with a value very big of noise the system measured a  
value of BER equal zero and the constellation was very clear.  
When I use this values of the model attached I can find results very  
near of the theorical values from the curve Eb/N0 plotted at matlab, but  
some samples are different of the theorical value.  
My doubt is, how can I do to make the BER equal the value theorical(  
from the curve of EB/N0 of the modulation)and get a good FFT signal ?