# BER measurement for GMSK transmission with USRP wirelessly

**URL:** <https://www.ruby-forum.com/t/ber-measurement-for-gmsk-transmission-with-usrp-wirelessly/230781>\
**Category:** GNU Radio\
**Created:** [July 4, 2014, 10:20am UTC](https://www.ruby-forum.com/t/ber-measurement-for-gmsk-transmission-with-usrp-wirelessly/230781 "2014-07-04T10:20:12Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [July 4, 2014, 10:20am UTC](https://www.ruby-forum.com/t/ber-measurement-for-gmsk-transmission-with-usrp-wirelessly/230781/1 "2014-07-04T10:20:12Z")

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Good day everyone,

My sincere apology in advance if this question has been asked before,  
but i tried search thru the archives but to no avail.

Currently, I am trying to calculate the BER for GMSK, But first I  
started off on a perfect channel without USRP.

My current block diagram is as follows:

“Random Source”  
0s and 1s, 10^6 windows -\> “Throttle” -\> “GMSK Mod (default settings)”  
-\> “GMSK Demod (default settings)” -\> “Error Rate Block”

I am feeding in “Error Rate block” with the random source and the “GMSK  
Demod” Output.

I am getting BER of 50%… Anyone knows what is wrong?

In fact, I saved the input and output as binary files. I found out that  
they are not very identical especially in terms of binary length. I  
tried input 9 bits of binary and I obtained 63 bits from the GMSK Demod  
Output.  
Is there something that is missing?  
Hope someone can advise me. Thank you 🙂

Best Regards,Sun

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**Author:** ![Sun\_Wenbin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/53a042/32.png) [@Sun\_Wenbin](https://www.ruby-forum.com/u/Sun_Wenbin)\
**Post date:** [July 4, 2014, 10:54am UTC](https://www.ruby-forum.com/t/ber-measurement-for-gmsk-transmission-with-usrp-wirelessly/230781/2 "2014-07-04T10:54:46Z")

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GMSK Mod takes in packed bytes, Demod outputs unpacked bytes (e.g. 1  
bit per byte). You may need to perform a conversion. Best way to  
figure out is to post a screenshot of your flowgraph.

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<div class="post-metadata">

**Author:** ![Sun\_Wenbin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/53a042/32.png) [@Sun\_Wenbin](https://www.ruby-forum.com/u/Sun_Wenbin)\
**Post date:** [July 9, 2014, 12:54pm UTC](https://www.ruby-forum.com/t/ber-measurement-for-gmsk-transmission-with-usrp-wirelessly/230781/3 "2014-07-09T12:54:31Z")

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Good day everyone,  
Cool. Got it working. Thank you Vanush V. for your reply.  
By the way, does anyone knows how does QAM Mod takes in and QAM Demod  
output their data?

Similarly i found out that they are both not identical but cant figure  
out how the data is formed.  
Thanks for your time reading.  
Regards,Sun