# The GMSK demodulation

**URL:** <https://www.ruby-forum.com/t/the-gmsk-demodulation/239482>\
**Category:** GNU Radio\
**Created:** [February 28, 2014, 3:32pm UTC](https://www.ruby-forum.com/t/the-gmsk-demodulation/239482 "2014-02-28T15:32:54Z")\
**Posts on this page:** 1\
**Page:** 2

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**Author:** ![zhenhua\_han](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/d2c977/32.png) [@zhenhua\_han](https://www.ruby-forum.com/u/zhenhua_han)\
**Post date:** [March 8, 2014, 5:50am UTC](https://www.ruby-forum.com/t/the-gmsk-demodulation/239482/21 "2014-03-08T05:50:39Z")

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W dniu 07.03.2014 06:06, zhenhua han pisze:

> ```
> > you said.
> fed to a frequency shifting fir filter.
> and its correction inside of xlating_fir_filter. Synchronisation
> of the gsm-receiver or with use of stream tags.
> --
> 
> ```
> 
> I’m writing the proposal to gr-gsm in GSoC.  
> Would it be possible to let me to fix the frequency correction as a  
> deliverable in my proposal ?  
> No matter if I get accepted in GSoC, I will finish this as a practice  
> of coding.
> 
> Best,  
> Zhenhua

Hi Zhenhua,

I’m not a member of GNU Radio developers team, so I’m not deciding about  
anything being accepted for GSoC.  
In my opinion fixing frequency correction on its own is a too simple  
task. I think that what is really needed is to solve the same problem  
that the airprobe’s gsm-receiver tried to solve in more modular and  
easier to understand fashion by taking advantage of GNU Radio  
capabilities such as stream tags and message inputs/outputs. What  
gsm-receiver does is frequency offset correction, synchronization,  
channel estimation and detetection of bits. You can think about clever  
ways to separate those tasks into smaller blocks.

As of now only broadcasting channel can be received by airprobe.  
Possible improvement would be implementation of reception of multiple  
frequency channels transmitted by a given GSM BTS.

On a little higher level - you can also implement gnuradio blocks that  
decode channel codes used in gsm using available sources such as  
airprobe and osmocom.

Best Regards,  
Piotr K.

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