# How are parameters of gfsk\_demod block assigned?

**URL:** <https://www.ruby-forum.com/t/how-are-parameters-of-gfsk-demod-block-assigned/231341>\
**Category:** GNU Radio\
**Created:** [August 4, 2014, 4:42am UTC](https://www.ruby-forum.com/t/how-are-parameters-of-gfsk-demod-block-assigned/231341 "2014-08-04T04:42:12Z")\
**Posts on this page:** 1\
**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:** [August 4, 2014, 4:42am UTC](https://www.ruby-forum.com/t/how-are-parameters-of-gfsk-demod-block-assigned/231341/1 "2014-08-04T04:42:12Z")

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Hi,

I recently triy to receive ibeacon signal whose modulation scheme is  
GFSK,  
so I use the /gfsk\_demod/ block in gnuradio and succeed to demodulate  
ibeacon signal. Yet I don’t understand the meaning of some of its  
parameters  
and why these parameters are assigned to some certain values. For  
example,  
the parameter /gain\_mu/ is set to 0.175 as default.

I then read the codes of /gfsk\_demod/ and find that there is actually  
one  
step of clock recovery there. Then I read the papers cited by the  
documentation of /gfsk\_demod/ block and learn the principle of the  
digital  
clock recovery algorithm used in it.

As far as I know, the Mueller and Muller algorithm uses linear  
combination  
of samples to estimate the timing error, which is then used to adjust  
the  
sampling phase. So the parameter /omega/ is the estimate of timing shift  
caused by carrier frequency shift, the parameter /mu/ is the estimate of  
final timing shift, and /gain\_omega/ and /gain\_mu/ are weights of  
estimate  
of timing error when adjust respective parameters, is it correct?

Then the last question is how are these parameters assigned? For  
example,  
/gain\_mu/ is set to be 0.175 and /gain\_omega/ is set to be  
0.25\*/gain\_mu/\*/gain\_mu/. Are these assignment related to any previous  
works  
or derivatives or some experiments or simulations? Do these values have  
any  
special meaning?

Thanks,

Kun Q.

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