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[Discuss-gnuradio] How are parameters of gfsk_demod block assigned?

From: Kun Qian
Subject: [Discuss-gnuradio] How are parameters of gfsk_demod block assigned?
Date: Sun, 3 Aug 2014 19:41:12 -0700 (PDT)


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?


Kun Qian

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