Re: [Discuss-gnuradio] The GMSK demodulation

[Perper]

W dniu 28.02.2014 15:31, zhenhua han pisze:
> Hi,
>
> As I have known, GSM uses GMSK modulation which BT = 0.3 and it
> uses Viterbi algorithm for demodulation. And I took a look at the code
> of GMSK demod code in GNU Radio, it use quadrature_demod but not
> Viterbi as demodulation method. So which one is better in doing
> demodulating GMSK?
>
> Moreover, GSM uses Viterbi algorithm to decode the convolution
> encoding. Would it be possible to use quadrature_demod to demodulate
> GSM signal instead of Viterbi? What about the convolution decoding
> part (maybe by some other method)?
>
> Cheers,
> Zhenhua
>
>
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Hello all,

Regarding usage of viterbi algorithm for maximum likelihood sequence
estimation in GSM - you may look at and try gsm-receiver that I once
submitted to airprobe. I've prepared version where I thrown out all of
decoding stuff and left only synchronization, channel estimation and
detection of GMKS symbols with viterbi algorithm. It's available for
download in here:
https://github.com/Jakotako/gr-gsm

It compiles with newest gnu-radio and it has gnuradio companion xml file
as well. It can be easily connected to different sources in gnuradio
(file, rtl-sdr, usrp). I've corrected some issues with synchronization
and turned off frequency offset correction that introduced instability
of the receiver. There are examples of in the "examples" directory.

P.S. If someone applied Achilleas's implementation of viterbi algorithm
from gnu-radio in GSM I'm very interested to see how it can be done.

--
Best Regards,
Piotr Krysik