[Discuss-gnuradio] decimation rate of GSM

[Jane Chen]

Hi all,

 

I have a question about the decimation rate of GSM (channel is 200kHz wide).

 

I search the decimation rate of GSM for GNURadio on the Google.  I got some information from http://www.segfault.net/gsm/The_Beginners_Guide_to_analyzing_GSM_data_in_MatLab.pdf

 

However, I don't understand why they said the sample rate has to be at least 400 kHz (after Nyquist’s theorem).  They used a decimation of 128.

I think through the Nyquist’s theorem, the sample rate should be 200kHz (fs>2fmax, and fmax should be 100kHz). I think the decimation factor is 256.

I am confused. Could anyone please help me?

 

Thank you,

Jane