Re: [Discuss-gnuradio] GMSK midamble template matching

[Ben Wojtowicz]

Isaac,

 

You are right, the midamble waveform is dependent on the data bits occuring before the midamble.  However, the dependency is just a constant phase offset.  Therefore, correlation with the GMSK modulated midamble bits will still result in good correlation scores.  One more point is that the bit just before the midamble can cause some uncertainty in the waveform at the very beginning.  You can resolve this by correlating with only the middle 16 bits of the midamble instead of using the entire 26.

 

Hope this helps,

Ben

 

On 5/28/08, isaacgerg <address@hidden> wrote:

I would like to identify the 26 midamble bits in each burst of GSM (GMSK)
data.  I hear that a lot of ppl use correlation to do this.  However, I am
struggling to understand how this technique could work due to the ISI from
the Gaussian pulse shaping.   It seems that the wavefrom of the 26 midamble
bits is depdented on the data coming before them and thus, template matching
would not work.  There must be something I am missing here. Any help would
be greatly appreciated.

Thanks in advanced,
Isaac
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