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Re: [Discuss-gnuradio] gsm gmsk demodulation

From: Steven Clark
Subject: Re: [Discuss-gnuradio] gsm gmsk demodulation
Date: Thu, 5 Jun 2008 15:21:59 -0400

On Thu, Jun 5, 2008 at 7:45 AM, isaacgerg <address@hidden> wrote:
> Hi,
>  Concerning GSM GMSK demodulation, due to the ISI, I initially thought many
> folks were using the Viterbi algorithm on the waveform to demodulate it
> properly.  After doing some lit review, I am finding that this is not the
> case and that when most folks talk about Viterbi concerning GSM GMSK
> demodulation, they are referring to undoing the convolution encoding and not
> referring to demodultion in the face of ISI.  Can anyone please confirm
> this?
> I see many demodulators simply just ignoring the ISI and just demodulating
> as if it wasnt present.  It seems they just rely on the convolutional
> encoding for error correction and therefore dont need to worry about the
> ISI......Is this true?

What you have said is true in my experience as well. More often than
not, Viterbi decoding is just used as part of the forward error
correction scheme.

Please look for my next email to the mailing list for an alternate
GMSK demodulator that reduces ISI...


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