Re: [Discuss-gnuradio] gsm gmsk demodulation

[isaacgerg]

My question to all of you responding on this question then is:  How do I
convert the amplitudes of my GMSK signal to probabilities for viterbi based
demodulation?

Isaac



Steven Clark-2 wrote:
> 
> 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...
> 
> -Steven
> 
> 
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