I agree with Bob, most gsm demodulators I have seen use a viterbi equalizer (sometimes called MLSE equalization).
Ben On 6/6/08, Bob McGwier <[EMAIL PROTECTED]> wrote: > > This is not my professional experience. The sounding data is used to find > the channel and then the data symbols are soft detected through a "viterbi > equalizer" in every implementation I am aware of that is any good at all > with the exception of one I wrote several years ago which estimates the data > given the channel and then restimates the channel and then the data and then > the channel and then the data, etc. MMSE and not MLE is the goal and this > was a suboptimal implementation of the EM algorithm. It was suboptimal > since it did not estimate the data bauds using ALL observations but only > those between sounding data. Further, assumptions that the conditional > distributions of the data given the observations could be described in 1st > and 2nd product moments (not Gaussian but having similar properties). This > has been published by many. The computational complexity is on a par with > the viterbi equalizer and it outperforms it. > > Most of the cell phones I know use the Viterbi equalizer. > > Bob > > > Steven Clark wrote: > >> On Thu, Jun 5, 2008 at 7:45 AM, isaacgerg <[EMAIL PROTECTED]> >> 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 >> >> >> _ >> > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
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