Re: [Discuss-gnuradio] gsm gmsk demodulation

[Steven Clark]

> On 6/6/08, Bob McGwier <address@hidden> 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

On Fri, Jun 6, 2008 at 9:41 AM, Ben Wojtowicz <address@hidden> wrote:
> I agree with Bob, most gsm demodulators I have seen use a viterbi equalizer
> (sometimes called MLSE equalization).
> Ben
>
>

Ok, good to hear from guys with more experience. So you would have a
viterbi equalizer to mitigate ISI, and then wrap that in a layer of
forward error correction? Is this computationally feasible for
cpu-based software radio? Sounds like it could get computationally
expensive pretty quick...

-Steven