Re: [Discuss-gnuradio] Re: gnuradio trellis

[Anastasopoulos Achilleas]

> > From your reply I think you are referring to problem 1B.
>
> I am indeed.
>
> This is great.   I did not know you had checked in the siso code in 
> gr_trellis.  I am now more anxious to go study it more carefully.  I am glad 
> I commented.

As a side note, this algorithm is the basis of all "turbo-like" receivers
that have appeared in the last 10 years. The idea is that when you have 
concatenated systems (eg, CC + interleaver + ISI) you want the inner 
decoder to provide NOT ONLY one sequence estimate, but reliability
information about each of the symbols, so that the outer decoder can use 
them as soft input information.
The trellis_siso block provides the optimal such solution, ie, the
most informative such symbol reliability Pr(x_k| y_1^N)
(the aposteriori probability about a specific input symbol based on the 
entire observation). The interesting thing is that this computation
has complexity linear in the sequence length and in the number of states,
and approximately twice that of Viterbi.

See the example test_turbo_equalization.py in 
gnuradio-examples/python/channel-coding to see how this is used
and the performance advantage it provides over one shot decoding.

Achilleas

PS: I am still working on the documentation of this part of gr_trellis.