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Rate 2/3 convolutional encoder + viterbi decoder

Started by aizza ahmed July 6, 2011
Hi,
    thanx for answers to previous mails. I did simulation of viterbi
(hard decision) of rate 1/2 ..soft decision still stuck on that LLR-
Soft decision understanding part :-(.

now my current question is, lets say i use 2 rate 1/2 decoders and do
puncture pattern as {1,1,0,1} assuming this is the trellis
poly2trellis( 4, [17 15]) (matlab notation..its in octal format) in
decimal it is 15 and 13

               (+)-----(+)----(+)------(+)------------>B1
               /         /       /         /
          ----/---------/-------/---------/----
inp--> | M   |   M    |   M   |   M   |               where M are
individual memory registers
         ----\---------\-----------------\------
              \         \                  \
              (+)-------(+)--------------(+)------------>B2


now my question is

from first encoder, we collect both bits B1 and B2

from second encoder, we collect only B2.


at decoder, i will insert zeros at punctured positions. now my
questions are


1. do we need to use 2 decoders at the receiving point.
2. assuming step1 is correct, in the SECOND ENCODER bits B2 and
puncture pattern filled zeros.under this condition
    assuming that all BEFORE PUNCTURE..the punctured bits are all ones
and we fill in all zeros (depuncturing). so we introduced around 50%
errors. how will the decoder pull of ML sequence with 50% sequence in
error..i meant will there not be any competing paths with equal metric
at end (assuming hard decision so only hamming distance)..



Thanks
A.Ahmed