Soft decision Viterbi decoding
(step 1)
Fig. 1 Viterbi decoding. The labels on the branches
indicate branch metrics; cumulative metrics of surviving paths are
given in frames. The decoding may continue.
In contrast to the situation in lesson 5 we assume now that the
demodulator outputs a graded multilevel confidence measure concerning
the probability of a binary one and a binary zero. This kind of
demodulator operation is referred to as soft decision demodulation.
Figure 1 shows the the Viterbi decoding proces. It is softdecision
Viterbi decoding. An encoded data sequence 1 0 1 1 … is transmitted.
The state sequence starts in state zero. We assume BPSK modulation.
The received sequence is
r = (1, 0.5), (1, 0.1), (1, 1,2), (0.8, 0,8), (0.8,+0.8),
(+0.5,+0.5)…
where the demodulator outputs +1 and 1 correspond to logical ‘1’
and ‘0’, respectively.
Please, verify the example with our Viterbi Algorithm
Applet
