Editing Viterbi algorithm (section)

== Soft output Viterbi algorithm ==

{{Unreferenced section|date=September 2023}}

The '''soft output Viterbi algorithm''' ('''SOVA''') is a variant of the classical Viterbi algorithm.

SOVA differs from the classical Viterbi algorithm in that it uses a modified path metric which takes into account the [[a priori probability|''a priori probabilities'']] of the input symbols, and produces a ''soft'' output indicating the ''reliability'' of the decision.

The first step in the SOVA is the selection of the survivor path, passing through one unique node at each time instant, ''t''. Since each node has 2 branches converging at it (with one branch being chosen to form the ''Survivor Path'', and the other being discarded), the difference in the branch metrics (or ''cost'') between the chosen and discarded branches indicate the ''amount of error'' in the choice.

This ''cost'' is accumulated over the entire sliding window (usually equals ''at least'' five constraint lengths), to indicate the ''soft output'' measure of reliability of the ''hard bit decision'' of the Viterbi algorithm.