Method for generalizing the viterbi algorithm and devices for executing

Abstract

In a method for generalizing the conventional Viterbi algorithm, in which the transition costs are formed in a metric increment unit (TMU) and adding, comparing and selection are performed in a succeeding add-compare-select (ACS) unit, the difference costs from two arriving paths are calculated for each individual state, the reliability information at the beginning of each path being set to the highest value. Then the reliability value of the path with the least costs is updated at the points where the information points differ from the competing path, updating being performed in accordance with a table, and where the prior value of the reliability information and the difference costs are inserted into the table as the new input values. Then this new value is taken from the table and is stored, together with hard decisions, as path memory, where storage can be in the form of fixed or floating point values. Finally the analog value decision is read out from the point which, after a decision delay, is the result for the path with the lowest cost and where the hard decisions of the conventional Viterbi algorithm are the sign of the analog value decision. By means of the method according to the invention a Viterbi algorithm has been created at the output of which analog value decisions, i.e. soft decisions are supplied.