Patent ID: 7055089

Claim:
A maximum likelihood decoder comprising: a first probability computing means for computing a logarithm of branch metric (γ), which is a logarithm of probability of a particular branch of a Trellis diagram, computed only based on the knowledge of input and output symbols associated with the particular branch; a second probability computing means for computing a logarithm of forward state metric (α), which is a logarithm of probability of a particular state of the Trellis diagram, given the probabilities of states at previous time instances; a third probability computing means for computing a logarithm of backward state metric (β), which is a logarithm of probability of the particular state of the Trellis diagram, given the probabilities of states at future time instances, wherein each of said second probability computing means and said third probability computing means includes a path selection means, said path selection means including: a plurality of comparator circuits to perform comparison operation, and a plurality of selectors to perform selection operation; and an absolute value selecting means, said absolute value selecting means including: a plurality of absolute value computation circuits to perform absolute value computation, and a plurality of selectors to perform selection operation, wherein comparison operations within the path selecting means and absolute value computation within the absolute value selecting means are carried out concurrently in log likelihood computations, and selection processing operations performed within the path selecting means and absolute value selecting means are carried out concurrently in log likelihood computations, and wherein said absolute value data selecting means compares said computed absolute value data to determine which is larger on the basis of information on the outcome of comparison obtained by a plurality of said comparator circuits, and wherein said path selection means operates to generate corrections to said probability of the particular state of the Trellis diagram using at least two paths, one path showing a maximum likelihood and another path showing a second maximum likelihood, from at least three paths in the Trellis diagram; and a soft-output determining means for determining a log soft-output logarithmically expressing a soft-output in each time slot, given said forward and backward state metrics as well as said branch metric.