Patent ID: 6813744
Filing Date: 2004-11-02
Classification: H03M

Abstract:
An ACS unit for a Viterbi decoder,with the ACS unit being intended for determining path metrics of a trellis diagram assigned to the Viterbi decoder, with a first and a second state of a time step (t+1) in the trellis diagram in each case being assigned to a third and a fourth state, which are each linked thereto via a path in the trellis diagram, from the preceding time step (t), with a first branch metric (&lgr;t(0)) in the trellis diagram for the branch which connects the first state to the fourth state and for the branch which connects the second state to the third state being of equal magnitude, and a second branch metric (&lgr;t(1)) being of the same magnitude for the branch which connects the first state to the third state and for the path which connects the second state to the fourth state, and with the ACS unit having a processor element for determining the path metrics (&ggr;t+1(0), &ggr;tâˆ’1(1)) associated with the first and second states, which processor element receives, as input values, the first and second branch metric (&lgr;t(0), &lgr;t(1)) as well as the path metrics (&ggr;t(0), &ggr;t(0)) associated with the third and fourth states, respectively, and comprising: a differentiation device for calculating a path metric difference (&Ggr;) between the path metrics (&ggr;t(0), &ggr;t(1)) associated with the third and fourth states, and an evaluation device for comparing the path metric difference (&Ggr;) with a branch metric difference (&Lgr;) between the first and second branch metrics (&lgr;t(0), &lgr;t(1)) and for determining the path metric (&ggr;t+1(0), &ggr;t+1(1)) associated with the first and second states, as a function of the comparison result, in which the evaluation device designed such that it determines the path metrics (&ggr;t+1(0), &ggr;t+1(1)) associated with the first and second states as a function of the comparison result, while additionally evaluating the mathematical signs of the path metrics difference (&Ggr;) and of the branch metrics difference (&Lgr;), wherein the evaluation device is designed such that it produces a first control signal for a first selection device associated with the first state and a second control signal for a second selection device associated with the second state, as a function of the comparison result and the mathematical signs of the branch metrics difference (&Ggr;) and the path metrics difference (&Lgr;), and wherein the first selection device is designed such that it emits either the sum of the path metric (&ggr;(t)(0)) of the fourth state and the first branch metric (&ggr;t(0)), or the sum of the path metric (&ggr;t(1)) of the third state and the second branch metric (&lgr;t(1) as a function of the first control signal as the path metric (&ggr;t+1(0)) of the first state, and wherein the second selection device is designed such that it emits either the sum of the path metric (&ggr;t(0)) of the fourth state and the second branch metric (&lgr;t(1)) or the sum of the path metric (&ggr;t(1)) of the third state and the first branch metric (&lgr;t(0)) as a function of the second control signal as the path metric (&ggr;t+1(1)) of the second state.