Patent ID: 7020832

Claim:
An apparatus comprising: a turbo decoder having a state metric, the turbo decoder including: branch metric calculation means for calculating a branch metric by receiving symbols through an input buffer; state metric calculation means for calculating a reverse state metric by using the calculated branch metric at said branch metric calculation means, storing the reverse state metric in a memory, calculating a forward state metric; and log likelihood ratio calculator for calculating a log likelihood ratio result by receiving the forward state metric from said state metric calculation means and reading the reverse state metric saved at a memory in said state metric calculation means, wherein the log likelihood ratio result L k is produced by computing a function E m - 0 2 v - 1 ⁡ ( A k 1 , m + B k s ⁡ ( m ) ) - E m - 0 2 v - 1 ⁡ ( A k 0 , m + B k m ) by the log likelihood ratio calculator, wherein m is a state of a trellis diagram; k is a stage; s(m) is a function a number complemented a Most Significant Bit(MSB)of binary number of m; E j - 0 1 is a function defined as E j = 0 1 ⁢ ⁢ A k j = A k 0 ⁢ ⁢ E ⁢ ⁢ A k 1 = log e ( ⅇ A k 0 + ⅇ A k 1 ) ; j is a (k−1) th input for a reverse state metric; A k 1,m is a k th forward state metric with state m and input 1; B k s(m) is a k th reverse state metric with state s(m); A k 0,m is a k th forward state metric with state m and input 0 and B k m is a k th reverse state metric with state m, and the log likelihood ratio is stored in a memory of the turbo decoder.