Patent ID: 6996765

Claim:
A method of forward error correction employing turbo decoding comprising the steps of: receiving a transmitted bit stream; iteratively calculating alpha state metrics employing maximum-a-posteriori (MAP) blocks having a predetermined constraint length in a plurality of sliding windows, each sliding window having a prolog section and a reliability section, said prolog section having a length between one half said predetermined constraint length and twice said predetermined constrain length; iteratively calculating beta state metrics employing maximum-a-posteriori (MAP) blocks having said predetermined constraint length in a plurality of sliding windows, each sliding window having a prolog section and a reliability section, said prolog section having a length between one half said predetermined constraint length and twice said predetermined constrain length; measuring a signal to noise ratio for said extrinsics calculated from each alpha metric sliding window and a corresponding beta metric sliding window; each of said steps of iteratively calculating alpha state metrics and iteratively calculating beta state metrics includes initializing trellis state probabilities to a uniform level for said prolog section of a first sliding window, and initializing trellis state probabilities for said prolog section of sliding windows after said first sliding window dependent upon said trellis states at the end of a prior sliding window and said measured signal to noise ratio for said extrinsics of said prior sliding window; calculating extrinsics from said alpha state metrics and said beta state metrics; and reconstructing an original bit stream from said calculated extrinsics.