Traceback-enhanced MAP decoding algorithm

Soft-input soft-output algorithms are the principal component of the iterative decoding used in turbo codes and other ´turbo´ feedback schemes. To enable efficient implementation, especially on energy constrained platforms such as portable devices, it is crucial to reduce the computational complexity to a minimum. We propose an enhancement to the MAX-LOG-MAP algorithm by adding a traceback operation similar to that used in the Viterbi algorithm, and devise a new efficient way to initialize the start state of the traceback. This enhancement is effective for each decoding iteration, and provides saving on top of existing techniques such as early termination and memory optimizations. It reduces the computational complexity by an additional 15%, without incurring any performance penalty.